mcrypt_encrypt错误怎么 解决

protected function encrypt($string) {		//加密用的密钥文件 		$key = md5("xxxxxxxx");		//加密方法 		$cipher_alg = MCRYPT_TRIPLEDES;		//初始化向量来增加安全性 		$iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher_alg,MCRYPT_MODE_ECB), MCRYPT_RAND); 		//开始加密 		$encrypted_string = mcrypt_encrypt($cipher_alg, $key, $string, MCRYPT_MODE_ECB, $iv);		var_dump($encrypted_string);		return base64_encode($encrypted_string);//转化成16进制    }protected function decrypt($string) {		$string = base64_decode($string);		//加密用的密钥文件 		$key = md5("xxxxxxxx");		//加密方法 		$cipher_alg = MCRYPT_TRIPLEDES;		//初始化向量来增加安全性 		$iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher_alg,MCRYPT_MODE_ECB), MCRYPT_RAND); 		//开始解密 		$decrypted_string = mcrypt_decrypt($cipher_alg, $key, $string, MCRYPT_MODE_ECB, $iv); 		return $decrypted_string;    }