Subject: [Ietf-krb-wg] Client aborting replacing-reply-key FAST exchange

From: [email-masked]
Date: Thu, 28 Aug 2008 07:14:40 -0400

Larry & Sam,

In his recent review of the OTP pre-auth ID, Srinivas Cheruku asked
about how the client should abort the authentication exchange if it
detected an error the final response from the KDC confirming the reply
key change (section 3.5 of draft-ietf-krb-otp-preauth-05). This is a
similar issue to the encrypted challenge FAST factor in section 6.5.5 of
draft-ietf-krb-wg-preauth-framework-08 where the client checks that the
encrypted timestamp returned by the KDC decrypts correctly.

What should the client do if the verification of the reply key change
fails?  Is there a standard method for it to fail the authentication
exchange?

--Gareth

>
>       Section 3.5:
>          The client then uses its generated Reply Key to decrypt the
PA-OTP-
>          ENC-CONFIRM from the encData of the PA-OTP-CONFIRM.  The
client MUST
>          fail the authentication process if the nonce value in the
PA-OTP-ENC-
>          CONFIRM is not the same as the nonce value sent in the
PA-OTP-
>          REQUEST.
>
>       With which error the client should fail the authentication?
>     Is this error implementation specific?
>
I would welcome some advice from the WG here.

The problem is that the mutual authentication process has failed since
the Reply Key generated by the client has not successfully decrypted the
nonce that that has been returned by the KDC encrypted with what should
be the same Reply Key.  The client cannot therefore permit the process
to continue and so must abort.

Are there any standard ways of a client aborting the authentication
process?
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