Can I Migrate from Mcrypt to OpenSSL Encryption While Maintaining Decryption Compatibility?

Upgrading my encryption library from Mcrypt to OpenSSL

Question:

Is it possible to upgrade my encryption library from Mcrypt to OpenSSL and retain the ability to decrypt data that was encrypted using Mcrypt?

Conflicting Information:

There appears to be conflicting information online regarding the compatibility between these two libraries.

• One source claims that decrypting Mcrypt-encrypted data with OpenSSL is impossible.
• Another source suggests that it is possible using padding.

Additional Context:

I am attempting to convert an encryption class that currently uses Mcrypt to one that uses OpenSSL. However, I am encountering difficulties in decrypting data encrypted with the Mcrypt version.

Working Code for Decryption:

The following revised code for the decryption routine in the OpenSSL version has been confirmed to work:

public function decrypt($data, $key) {
    $salt = substr($data, 0, 128);
    $enc = substr($data, 128, -64);
    $mac = substr($data, -64);

    list ($cipherKey, $macKey, $iv) = $this->getKeys($salt, $key);

    if ($mac !== hash_hmac('sha512', $enc, $macKey, true)) {
        return false;
    }

    $dec = openssl_decrypt($enc, $this->cipher, $cipherKey, OPENSSL_RAW_DATA, $iv);

    return $dec;
}

Test Results:

Testing this revised code with various data and keys yielded no failures.

Conclusion:

It is possible to upgrade the encryption library from Mcrypt to OpenSSL and successfully decrypt data that was encrypted with the previous library, provided that you use the updated decryption routine.

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