wp/wp-includes/sodium_compat/src/Compat.php
changeset 9 177826044cd9
child 16 a86126ab1dd4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/sodium_compat/src/Compat.php	Mon Oct 14 18:28:13 2019 +0200
@@ -0,0 +1,2863 @@
+<?php
+
+/**
+ * Libsodium compatibility layer
+ *
+ * This is the only class you should be interfacing with, as a user of
+ * sodium_compat.
+ *
+ * If the PHP extension for libsodium is installed, it will always use that
+ * instead of our implementations. You get better performance and stronger
+ * guarantees against side-channels that way.
+ *
+ * However, if your users don't have the PHP extension installed, we offer a
+ * compatible interface here. It will give you the correct results as if the
+ * PHP extension was installed. It won't be as fast, of course.
+ *
+ * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION *
+ *                                                                               *
+ *     Until audited, this is probably not safe to use! DANGER WILL ROBINSON     *
+ *                                                                               *
+ * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION * CAUTION *
+ */
+
+if (class_exists('ParagonIE_Sodium_Compat', false)) {
+    return;
+}
+
+class ParagonIE_Sodium_Compat
+{
+    /**
+     * This parameter prevents the use of the PECL extension.
+     * It should only be used for unit testing.
+     *
+     * @var bool
+     */
+    public static $disableFallbackForUnitTests = false;
+
+    /**
+     * Use fast multiplication rather than our constant-time multiplication
+     * implementation. Can be enabled at runtime. Only enable this if you
+     * are absolutely certain that there is no timing leak on your platform.
+     *
+     * @var bool
+     */
+    public static $fastMult = false;
+
+    const LIBRARY_VERSION_MAJOR = 9;
+    const LIBRARY_VERSION_MINOR = 1;
+    const VERSION_STRING = 'polyfill-1.0.8';
+
+    // From libsodium
+    const CRYPTO_AEAD_AES256GCM_KEYBYTES = 32;
+    const CRYPTO_AEAD_AES256GCM_NSECBYTES = 0;
+    const CRYPTO_AEAD_AES256GCM_NPUBBYTES = 12;
+    const CRYPTO_AEAD_AES256GCM_ABYTES = 16;
+    const CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES = 32;
+    const CRYPTO_AEAD_CHACHA20POLY1305_NSECBYTES = 0;
+    const CRYPTO_AEAD_CHACHA20POLY1305_NPUBBYTES = 8;
+    const CRYPTO_AEAD_CHACHA20POLY1305_ABYTES = 16;
+    const CRYPTO_AEAD_CHACHA20POLY1305_IETF_KEYBYTES = 32;
+    const CRYPTO_AEAD_CHACHA20POLY1305_IETF_NSECBYTES = 0;
+    const CRYPTO_AEAD_CHACHA20POLY1305_IETF_NPUBBYTES = 12;
+    const CRYPTO_AEAD_CHACHA20POLY1305_IETF_ABYTES = 16;
+    const CRYPTO_AEAD_XCHACHA20POLY1305_IETF_KEYBYTES = 32;
+    const CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NSECBYTES = 0;
+    const CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES = 24;
+    const CRYPTO_AEAD_XCHACHA20POLY1305_IETF_ABYTES = 16;
+    const CRYPTO_AUTH_BYTES = 32;
+    const CRYPTO_AUTH_KEYBYTES = 32;
+    const CRYPTO_BOX_SEALBYTES = 16;
+    const CRYPTO_BOX_SECRETKEYBYTES = 32;
+    const CRYPTO_BOX_PUBLICKEYBYTES = 32;
+    const CRYPTO_BOX_KEYPAIRBYTES = 64;
+    const CRYPTO_BOX_MACBYTES = 16;
+    const CRYPTO_BOX_NONCEBYTES = 24;
+    const CRYPTO_BOX_SEEDBYTES = 32;
+    const CRYPTO_KX_BYTES = 32;
+    const CRYPTO_KX_SEEDBYTES = 32;
+    const CRYPTO_KX_PUBLICKEYBYTES = 32;
+    const CRYPTO_KX_SECRETKEYBYTES = 32;
+    const CRYPTO_GENERICHASH_BYTES = 32;
+    const CRYPTO_GENERICHASH_BYTES_MIN = 16;
+    const CRYPTO_GENERICHASH_BYTES_MAX = 64;
+    const CRYPTO_GENERICHASH_KEYBYTES = 32;
+    const CRYPTO_GENERICHASH_KEYBYTES_MIN = 16;
+    const CRYPTO_GENERICHASH_KEYBYTES_MAX = 64;
+    const CRYPTO_PWHASH_SALTBYTES = 16;
+    const CRYPTO_PWHASH_STRPREFIX = '$argon2i$';
+    const CRYPTO_PWHASH_ALG_ARGON2I13 = 1;
+    const CRYPTO_PWHASH_ALG_ARGON2ID13 = 2;
+    const CRYPTO_PWHASH_MEMLIMIT_INTERACTIVE = 33554432;
+    const CRYPTO_PWHASH_OPSLIMIT_INTERACTIVE = 4;
+    const CRYPTO_PWHASH_MEMLIMIT_MODERATE = 134217728;
+    const CRYPTO_PWHASH_OPSLIMIT_MODERATE = 6;
+    const CRYPTO_PWHASH_MEMLIMIT_SENSITIVE = 536870912;
+    const CRYPTO_PWHASH_OPSLIMIT_SENSITIVE = 8;
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_SALTBYTES = 32;
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_STRPREFIX = '$7$';
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_OPSLIMIT_INTERACTIVE = 534288;
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_MEMLIMIT_INTERACTIVE = 16777216;
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_OPSLIMIT_SENSITIVE = 33554432;
+    const CRYPTO_PWHASH_SCRYPTSALSA208SHA256_MEMLIMIT_SENSITIVE = 1073741824;
+    const CRYPTO_SCALARMULT_BYTES = 32;
+    const CRYPTO_SCALARMULT_SCALARBYTES = 32;
+    const CRYPTO_SHORTHASH_BYTES = 8;
+    const CRYPTO_SHORTHASH_KEYBYTES = 16;
+    const CRYPTO_SECRETBOX_KEYBYTES = 32;
+    const CRYPTO_SECRETBOX_MACBYTES = 16;
+    const CRYPTO_SECRETBOX_NONCEBYTES = 24;
+    const CRYPTO_SIGN_BYTES = 64;
+    const CRYPTO_SIGN_SEEDBYTES = 32;
+    const CRYPTO_SIGN_PUBLICKEYBYTES = 32;
+    const CRYPTO_SIGN_SECRETKEYBYTES = 64;
+    const CRYPTO_SIGN_KEYPAIRBYTES = 96;
+    const CRYPTO_STREAM_KEYBYTES = 32;
+    const CRYPTO_STREAM_NONCEBYTES = 24;
+
+    /**
+     * Cache-timing-safe implementation of bin2hex().
+     *
+     * @param string $string A string (probably raw binary)
+     * @return string        A hexadecimal-encoded string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function bin2hex($string)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($string, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_bin2hex($string);
+        }
+        if (self::use_fallback('bin2hex')) {
+            return (string) call_user_func('\\Sodium\\bin2hex', $string);
+        }
+        return ParagonIE_Sodium_Core_Util::bin2hex($string);
+    }
+
+    /**
+     * Compare two strings, in constant-time.
+     * Compared to memcmp(), compare() is more useful for sorting.
+     *
+     * @param string $left  The left operand; must be a string
+     * @param string $right The right operand; must be a string
+     * @return int          If < 0 if the left operand is less than the right
+     *                      If = 0 if both strings are equal
+     *                      If > 0 if the right operand is less than the left
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function compare($left, $right)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($left, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($right, 'string', 2);
+
+        if (self::useNewSodiumAPI()) {
+            return (int) sodium_compare($left, $right);
+        }
+        if (self::use_fallback('compare')) {
+            return (int) call_user_func('\\Sodium\\compare', $left, $right);
+        }
+        return ParagonIE_Sodium_Core_Util::compare($left, $right);
+    }
+
+    /**
+     * Is AES-256-GCM even available to use?
+     *
+     * @return bool
+     * @psalm-suppress UndefinedFunction
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_aead_aes256gcm_is_available()
+    {
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_aead_aes256gcm_is_available();
+        }
+        if (self::use_fallback('crypto_aead_aes256gcm_is_available')) {
+            return call_user_func('\\Sodium\\crypto_aead_aes256gcm_is_available');
+        }
+        if (PHP_VERSION_ID < 70100) {
+            // OpenSSL doesn't support AEAD before 7.1.0
+            return false;
+        }
+        if (!is_callable('openssl_encrypt') || !is_callable('openssl_decrypt')) {
+            // OpenSSL isn't installed
+            return false;
+        }
+        return (bool) in_array('aes-256-gcm', openssl_get_cipher_methods());
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data: Decryption
+     *
+     * Algorithm:
+     *     AES-256-GCM
+     *
+     * This mode uses a 64-bit random nonce with a 64-bit counter.
