Authcode function code of a reversible encryption function in UCenter

When you browse the UCenter source code, you will find this function. If necessary, record it.

When you browse the UCenter source code, you will find this function. If necessary, record it.

The Code is as follows:
Function authcode ($ string, $ operation = 'decode', $ key = '', $ expiry = 0 ){

$ Ckey_length = 4; // the random key length ranges from 0 to 32;
// Adding a random key can make the ciphertext irregular. Even if the original text and the key are identical, the encryption results will be different each time, increasing the difficulty of cracking.
// The larger the value, the larger the ciphertext change law. The ciphertext change is equal to the power of $ ckey_length of 16.
// When this value is 0, no random key is generated

$ Key = md5 ($ key? $ Key: UC_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, 16). $ string;
$ String_length = strlen ($ string );

$ Result = '';
$ Box = range (1, 0,255 );

$ Rndkey = array ();
For ($ I = 0; $ I <= 255; $ I ++ ){
$ Rndkey [$ I] = ord ($ cryptkey [$ I % $ key_length]);
}

For ($ j = $ I = 0; I 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 = 'decode '){
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 '';
}
} Else {
Return $ keyc. str_replace ('=', '', base64_encode ($ result ));
}
}
/*************************************** ************************************/
$ String = authcode ("Hello", "ENCODE", "HTML_TCCJ_AUTH ");
Echo $ string ,'
';
Echo authcode ($ string, "DECODE", "HTML_TCCJ_AUTH "),'
';