PHP加密解密函數

<?php

//加密函數
function passport_encrypt($txt, $key) {
    srand((double)microtime() * 1000000);
    $encrypt_key = md5(rand(0, 32000));
    $ctr = 0;
    $tmp = '';
    for($i = 0;$i < strlen($txt); $i++) {
       $ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr;
       $tmp .= $encrypt_key[$ctr].($txt[$i] ^ $encrypt_key[$ctr++]);
    }
    return base64_encode(passport_key($tmp, $key));
}
//解密函數
function passport_decrypt($txt, $key) {
    $txt = passport_key(base64_decode($txt), $key);
    $tmp = '';
    for($i = 0;$i < strlen($txt); $i++) {
       $md5 = $txt[$i];
       $tmp .= $txt[++$i] ^ $md5;
    }
    return $tmp;
}

function passport_key($txt, $encrypt_key) {
    $encrypt_key = md5($encrypt_key);
    $ctr = 0;
    $tmp = '';
    for($i = 0; $i < strlen($txt); $i++) {
       $ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr;
       $tmp .= $txt[$i] ^ $encrypt_key[$ctr++];
    }
    return $tmp;
    }
?>

網上搜的加密解密函數，保存下