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     *
+     * @param string $ciphertext Encrypted message (with Poly1305 MAC appended)
+     * @param string $assocData  Authenticated Associated Data (unencrypted)
+     * @param string $nonce      Number to be used only Once; must be 8 bytes
+     * @param string $key        Encryption key
+     *
+     * @return string|bool       The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_aead_aes256gcm_decrypt(
+        $ciphertext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        if (!self::crypto_aead_aes256gcm_is_available()) {
+            throw new SodiumException('AES-256-GCM is not available');
+        }
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_AES256GCM_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_AES256GCM_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_AES256GCM_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_AES256GCM_KEYBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($ciphertext) < self::CRYPTO_AEAD_AES256GCM_ABYTES) {
+            throw new SodiumException('Message must be at least CRYPTO_AEAD_AES256GCM_ABYTES long');
+        }
+        if (!is_callable('openssl_decrypt')) {
+            throw new SodiumException('The OpenSSL extension is not installed, or openssl_decrypt() is not available');
+        }
+
+        /** @var string $ctext */
+        $ctext = ParagonIE_Sodium_Core_Util::substr($ciphertext, 0, -self::CRYPTO_AEAD_AES256GCM_ABYTES);
+        /** @var string $authTag */
+        $authTag = ParagonIE_Sodium_Core_Util::substr($ciphertext, -self::CRYPTO_AEAD_AES256GCM_ABYTES, 16);
+        return openssl_decrypt(
+            $ctext,
+            'aes-256-gcm',
+            $key,
+            OPENSSL_RAW_DATA,
+            $nonce,
+            $authTag,
+            $assocData
+        );
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data: Encryption
+     *
+     * Algorithm:
+     *     AES-256-GCM
+     *
+     * @param string $plaintext Message to be encrypted
+     * @param string $assocData Authenticated Associated Data (unencrypted)
+     * @param string $nonce     Number to be used only Once; must be 8 bytes
+     * @param string $key       Encryption key
+     *
+     * @return string           Ciphertext with a 16-byte GCM message
+     *                          authentication code appended
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_aead_aes256gcm_encrypt(
+        $plaintext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        if (!self::crypto_aead_aes256gcm_is_available()) {
+            throw new SodiumException('AES-256-GCM is not available');
+        }
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_AES256GCM_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_AES256GCM_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_AES256GCM_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_AES256GCM_KEYBYTES long');
+        }
+
+        if (!is_callable('openssl_encrypt')) {
+            throw new SodiumException('The OpenSSL extension is not installed, or openssl_encrypt() is not available');
+        }
+
+        $authTag = '';
+        $ciphertext = openssl_encrypt(
+            $plaintext,
+            'aes-256-gcm',
+            $key,
+            OPENSSL_RAW_DATA,
+            $nonce,
+            $authTag,
+            $assocData
+        );
+        return $ciphertext . $authTag;
+    }
+
+    /**
+     * Return a secure random key for use with the AES-256-GCM
+     * symmetric AEAD interface.
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_aead_aes256gcm_keygen()
+    {
+        return random_bytes(self::CRYPTO_AEAD_AES256GCM_KEYBYTES);
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data: Decryption
+     *
+     * Algorithm:
+     *     ChaCha20-Poly1305
+     *
+     * This mode uses a 64-bit random nonce with a 64-bit counter.
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     *
+     * @param string $ciphertext Encrypted message (with Poly1305 MAC appended)
+     * @param string $assocData  Authenticated Associated Data (unencrypted)
+     * @param string $nonce      Number to be used only Once; must be 8 bytes
+     * @param string $key        Encryption key
+     *
+     * @return string            The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_aead_chacha20poly1305_decrypt(
+        $ciphertext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_CHACHA20POLY1305_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_CHACHA20POLY1305_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($ciphertext) < self::CRYPTO_AEAD_CHACHA20POLY1305_ABYTES) {
+            throw new SodiumException('Message must be at least CRYPTO_AEAD_CHACHA20POLY1305_ABYTES long');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_aead_chacha20poly1305_decrypt(
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (self::use_fallback('crypto_aead_chacha20poly1305_decrypt')) {
+            return call_user_func(
+                '\\Sodium\\crypto_aead_chacha20poly1305_decrypt',
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_chacha20poly1305_decrypt(
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_chacha20poly1305_decrypt(
+            $ciphertext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data
+     *
+     * Algorithm:
+     *     ChaCha20-Poly1305
+     *
+     * This mode uses a 64-bit random nonce with a 64-bit counter.
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     *
+     * @param string $plaintext Message to be encrypted
+     * @param string $assocData Authenticated Associated Data (unencrypted)
+     * @param string $nonce     Number to be used only Once; must be 8 bytes
+     * @param string $key       Encryption key
+     *
+     * @return string           Ciphertext with a 16-byte Poly1305 message
+     *                          authentication code appended
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_aead_chacha20poly1305_encrypt(
+        $plaintext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_CHACHA20POLY1305_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_CHACHA20POLY1305_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES long');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_aead_chacha20poly1305_encrypt(
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (self::use_fallback('crypto_aead_chacha20poly1305_encrypt')) {
+            return (string) call_user_func(
+                '\\Sodium\\crypto_aead_chacha20poly1305_encrypt',
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_chacha20poly1305_encrypt(
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_chacha20poly1305_encrypt(
+            $plaintext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data: Decryption
+     *
+     * Algorithm:
+     *     ChaCha20-Poly1305
+     *
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     * Regular mode uses a 64-bit random nonce with a 64-bit counter.
+     *
+     * @param string $ciphertext Encrypted message (with Poly1305 MAC appended)
+     * @param string $assocData  Authenticated Associated Data (unencrypted)
+     * @param string $nonce      Number to be used only Once; must be 12 bytes
+     * @param string $key        Encryption key
+     *
+     * @return string            The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_aead_chacha20poly1305_ietf_decrypt(
+        $ciphertext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_CHACHA20POLY1305_IETF_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_CHACHA20POLY1305_IETF_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($ciphertext) < self::CRYPTO_AEAD_CHACHA20POLY1305_ABYTES) {
+            throw new SodiumException('Message must be at least CRYPTO_AEAD_CHACHA20POLY1305_ABYTES long');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_aead_chacha20poly1305_ietf_decrypt(
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (self::use_fallback('crypto_aead_chacha20poly1305_ietf_decrypt')) {
+            return call_user_func(
+                '\\Sodium\\crypto_aead_chacha20poly1305_ietf_decrypt',
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_chacha20poly1305_ietf_decrypt(
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_chacha20poly1305_ietf_decrypt(
+            $ciphertext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Return a secure random key for use with the ChaCha20-Poly1305
+     * symmetric AEAD interface.
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_aead_chacha20poly1305_keygen()
+    {
+        return random_bytes(self::CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES);
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data
+     *
+     * Algorithm:
+     *     ChaCha20-Poly1305
+     *
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     * Regular mode uses a 64-bit random nonce with a 64-bit counter.
+     *
+     * @param string $plaintext Message to be encrypted
+     * @param string $assocData Authenticated Associated Data (unencrypted)
+     * @param string $nonce Number to be used only Once; must be 8 bytes
+     * @param string $key Encryption key
+     *
+     * @return string           Ciphertext with a 16-byte Poly1305 message
+     *                          authentication code appended
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_aead_chacha20poly1305_ietf_encrypt(
+        $plaintext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = ''
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_CHACHA20POLY1305_IETF_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_CHACHA20POLY1305_IETF_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_CHACHA20POLY1305_KEYBYTES long');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_aead_chacha20poly1305_ietf_encrypt(
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (self::use_fallback('crypto_aead_chacha20poly1305_ietf_encrypt')) {
+            return (string) call_user_func(
+                '\\Sodium\\crypto_aead_chacha20poly1305_ietf_encrypt',
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_chacha20poly1305_ietf_encrypt(
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_chacha20poly1305_ietf_encrypt(
+            $plaintext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Return a secure random key for use with the ChaCha20-Poly1305
+     * symmetric AEAD interface. (IETF version)
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_aead_chacha20poly1305_ietf_keygen()
+    {
+        return random_bytes(self::CRYPTO_AEAD_CHACHA20POLY1305_IETF_KEYBYTES);
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data: Decryption
+     *
+     * Algorithm:
+     *     XChaCha20-Poly1305
+     *
+     * This mode uses a 64-bit random nonce with a 64-bit counter.
