trying to implement it quickly, I get the same questions than you

# https://www.php.net/manual/en/function.openssl-pbkdf2.php
    $password = $sharedKey;
    $salt = openssl_random_pseudo_bytes(16);  # What's the salt length ?
    $keyLength = 20;  # What's the key length here ?
    $iterations = 100000;
    $generatedKey = openssl_pbkdf2($password, $salt, $keyLength, $iterations, 'sha256');
    echo bin2hex($generatedKey)."\n";
    echo base64_encode($generatedKey)."\n";

    $iv = openssl_random_pseudo_bytes(16); // AES-256-CBC requires 16-byte IV
    $cipherText = openssl_encrypt($message, 'aes-256-cbc', $generatedKey, OPENSSL_RAW_DATA, $iv);
    return base64_encode($iv . $cipherText);

@eapl.me@eapl.me Here is what I’ve got so far: https://github.com/upputter/testing-twtxt-dm

There is a “00_well_known_message.enc” file, which I have the encryption paremters for (https://github.com/upputter/testing-twtxt-dm/blob/9fdf3be6aa8fe810a4cb275375dbb3d4a2a958ee/wellknown_test.php#L28).

According to my finding, I assume, that the saltsize in openssl is “8” and the PBKDF2 algo is “sha256”.