Change authcode in DX to JS version, which is difficult to convert

Change the authcode in DX to the JS version. difficult conversion & nbsp; parameter explanation & nbsp; $ string: & nbsp; plaintext & nbsp; or & nbsp; ciphertext & nbsp; $ operation: DECODE indicates decryption, others indicate encryption & nbsp; change authcode in DX to JS version, which is difficult to convert

// Parameter description
// $ String: plaintext or ciphertext
// $ Operation: DECODE indicates decryption, and others indicates encryption
// $ Key: key
// $ Expiry: ciphertext validity period
Function authcode ($ string, $ operation = 'Decode', $ key = '', $ expiry = 0 ){
// The length of the dynamic key. different ciphertext values are generated for the same plaintext based on the dynamic key.
$ Ckey_length = 4;
      
// Key
$ Key = md5 ($ key? $ Key: $ GLOBALS ['discuz _ auth_key ']);
      
// Key a is used for encryption and decryption.
$ Keya = md5 (substr ($ key, 0, 16 ));
// Key B is used for data integrity verification.
$ Keyb = md5 (substr ($ key, 16, 16 ));
// Key c is used to change the generated ciphertext
$ Keyc = $ ckey_length? ($ Operation = 'decode '? Substr ($ string, 0, $ ckey_length): substr (md5 (microtime (),-$ ckey_length )):'';
// Key used for calculation
$ Cryptkey = $ keya. md5 ($ keya. $ keyc );
$ Key_length = strlen ($ cryptkey );
// Plaintext. the first 10 digits are used to save the timestamp. data validity is verified during decryption, and 10 to 26 digits are used to save $ keyb (key B). Data integrity is verified through this key during decryption.
// If it is decoded, it starts from the $ ckey_length bit, because the $ ckey_length bit before the ciphertext stores the dynamic key to ensure correct decryption.
$ 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 ();
// Generate a key book
For ($ I = 0; $ I <= 255; $ I ++ ){
$ Rndkey [$ I] = ord ($ cryptkey [$ I % $ key_length]);
}
// Use a fixed algorithm to disrupt the key book and increase randomness. it seems complicated. In fact, it does not increase the ciphertext strength.
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;
}
// Core encryption/decryption part
For ($ a = $ j = $ I = 0; $ I <$ string_length; $ I ++ ){
$ A = ($ a + 1) % 256;
$ J = ($ j + $ box [$ a]) % 256;
$ Tmp = $ box [$ a];