PHP encryption and decryption string example

The application of encryption and decryption in a system is a very common requirement. In websites made with PHP, the PHP encryption and decryption string functions are often used.

includes some classic PHP encryption and decryption methods. Function code, share it with everyone. The principle of encryption and decryption is generally to use a certain encryption and decryption algorithm, add the key to the algorithm, and finally obtain the encryption and decryption results.

function authcode($string, $operation = 'DECODE', $key = '', $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)); 

  } 

 }

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