[jdev] sasl help

[Dave Cridland]

On Tue Oct 23 08:25:59 2007, Jacob Wright wrote:
> I'm working on the DIGEST-MD5 SASL authentication and feel like I'm  
> doing it
> perfectly, but my server is telling me I've got an incorrect auth  
> for the
> right username and password.

Now you know one of the reasons that the IETF is deprecating it. :-/

> var dataStr:String = bytes.readUTFBytes(bytes.bytesAvailable);

Hmmm... DIGEST-MD5 isn't UTF-8, by default. (It's iso-8859-1, I  
think, due to HTTP-isms in it). This will probably work, though.



> // transcode the string into an object
> 
> var data:Object = stringToObject(dataStr);
> 
> 
What does this actually do?

> obj["digest-uri"] = "xmpp/" + (conn.domain || conn.host);
> 
> 
Actually, this should probably be:

if conn.domain != conn.host {
  obj["serv-name"] = conn.domain
  obj["digest-uri"] = "xmpp/" + conn.host + "/" + conn.domain
} else {
  obj["digest-uri"] = "xmpp/" + conn.host
}

or something similar. Although I note you have one or other  
populated, by the looks of things, so you'll need to adjust to fit.

Except this is one of those areas that's probably ignored, so maybe  
just stick with whatever seems to work. To be honest, you can  
probably send utter rubbish here as long as you get the service  
right. (I've seen failures to to the wrong service name used, but  
never due to the wrong host. My bet is that nobody cares.)


> if (data.algorithm)
> 
> obj.algorithm = data.algorithm;
> 
> 
It doesn't seem very likely that you want to be messing with  
algorithm. It's not present in RFC2831, after all, and has no effect  
unless you're doing something other than qop=auth.


> obj.nc = "00000001";
> 
> if (data.qop)
> 
> obj.qop = "auth";
> 
> 
qop absent, or qop=auth, are the same thing. You don't need to be  
conditional on whether the remote end gives you a choice. (Unless  
you're trying to do auth-int).


> obj.cnonce = conn.generateId();
> 
> 
This isn't secure enough, but it should still work, of course.


> var a1:String, a2:String;
> 
> 
> a1 = MD5.hash(obj.username + ":" + obj.realm + ":" + password) +  
> ":" +
> obj.nonce + ":" + obj.cnonce;
> 
> 
Ooops - does MD5.hash() return a hex digest or a binary one? You want  
a binary digest here.


> a2 = "AUTHENTICATE:" + obj["digest-uri"];
> 
> 
> var response:String;
> 
> 
> if (obj.qop)
> 
> response = MD5.hash(MD5.hash(a1) + ":" + obj.nonce + ":" + obj.nc +  
> ":" +
> obj.cnonce + ":" + obj.qop + ":" + MD5.hash(a2));
> 
> 
All the hashes here are hex strings, and need to be in lower case.

Response does vary based on qop, but you should always be using  
qop=auth anyway, which is also the default if not present.

> var resultStr:String = objectToString(obj);
> 
> 
And again, what is this doing? Bear in mind that if it's some  
convenient built-in that produces output that's similar to  
DIGEST-MD5's syntax, this may not be quite right.

Hope this gives you some pointers, anyway. I'm pretty sure it'll be  
down to the distinction between H() and HEX(H()).

http://svn.dave.cridland.net/svn/projects/infotrope/python/infotrope/sasl.py 
contains an implementation of DIGEST-MD5 in Python, if that helps.  
The method "gen_hash" does the serious magic.

Dave.
-- 
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