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     *
+     * @param string $ciphertext   Encrypted message (with Poly1305 MAC appended)
+     * @param string $assocData    Authenticated Associated Data (unencrypted)
+     * @param string $nonce        Number to be used only Once; must be 8 bytes
+     * @param string $key          Encryption key
+     * @param bool   $dontFallback Don't fallback to ext/sodium
+     *
+     * @return string|bool         The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_aead_xchacha20poly1305_ietf_decrypt(
+        $ciphertext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = '',
+        $dontFallback = false
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_XCHACHA20POLY1305_IETF_KEYBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($ciphertext) < self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_ABYTES) {
+            throw new SodiumException('Message must be at least CRYPTO_AEAD_XCHACHA20POLY1305_IETF_ABYTES long');
+        }
+        if (self::useNewSodiumAPI() && !$dontFallback) {
+            if (is_callable('sodium_crypto_aead_xchacha20poly1305_ietf_decrypt')) {
+                return sodium_crypto_aead_xchacha20poly1305_ietf_decrypt(
+                    $ciphertext,
+                    $assocData,
+                    $nonce,
+                    $key
+                );
+            }
+        }
+
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_xchacha20poly1305_ietf_decrypt(
+                $ciphertext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_xchacha20poly1305_ietf_decrypt(
+            $ciphertext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Authenticated Encryption with Associated Data
+     *
+     * Algorithm:
+     *     XChaCha20-Poly1305
+     *
+     * This mode uses a 64-bit random nonce with a 64-bit counter.
+     * IETF mode uses a 96-bit random nonce with a 32-bit counter.
+     *
+     * @param string $plaintext    Message to be encrypted
+     * @param string $assocData    Authenticated Associated Data (unencrypted)
+     * @param string $nonce        Number to be used only Once; must be 8 bytes
+     * @param string $key          Encryption key
+     * @param bool   $dontFallback Don't fallback to ext/sodium
+     *
+     * @return string           Ciphertext with a 16-byte Poly1305 message
+     *                          authentication code appended
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_aead_xchacha20poly1305_ietf_encrypt(
+        $plaintext = '',
+        $assocData = '',
+        $nonce = '',
+        $key = '',
+        $dontFallback = false
+    ) {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($assocData, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_NPUBBYTES) {
+            throw new SodiumException('Nonce must be CRYPTO_AEAD_XCHACHA20POLY1305_NPUBBYTES long');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_KEYBYTES) {
+            throw new SodiumException('Key must be CRYPTO_AEAD_XCHACHA20POLY1305_KEYBYTES long');
+        }
+        if (self::useNewSodiumAPI() && !$dontFallback) {
+            if (is_callable('sodium_crypto_aead_xchacha20poly1305_ietf_encrypt')) {
+                return sodium_crypto_aead_xchacha20poly1305_ietf_encrypt(
+                    $plaintext,
+                    $assocData,
+                    $nonce,
+                    $key
+                );
+            }
+        }
+
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::aead_xchacha20poly1305_ietf_encrypt(
+                $plaintext,
+                $assocData,
+                $nonce,
+                $key
+            );
+        }
+        return ParagonIE_Sodium_Crypto::aead_xchacha20poly1305_ietf_encrypt(
+            $plaintext,
+            $assocData,
+            $nonce,
+            $key
+        );
+    }
+
+    /**
+     * Return a secure random key for use with the XChaCha20-Poly1305
+     * symmetric AEAD interface.
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_aead_xchacha20poly1305_ietf_keygen()
+    {
+        return random_bytes(self::CRYPTO_AEAD_XCHACHA20POLY1305_IETF_KEYBYTES);
+    }
+
+    /**
+     * Authenticate a message. Uses symmetric-key cryptography.
+     *
+     * Algorithm:
+     *     HMAC-SHA512-256. Which is HMAC-SHA-512 truncated to 256 bits.
+     *     Not to be confused with HMAC-SHA-512/256 which would use the
+     *     SHA-512/256 hash function (uses different initial parameters
+     *     but still truncates to 256 bits to sidestep length-extension
+     *     attacks).
+     *
+     * @param string $message Message to be authenticated
+     * @param string $key Symmetric authentication key
+     * @return string         Message authentication code
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_auth($message, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AUTH_KEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_AUTH_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_auth($message, $key);
+        }
+        if (self::use_fallback('crypto_auth')) {
+            return (string) call_user_func('\\Sodium\\crypto_auth', $message, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::auth($message, $key);
+        }
+        return ParagonIE_Sodium_Crypto::auth($message, $key);
+    }
+
+    /**
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_auth_keygen()
+    {
+        return random_bytes(self::CRYPTO_AUTH_KEYBYTES);
+    }
+
+    /**
+     * Verify the MAC of a message previously authenticated with crypto_auth.
+     *
+     * @param string $mac Message authentication code
+     * @param string $message Message whose authenticity you are attempting to
+     *                        verify (with a given MAC and key)
+     * @param string $key Symmetric authentication key
+     * @return bool           TRUE if authenticated, FALSE otherwise
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_auth_verify($mac, $message, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($mac, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($mac) !== self::CRYPTO_AUTH_BYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_AUTH_BYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_AUTH_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_AUTH_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (bool) sodium_crypto_auth_verify($mac, $message, $key);
+        }
+        if (self::use_fallback('crypto_auth_verify')) {
+            return (bool) call_user_func('\\Sodium\\crypto_auth_verify', $mac, $message, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::auth_verify($mac, $message, $key);
+        }
+        return ParagonIE_Sodium_Crypto::auth_verify($mac, $message, $key);
+    }
+
+    /**
+     * Authenticated asymmetric-key encryption. Both the sender and recipient
+     * may decrypt messages.
+     *
+     * Algorithm: X25519-XSalsa20-Poly1305.
+     *     X25519: Elliptic-Curve Diffie Hellman over Curve25519.
+     *     XSalsa20: Extended-nonce variant of salsa20.
+     *     Poyl1305: Polynomial MAC for one-time message authentication.
+     *
+     * @param string $plaintext The message to be encrypted
+     * @param string $nonce A Number to only be used Once; must be 24 bytes
+     * @param string $keypair Your secret key and your recipient's public key
+     * @return string           Ciphertext with 16-byte Poly1305 MAC
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box($plaintext, $nonce, $keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_BOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_BOX_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box($plaintext, $nonce, $keypair);
+        }
+        if (self::use_fallback('crypto_box')) {
+            return (string) call_user_func('\\Sodium\\crypto_box', $plaintext, $nonce, $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box($plaintext, $nonce, $keypair);
+        }
+        return ParagonIE_Sodium_Crypto::box($plaintext, $nonce, $keypair);
+    }
+
+    /**
+     * Anonymous public-key encryption. Only the recipient may decrypt messages.
+     *
+     * Algorithm: X25519-XSalsa20-Poly1305, as with crypto_box.
+     *     The sender's X25519 keypair is ephemeral.
+     *     Nonce is generated from the BLAKE2b hash of both public keys.
+     *
+     * This provides ciphertext integrity.
+     *
+     * @param string $plaintext Message to be sealed
+     * @param string $publicKey Your recipient's public key
+     * @return string           Sealed message that only your recipient can
+     *                          decrypt
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_seal($plaintext, $publicKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($publicKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($publicKey) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_seal($plaintext, $publicKey);
+        }
+        if (self::use_fallback('crypto_box_seal')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_seal', $plaintext, $publicKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_seal($plaintext, $publicKey);
+        }
+        return ParagonIE_Sodium_Crypto::box_seal($plaintext, $publicKey);
+    }
+
+    /**
+     * Opens a message encrypted with crypto_box_seal(). Requires
+     * the recipient's keypair (sk || pk) to decrypt successfully.
+     *
+     * This validates ciphertext integrity.
+     *
+     * @param string $ciphertext Sealed message to be opened
+     * @param string $keypair    Your crypto_box keypair
+     * @return string            The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_box_seal_open($ciphertext, $keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_box_seal_open($ciphertext, $keypair);
+        }
+        if (self::use_fallback('crypto_box_seal_open')) {
+            return call_user_func('\\Sodium\\crypto_box_seal_open', $ciphertext, $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_seal_open($ciphertext, $keypair);
+        }
+        return ParagonIE_Sodium_Crypto::box_seal_open($ciphertext, $keypair);
+    }
+
+    /**
+     * Generate a new random X25519 keypair.
+     *
+     * @return string A 64-byte string; the first 32 are your secret key, while
+     *                the last 32 are your public key. crypto_box_secretkey()
+     *                and crypto_box_publickey() exist to separate them so you
+     *                don't accidentally get them mixed up!
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_keypair()
+    {
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_keypair();
+        }
+        if (self::use_fallback('crypto_box_keypair')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_keypair');
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_keypair();
+        }
+        return ParagonIE_Sodium_Crypto::box_keypair();
+    }
+
+    /**
+     * Combine two keys into a keypair for use in library methods that expect
+     * a keypair. This doesn't necessarily have to be the same person's keys.
+     *
+     * @param string $secretKey Secret key
+     * @param string $publicKey Public key
+     * @return string    Keypair
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_keypair_from_secretkey_and_publickey($secretKey, $publicKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($publicKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_BOX_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_SECRETKEYBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($publicKey) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_keypair_from_secretkey_and_publickey($secretKey, $publicKey);
+        }
+        if (self::use_fallback('crypto_box_keypair_from_secretkey_and_publickey')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_keypair_from_secretkey_and_publickey', $secretKey, $publicKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_keypair_from_secretkey_and_publickey($secretKey, $publicKey);
+        }
+        return ParagonIE_Sodium_Crypto::box_keypair_from_secretkey_and_publickey($secretKey, $publicKey);
+    }
+
+    /**
+     * Decrypt a message previously encrypted with crypto_box().
