C＃SSO哈希迁移到PHP

Question

I'm working on an SSO implementation in PHP that authenticates to a system written in C#. Here's some pseudo code to demonstrate:

$token = "MqsXexqpYRUNAHR_lHkPRic1g1BYhH6bFNVPagEkuaL8Mf80l_tOirhThQYIbfWYErgu4bDwl-7brVhXTWnJNQ2";
$id = "[e-mail]";
$ssokey = "7MpszrQpO95p7H";
$idAndKey = $id . $ssokey;
$salt = base64_decode(substr($token, 0, -1));
$hashed = hash_pbkdf2("sha256", $idAndKey, mb_convert_encoding($salt, 'UTF-16LE'), 1000, 24, false);
$data = base64_encode($hashed);

This outputs: NWZiMTBhZmNhNTlmYzMxMTEzMThhZmVl

Here's the C# version from the system with which I'm integrating:

var token = "MqsXexqpYRUNAHR_lHkPRic1g1BYhH6bFNVPagEkuaL8Mf80l_tOirhThQYIbfWYErgu4bDwl-7brVhXTWnJNQ2";
var id = "[e-mail]";
var ssokey = "7MpszrQpO95p7H";
string idAndKey = id + ssokey;
var salt = HttpServerUtility.UrlTokenDecode(token);
var pbkdf2 = new Rfc2898DeriveBytes(idAndKey, salt) {IterationCount = 1000};
var key = HttpServerUtility.UrlTokenEncode(pbkdf2.GetBytes(24)); 
Console.WriteLine(key.ToString());

This outputs: aE1k9-djZ66WbUATqdHbWyJzskMI5ABS0

I cannot figure out how to get my PHP code to do the same thing. I have a feeling it is in the salt generation.

I've tried to translate the C# HttpServerUtility.UrlTokenDecode function to PHP like so:

function UrlTokenDecode($token) {
    $numPadChars = substr($token, -1);

    // add the padded count to the end
    $salt = substr($token, 0, -1) . $numPadChars;

    // Transform the "-" to "+", and "*" to "/"
    $salt = str_replace('-', '+', str_replace('*', '/', $salt));

    // base64_decode
    $salt = base64_decode($salt);

    return $salt;
}

That didn't get me to where I needed to go. Halp!

This is for Absorb LMS. Documentation of their methods are here: https://support.absorblms.com/hc/en-us/articles/222446647-Incoming-Absorb-Single-Sign-On#Methods

Thanks!

Answer 1

I don't know php at all, but still can help I think. First, as stated in my comment, Rfc2898DeriveBytes in C# uses SHA1 as hash function, not SHA256, doesn't matter what your documentation says.

Next, UrlTokenDecode (and Encode) is quite strange thing I rarely seen in practice. It converts regular base64 to "url safe" version as follows:

• replaces '+' with '-'
• replaces '/' with '_'
• removes padding ('==' at the end) and appends length of removed padding as a number as last character (if there were no padding - it still appends "0"). This step doesn't make any sense to me, but it's how it works.

So to replicate you need to base64_encode, replace, remove padding, and then add padding length as character. So if your base64 string ended with == - you remove that and add "2" at the end. If there was no padding - you add "0".

So to decode that string you need to make back replacement, then remove last character and add that much '=' to the end as indicated by that character.

So string

MqsXexqpYRUNAHR_lHkPRic1g1BYhH6bFNVPagEkuaL8Mf80l_tOirhThQYIbfWYErgu4bDwl-7brVhXTWnJNQ2

In normal base64 is MqsXexqpYRUNAHR/lHkPRic1g1BYhH6bFNVPagEkuaL8Mf80l/tOirhThQYIbfWYErgu4bDwl+7brVhXTWnJNQ==

Then, I have no idea why you do that

mb_convert_encoding($salt, 'UTF-16LE')

Just remove it (though as I don't know php - there might be some reason you are doing that, but I just cannot imagine which, so take care).

Then as other answer states - the last argument to hash_pbkdf2() should be true.

After making this changes your code will work (I used token already converted to normal base64 string):

$token = "MqsXexqpYRUNAHR/lHkPRic1g1BYhH6bFNVPagEkuaL8Mf80l/tOirhThQYIbfWYErgu4bDwl+7brVhXTWnJNQ==";
$id = "[e-mail]";
$ssokey = "7MpszrQpO95p7H";
$idAndKey = $id . $ssokey;
$salt = base64_decode($token);
$hashed = hash_pbkdf2("sha1", $idAndKey, $salt, 1000, 24, true);
$data = base64_encode($hashed);
echo $data;

produces expected answer (in normal base64 - you need to "url encode" it to get exact match).