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Filename : RC2.php
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<?php

/**
 * Pure-PHP implementation of RC2.
 *
 * Uses mcrypt, if available, and an internal implementation, otherwise.
 *
 * PHP version 5
 *
 * Useful resources are as follows:
 *
 *  - {@link http://tools.ietf.org/html/rfc2268}
 *
 * Here's a short example of how to use this library:
 * <code>
 * <?php
 *    include 'vendor/autoload.php';
 *
 *    $rc2 = new \phpseclib3\Crypt\RC2('ctr');
 *
 *    $rc2->setKey('abcdefgh');
 *
 *    $plaintext = str_repeat('a', 1024);
 *
 *    echo $rc2->decrypt($rc2->encrypt($plaintext));
 * ?>
 * </code>
 *
 * @author   Patrick Monnerat <pm@datasphere.ch>
 * @license  http://www.opensource.org/licenses/mit-license.html  MIT License
 * @link     http://phpseclib.sourceforge.net
 */

namespace phpseclib3\Crypt;

use phpseclib3\Crypt\Common\BlockCipher;
use phpseclib3\Exception\BadModeException;

/**
 * Pure-PHP implementation of RC2.
 *
 */
class RC2 extends BlockCipher
{
    /**
     * Block Length of the cipher
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::block_size
     * @var int
     */
    protected $block_size = 8;

    /**
     * The Key
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::key
     * @see self::setKey()
     * @var string
     */
    protected $key;

    /**
     * The Original (unpadded) Key
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::key
     * @see self::setKey()
     * @see self::encrypt()
     * @see self::decrypt()
     * @var string
     */
    private $orig_key;

    /**
     * Key Length (in bytes)
     *
     * @see \phpseclib3\Crypt\RC2::setKeyLength()
     * @var int
     */
    protected $key_length = 16; // = 128 bits

    /**
     * The mcrypt specific name of the cipher
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::cipher_name_mcrypt
     * @var string
     */
    protected $cipher_name_mcrypt = 'rc2';

    /**
     * Optimizing value while CFB-encrypting
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::cfb_init_len
     * @var int
     */
    protected $cfb_init_len = 500;

    /**
     * The key length in bits.
     *
     * {@internal Should be in range [1..1024].}
     *
     * {@internal Changing this value after setting the key has no effect.}
     *
     * @see self::setKeyLength()
     * @see self::setKey()
     * @var int
     */
    private $default_key_length = 1024;

    /**
     * The key length in bits.
     *
     * {@internal Should be in range [1..1024].}
     *
     * @see self::isValidEnine()
     * @see self::setKey()
     * @var int
     */
    private $current_key_length;

    /**
     * The Key Schedule
     *
     * @see self::setupKey()
     * @var array
     */
    private $keys;

