How PHP generates timely ciphertext

How does PHP generate sensitive ciphertext? Recently found a very good encryption and decryption function in Discuz. The great thing about this function is that you can encrypt the restore string within a specified time, and the timeout cannot be restored. Share for your reference, we hope to help you.

So we can use this function to do a lot of purposes, such as: Single Sign-on token encryption transmission, temporary password, etc.

/** * @param string $string original text or ciphertext * @param string $operation operation (ENCODE |  DECODE), default is DECODE * @param string $key key * @param int $expiry ciphertext expiration, encryption time valid, unit seconds, 0 is permanent valid * @return The original text after string processing or after Base64_encode processed Ciphertext * * @example * * $a = authcode (' abc ', ' Encode ', ' key '); * $b = Authcode ($a, ' DECODE ', ' key '); $b (ABC) * * $a = authcode (' abc ', ' ENCODE ', ' key ', 3600); * $b = Authcode (' abc ', ' DECODE ', ' key '); Within one hours, $b (ABC), otherwise $b is empty */function Authcode ($string, $operation = ' DECODE ', $key = ', $expiry = 3600) {$ckey _len     Gth = 4;     Random key length value 0-32;     Join with the secret key, you can make ciphertext no rules, even if the original and key exactly the same, the encryption results will be different each time, increase the difficulty of cracking. The greater the value, the greater the ciphertext variation, the ciphertext change = 16 $ckey _length//When this value is 0 o'clock, the random key is not generated $key = MD5 ($key? $key: Eabax::getappinf (' key ')     );     $keya = MD5 (substr ($key, 0, 16));     $KEYB = MD5 (substr ($key, 16, 16)); $KEYC = $ckey _length?     ($operation = = ' DECODE '? substr ($string, 0, $ckey _length): substr (MD5 (Microtime ()),-$ckey _length)): "; $cryptkey = $keya. MD5 ($keya. $keyc);     $key _length = strlen ($cryptkey); $string = $operation = = = ' DECODE '? Base64_decode (substr ($string, $ckey _length)): sprintf ('%010d ', $expiry? $expiry + Time (): 0). substr (MD5 ($string. $keyb     ), 0, (+). $string;     $string _length = strlen ($string);     $result = ";     $box = Range (0, 255);     $rndkey = Array ();     for ($i = 0; $i <= 255; $i + +) {$rndkey [$i] = Ord ($cryptkey [$i% $key _length]);         } for ($j = $i = 0; $i <, $i + +) {$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 ($operation = = ' DECODE ') {if (substr ($result, 0, ten) = = 0 | | substr ($result, 0, Ten)-time (); 0) && substr ($result, ten, +) = = substr (MD5 ($result, $keyb), 0, +) {return substr ($resul         T, 26);         } else {return ';     }} else {return $KEYC. Str_replace (' = ', ' ', Base64_encode ($result)); } }

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