+     *
+     * @param string $ciphertext Encrypted message
+     * @param string $nonce      Number to only be used Once; must be 24 bytes
+     * @param string $keypair    Your secret key and the sender's public key
+     * @return string            The original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_box_open($ciphertext, $nonce, $keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($ciphertext) < self::CRYPTO_BOX_MACBYTES) {
+            throw new SodiumException('Argument 1 must be at least CRYPTO_BOX_MACBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_BOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_BOX_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_box_open($ciphertext, $nonce, $keypair);
+        }
+        if (self::use_fallback('crypto_box_open')) {
+            return call_user_func('\\Sodium\\crypto_box_open', $ciphertext, $nonce, $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_open($ciphertext, $nonce, $keypair);
+        }
+        return ParagonIE_Sodium_Crypto::box_open($ciphertext, $nonce, $keypair);
+    }
+
+    /**
+     * Extract the public key from a crypto_box keypair.
+     *
+     * @param string $keypair Keypair containing secret and public key
+     * @return string         Your crypto_box public key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_publickey($keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_publickey($keypair);
+        }
+        if (self::use_fallback('crypto_box_publickey')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_publickey', $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_publickey($keypair);
+        }
+        return ParagonIE_Sodium_Crypto::box_publickey($keypair);
+    }
+
+    /**
+     * Calculate the X25519 public key from a given X25519 secret key.
+     *
+     * @param string $secretKey Any X25519 secret key
+     * @return string           The corresponding X25519 public key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_publickey_from_secretkey($secretKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_BOX_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_SECRETKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_publickey_from_secretkey($secretKey);
+        }
+        if (self::use_fallback('crypto_box_publickey_from_secretkey')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_publickey_from_secretkey', $secretKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_publickey_from_secretkey($secretKey);
+        }
+        return ParagonIE_Sodium_Crypto::box_publickey_from_secretkey($secretKey);
+    }
+
+    /**
+     * Extract the secret key from a crypto_box keypair.
+     *
+     * @param string $keypair
+     * @return string         Your crypto_box secret key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_box_secretkey($keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_secretkey($keypair);
+        }
+        if (self::use_fallback('crypto_box_secretkey')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_secretkey', $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_secretkey($keypair);
+        }
+        return ParagonIE_Sodium_Crypto::box_secretkey($keypair);
+    }
+
+    /**
+     * Generate an X25519 keypair from a seed.
+     *
+     * @param string $seed
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress UndefinedFunction
+     */
+    public static function crypto_box_seed_keypair($seed)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($seed, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_box_seed_keypair($seed);
+        }
+        if (self::use_fallback('crypto_box_seed_keypair')) {
+            return (string) call_user_func('\\Sodium\\crypto_box_seed_keypair', $seed);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::box_seed_keypair($seed);
+        }
+        return ParagonIE_Sodium_Crypto::box_seed_keypair($seed);
+    }
+
+    /**
+     * Calculates a BLAKE2b hash, with an optional key.
+     *
+     * @param string      $message The message to be hashed
+     * @param string|null $key     If specified, must be a string between 16
+     *                             and 64 bytes long
+     * @param int         $length  Output length in bytes; must be between 16
+     *                             and 64 (default = 32)
+     * @return string              Raw binary
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_generichash($message, $key = '', $length = self::CRYPTO_GENERICHASH_BYTES)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        if (is_null($key)) {
+            $key = '';
+        }
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($length, 'int', 3);
+
+        /* Input validation: */
+        if (!empty($key)) {
+            if (ParagonIE_Sodium_Core_Util::strlen($key) < self::CRYPTO_GENERICHASH_KEYBYTES_MIN) {
+                throw new SodiumException('Unsupported key size. Must be at least CRYPTO_GENERICHASH_KEYBYTES_MIN bytes long.');
+            }
+            if (ParagonIE_Sodium_Core_Util::strlen($key) > self::CRYPTO_GENERICHASH_KEYBYTES_MAX) {
+                throw new SodiumException('Unsupported key size. Must be at most CRYPTO_GENERICHASH_KEYBYTES_MAX bytes long.');
+            }
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_generichash($message, $key, $length);
+        }
+        if (self::use_fallback('crypto_generichash')) {
+            return (string) call_user_func('\\Sodium\\crypto_generichash', $message, $key, $length);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::generichash($message, $key, $length);
+        }
+        return ParagonIE_Sodium_Crypto::generichash($message, $key, $length);
+    }
+
+    /**
+     * Get the final BLAKE2b hash output for a given context.
+     *
+     * @param string $ctx BLAKE2 hashing context. Generated by crypto_generichash_init().
+     * @param int $length Hash output size.
+     * @return string     Final BLAKE2b hash.
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress ReferenceConstraintViolation
+     */
+    public static function crypto_generichash_final(&$ctx, $length = self::CRYPTO_GENERICHASH_BYTES)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ctx, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($length, 'int', 2);
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_generichash_final($ctx, $length);
+        }
+        if (self::use_fallback('crypto_generichash_final')) {
+            $func = '\\Sodium\\crypto_generichash_final';
+            return (string) $func($ctx, $length);
+        }
+        if (PHP_INT_SIZE === 4) {
+            $result = ParagonIE_Sodium_Crypto32::generichash_final($ctx, $length);
+        } else {
+            $result = ParagonIE_Sodium_Crypto::generichash_final($ctx, $length);
+        }
+        try {
+            self::memzero($ctx);
+        } catch (SodiumException $ex) {
+            unset($ctx);
+        }
+        return $result;
+    }
+
+    /**
+     * Initialize a BLAKE2b hashing context, for use in a streaming interface.
+     *
+     * @param string|null $key If specified must be a string between 16 and 64 bytes
+     * @param int $length      The size of the desired hash output
+     * @return string          A BLAKE2 hashing context, encoded as a string
+     *                         (To be 100% compatible with ext/libsodium)
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_generichash_init($key = '', $length = self::CRYPTO_GENERICHASH_BYTES)
+    {
+        /* Type checks: */
+        if (is_null($key)) {
+            $key = '';
+        }
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($length, 'int', 2);
+
+        /* Input validation: */
+        if (!empty($key)) {
+            if (ParagonIE_Sodium_Core_Util::strlen($key) < self::CRYPTO_GENERICHASH_KEYBYTES_MIN) {
+                throw new SodiumException('Unsupported key size. Must be at least CRYPTO_GENERICHASH_KEYBYTES_MIN bytes long.');
+            }
+            if (ParagonIE_Sodium_Core_Util::strlen($key) > self::CRYPTO_GENERICHASH_KEYBYTES_MAX) {
+                throw new SodiumException('Unsupported key size. Must be at most CRYPTO_GENERICHASH_KEYBYTES_MAX bytes long.');
+            }
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_generichash_init($key, $length);
+        }
+        if (self::use_fallback('crypto_generichash_init')) {
+            return (string) call_user_func('\\Sodium\\crypto_generichash_init', $key, $length);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::generichash_init($key, $length);
+        }
+        return ParagonIE_Sodium_Crypto::generichash_init($key, $length);
+    }
+
+    /**
+     * Update a BLAKE2b hashing context with additional data.
+     *
+     * @param string $ctx    BLAKE2 hashing context. Generated by crypto_generichash_init().
+     *                       $ctx is passed by reference and gets updated in-place.
+     * @param-out string $ctx
+     * @param string $message The message to append to the existing hash state.
+     * @return void
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress ReferenceConstraintViolation
+     */
+    public static function crypto_generichash_update(&$ctx, $message)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ctx, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 2);
+
+        if (self::useNewSodiumAPI()) {
+            sodium_crypto_generichash_update($ctx, $message);
+            return;
+        }
+        if (self::use_fallback('crypto_generichash_update')) {
+            $func = '\\Sodium\\crypto_generichash_update';
+            $func($ctx, $message);
+            return;
+        }
+        if (PHP_INT_SIZE === 4) {
+            $ctx = ParagonIE_Sodium_Crypto32::generichash_update($ctx, $message);
+        } else {
+            $ctx = ParagonIE_Sodium_Crypto::generichash_update($ctx, $message);
+        }
+    }
+
+    /**
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_generichash_keygen()
+    {
+        return random_bytes(self::CRYPTO_GENERICHASH_KEYBYTES);
+    }
+
+    /**
+     * Perform a key exchange, between a designated client and a server.
+     *
+     * Typically, you would designate one machine to be the client and the
+     * other to be the server. The first two keys are what you'd expect for
+     * scalarmult() below, but the latter two public keys don't swap places.
