September 13, 2022 at 12:47 AM
(July 15, 2022, 03:04 PM)f yuppie Wrote: hey guys! I found an encryption algorithm in a website source which is written by PHP code.
Here is it
[php]
function encode($string, $type = 0, $key = '', $expiry = 0) {
if(is_array($string)) $string = json_encode($string);
if($type == 1) $string = str_replace('-','+',$string);
$ckey_length = 4;
$key = md5($key);
$keya = md5(substr($key, 0, 16));
$keyb = md5(substr($key, 16, 16));
$keyc = $ckey_length ? ($type == 1 ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : '';
$cryptkey = $keya.md5($keya.$keyc);
$key_length = strlen($cryptkey);
$string = $type == 1 ? base64_decode(substr($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);
$rndkey = array();
for($i = 0; $i <= 255; $i++) {
$rndkey[$i] = ord($cryptkey[$i % $key_length]); //$key_length = 64
}
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($type == 1) {
if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16)) {
$result = substr($result, 26);
$json = json_decode($result,1);
if(!is_numeric($result) && $json){
return $json;
}else{
return $result;
}
}
return '';
}
return str_replace('+', '-', $keyc.str_replace('=', '', base64_encode($result)));[/php]
when $type is '0', it means to encrypt $string with $key,when $type is '1',it means to decrypt $string with $key.The fourth argument is usually 0.
For example
[php]<?php
$string = '2';
$key = 'mjDZLqSNJEzxg9W';
$encrypt = encode($string,0,$key);
echo "$encrypt -> ".$encrypt;
echo '
';
$decrypt = encode($encrypt,1,$key);
echo "$decrypt -> ".$decrypt;
echo '
';
?>[/php]
So I want to know, in the case of knowing plaintext and ciphertext, can i decrypt the key?
Or, can I forge ciphertext that can be decrypted without knowing the key?
I'd be grateful if you could help me solve this problem!!!!
