Explanation of encryption and decryption algorithms commonly used in php (code)

The content of this article is about the explanation (code) of encryption and decryption algorithms commonly used in PHP. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Here we mainly introduce three commonly used encryption and decryption algorithms:
Method 1:

/**
 * @param $string    要加密/解密的字符串
 * @param string $operation   类型，ENCODE 加密；DECODE 解密
 * @param string $key    密匙
 * @param int $expiry    有效期
 * @return string
 */
function authcode($string, $operation = 'DECODE', $key = 'encrypt', $expiry = 0)
{
    // 动态密匙长度，相同的明文会生成不同密文就是依靠动态密匙
    $ckey_length = 4;
    // 密匙
    $key = md5($key ? $key : $GLOBALS['discuz_auth_key']);
    // 密匙a会参与加解密
    $keya = md5(substr($key, 0, 16));
    // 密匙b会用来做数据完整性验证
    $keyb = md5(substr($key, 16, 16));
    // 密匙c用于变化生成的密文
    $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length) :
        substr(md5(microtime()), -$ckey_length)) : '';
    // 参与运算的密匙
    $cryptkey = $keya . md5($keya . $keyc);
    $key_length = strlen($cryptkey);
    // 明文，前10位用来保存时间戳，解密时验证数据有效性，10到26位用来保存$keyb(密匙b)，
    //解密时会通过这个密匙验证数据完整性
    // 如果是解码的话，会从第$ckey_length位开始，因为密文前$ckey_length位保存 动态密匙，以保证解密正确
    $string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) :
        sprintf('%010d', $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string;
    $string_length = strlen($string);
    $result = '';
    $box = range(0, 255);
    $rndkey = array();
    // 产生密匙簿
    for ($i = 0; $i <= 255; $i++) {
        $rndkey[$i] = ord($cryptkey[$i % $key_length]);
    }
    // 用固定的算法，打乱密匙簿，增加随机性，好像很复杂，实际上对并不会增加密文的强度
    for ($j = $i = 0; $i < 256; $i++) {
        $j = ($j + $box[$i] + $rndkey[$i]) % 256;
        $tmp = $box[$i];
        $box[$i] = $box[$j];
        $box[$j] = $tmp;
    }
    // 核心加解密部分
    for ($a = $j = $i = 0; $i < $string_length; $i++) {
        $a = ($a + 1) % 256;
        $j = ($j + $box[$a]) % 256;
        $tmp = $box[$a];
        $box[$a] = $box[$j];
        $box[$j] = $tmp;
        // 从密匙簿得出密匙进行异或，再转成字符
        $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
    }
    if ($operation == &#39;DECODE&#39;) {
        // 验证数据有效性，请看未加密明文的格式
        if ((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) &&
            substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16)
        ) {
            return substr($result, 26);
        } else {
            return &#39;&#39;;
        }
    } else {
        // 把动态密匙保存在密文里，这也是为什么同样的明文，生产不同密文后能解密的原因
        // 因为加密后的密文可能是一些特殊字符，复制过程可能会丢失，所以用base64编码
        return $keyc . str_replace(&#39;=&#39;, &#39;&#39;, base64_encode($result));
    }
}

Usage:

$string = '加密字符串';
// 加密
$encode = authcode($string, 'ENCODE');
echo $encode . &#39;</br>&#39;;       // a2f4bSYyUrTum1nAAA9X9BrC4Z3DZazcSa4eLcvDoCnmYc1LTdvtqS4aCds
// 解密
$decode = authcode($encode, &#39;DECODE&#39;);
echo $decode;     // 加密字符串

Method Two:

/**
 * @param $string    要加密/解密的字符串
 * @param $operation    类型，E 加密；D 解密
 * @param string $key   密钥
 * @return mixed|string
 */
function encrypt($string, $operation, $key = 'encrypt')
{
    $key = md5($key);
    $key_length = strlen($key);
    $string = $operation == 'D' ? base64_decode($string) : substr(md5($string . $key), 0, 8) . $string;
    $string_length = strlen($string);
    $rndkey = $box = array();
    $result = '';
    for ($i = 0; $i <= 255; $i++) {
        $rndkey[$i] = ord($key[$i % $key_length]);
        $box[$i] = $i;
    }
    for ($j = $i = 0; $i < 256; $i++) {
        $j = ($j + $box[$i] + $rndkey[$i]) % 256;
        $tmp = $box[$i];
        $box[$i] = $box[$j];
        $box[$j] = $tmp;
    }
    for ($a = $j = $i = 0; $i < $string_length; $i++) {
        $a = ($a + 1) % 256;
        $j = ($j + $box[$a]) % 256;
        $tmp = $box[$a];
        $box[$a] = $box[$j];
        $box[$j] = $tmp;
        $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
    }
    if ($operation == &#39;D&#39;) {
        if (substr($result, 0, 8) == substr(md5(substr($result, 8) . $key), 0, 8)) {
            return substr($result, 8);
        } else {
            return &#39;&#39;;
        }
    } else {
        return str_replace(&#39;=&#39;, &#39;&#39;, base64_encode($result));
    }
}

Use:

$string = '加密字符串';
// 加密
$encode = encrypt($string, 'E');
echo $encode . &#39;</br>&#39;;       // 0Jzym5UzkRKH726U7Pyt7ixzLz9YEEA
// 解密
$decode = encrypt($encode, &#39;D&#39;);
echo $decode;     // 加密字符串

Method Three:

/**
 * @param $data  要加密的字符串
 * @param $key   密钥
 * @return string
 */
function encrypt($data, $key = 'encrypt')
{
    $key = md5($key);
    $x = 0;
    $len = strlen($data);
    $l = strlen($key);
    $char = '';
    for ($i = 0; $i < $len; $i++) {
        if ($x == $l) {
            $x = 0;
        }
        $char .= $key{$x};
        $x++;
    }
    $str = &#39;&#39;;
    for ($i = 0; $i < $len; $i++) {
        $str .= chr(ord($data{$i}) + (ord($char{$i})) % 256);
    }
    return base64_encode($str);
}


/**
 * @param $data    要解密的字符串
 * @param $key     密钥
 * @return string
 */
function decrypt($data, $key = &#39;encrypt&#39;)
{
    $key = md5($key);
    $x = 0;
    $data = base64_decode($data);
    $len = strlen($data);
    $l = strlen($key);
    $char = &#39;&#39;;
    for ($i = 0; $i < $len; $i++) {
        if ($x == $l) {
            $x = 0;
        }
        $char .= substr($key, $x, 1);
        $x++;
    }
    $str = &#39;&#39;;
    for ($i = 0; $i < $len; $i++) {
        if (ord(substr($data, $i, 1)) < ord(substr($char, $i, 1))) {
            $str .= chr((ord(substr($data, $i, 1)) + 256) - ord(substr($char, $i, 1)));
        } else {
            $str .= chr(ord(substr($data, $i, 1)) - ord(substr($char, $i, 1)));
        }
    }
    return $str;
}

Use:

$string = '加密字符串';
// 加密
$encode = encrypt($string);
echo $encode . &#39;</br>&#39;;       // Gr0DHeHrRw7KGBLcSOzj
// 解密
$decode = decrypt($encode);
echo $decode;     // 加密字符串

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