不清楚DES算法的可以看维基百科

<?php
class DESede{

    /**
     * 加密
     * @param $data 待加密明文
     * @param $key DES私钥
     * @param $use3des 是否启用3DES加密，默认不启用
     */
    function encrypt($data='', $key='', $use3des = False)
    {
        if (empty($data) || empty($key))
        {
            return False;
        }

        $cipher = $use3des ? MCRYPT_TRIPLEDES : MCRYPT_DES;
        $modes = MCRYPT_MODE_ECB;

        # Add PKCS7 padding.
        $block = mcrypt_get_block_size($cipher, $modes);
        $pad = $block - (strlen($data) % $block);
        $data .= str_repeat(chr($pad), $pad);

        $iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher, $modes), MCRYPT_RAND);
        $encrypted = @mcrypt_encrypt($cipher, $key, $data, $modes, $iv);

        return $encrypted;
    }

    /**
     * 解密
     * @param $data 待解密密文
     * @param $key DES私钥
     * @param $use3des 是否启用3DES加密，默认不启用
     */
    function decrypt($data='', $key='', $use3des = False)
    {
        if (empty($data) || empty($key))
        {
            return False;
        }

        $cipher = $use3des ? MCRYPT_TRIPLEDES : MCRYPT_DES;
        $modes = MCRYPT_MODE_ECB;

        $iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher, $modes), MCRYPT_RAND);
        $data = @mcrypt_decrypt($cipher, $key, $data, $modes, $iv);

        # Strip padding out.
        $block = mcrypt_get_block_size($cipher, $modes);
        $pad = ord($data[($len = strlen($data)) - 1]);
        $decrypted = substr($data, 0, strlen($data) - $pad);

        return $decrypted;
    }

}