+     *
+     * | ALICE                          | BOB                                 |
+     * | Client                         | Server                              |
+     * |--------------------------------|-------------------------------------|
+     * | shared = crypto_kx(            | shared = crypto_kx(                 |
+     * |     alice_sk,                  |     bob_sk,                         | <- contextual
+     * |     bob_pk,                    |     alice_pk,                       | <- contextual
+     * |     alice_pk,                  |     alice_pk,                       | <----- static
+     * |     bob_pk                     |     bob_pk                          | <----- static
+     * | )                              | )                                   |
+     *
+     * They are used along with the scalarmult product to generate a 256-bit
+     * BLAKE2b hash unique to the client and server keys.
+     *
+     * @param string $my_secret
+     * @param string $their_public
+     * @param string $client_public
+     * @param string $server_public
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_kx($my_secret, $their_public, $client_public, $server_public)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($my_secret, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($their_public, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($client_public, 'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($server_public, 'string', 4);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($my_secret) !== self::CRYPTO_BOX_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_SECRETKEYBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($their_public) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($client_public) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($server_public) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 4 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            if (is_callable('sodium_crypto_kx')) {
+                return (string) sodium_crypto_kx(
+                    $my_secret,
+                    $their_public,
+                    $client_public,
+                    $server_public
+                );
+            }
+        }
+        if (self::use_fallback('crypto_kx')) {
+            return (string) call_user_func(
+                '\\Sodium\\crypto_kx',
+                $my_secret,
+                $their_public,
+                $client_public,
+                $server_public
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::keyExchange(
+                $my_secret,
+                $their_public,
+                $client_public,
+                $server_public
+            );
+        }
+        return ParagonIE_Sodium_Crypto::keyExchange(
+            $my_secret,
+            $their_public,
+            $client_public,
+            $server_public
+        );
+    }
+
+    /**
+     * @param int $outlen
+     * @param string $passwd
+     * @param string $salt
+     * @param int $opslimit
+     * @param int $memlimit
+     * @param int|null $alg
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_pwhash($outlen, $passwd, $salt, $opslimit, $memlimit, $alg = null)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($outlen, 'int', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($salt,  'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($opslimit, 'int', 4);
+        ParagonIE_Sodium_Core_Util::declareScalarType($memlimit, 'int', 5);
+
+        if (self::useNewSodiumAPI()) {
+            if (!is_null($alg)) {
+                ParagonIE_Sodium_Core_Util::declareScalarType($alg, 'int', 6);
+                return sodium_crypto_pwhash($outlen, $passwd, $salt, $opslimit, $memlimit, $alg);
+            }
+            return sodium_crypto_pwhash($outlen, $passwd, $salt, $opslimit, $memlimit);
+        }
+        if (self::use_fallback('crypto_pwhash')) {
+            return (string) call_user_func('\\Sodium\\crypto_pwhash', $outlen, $passwd, $salt, $opslimit, $memlimit);
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Argon2i with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * !Exclusive to sodium_compat!
+     *
+     * This returns TRUE if the native crypto_pwhash API is available by libsodium.
+     * This returns FALSE if only sodium_compat is available.
+     *
+     * @return bool
+     */
+    public static function crypto_pwhash_is_available()
+    {
+        if (self::useNewSodiumAPI()) {
+            return true;
+        }
+        if (self::use_fallback('crypto_pwhash')) {
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * @param string $passwd
+     * @param int $opslimit
+     * @param int $memlimit
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_pwhash_str($passwd, $opslimit, $memlimit)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($opslimit, 'int', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($memlimit, 'int', 3);
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_pwhash_str($passwd, $opslimit, $memlimit);
+        }
+        if (self::use_fallback('crypto_pwhash_str')) {
+            return (string) call_user_func('\\Sodium\\crypto_pwhash_str', $passwd, $opslimit, $memlimit);
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Argon2i with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * @param string $passwd
+     * @param string $hash
+     * @return bool
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_pwhash_str_verify($passwd, $hash)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($hash, 'string', 2);
+
+        if (self::useNewSodiumAPI()) {
+            return (bool) sodium_crypto_pwhash_str_verify($passwd, $hash);
+        }
+        if (self::use_fallback('crypto_pwhash_str_verify')) {
+            return (bool) call_user_func('\\Sodium\\crypto_pwhash_str_verify', $passwd, $hash);
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Argon2i with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * @param int $outlen
+     * @param string $passwd
+     * @param string $salt
+     * @param int $opslimit
+     * @param int $memlimit
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     */
+    public static function crypto_pwhash_scryptsalsa208sha256($outlen, $passwd, $salt, $opslimit, $memlimit)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($outlen, 'int', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($salt,  'string', 3);
+        ParagonIE_Sodium_Core_Util::declareScalarType($opslimit, 'int', 4);
+        ParagonIE_Sodium_Core_Util::declareScalarType($memlimit, 'int', 5);
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_pwhash_scryptsalsa208sha256(
+                (int) $outlen,
+                (string) $passwd,
+                (string) $salt,
+                (int) $opslimit,
+                (int) $memlimit
+            );
+        }
+        if (self::use_fallback('crypto_pwhash_scryptsalsa208sha256')) {
+            return (string) call_user_func(
+                '\\Sodium\\crypto_pwhash_scryptsalsa208sha256',
+                (int) $outlen,
+                (string) $passwd,
+                (string) $salt,
+                (int) $opslimit,
+                (int) $memlimit
+            );
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Scrypt with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * !Exclusive to sodium_compat!
+     *
+     * This returns TRUE if the native crypto_pwhash API is available by libsodium.
+     * This returns FALSE if only sodium_compat is available.
+     *
+     * @return bool
+     */
+    public static function crypto_pwhash_scryptsalsa208sha256_is_available()
+    {
+        if (self::useNewSodiumAPI()) {
+            return true;
+        }
+        if (self::use_fallback('crypto_pwhash_scryptsalsa208sha256')) {
+            return true;
+        }
+        return false;
+    }
+
+    /**
+     * @param string $passwd
+     * @param int $opslimit
+     * @param int $memlimit
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     */
+    public static function crypto_pwhash_scryptsalsa208sha256_str($passwd, $opslimit, $memlimit)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($opslimit, 'int', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($memlimit, 'int', 3);
+
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_crypto_pwhash_scryptsalsa208sha256_str(
+                (string) $passwd,
+                (int) $opslimit,
+                (int) $memlimit
+            );
+        }
+        if (self::use_fallback('crypto_pwhash_scryptsalsa208sha256_str')) {
+            return (string) call_user_func(
+                '\\Sodium\\crypto_pwhash_scryptsalsa208sha256_str',
+                (string) $passwd,
+                (int) $opslimit,
+                (int) $memlimit
+            );
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Scrypt with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * @param string $passwd
+     * @param string $hash
+     * @return bool
+     * @throws SodiumException
+     * @throws TypeError
+     */
+    public static function crypto_pwhash_scryptsalsa208sha256_str_verify($passwd, $hash)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($passwd, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($hash, 'string', 2);
+
+        if (self::useNewSodiumAPI()) {
+            return (bool) sodium_crypto_pwhash_scryptsalsa208sha256_str_verify(
+                (string) $passwd,
+                (string) $hash
+            );
+        }
+        if (self::use_fallback('crypto_pwhash_scryptsalsa208sha256_str_verify')) {
+            return (bool) call_user_func(
+                '\\Sodium\\crypto_pwhash_scryptsalsa208sha256_str_verify',
+                (string) $passwd,
+                (string) $hash
+            );
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented, as it is not possible to implement Scrypt with acceptable performance in pure-PHP'
+        );
+    }
+
+    /**
+     * Calculate the shared secret between your secret key and your
+     * recipient's public key.
+     *
+     * Algorithm: X25519 (ECDH over Curve25519)
+     *
+     * @param string $secretKey
+     * @param string $publicKey
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_scalarmult($secretKey, $publicKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($publicKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_BOX_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_SECRETKEYBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($publicKey) !== self::CRYPTO_BOX_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_BOX_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_scalarmult($secretKey, $publicKey);
+        }
+        if (self::use_fallback('crypto_scalarmult')) {
+            return (string) call_user_func('\\Sodium\\crypto_scalarmult', $secretKey, $publicKey);
+        }
+
+        /* Output validation: Forbid all-zero keys */
+        if (ParagonIE_Sodium_Core_Util::hashEquals($secretKey, str_repeat("\0", self::CRYPTO_BOX_SECRETKEYBYTES))) {
+            throw new SodiumException('Zero secret key is not allowed');
+        }
+        if (ParagonIE_Sodium_Core_Util::hashEquals($publicKey, str_repeat("\0", self::CRYPTO_BOX_PUBLICKEYBYTES))) {
+            throw new SodiumException('Zero public key is not allowed');
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::scalarmult($secretKey, $publicKey);
+        }
+        return ParagonIE_Sodium_Crypto::scalarmult($secretKey, $publicKey);
+    }
+
+    /**
+     * Calculate an X25519 public key from an X25519 secret key.
