Re: Security Question

> Mailing-List: contact [email protected]; run by ezmlm
> Date: Thu, 10 Jun 2004 10:01:36 -0700 (PDT)
> From: "joe o'toole" <[email protected]>
> 
> The following text is taken from the SFS FAQ
> (http://www.fs.net/sfswww/sfsfaq.html):
> "AFS, another widely-used network file system, does
> not keep the contents of private files secret from
> network eavesdroppers. Moreover, AFS uses an insecure
> message authentication code (MAC) to protect the
> integrity of communication between clients and
> servers. An active attacker can, with very little
> computation, tamper with and change the contents of
> AFS messages in transit."
> 
> Based on my high level understanding of Kerberos (used
> by AFS), once the users have obtained credentials and
> are authenticated the traffic between parties is
> securely transmitted.  This seems to clash with the
> statements in the FAQ.  Is there further documentation
> to be read or can someone explain this?

Unfortunately, the AFS protocol isn't really documented anywhere
(unlike SFS, which is documented pretty much down-to-the-byte in my
thesis and the XDR files of the distribution).

However, you don't need documentation to see that AFS is not secure.
Just run:

   tcpdump -s 1500 -v -X

While you create or read some files on AFS.  You'll see the contents
of the files going over the network in cleartext.  As for the MAC, you
would have to check the source code.  Those who have tell me AFS uses
an encrypted CRC with a known polynomial.  It is well known how to
"weight" messages to produce a particular CRC.

David