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Challenge-response? [Jun. 22nd, 2005|09:14 pm]
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I'm using the flat protocol, and I'm trying to authenticate using the challenge-response system. When I send the "getchallenge" command to the server, I'm getting this back:


No matter how hard I try, I can't get it to authenticate. I've tried using the whole string, colon-separated chunks of the string, and the last two chunks together (I noticed they're the main two that change), but nothing's working. I've checked my MD5 function and it's working correctly (I can generate hpassword's just fine), and I'm using the MD5_hex(challenge + MD5_hex(password)) formula. So, which part of that string do I need to return as "auth_challenge", and which part do I need to manipulate using that formula to return as "auth_response"?

[User Picture]From: talisker
2005-06-23 07:29 pm (UTC)
you need to return the whole challenge string, as well as your response to it.

Basically, if you're using the flat interface, you need to do something like this:

string challenge = /* LJ challenge string */

//this class computes md5(challenge + md5(password))
string auth_response = MD5Hasher.Compute(challenge + hpasswd);

string body = "mode=sessiongenerate&";
body += "user=" + uname + "&";
body += "auth_method=challenge&";
body += "auth_challenge=" + challenge + "&";
body += "auth_response=" + auth_response + "&";
body += "expiration=long&";
body += "ver=" + pver;

And you need to send the body string to the server in a POST. This will return you a ljsession cookie that you can use for your subsequent calls to the server.

Hope this helps.
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[User Picture]From: marksmith
2005-06-23 08:14 pm (UTC)
Ensure all MD5 hashes you generate and use are lowercase. That's the #1 cause of verification failures. Unix does lowercase, many Windows libraries do uppercase.
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