    /**
     * Key expansion randomization table.
     * Twice the same 256-value sequence to save a modulus in key expansion.
     *
     * @see self::setKey()
     * @var array
     */
    private static $pitable = [
        0xD9, 0x78, 0xF9, 0xC4, 0x19, 0xDD, 0xB5, 0xED,
        0x28, 0xE9, 0xFD, 0x79, 0x4A, 0xA0, 0xD8, 0x9D,
        0xC6, 0x7E, 0x37, 0x83, 0x2B, 0x76, 0x53, 0x8E,
        0x62, 0x4C, 0x64, 0x88, 0x44, 0x8B, 0xFB, 0xA2,
        0x17, 0x9A, 0x59, 0xF5, 0x87, 0xB3, 0x4F, 0x13,
        0x61, 0x45, 0x6D, 0x8D, 0x09, 0x81, 0x7D, 0x32,
        0xBD, 0x8F, 0x40, 0xEB, 0x86, 0xB7, 0x7B, 0x0B,
        0xF0, 0x95, 0x21, 0x22, 0x5C, 0x6B, 0x4E, 0x82,
        0x54, 0xD6, 0x65, 0x93, 0xCE, 0x60, 0xB2, 0x1C,
        0x73, 0x56, 0xC0, 0x14, 0xA7, 0x8C, 0xF1, 0xDC,
        0x12, 0x75, 0xCA, 0x1F, 0x3B, 0xBE, 0xE4, 0xD1,
        0x42, 0x3D, 0xD4, 0x30, 0xA3, 0x3C, 0xB6, 0x26,
        0x6F, 0xBF, 0x0E, 0xDA, 0x46, 0x69, 0x07, 0x57,
        0x27, 0xF2, 0x1D, 0x9B, 0xBC, 0x94, 0x43, 0x03,
        0xF8, 0x11, 0xC7, 0xF6, 0x90, 0xEF, 0x3E, 0xE7,
        0x06, 0xC3, 0xD5, 0x2F, 0xC8, 0x66, 0x1E, 0xD7,
        0x08, 0xE8, 0xEA, 0xDE, 0x80, 0x52, 0xEE, 0xF7,
        0x84, 0xAA, 0x72, 0xAC, 0x35, 0x4D, 0x6A, 0x2A,
        0x96, 0x1A, 0xD2, 0x71, 0x5A, 0x15, 0x49, 0x74,
        0x4B, 0x9F, 0xD0, 0x5E, 0x04, 0x18, 0xA4, 0xEC,
        0xC2, 0xE0, 0x41, 0x6E, 0x0F, 0x51, 0xCB, 0xCC,
        0x24, 0x91, 0xAF, 0x50, 0xA1, 0xF4, 0x70, 0x39,
        0x99, 0x7C, 0x3A, 0x85, 0x23, 0xB8, 0xB4, 0x7A,
        0xFC, 0x02, 0x36, 0x5B, 0x25, 0x55, 0x97, 0x31,
        0x2D, 0x5D, 0xFA, 0x98, 0xE3, 0x8A, 0x92, 0xAE,
        0x05, 0xDF, 0x29, 0x10, 0x67, 0x6C, 0xBA, 0xC9,
        0xD3, 0x00, 0xE6, 0xCF, 0xE1, 0x9E, 0xA8, 0x2C,
        0x63, 0x16, 0x01, 0x3F, 0x58, 0xE2, 0x89, 0xA9,
        0x0D, 0x38, 0x34, 0x1B, 0xAB, 0x33, 0xFF, 0xB0,
        0xBB, 0x48, 0x0C, 0x5F, 0xB9, 0xB1, 0xCD, 0x2E,
        0xC5, 0xF3, 0xDB, 0x47, 0xE5, 0xA5, 0x9C, 0x77,
        0x0A, 0xA6, 0x20, 0x68, 0xFE, 0x7F, 0xC1, 0xAD,
        0xD9, 0x78, 0xF9, 0xC4, 0x19, 0xDD, 0xB5, 0xED,
        0x28, 0xE9, 0xFD, 0x79, 0x4A, 0xA0, 0xD8, 0x9D,
        0xC6, 0x7E, 0x37, 0x83, 0x2B, 0x76, 0x53, 0x8E,
        0x62, 0x4C, 0x64, 0x88, 0x44, 0x8B, 0xFB, 0xA2,
        0x17, 0x9A, 0x59, 0xF5, 0x87, 0xB3, 0x4F, 0x13,
        0x61, 0x45, 0x6D, 0x8D, 0x09, 0x81, 0x7D, 0x32,
        0xBD, 0x8F, 0x40, 0xEB, 0x86, 0xB7, 0x7B, 0x0B,
        0xF0, 0x95, 0x21, 0x22, 0x5C, 0x6B, 0x4E, 0x82,
        0x54, 0xD6, 0x65, 0x93, 0xCE, 0x60, 0xB2, 0x1C,
        0x73, 0x56, 0xC0, 0x14, 0xA7, 0x8C, 0xF1, 0xDC,
        0x12, 0x75, 0xCA, 0x1F, 0x3B, 0xBE, 0xE4, 0xD1,
        0x42, 0x3D, 0xD4, 0x30, 0xA3, 0x3C, 0xB6, 0x26,
        0x6F, 0xBF, 0x0E, 0xDA, 0x46, 0x69, 0x07, 0x57,
        0x27, 0xF2, 0x1D, 0x9B, 0xBC, 0x94, 0x43, 0x03,
        0xF8, 0x11, 0xC7, 0xF6, 0x90, 0xEF, 0x3E, 0xE7,
        0x06, 0xC3, 0xD5, 0x2F, 0xC8, 0x66, 0x1E, 0xD7,
        0x08, 0xE8, 0xEA, 0xDE, 0x80, 0x52, 0xEE, 0xF7,
        0x84, 0xAA, 0x72, 0xAC, 0x35, 0x4D, 0x6A, 0x2A,
        0x96, 0x1A, 0xD2, 0x71, 0x5A, 0x15, 0x49, 0x74,
        0x4B, 0x9F, 0xD0, 0x5E, 0x04, 0x18, 0xA4, 0xEC,
        0xC2, 0xE0, 0x41, 0x6E, 0x0F, 0x51, 0xCB, 0xCC,
        0x24, 0x91, 0xAF, 0x50, 0xA1, 0xF4, 0x70, 0x39,
        0x99, 0x7C, 0x3A, 0x85, 0x23, 0xB8, 0xB4, 0x7A,
        0xFC, 0x02, 0x36, 0x5B, 0x25, 0x55, 0x97, 0x31,
        0x2D, 0x5D, 0xFA, 0x98, 0xE3, 0x8A, 0x92, 0xAE,
        0x05, 0xDF, 0x29, 0x10, 0x67, 0x6C, 0xBA, 0xC9,
        0xD3, 0x00, 0xE6, 0xCF, 0xE1, 0x9E, 0xA8, 0x2C,
        0x63, 0x16, 0x01, 0x3F, 0x58, 0xE2, 0x89, 0xA9,
        0x0D, 0x38, 0x34, 0x1B, 0xAB, 0x33, 0xFF, 0xB0,
        0xBB, 0x48, 0x0C, 0x5F, 0xB9, 0xB1, 0xCD, 0x2E,
        0xC5, 0xF3, 0xDB, 0x47, 0xE5, 0xA5, 0x9C, 0x77,
        0x0A, 0xA6, 0x20, 0x68, 0xFE, 0x7F, 0xC1, 0xAD
    ];

