1. 简易型

function encryptDecrypt($key, $string, $decrypt){  
    if($decrypt){  
        $decrypted = rtrim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, md5($key), base64_decode($string), MCRYPT_MODE_CBC, md5(md5($key))), "12");  
        return $decrypted;  
    }else{  
        $encrypted = base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, md5($key), $string, MCRYPT_MODE_CBC, md5(md5($key))));  
        return $encrypted;  
    }  
}  
 
//加密:"z0JAx4qMwcF+db5TNbp/xwdUM84snRsXvvpXuaCa4Bk=" 
echo encryptDecrypt('password', 'Hello',0);  
//解密:"Helloweba欢迎您" 
echo encryptDecrypt('password', 'xxxxxx',1); 

2. 普通型

//加密函数 
function lock_url($txt,$key='liiu'){ 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $nh = rand(0,64); 
    $ch = $chars[$nh]; 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = base64_encode($txt); 
    $tmp = ''; 
    $i=0;$j=0;$k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = ($nh+strpos($chars,$txt[$i])+ord($mdKey[$k++]))%64; 
        $tmp .= $chars[$j]; 
    } 
    return urlencode($ch.$tmp); 
} 
//解密函数 
function unlock_url($txt,$key='liiu'){ 
    $txt = urldecode($txt); 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $ch = $txt[0]; 
    $nh = strpos($chars,$ch); 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = substr($txt,1); 
    $tmp = ''; 
    $i=0;$j=0; $k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = strpos($chars,$txt[$i])-$nh - ord($mdKey[$k++]); 
        while ($j<0) $j+=64; 
        $tmp .= $chars[$j]; 
    } 
    return base64_decode($tmp); 
} 

3. 普通改良型

//改进后的算法 
//加密函数 
function lock_url($txt,$key='str'){ 
    $txt = $txt.$key; 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $nh = rand(0,64); 
    $ch = $chars[$nh]; 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = base64_encode($txt); 
    $tmp = ''; 
    $i=0;$j=0;$k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = ($nh+strpos($chars,$txt[$i])+ord($mdKey[$k++]))%64; 
        $tmp .= $chars[$j]; 
    } 
    return urlencode(base64_encode($ch.$tmp)); 
} 
//解密函数 
function unlock_url($txt,$key='str'){ 
    $txt = base64_decode(urldecode($txt)); 
    $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-=+"; 
    $ch = $txt[0]; 
    $nh = strpos($chars,$ch); 
    $mdKey = md5($key.$ch); 
    $mdKey = substr($mdKey,$nh%8, $nh%8+7); 
    $txt = substr($txt,1); 
    $tmp = ''; 
    $i=0;$j=0; $k = 0; 
    for ($i=0; $i<strlen($txt); $i++) { 
        $k = $k == strlen($mdKey) ? 0 : $k; 
        $j = strpos($chars,$txt[$i])-$nh - ord($mdKey[$k++]); 
        while ($j<0) $j+=64; 
        $tmp .= $chars[$j]; 
    } 
    return trim(base64_decode($tmp),$key); 
} 
 

4. 高效型

function passport_encrypt($txt, $key = 'liiu') {  
    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 urlencode(base64_encode(passport_key($tmp, $key)));  
}  
 
function passport_decrypt($txt, $key = 'liiu') {  
    $txt = passport_key(base64_decode(urldecode($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;  
}  
 
 
$txt = "1";  
$key = "testkey";  
$encrypt = passport_encrypt($txt,$key);  
$decrypt = passport_decrypt($encrypt,$key);  
 
echo $encrypt."<br>";  
echo $decrypt."<br>";  
 

5. 复杂型

非常给力的authcode加密函数,Discuz!经典代码(带详解)
函数authcode($string, $operation, $key, $expiry)
$string：字符串，明文或密文；
$operation： DECODE表示解密，其它表示加密
$key：密匙
$expiry：有效期

function authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {    
    // 动态密匙长度，相同的明文会生成不同密文就是依靠动态密匙    
    $ckey_length = 4;    
 
    // 密匙    
    $key = md5($key ? $key : $GLOBALS['discuz_auth_key']);    
 
    // 密匙a会参与加解密    
    $keya = md5(substr($key, 0, 16));    
    // 密匙b会用来做数据完整性验证    
    $keyb = md5(substr($key, 16, 16));    
    // 密匙c用于变化生成的密文    
    $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length): substr(md5(microtime()), -$ckey_length)) : '';    
    // 参与运算的密匙    
    $cryptkey = $keya.md5($keya.$keyc);    
    $key_length = strlen($cryptkey);    
    // 明文，前10位用来保存时间戳，解密时验证数据有效性，10到26位用来保存$keyb(密匙b)，  
    //解密时会通过这个密匙验证数据完整性    
    // 如果是解码的话，会从第$ckey_length位开始，因为密文前$ckey_length位保存 动态密匙，以保证解密正确    
    $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(0, 255);    
    $rndkey = array();    
    // 产生密匙簿    
    for($i = 0; $i <= 255; $i++) {    
        $rndkey[$i] = ord($cryptkey[$i % $key_length]);    
    }    
    // 用固定的算法，打乱密匙簿，增加随机性，好像很复杂，实际上对并不会增加密文的强度    
    for($j = $i = 0; $i < 256; $i++) {    
        $j = ($j + $box[$i] + $rndkey[$i]) % 256;    
        $tmp = $box[$i];    
        $box[$i] = $box[$j];    
        $box[$j] = $tmp;    
    }    
    // 核心加解密部分    
    for($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;    
        // 从密匙簿得出密匙进行异或，再转成字符    
        $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));    
    }    
    if($operation == 'DECODE') {   
        // 验证数据有效性，请看未加密明文的格式    
        if((substr($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 {    
        // 把动态密匙保存在密文里，这也是为什么同样的明文，生产不同密文后能解密的原因    
        // 因为加密后的密文可能是一些特殊字符，复制过程可能会丢失，所以用base64编码    
        return $keyc.str_replace('=', '', base64_encode($result));    
    }    
}  
 
$str = 'abcdef';  
$key = 'www.telidy.com';  
echo authcode($str,'ENCODE',$key,0); //加密  
$str = '56f4yER1DI2WTzWMqsfPpS9hwyoJnFP2MpC8SOhRrxO7BOk';  
echo authcode($str,'DECODE',$key,0); //解密  
 

6. 难度型

函数encrypt($string,$operation,$key)
$string：需要加密解密的字符串
$operation：判断是加密还是解密，E表示加密，D表示解密
$key：密匙

function encrypt($string,$operation,$key=''){  
    $key=md5($key);  
    $key_length=strlen($key);  
      $string=$operation=='D'?base64_decode($string):substr(md5($string.$key),0,8).$string;  
    $string_length=strlen($string);  
    $rndkey=$box=array();  
    $result='';  
    for($i=0;$i<=255;$i++){  
           $rndkey[$i]=ord($key[$i%$key_length]);  
        $box[$i]=$i;  
    }  
    for($j=$i=0;$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($operation=='D'){  
        if(substr($result,0,8)==substr(md5(substr($result,8).$key),0,8)){  
            return substr($result,8);  
        }else{  
            return'';  
        }  
    }else{  
        return str_replace('=','',base64_encode($result));  
    }  
}  
 
$str = 'abc';  
$key = 'www.telidy.com';  
$token = encrypt($str, 'E', $key);  
echo '加密:'.encrypt($str, 'E', $key);  
echo '解密：'.encrypt($str, 'D', $key);