Subject: Re: SSH_MSG_USERAUTH_GSSAPI_HASH in draft-galb-secsh-gssapi

From: "Joseph Galbraith" <[email-masked]>
Date: Tue, 27 Feb 2001 08:52:22 -0700

> draft-galb-secsh-gssapi-00.txt uses a user authentication exchange packet
to
> provide additional trust in the server's host key, by sending the client a
> GSSAPI MIC of the host key after a GSSAPI context has been established.
> However, I believe that this does not provide any additional protection
> against man in the middle attacks, as claimed.
>
> The draft has no clear requirement that the client receives this packet
> before continuing with authentication, so allowing a man in the middle
> attacker to simply remove that packet from the exchange that it is
proxying
> between the client and the server. I think that in order to receive the
> required protection, clients must not accept a success message unless the
> hash packet has been successfully received and verified. Could this be
stated
> more clearly in the document?

Yes, this is much clearer in my working version of the
draft, and I have just clarified it further to specify
that if the client doesn't receive the packet, it is
a protocol error.

Thanks for pointing this out.

We have been remiss getting this draft out; we will
be publishing a revision before the Friday deadline
though, containing the results of the discussion
last working group meeting.

- Joseph

---

From: Simon Wilkinson <[email-masked]>
Date: Tue, 27 Feb 2001 15:36:29 +0000

draft-galb-secsh-gssapi-00.txt uses a user authentication exchange packet to 

The draft has no clear requirement that the client receives this packet 
before continuing with authentication, so allowing a man in the middle 
attacker to simply remove that packet from the exchange that it is proxying 
between the client and the server. I think that in order to receive the 
required protection, clients must not accept a success message unless the 
hash packet has been successfully received and verified. Could this be stated 
more clearly in the document?

Cheers,

Simon.