    /**
     * Inverse key expansion randomization table.
     *
     * @see self::setKey()
     * @var array
     */
    private static $invpitable = [
        0xD1, 0xDA, 0xB9, 0x6F, 0x9C, 0xC8, 0x78, 0x66,
        0x80, 0x2C, 0xF8, 0x37, 0xEA, 0xE0, 0x62, 0xA4,
        0xCB, 0x71, 0x50, 0x27, 0x4B, 0x95, 0xD9, 0x20,
        0x9D, 0x04, 0x91, 0xE3, 0x47, 0x6A, 0x7E, 0x53,
        0xFA, 0x3A, 0x3B, 0xB4, 0xA8, 0xBC, 0x5F, 0x68,
        0x08, 0xCA, 0x8F, 0x14, 0xD7, 0xC0, 0xEF, 0x7B,
        0x5B, 0xBF, 0x2F, 0xE5, 0xE2, 0x8C, 0xBA, 0x12,
        0xE1, 0xAF, 0xB2, 0x54, 0x5D, 0x59, 0x76, 0xDB,
        0x32, 0xA2, 0x58, 0x6E, 0x1C, 0x29, 0x64, 0xF3,
        0xE9, 0x96, 0x0C, 0x98, 0x19, 0x8D, 0x3E, 0x26,
        0xAB, 0xA5, 0x85, 0x16, 0x40, 0xBD, 0x49, 0x67,
        0xDC, 0x22, 0x94, 0xBB, 0x3C, 0xC1, 0x9B, 0xEB,
        0x45, 0x28, 0x18, 0xD8, 0x1A, 0x42, 0x7D, 0xCC,
        0xFB, 0x65, 0x8E, 0x3D, 0xCD, 0x2A, 0xA3, 0x60,
        0xAE, 0x93, 0x8A, 0x48, 0x97, 0x51, 0x15, 0xF7,
        0x01, 0x0B, 0xB7, 0x36, 0xB1, 0x2E, 0x11, 0xFD,
        0x84, 0x2D, 0x3F, 0x13, 0x88, 0xB3, 0x34, 0x24,
        0x1B, 0xDE, 0xC5, 0x1D, 0x4D, 0x2B, 0x17, 0x31,
        0x74, 0xA9, 0xC6, 0x43, 0x6D, 0x39, 0x90, 0xBE,
        0xC3, 0xB0, 0x21, 0x6B, 0xF6, 0x0F, 0xD5, 0x99,
        0x0D, 0xAC, 0x1F, 0x5C, 0x9E, 0xF5, 0xF9, 0x4C,
        0xD6, 0xDF, 0x89, 0xE4, 0x8B, 0xFF, 0xC7, 0xAA,
        0xE7, 0xED, 0x46, 0x25, 0xB6, 0x06, 0x5E, 0x35,
        0xB5, 0xEC, 0xCE, 0xE8, 0x6C, 0x30, 0x55, 0x61,
        0x4A, 0xFE, 0xA0, 0x79, 0x03, 0xF0, 0x10, 0x72,
        0x7C, 0xCF, 0x52, 0xA6, 0xA7, 0xEE, 0x44, 0xD3,
        0x9A, 0x57, 0x92, 0xD0, 0x5A, 0x7A, 0x41, 0x7F,
        0x0E, 0x00, 0x63, 0xF2, 0x4F, 0x05, 0x83, 0xC9,
        0xA1, 0xD4, 0xDD, 0xC4, 0x56, 0xF4, 0xD2, 0x77,
        0x81, 0x09, 0x82, 0x33, 0x9F, 0x07, 0x86, 0x75,
        0x38, 0x4E, 0x69, 0xF1, 0xAD, 0x23, 0x73, 0x87,
        0x70, 0x02, 0xC2, 0x1E, 0xB8, 0x0A, 0xFC, 0xE6
    ];