+     *
+     * @param string $secretKey
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress TooFewArguments
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_scalarmult_base($secretKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_BOX_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_BOX_SECRETKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_scalarmult_base($secretKey);
+        }
+        if (self::use_fallback('crypto_scalarmult_base')) {
+            return (string) call_user_func('\\Sodium\\crypto_scalarmult_base', $secretKey);
+        }
+        if (ParagonIE_Sodium_Core_Util::hashEquals($secretKey, str_repeat("\0", self::CRYPTO_BOX_SECRETKEYBYTES))) {
+            throw new SodiumException('Zero secret key is not allowed');
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::scalarmult_base($secretKey);
+        }
+        return ParagonIE_Sodium_Crypto::scalarmult_base($secretKey);
+    }
+
+    /**
+     * Authenticated symmetric-key encryption.
+     *
+     * Algorithm: XSalsa20-Poly1305
+     *
+     * @param string $plaintext The message you're encrypting
+     * @param string $nonce A Number to be used Once; must be 24 bytes
+     * @param string $key Symmetric encryption key
+     * @return string           Ciphertext with Poly1305 MAC
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_secretbox($plaintext, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_SECRETBOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SECRETBOX_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_secretbox($plaintext, $nonce, $key);
+        }
+        if (self::use_fallback('crypto_secretbox')) {
+            return (string) call_user_func('\\Sodium\\crypto_secretbox', $plaintext, $nonce, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::secretbox($plaintext, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Crypto::secretbox($plaintext, $nonce, $key);
+    }
+
+    /**
+     * Decrypts a message previously encrypted with crypto_secretbox().
+     *
+     * @param string $ciphertext Ciphertext with Poly1305 MAC
+     * @param string $nonce      A Number to be used Once; must be 24 bytes
+     * @param string $key        Symmetric encryption key
+     * @return string            Original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_secretbox_open($ciphertext, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_SECRETBOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SECRETBOX_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_secretbox_open($ciphertext, $nonce, $key);
+        }
+        if (self::use_fallback('crypto_secretbox_open')) {
+            return call_user_func('\\Sodium\\crypto_secretbox_open', $ciphertext, $nonce, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::secretbox_open($ciphertext, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Crypto::secretbox_open($ciphertext, $nonce, $key);
+    }
+
+    /**
+     * Return a secure random key for use with crypto_secretbox
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_secretbox_keygen()
+    {
+        return random_bytes(self::CRYPTO_SECRETBOX_KEYBYTES);
+    }
+
+    /**
+     * Authenticated symmetric-key encryption.
+     *
+     * Algorithm: XChaCha20-Poly1305
+     *
+     * @param string $plaintext The message you're encrypting
+     * @param string $nonce     A Number to be used Once; must be 24 bytes
+     * @param string $key       Symmetric encryption key
+     * @return string           Ciphertext with Poly1305 MAC
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_secretbox_xchacha20poly1305($plaintext, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($plaintext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_SECRETBOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SECRETBOX_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::secretbox_xchacha20poly1305($plaintext, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Crypto::secretbox_xchacha20poly1305($plaintext, $nonce, $key);
+    }
+    /**
+     * Decrypts a message previously encrypted with crypto_secretbox_xchacha20poly1305().
+     *
+     * @param string $ciphertext Ciphertext with Poly1305 MAC
+     * @param string $nonce      A Number to be used Once; must be 24 bytes
+     * @param string $key        Symmetric encryption key
+     * @return string            Original plaintext message
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_secretbox_xchacha20poly1305_open($ciphertext, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($ciphertext, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_SECRETBOX_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SECRETBOX_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
+        }
+
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::secretbox_xchacha20poly1305_open($ciphertext, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Crypto::secretbox_xchacha20poly1305_open($ciphertext, $nonce, $key);
+    }
+
+    /**
+     * Calculates a SipHash-2-4 hash of a message for a given key.
+     *
+     * @param string $message Input message
+     * @param string $key SipHash-2-4 key
+     * @return string         Hash
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_shorthash($message, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_SHORTHASH_KEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SHORTHASH_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_shorthash($message, $key);
+        }
+        if (self::use_fallback('crypto_shorthash')) {
+            return (string) call_user_func('\\Sodium\\crypto_shorthash', $message, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_SipHash::sipHash24($message, $key);
+        }
+        return ParagonIE_Sodium_Core_SipHash::sipHash24($message, $key);
+    }
+
+    /**
+     * Return a secure random key for use with crypto_shorthash
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_shorthash_keygen()
+    {
+        return random_bytes(self::CRYPTO_SHORTHASH_KEYBYTES);
+    }
+
+    /**
+     * Returns a signed message. You probably want crypto_sign_detached()
+     * instead, which only returns the signature.
+     *
+     * Algorithm: Ed25519 (EdDSA over Curve25519)
+     *
+     * @param string $message Message to be signed.
+     * @param string $secretKey Secret signing key.
+     * @return string           Signed message (signature is prefixed).
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_sign($message, $secretKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_SIGN_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SIGN_SECRETKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign($message, $secretKey);
+        }
+        if (self::use_fallback('crypto_sign')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign', $message, $secretKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::sign($message, $secretKey);
+        }
+        return ParagonIE_Sodium_Crypto::sign($message, $secretKey);
+    }
+
+    /**
+     * Validates a signed message then returns the message.
+     *
+     * @param string $signedMessage A signed message
+     * @param string $publicKey A public key
+     * @return string               The original message (if the signature is
+     *                              valid for this public key)
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress MixedReturnStatement
+     */
+    public static function crypto_sign_open($signedMessage, $publicKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($signedMessage, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($publicKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($signedMessage) < self::CRYPTO_SIGN_BYTES) {
+            throw new SodiumException('Argument 1 must be at least CRYPTO_SIGN_BYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($publicKey) !== self::CRYPTO_SIGN_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SIGN_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            /**
+             * @psalm-suppress InvalidReturnStatement
+             * @psalm-suppress FalsableReturnStatement
+             */
+            return sodium_crypto_sign_open($signedMessage, $publicKey);
+        }
+        if (self::use_fallback('crypto_sign_open')) {
+            return call_user_func('\\Sodium\\crypto_sign_open', $signedMessage, $publicKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::sign_open($signedMessage, $publicKey);
+        }
+        return ParagonIE_Sodium_Crypto::sign_open($signedMessage, $publicKey);
+    }
+
+    /**
+     * Generate a new random Ed25519 keypair.
+     *
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     */
+    public static function crypto_sign_keypair()
+    {
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_keypair();
+        }
+        if (self::use_fallback('crypto_sign_keypair')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_keypair');
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_Ed25519::keypair();
+        }
+        return ParagonIE_Sodium_Core_Ed25519::keypair();
+    }
+
+    /**
+     * Generate an Ed25519 keypair from a seed.
+     *
+     * @param string $seed Input seed
+     * @return string      Keypair
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_seed_keypair($seed)
+    {
+        ParagonIE_Sodium_Core_Util::declareScalarType($seed, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_seed_keypair($seed);
+        }
+        if (self::use_fallback('crypto_sign_keypair')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_seed_keypair', $seed);
+        }
+        $publicKey = '';
+        $secretKey = '';
+        if (PHP_INT_SIZE === 4) {
+            ParagonIE_Sodium_Core32_Ed25519::seed_keypair($publicKey, $secretKey, $seed);
+        } else {
+            ParagonIE_Sodium_Core_Ed25519::seed_keypair($publicKey, $secretKey, $seed);
+        }
+        return $secretKey . $publicKey;
+    }
+
+    /**
+     * Extract an Ed25519 public key from an Ed25519 keypair.
+     *
+     * @param string $keypair Keypair
+     * @return string         Public key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_publickey($keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_SIGN_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_SIGN_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_publickey($keypair);
+        }
+        if (self::use_fallback('crypto_sign_publickey')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_publickey', $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_Ed25519::publickey($keypair);
+        }
+        return ParagonIE_Sodium_Core_Ed25519::publickey($keypair);
+    }
+
+    /**
+     * Calculate an Ed25519 public key from an Ed25519 secret key.
+     *
+     * @param string $secretKey Your Ed25519 secret key
+     * @return string           The corresponding Ed25519 public key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_publickey_from_secretkey($secretKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_SIGN_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_SIGN_SECRETKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_publickey_from_secretkey($secretKey);
+        }
+        if (self::use_fallback('crypto_sign_publickey_from_secretkey')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_publickey_from_secretkey', $secretKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_Ed25519::publickey_from_secretkey($secretKey);
+        }
+        return ParagonIE_Sodium_Core_Ed25519::publickey_from_secretkey($secretKey);
+    }
+
+    /**
+     * Extract an Ed25519 secret key from an Ed25519 keypair.
