具有时效性的php加密解密函数代码

代码如下:
<?php
function encode_pass($tex,$key,$type="encode",$expiry=0){
    $chrArr=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
                  'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
                  '0','1','2','3','4','5','6','7','8','9');
    if($type=="decode"){
        if(strlen($tex)<14)return false;
        $verity_str=substr($tex, 0,8);
        $tex=substr($tex, 8);
        if($verity_str!=substr(md5($tex),0,8)){
            //完整性验证失败
            return false;
        }   
    }
    $key_b=$type=="decode"?substr($tex,0,6):$chrArr[rand()%62].$chrArr[rand()%62].$chrArr[rand()%62].$chrArr[rand()%62].$chrArr[rand()%62].$chrArr[rand()%62];

    $rand_key=$key_b.$key;   
    //设置时间选项
    $modnum=0;$modCount=0;$modCountStr="";
    if($expiry>0){
        if($type=="decode"){
            $modCountStr=substr($tex,6,1);
            $modCount=$modCountStr=="a"?10:floor($modCountStr);
            $modnum=substr($tex,7,$modCount);
            $rand_key=$rand_key.(floor((time()-$modnum)/$expiry));
        }else{
            $modnum=time()%$expiry;
            $modCount=strlen($modnum);
            $modCountStr=$modCount==10?"a":$modCount;

            $rand_key=$rand_key.(floor(time()/$expiry));           
        }
        $tex=$type=="decode"?base64_decode(substr($tex, (7+$modCount))):"xugui".$tex;
    }else{
        $tex=$type=="decode"?base64_decode(substr($tex, 6)):"xugui".$tex;
    }
    $rand_key=md5($rand_key);

    $texlen=strlen($tex);