<?php
 
 
class Des {
 
    private $key;
    private $iv; //偏移量
 
    public function __construct($key, $iv = 0) {
        $this->key = $key;
        $this->iv = $iv == 0 ? $key : $iv;
    }
 
    //加密
    public function encrypt($str) {
        $size = mcrypt_get_block_size(MCRYPT_DES, MCRYPT_MODE_CBC);
        $str = $this->pkcs5Pad($str, $size);
        @$data = mcrypt_cbc(MCRYPT_DES, $this->key, $str, MCRYPT_ENCRYPT, $this->iv);
        //$data=strtoupper(bin2hex($data)); //返回大写十六进制字符串
        return base64_encode($data);
    }
 
    //解密
    public function decrypt($str) {
        $str = base64_decode($str);
        $str = mcrypt_cbc(MCRYPT_DES, $this->key, $str, MCRYPT_DECRYPT, $this->iv);
        $str = $this->pkcs5Unpad($str);
        return $str;
    }
 
    public function hex2bin($hexData) {
        $binData = "";
        for ($i = 0; $i < strlen($hexData); $i += 2) {
            $binData .= chr(hexdec(substr($hexData, $i, 2)));
        }
        return $binData;
    }
 
    public function pkcs5Pad($text, $blocksize) {
        $pad = $blocksize - (strlen($text) % $blocksize);
        return $text . str_repeat(chr($pad), $pad);
    }
 
    public function pkcs5Unpad($text) {
        $pad = ord($text {strlen($text) - 1});
        if ($pad > strlen($text))
            return false;
        if (strspn($text, chr($pad), strlen($text) - $pad) != $pad)
            return false;
        return substr($text, 0, - 1 * $pad);
    }
 
}

<?php
$key = '12345678';
$iv = 0;//偏移量
$des = new Des($key,$iv);
//加密
$str = 'abcd';//待加密串
$result1 = $des->encrypt($str);
var_dump($result1 );
//解密
$result2 = $des->decrypt($result1 );
var_dump($result2);