+     *
+     * @param string $keypair Keypair
+     * @return string         Secret key
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_secretkey($keypair)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($keypair, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_SIGN_KEYPAIRBYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_SIGN_KEYPAIRBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_secretkey($keypair);
+        }
+        if (self::use_fallback('crypto_sign_secretkey')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_secretkey', $keypair);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_Ed25519::secretkey($keypair);
+        }
+        return ParagonIE_Sodium_Core_Ed25519::secretkey($keypair);
+    }
+
+    /**
+     * Calculate the Ed25519 signature of a message and return ONLY the signature.
+     *
+     * Algorithm: Ed25519 (EdDSA over Curve25519)
+     *
+     * @param string $message Message to be signed
+     * @param string $secretKey Secret signing key
+     * @return string           Digital signature
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_detached($message, $secretKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($secretKey, 'string', 2);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($secretKey) !== self::CRYPTO_SIGN_SECRETKEYBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SIGN_SECRETKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_detached($message, $secretKey);
+        }
+        if (self::use_fallback('crypto_sign_detached')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_detached', $message, $secretKey);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::sign_detached($message, $secretKey);
+        }
+        return ParagonIE_Sodium_Crypto::sign_detached($message, $secretKey);
+    }
+
+    /**
+     * Verify the Ed25519 signature of a message.
+     *
+     * @param string $signature Digital sginature
+     * @param string $message Message to be verified
+     * @param string $publicKey Public key
+     * @return bool             TRUE if this signature is good for this public key;
+     *                          FALSE otherwise
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_verify_detached($signature, $message, $publicKey)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($signature, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($publicKey, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($signature) !== self::CRYPTO_SIGN_BYTES) {
+            throw new SodiumException('Argument 1 must be CRYPTO_SIGN_BYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($publicKey) !== self::CRYPTO_SIGN_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SIGN_PUBLICKEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_sign_verify_detached($signature, $message, $publicKey);
+        }
+        if (self::use_fallback('crypto_sign_verify_detached')) {
+            return (bool) call_user_func(
+                '\\Sodium\\crypto_sign_verify_detached',
+                $signature,
+                $message,
+                $publicKey
+            );
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Crypto32::sign_verify_detached($signature, $message, $publicKey);
+        }
+        return ParagonIE_Sodium_Crypto::sign_verify_detached($signature, $message, $publicKey);
+    }
+
+    /**
+     * Convert an Ed25519 public key to a Curve25519 public key
+     *
+     * @param string $pk
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_ed25519_pk_to_curve25519($pk)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($pk, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($pk) < self::CRYPTO_SIGN_PUBLICKEYBYTES) {
+            throw new SodiumException('Argument 1 must be at least CRYPTO_SIGN_PUBLICKEYBYTES long.');
+        }
+        if (self::useNewSodiumAPI()) {
+            if (is_callable('crypto_sign_ed25519_pk_to_curve25519')) {
+                return (string) sodium_crypto_sign_ed25519_pk_to_curve25519($pk);
+            }
+        }
+        if (self::use_fallback('crypto_sign_ed25519_pk_to_curve25519')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_ed25519_pk_to_curve25519', $pk);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_Ed25519::pk_to_curve25519($pk);
+        }
+        return ParagonIE_Sodium_Core_Ed25519::pk_to_curve25519($pk);
+    }
+
+    /**
+     * Convert an Ed25519 secret key to a Curve25519 secret key
+     *
+     * @param string $sk
+     * @return string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_sign_ed25519_sk_to_curve25519($sk)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($sk, 'string', 1);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($sk) < self::CRYPTO_SIGN_SEEDBYTES) {
+            throw new SodiumException('Argument 1 must be at least CRYPTO_SIGN_SEEDBYTES long.');
+        }
+        if (self::useNewSodiumAPI()) {
+            if (is_callable('crypto_sign_ed25519_sk_to_curve25519')) {
+                return sodium_crypto_sign_ed25519_sk_to_curve25519($sk);
+            }
+        }
+        if (self::use_fallback('crypto_sign_ed25519_sk_to_curve25519')) {
+            return (string) call_user_func('\\Sodium\\crypto_sign_ed25519_sk_to_curve25519', $sk);
+        }
+
+        $h = hash('sha512', ParagonIE_Sodium_Core_Util::substr($sk, 0, 32), true);
+        $h[0] = ParagonIE_Sodium_Core_Util::intToChr(
+            ParagonIE_Sodium_Core_Util::chrToInt($h[0]) & 248
+        );
+        $h[31] = ParagonIE_Sodium_Core_Util::intToChr(
+            (ParagonIE_Sodium_Core_Util::chrToInt($h[31]) & 127) | 64
+        );
+        return ParagonIE_Sodium_Core_Util::substr($h, 0, 32);
+    }
+
+    /**
+     * Expand a key and nonce into a keystream of pseudorandom bytes.
+     *
+     * @param int $len Number of bytes desired
+     * @param string $nonce Number to be used Once; must be 24 bytes
+     * @param string $key XSalsa20 key
+     * @return string       Pseudorandom stream that can be XORed with messages
+     *                      to provide encryption (but not authentication; see
+     *                      Poly1305 or crypto_auth() for that, which is not
+     *                      optional for security)
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_stream($len, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($len, 'int', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_STREAM_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_STREAM_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_STREAM_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_stream($len, $nonce, $key);
+        }
+        if (self::use_fallback('crypto_stream')) {
+            return (string) call_user_func('\\Sodium\\crypto_stream', $len, $nonce, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_XSalsa20::xsalsa20($len, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Core_XSalsa20::xsalsa20($len, $nonce, $key);
+    }
+
+    /**
+     * DANGER! UNAUTHENTICATED ENCRYPTION!
+     *
+     * Unless you are following expert advice, do not used this feature.
+     *
+     * Algorithm: XSalsa20
+     *
+     * This DOES NOT provide ciphertext integrity.
+     *
+     * @param string $message Plaintext message
+     * @param string $nonce Number to be used Once; must be 24 bytes
+     * @param string $key Encryption key
+     * @return string         Encrypted text which is vulnerable to chosen-
+     *                        ciphertext attacks unless you implement some
+     *                        other mitigation to the ciphertext (i.e.
+     *                        Encrypt then MAC)
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function crypto_stream_xor($message, $nonce, $key)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($message, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($nonce, 'string', 2);
+        ParagonIE_Sodium_Core_Util::declareScalarType($key, 'string', 3);
+
+        /* Input validation: */
+        if (ParagonIE_Sodium_Core_Util::strlen($nonce) !== self::CRYPTO_STREAM_NONCEBYTES) {
+            throw new SodiumException('Argument 2 must be CRYPTO_SECRETBOX_NONCEBYTES long.');
+        }
+        if (ParagonIE_Sodium_Core_Util::strlen($key) !== self::CRYPTO_STREAM_KEYBYTES) {
+            throw new SodiumException('Argument 3 must be CRYPTO_SECRETBOX_KEYBYTES long.');
+        }
+
+        if (self::useNewSodiumAPI()) {
+            return sodium_crypto_stream_xor($message, $nonce, $key);
+        }
+        if (self::use_fallback('crypto_stream_xor')) {
+            return (string) call_user_func('\\Sodium\\crypto_stream_xor', $message, $nonce, $key);
+        }
+        if (PHP_INT_SIZE === 4) {
+            return ParagonIE_Sodium_Core32_XSalsa20::xsalsa20_xor($message, $nonce, $key);
+        }
+        return ParagonIE_Sodium_Core_XSalsa20::xsalsa20_xor($message, $nonce, $key);
+    }
+
+    /**
+     * Return a secure random key for use with crypto_stream
+     *
+     * @return string
+     * @throws Exception
+     * @throws Error
+     */
+    public static function crypto_stream_keygen()
+    {
+        return random_bytes(self::CRYPTO_STREAM_KEYBYTES);
+    }
+
+    /**
+     * Cache-timing-safe implementation of hex2bin().
+     *
+     * @param string $string Hexadecimal string
+     * @return string        Raw binary string
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress TooFewArguments
+     * @psalm-suppress MixedArgument
+     */
+    public static function hex2bin($string)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($string, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            if (is_callable('sodium_hex2bin')) {
+                return (string) sodium_hex2bin($string);
+            }
+        }
+        if (self::use_fallback('hex2bin')) {
+            return (string) call_user_func('\\Sodium\\hex2bin', $string);
+        }
+        return ParagonIE_Sodium_Core_Util::hex2bin($string);
+    }
+
+    /**
+     * Increase a string (little endian)
+     *
+     * @param string $var
+     *
+     * @return void
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function increment(&$var)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($var, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            sodium_increment($var);
+            return;
+        }
+        if (self::use_fallback('increment')) {
+            $func = '\\Sodium\\increment';
+            $func($var);
+            return;
+        }
+
+        $len = ParagonIE_Sodium_Core_Util::strlen($var);
+        $c = 1;
+        $copy = '';
+        for ($i = 0; $i < $len; ++$i) {
+            $c += ParagonIE_Sodium_Core_Util::chrToInt(
+                ParagonIE_Sodium_Core_Util::substr($var, $i, 1)
+            );
+            $copy .= ParagonIE_Sodium_Core_Util::intToChr($c);
+            $c >>= 8;
+        }
+        $var = $copy;
+    }
+
+    /**
+     * The equivalent to the libsodium minor version we aim to be compatible
+     * with (sans pwhash and memzero).