    /**
     * Default Constructor.
     *
     * @param string $mode
     * @throws \InvalidArgumentException if an invalid / unsupported mode is provided
     */
    public function __construct($mode)
    {
        parent::__construct($mode);

        if ($this->mode == self::MODE_STREAM) {
            throw new BadModeException('Block ciphers cannot be ran in stream mode');
        }
    }

    /**
     * Test for engine validity
     *
     * This is mainly just a wrapper to set things up for \phpseclib3\Crypt\Common\SymmetricKey::isValidEngine()
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::__construct()
     * @param int $engine
     * @return bool
     */
    protected function isValidEngineHelper($engine)
    {
        switch ($engine) {
            case self::ENGINE_OPENSSL:
                if ($this->current_key_length != 128 || strlen($this->orig_key) < 16) {
                    return false;
                }
                // quoting https://www.openssl.org/news/openssl-3.0-notes.html, OpenSSL 3.0.1
                // "Moved all variations of the EVP ciphers CAST5, BF, IDEA, SEED, RC2, RC4, RC5, and DES to the legacy provider"
                // in theory openssl_get_cipher_methods() should catch this but, on GitHub Actions, at least, it does not
                if (defined('OPENSSL_VERSION_TEXT') && version_compare(preg_replace('#OpenSSL (\d+\.\d+\.\d+) .*#', '$1', OPENSSL_VERSION_TEXT), '3.0.1', '>=')) {
                    return false;
                }
                $this->cipher_name_openssl_ecb = 'rc2-ecb';
                $this->cipher_name_openssl = 'rc2-' . $this->openssl_translate_mode();
        }

        return parent::isValidEngineHelper($engine);
    }

    /**
     * Sets the key length.
     *
     * Valid key lengths are 8 to 1024.
     * Calling this function after setting the key has no effect until the next
     *  \phpseclib3\Crypt\RC2::setKey() call.
     *
     * @param int $length in bits
     * @throws \LengthException if the key length isn't supported
     */
    public function setKeyLength($length)
    {
        if ($length < 8 || $length > 1024) {
            throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys between 1 and 1024 bits, inclusive, are supported');
        }

