Defuse\Crypto\Crypto::decryptInternal PHP Method

    private static function decryptInternal($ciphertext, KeyOrPassword $secret, $raw_binary)
    {
        RuntimeTests::runtimeTest();
        if (!$raw_binary) {
            try {
                $ciphertext = Encoding::hexToBin($ciphertext);
            } catch (Ex\BadFormatException $ex) {
                throw new Ex\WrongKeyOrModifiedCiphertextException('Ciphertext has invalid hex encoding.');
            }
        }
        if (Core::ourStrlen($ciphertext) < Core::MINIMUM_CIPHERTEXT_SIZE) {
            throw new Ex\WrongKeyOrModifiedCiphertextException('Ciphertext is too short.');
        }
        // Get and check the version header.
        $header = Core::ourSubstr($ciphertext, 0, Core::HEADER_VERSION_SIZE);
        if ($header !== Core::CURRENT_VERSION) {
            throw new Ex\WrongKeyOrModifiedCiphertextException('Bad version header.');
        }
        // Get the salt.
        $salt = Core::ourSubstr($ciphertext, Core::HEADER_VERSION_SIZE, Core::SALT_BYTE_SIZE);
        if ($salt === false) {
            throw new Ex\EnvironmentIsBrokenException();
        }
        // Get the IV.
        $iv = Core::ourSubstr($ciphertext, Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE, Core::BLOCK_BYTE_SIZE);
        if ($iv === false) {
            throw new Ex\EnvironmentIsBrokenException();
        }
        // Get the HMAC.
        $hmac = Core::ourSubstr($ciphertext, Core::ourStrlen($ciphertext) - Core::MAC_BYTE_SIZE, Core::MAC_BYTE_SIZE);
        if ($hmac === false) {
            throw new Ex\EnvironmentIsBrokenException();
        }
        // Get the actual encrypted ciphertext.
        $encrypted = Core::ourSubstr($ciphertext, Core::HEADER_VERSION_SIZE + Core::SALT_BYTE_SIZE + Core::BLOCK_BYTE_SIZE, Core::ourStrlen($ciphertext) - Core::MAC_BYTE_SIZE - Core::SALT_BYTE_SIZE - Core::BLOCK_BYTE_SIZE - Core::HEADER_VERSION_SIZE);
        if ($encrypted === false) {
            throw new Ex\EnvironmentIsBrokenException();
        }
        // Derive the separate encryption and authentication keys from the key
        // or password, whichever it is.
        $keys = $secret->deriveKeys($salt);
        if (self::verifyHMAC($hmac, $header . $salt . $iv . $encrypted, $keys->getAuthenticationKey())) {
            $plaintext = self::plainDecrypt($encrypted, $keys->getEncryptionKey(), $iv, Core::CIPHER_METHOD);
            return $plaintext;
        } else {
            throw new Ex\WrongKeyOrModifiedCiphertextException('Integrity check failed.');
        }
    }