+     *
+     * @return int
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress UndefinedFunction
+     */
+    public static function library_version_major()
+    {
+        if (self::useNewSodiumAPI()) {
+            return sodium_library_version_major();
+        }
+        if (self::use_fallback('library_version_major')) {
+            return (int) call_user_func('\\Sodium\\library_version_major');
+        }
+        return self::LIBRARY_VERSION_MAJOR;
+    }
+
+    /**
+     * The equivalent to the libsodium minor version we aim to be compatible
+     * with (sans pwhash and memzero).
+     *
+     * @return int
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress UndefinedFunction
+     */
+    public static function library_version_minor()
+    {
+        if (self::useNewSodiumAPI()) {
+            return sodium_library_version_minor();
+        }
+        if (self::use_fallback('library_version_minor')) {
+            return (int) call_user_func('\\Sodium\\library_version_minor');
+        }
+        return self::LIBRARY_VERSION_MINOR;
+    }
+
+    /**
+     * Compare two strings.
+     *
+     * @param string $left
+     * @param string $right
+     * @return int
+     * @throws SodiumException
+     * @throws TypeError
+     * @psalm-suppress MixedArgument
+     */
+    public static function memcmp($left, $right)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($left, 'string', 1);
+        ParagonIE_Sodium_Core_Util::declareScalarType($right, 'string', 2);
+
+        if (self::use_fallback('memcmp')) {
+            return (int) call_user_func('\\Sodium\\memcmp', $left, $right);
+        }
+        /** @var string $left */
+        /** @var string $right */
+        return ParagonIE_Sodium_Core_Util::memcmp($left, $right);
+    }
+
+    /**
+     * It's actually not possible to zero memory buffers in PHP. You need the
+     * native library for that.
+     *
+     * @param string|null $var
+     * @param-out string|null $var
+     *
+     * @return void
+     * @throws SodiumException (Unless libsodium is installed)
+     * @throws TypeError
+     * @psalm-suppress TooFewArguments
+     */
+    public static function memzero(&$var)
+    {
+        /* Type checks: */
+        ParagonIE_Sodium_Core_Util::declareScalarType($var, 'string', 1);
+
+        if (self::useNewSodiumAPI()) {
+            /** @psalm-suppress MixedArgument */
+            sodium_memzero($var);
+            return;
+        }
+        if (self::use_fallback('memzero')) {
+            $func = '\\Sodium\\memzero';
+            $func($var);
+            if ($var === null) {
+                return;
+            }
+        }
+        // This is the best we can do.
+        throw new SodiumException(
+            'This is not implemented in sodium_compat, as it is not possible to securely wipe memory from PHP. ' .
+            'To fix this error, make sure libsodium is installed and the PHP extension is enabled.'
+        );
+    }
+
+    /**
+     * Will sodium_compat run fast on the current hardware and PHP configuration?
+     *
+     * @return bool
+     */
+    public static function polyfill_is_fast()
+    {
+        if (extension_loaded('sodium')) {
+            return true;
+        }
+        if (extension_loaded('libsodium')) {
+            return true;
+        }
+        return PHP_INT_SIZE === 8;
+    }
+
+    /**
+     * Generate a string of bytes from the kernel's CSPRNG.
+     * Proudly uses /dev/urandom (if getrandom(2) is not available).
+     *
+     * @param int $numBytes
+     * @return string
+     * @throws Exception
+     * @throws TypeError
+     */
+    public static function randombytes_buf($numBytes)
+    {
+        /* Type checks: */
+        if (!is_int($numBytes)) {
+            if (is_numeric($numBytes)) {
+                $numBytes = (int) $numBytes;
+            } else {
+                throw new TypeError(
+                    'Argument 1 must be an integer, ' . gettype($numBytes) . ' given.'
+                );
+            }
+        }
+        if (self::use_fallback('randombytes_buf')) {
+            return (string) call_user_func('\\Sodium\\randombytes_buf', $numBytes);
+        }
+        return random_bytes($numBytes);
+    }
+
+    /**
+     * Generate an integer between 0 and $range (non-inclusive).
+     *
+     * @param int $range
+     * @return int
+     * @throws Exception
+     * @throws Error
+     * @throws TypeError
+     */
+    public static function randombytes_uniform($range)
+    {
+        /* Type checks: */
+        if (!is_int($range)) {
+            if (is_numeric($range)) {
+                $range = (int) $range;
+            } else {
+                throw new TypeError(
+                    'Argument 1 must be an integer, ' . gettype($range) . ' given.'
+                );
+            }
+        }
+        if (self::use_fallback('randombytes_uniform')) {
+            return (int) call_user_func('\\Sodium\\randombytes_uniform', $range);
+        }
+        return random_int(0, $range - 1);
+    }
+
+    /**
+     * Generate a random 16-bit integer.
+     *
+     * @return int
+     * @throws Exception
+     * @throws Error
+     * @throws TypeError
+     */
+    public static function randombytes_random16()
+    {
+        if (self::use_fallback('randombytes_random16')) {
+            return (int) call_user_func('\\Sodium\\randombytes_random16');
+        }
+        return random_int(0, 65535);
+    }
+
+    /**
+     * Runtime testing method for 32-bit platforms.
+     *
+     * Usage: If runtime_speed_test() returns FALSE, then our 32-bit
+     *        implementation is to slow to use safely without risking timeouts.
+     *        If this happens, install sodium from PECL to get acceptable
+     *        performance.
+     *
+     * @param int $iterations Number of multiplications to attempt
+     * @param int $maxTimeout Milliseconds
+     * @return bool           TRUE if we're fast enough, FALSE is not
+     * @throws SodiumException
+     */
+    public static function runtime_speed_test($iterations, $maxTimeout)
+    {
+        if (self::polyfill_is_fast()) {
+            return true;
+        }
+        /** @var float $end */
+        $end = 0.0;
+        /** @var float $start */
+        $start = microtime(true);
+        /** @var ParagonIE_Sodium_Core32_Int64 $a */
+        $a = ParagonIE_Sodium_Core32_Int64::fromInt(random_int(3, 1 << 16));
+        for ($i = 0; $i < $iterations; ++$i) {
+            /** @var ParagonIE_Sodium_Core32_Int64 $b */
+            $b = ParagonIE_Sodium_Core32_Int64::fromInt(random_int(3, 1 << 16));
+            $a->mulInt64($b);
+        }
+        /** @var float $end */
+        $end = microtime(true);
+        /** @var int $diff */
+        $diff = (int) ceil(($end - $start) * 1000);
+        return $diff < $maxTimeout;
+    }
+
+    /**
+     * This emulates libsodium's version_string() function, except ours is
+     * prefixed with 'polyfill-'.
+     *
+     * @return string
+     * @psalm-suppress MixedInferredReturnType
+     * @psalm-suppress UndefinedFunction
+     */
+    public static function version_string()
+    {
+        if (self::useNewSodiumAPI()) {
+            return (string) sodium_version_string();
+        }
+        if (self::use_fallback('version_string')) {
+            return (string) call_user_func('\\Sodium\\version_string');
+        }
+        return (string) self::VERSION_STRING;
+    }
+
+    /**
+     * Should we use the libsodium core function instead?
+     * This is always a good idea, if it's available. (Unless we're in the
+     * middle of running our unit test suite.)
+     *
+     * If ext/libsodium is available, use it. Return TRUE.
+     * Otherwise, we have to use the code provided herein. Return FALSE.
+     *
+     * @param string $sodium_func_name
+     *
+     * @return bool
+     */
+    protected static function use_fallback($sodium_func_name = '')
+    {
+        static $res = null;
+        if ($res === null) {
+            $res = extension_loaded('libsodium') && PHP_VERSION_ID >= 50300;
+        }
+        if ($res === false) {
+            // No libsodium installed
+            return false;
+        }
+        if (self::$disableFallbackForUnitTests) {
+            // Don't fallback. Use the PHP implementation.
+            return false;
+        }
+        if (!empty($sodium_func_name)) {
+            return is_callable('\\Sodium\\' . $sodium_func_name);
+        }
+        return true;
+    }
+
+    /**
+     * Libsodium as implemented in PHP 7.2
+     * and/or ext/sodium (via PECL)
+     *
+     * @ref https://wiki.php.net/rfc/libsodium
+     * @return bool
+     */
+    protected static function useNewSodiumAPI()
+    {
+        static $res = null;
+        if ($res === null) {
+            $res = PHP_VERSION_ID >= 70000 && extension_loaded('sodium');
+        }
+        if (self::$disableFallbackForUnitTests) {
+            // Don't fallback. Use the PHP implementation.
+            return false;
+        }
+        return (bool) $res;
+    }
+}