PHP encryption/decryption function dencrypt (dynamic ciphertext, with compression function, supports Chinese)

Use SHA1 to generate the key book. ZLIB compression for more than 300 characters supports Chinese characters. you can test it. The code is as follows:
// + ------------------------------------------------------------------------ +
// | Willko Framework |
// + ------------------------------------------------------------------------ +
// | Copyright (c) 2008-2009 Willko Cheng |
// + ------------------------------------------------------------------------ +
// | Authors: Willko Cheng |
// + ------------------------------------------------------------------------ +
// $ String plaintext or ciphertext
// $ Whether isEncrypt is encrypted
// $ Key
// Use SHA1 to generate the key book, and use ZLIB to compress more than 300 characters
Function dencrypt ($ string, $ isEncrypt = true, $ key = KEY_SPACE ){
If (! Isset ($ string {0}) |! Isset ($ key {0 })){
Return false;
}

$ DynKey = $ isEncrypt? Hash ('sha1', microtime (true): substr ($ string, 0, 40 );
$ FixedKey = hash ('sha1', $ key );

$ DynKeyPart1 = substr ($ dynKey, 0, 20 );
$ DynKeyPart2 = substr ($ dynKey, 20 );
$ FixedKeyPart1 = substr ($ fixedKey, 0, 20 );
$ FixedKeyPart2 = substr ($ fixedKey, 20 );
$ Key = hash ('sha1', $ dynKeyPart1. $ fixedKeyPart1. $ dynKeyPart2. $ fixedKeyPart2 );

$ String = $ isEncrypt? $ FixedKeyPart1. $ string. $ dynKeyPart2: (isset ($ string {339 })? Gzuncompress (base64_decode (substr ($ string, 40): base64_decode (substr ($ string, 40 )));

$ N = 0;
$ Result = '';
$ Len = strlen ($ string );

For ($ n = 0; $ n <$ len; $ n ++ ){
$ Result. = chr (ord ($ string {$ n}) ^ ord ($ key {$ n % 40 }));
}
Return $ isEncrypt? $ DynKey. str_replace ('=', '', base64_encode ($ n> 299? Gzcompress ($ result): substr ($ result, 20,-20 );
}