        $this->default_key_length = $this->current_key_length = $length;
        $this->explicit_key_length = $length >> 3;
    }

    /**
     * Returns the current key length
     *
     * @return int
     */
    public function getKeyLength()
    {
        return $this->current_key_length;
    }

    /**
     * Sets the key.
     *
     * Keys can be of any length. RC2, itself, uses 8 to 1024 bit keys (eg.
     * strlen($key) <= 128), however, we only use the first 128 bytes if $key
     * has more then 128 bytes in it, and set $key to a single null byte if
     * it is empty.
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::setKey()
     * @param string $key
     * @param int|boolean $t1 optional Effective key length in bits.
     * @throws \LengthException if the key length isn't supported
     */
    public function setKey($key, $t1 = false)
    {
        $this->orig_key = $key;

        if ($t1 === false) {
            $t1 = $this->default_key_length;
        }

        if ($t1 < 1 || $t1 > 1024) {
            throw new \LengthException('Key size of ' . $length . ' bits is not supported by this algorithm. Only keys between 1 and 1024 bits, inclusive, are supported');
        }

        $this->current_key_length = $t1;
        if (strlen($key) < 1 || strlen($key) > 128) {
            throw new \LengthException('Key of size ' . strlen($key) . ' not supported by this algorithm. Only keys of sizes between 8 and 1024 bits, inclusive, are supported');
        }

        $t = strlen($key);

        // The mcrypt RC2 implementation only supports effective key length
        // of 1024 bits. It is however possible to handle effective key
        // lengths in range 1..1024 by expanding the key and applying
        // inverse pitable mapping to the first byte before submitting it
        // to mcrypt.

        // Key expansion.
        $l = array_values(unpack('C*', $key));
        $t8 = ($t1 + 7) >> 3;
        $tm = 0xFF >> (8 * $t8 - $t1);

        // Expand key.
        $pitable = self::$pitable;
        for ($i = $t; $i < 128; $i++) {
            $l[$i] = $pitable[$l[$i - 1] + $l[$i - $t]];
        }
        $i = 128 - $t8;
        $l[$i] = $pitable[$l[$i] & $tm];
        while ($i--) {
            $l[$i] = $pitable[$l[$i + 1] ^ $l[$i + $t8]];
        }

        // Prepare the key for mcrypt.
        $l[0] = self::$invpitable[$l[0]];
        array_unshift($l, 'C*');

        $this->key = pack(...$l);
        $this->key_length = strlen($this->key);
        $this->changed = $this->nonIVChanged = true;
        $this->setEngine();
    }

    /**
     * Encrypts a message.
     *
     * Mostly a wrapper for \phpseclib3\Crypt\Common\SymmetricKey::encrypt, with some additional OpenSSL handling code
     *
     * @see self::decrypt()
     * @param string $plaintext
     * @return string $ciphertext
     */
    public function encrypt($plaintext)
    {
        if ($this->engine == self::ENGINE_OPENSSL) {
            $temp = $this->key;
            $this->key = $this->orig_key;
            $result = parent::encrypt($plaintext);
            $this->key = $temp;
            return $result;
        }

        return parent::encrypt($plaintext);
    }

    /**
     * Decrypts a message.
     *
     * Mostly a wrapper for \phpseclib3\Crypt\Common\SymmetricKey::decrypt, with some additional OpenSSL handling code
     *
     * @see self::encrypt()
     * @param string $ciphertext
     * @return string $plaintext
     */
    public function decrypt($ciphertext)
    {
        if ($this->engine == self::ENGINE_OPENSSL) {
            $temp = $this->key;
            $this->key = $this->orig_key;
            $result = parent::decrypt($ciphertext);
            $this->key = $temp;
            return $result;
        }

        return parent::decrypt($ciphertext);
    }

    /**
     * Encrypts a block
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::encryptBlock()
     * @see \phpseclib3\Crypt\Common\SymmetricKey::encrypt()
     * @param string $in
     * @return string
     */
    protected function encryptBlock($in)
    {
        list($r0, $r1, $r2, $r3) = array_values(unpack('v*', $in));
        $keys = $this->keys;
        $limit = 20;
        $actions = [$limit => 44, 44 => 64];
        $j = 0;

