Problem with secrets

[David Goodenough]

On Wednesday 19 July 2006 13:55, Michael Lecuyer wrote:
> This has been explained before in this list and it's how RADIUS works.
>
> The Even though the secret is incorrect the authentication can be
> correct. The server returns an Access-Accept. Why? The server trusts the
> client (it's in the accepted NAS list) and performs the authentication.
Why then if the secret is a lot different does the server reject the client?
Or is it just that MD5 can generate identical results from two different 
input strings, and we were just unlucky?

David
> The server then signs the response packet with it's version of the
> secret. The client doesn't trust the server and checks the signature. If
> the signature is not correct the client rejects the packet.
>
> The opposite is true with accounting packets - the client signs the
> request and the server checks the signature.
>
> The Message-Authenticator attribute can be used to sign the
> Access-Request packet which will cause the server to reject a packet
> with the an incorrect MA signature.
>
> David Goodenough wrote:
> > I just hit a really odd problem with a secrets.
> >
> > We were asked to use FreeRadius to provide IP addresses to an Ericsonn
> > NAS.  We set up the server and have some test clients with simple
> > secrets. If those are right it works, if they are wrong it fails.
> >
> > Then we put in the secret for the Ericsonn (I can not put it in this
> > note as it is someone else's secret and I do not know what else it might
> > be the secret for, but privately I could make it available for testing).
> >
> > This secret is 13 digits long, mixed numbers and letters, looks
> > reasonably random, and in the proper secret all the letters were upper
> > case.  However somehow one of the letters (an O) got put into the server
> > in lower case.
> >
> > The server happily accepts Access-Request packets with an authenticator
> > built from the all upper case secret, even though its secret was
> > different, it was only the client which rejected the Access-Accept. 
> > Diagnosing this however was very difficult as we had no access to the
> > Ericsonn box and any console messages it might log (we could only see
> > what went on the wire and whether the connection succeeded).
> >
> > A quick look at the code did not find anywhere where the secret gets
> > folded to all upper case (but I might have missed it) and if there were
> > such folding it would be unfortunate if this was only done on checking
> > the received packet not on generating the reply.
> >
> > I am new to RADIUS, and I could not find any rules about case folding for
> > secrets, but I might have missed them.
> >
> > It could simply be one of those freak places where the MD5 checksum
> > happens to be the same for the request but not the response, but that
> > does not feel right.
> >
> > I am using 1.1.1 (I am also using JRadius which last time I looked only
> > produced patches for 1.1.1, not 1.1.2).
> >
> > David
> > -
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