MCrypt rijndael-128 to OpenSSL aes-128-ecb conversion

Question

Since Mcrypt is deprecated, I want to use OpenSSL instead in my code since we already using php 7.0.17 in our server and there's no tell when they upgrade it.

Some third party API (hosted on PHP 5.x probably and using mcrypt), is taking encrypted data. They've provided methods which they are using to encrypt/decrypt strings.

Here are they

$secret = 'a0a7e7997b6d5fcd55f4b5c32611b87c' ;

public function encrypt128($str)
    {
        $block = mcrypt_get_block_size("rijndael_128", "ecb");
        $pad   = $block - (strlen($str) % $block);
        $str .= str_repeat(chr($pad), $pad);

        return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_128, $secret, $str, MCRYPT_MODE_ECB));
    }

public function decrypt128($str)
    {
        $str = base64_decode($str);
        $str = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $secret, $str, MCRYPT_MODE_ECB);

        $len = strlen($str);
        $pad = ord($str[$len - 1]);

        return substr($str, 0, strlen($str) - $pad);
    }

using these methods string small1 if encrypted becomes v7IXp5vVaFVXXlt/MN8BVw==

---

We want to use openssl_encrypt in our side such that if we encrypt same string with OpenSSL it must give same results as Mcrypt. I've researched that mcrypt using rijndael-128 Mode ecb should be compatible with OpenSSL aes-128-ecb.

For last few hours, I've been trying to make my own method to encrypt strings serving same result by using OpenSSL. So far I've come to this

public function sslEncrypt128($str)
{
    $secret = 'a0a7e7997b6d5fcd55f4b5c32611b87c';
    return base64_encode(openssl_encrypt($str, 'aes-128-ecb', $secret, OPENSSL_RAW_DATA));
}

But it produces different string SxJ3+EdaeItZx3/EwGTUbw== for same as above input. I don't know if it is flag's problem or padding's, any pointers will be welcome.

I've added the code here to test online https://3v4l.org/v2J2N

Thanks in advance.

Answer 1

In your specific example I've found that by changing aes-128-ecb to aes-256-ecb, it produces the same output as the legacy mcrypt_encrypt.