        for (;;) {
            // Mixing round.
            $r0 = (($r0 + $keys[$j++] + ((($r1 ^ $r2) & $r3) ^ $r1)) & 0xFFFF) << 1;
            $r0 |= $r0 >> 16;
            $r1 = (($r1 + $keys[$j++] + ((($r2 ^ $r3) & $r0) ^ $r2)) & 0xFFFF) << 2;
            $r1 |= $r1 >> 16;
            $r2 = (($r2 + $keys[$j++] + ((($r3 ^ $r0) & $r1) ^ $r3)) & 0xFFFF) << 3;
            $r2 |= $r2 >> 16;
            $r3 = (($r3 + $keys[$j++] + ((($r0 ^ $r1) & $r2) ^ $r0)) & 0xFFFF) << 5;
            $r3 |= $r3 >> 16;

            if ($j === $limit) {
                if ($limit === 64) {
                    break;
                }

                // Mashing round.
                $r0 += $keys[$r3 & 0x3F];
                $r1 += $keys[$r0 & 0x3F];
                $r2 += $keys[$r1 & 0x3F];
                $r3 += $keys[$r2 & 0x3F];
                $limit = $actions[$limit];
            }
        }

        return pack('vvvv', $r0, $r1, $r2, $r3);
    }

    /**
     * Decrypts a block
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::decryptBlock()
     * @see \phpseclib3\Crypt\Common\SymmetricKey::decrypt()
     * @param string $in
     * @return string
     */
    protected function decryptBlock($in)
    {
        list($r0, $r1, $r2, $r3) = array_values(unpack('v*', $in));
        $keys = $this->keys;
        $limit = 44;
        $actions = [$limit => 20, 20 => 0];
        $j = 64;

        for (;;) {
            // R-mixing round.
            $r3 = ($r3 | ($r3 << 16)) >> 5;
            $r3 = ($r3 - $keys[--$j] - ((($r0 ^ $r1) & $r2) ^ $r0)) & 0xFFFF;
            $r2 = ($r2 | ($r2 << 16)) >> 3;
            $r2 = ($r2 - $keys[--$j] - ((($r3 ^ $r0) & $r1) ^ $r3)) & 0xFFFF;
            $r1 = ($r1 | ($r1 << 16)) >> 2;
            $r1 = ($r1 - $keys[--$j] - ((($r2 ^ $r3) & $r0) ^ $r2)) & 0xFFFF;
            $r0 = ($r0 | ($r0 << 16)) >> 1;
            $r0 = ($r0 - $keys[--$j] - ((($r1 ^ $r2) & $r3) ^ $r1)) & 0xFFFF;

            if ($j === $limit) {
                if ($limit === 0) {
                    break;
                }

                // R-mashing round.
                $r3 = ($r3 - $keys[$r2 & 0x3F]) & 0xFFFF;
                $r2 = ($r2 - $keys[$r1 & 0x3F]) & 0xFFFF;
                $r1 = ($r1 - $keys[$r0 & 0x3F]) & 0xFFFF;
                $r0 = ($r0 - $keys[$r3 & 0x3F]) & 0xFFFF;
                $limit = $actions[$limit];
            }
        }

        return pack('vvvv', $r0, $r1, $r2, $r3);
    }

    /**
     * Creates the key schedule
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::setupKey()
     */
    protected function setupKey()
    {
        if (!isset($this->key)) {
            $this->setKey('');
        }

        // Key has already been expanded in \phpseclib3\Crypt\RC2::setKey():
        // Only the first value must be altered.
        $l = unpack('Ca/Cb/v*', $this->key);
        array_unshift($l, self::$pitable[$l['a']] | ($l['b'] << 8));
        unset($l['a']);
        unset($l['b']);
        $this->keys = $l;
    }

    /**
     * Setup the performance-optimized function for de/encrypt()
     *
     * @see \phpseclib3\Crypt\Common\SymmetricKey::setupInlineCrypt()
     */
    protected function setupInlineCrypt()
    {
        // Init code for both, encrypt and decrypt.
        $init_crypt = '$keys = $this->keys;';

        $keys = $this->keys;

        // $in is the current 8 bytes block which has to be en/decrypt
        $encrypt_block = $decrypt_block = '
            $in = unpack("v4", $in);
            $r0 = $in[1];
            $r1 = $in[2];
            $r2 = $in[3];
            $r3 = $in[4];
        ';

        // Create code for encryption.
        $limit = 20;
        $actions = [$limit => 44, 44 => 64];
        $j = 0;

        for (;;) {
            // Mixing round.
            $encrypt_block .= '
                $r0 = (($r0 + ' . $keys[$j++] . ' +
                       ((($r1 ^ $r2) & $r3) ^ $r1)) & 0xFFFF) << 1;
                $r0 |= $r0 >> 16;
                $r1 = (($r1 + ' . $keys[$j++] . ' +
                       ((($r2 ^ $r3) & $r0) ^ $r2)) & 0xFFFF) << 2;
                $r1 |= $r1 >> 16;
                $r2 = (($r2 + ' . $keys[$j++] . ' +
                       ((($r3 ^ $r0) & $r1) ^ $r3)) & 0xFFFF) << 3;
                $r2 |= $r2 >> 16;
                $r3 = (($r3 + ' . $keys[$j++] . ' +
                       ((($r0 ^ $r1) & $r2) ^ $r0)) & 0xFFFF) << 5;
                $r3 |= $r3 >> 16;';

            if ($j === $limit) {
                if ($limit === 64) {
                    break;
                }

                // Mashing round.
                $encrypt_block .= '
                    $r0 += $keys[$r3 & 0x3F];
                    $r1 += $keys[$r0 & 0x3F];
                    $r2 += $keys[$r1 & 0x3F];
                    $r3 += $keys[$r2 & 0x3F];';
                $limit = $actions[$limit];
            }
        }

        $encrypt_block .= '$in = pack("v4", $r0, $r1, $r2, $r3);';

        // Create code for decryption.
        $limit = 44;
        $actions = [$limit => 20, 20 => 0];
        $j = 64;

        for (;;) {
            // R-mixing round.
            $decrypt_block .= '
                $r3 = ($r3 | ($r3 << 16)) >> 5;
                $r3 = ($r3 - ' . $keys[--$j] . ' -
                       ((($r0 ^ $r1) & $r2) ^ $r0)) & 0xFFFF;
                $r2 = ($r2 | ($r2 << 16)) >> 3;
                $r2 = ($r2 - ' . $keys[--$j] . ' -
                       ((($r3 ^ $r0) & $r1) ^ $r3)) & 0xFFFF;
                $r1 = ($r1 | ($r1 << 16)) >> 2;
                $r1 = ($r1 - ' . $keys[--$j] . ' -
                       ((($r2 ^ $r3) & $r0) ^ $r2)) & 0xFFFF;
                $r0 = ($r0 | ($r0 << 16)) >> 1;
                $r0 = ($r0 - ' . $keys[--$j] . ' -
                       ((($r1 ^ $r2) & $r3) ^ $r1)) & 0xFFFF;';

            if ($j === $limit) {
                if ($limit === 0) {
                    break;
                }

                // R-mashing round.
                $decrypt_block .= '
                    $r3 = ($r3 - $keys[$r2 & 0x3F]) & 0xFFFF;
                    $r2 = ($r2 - $keys[$r1 & 0x3F]) & 0xFFFF;
                    $r1 = ($r1 - $keys[$r0 & 0x3F]) & 0xFFFF;
                    $r0 = ($r0 - $keys[$r3 & 0x3F]) & 0xFFFF;';
                $limit = $actions[$limit];
            }
        }

        $decrypt_block .= '$in = pack("v4", $r0, $r1, $r2, $r3);';

        // Creates the inline-crypt function
        $this->inline_crypt = $this->createInlineCryptFunction(
            [
               'init_crypt'    => $init_crypt,
               'encrypt_block' => $encrypt_block,
               'decrypt_block' => $decrypt_block
            ]
        );
    }
}