Re: Digest mess
John Franks (john@math.nwu.edu)
Fri, 19 Dec 1997 10:08:15 -0600 (CST)
Note the temporary mailing list: ietf-http-wg@w3.org
On Fri, 19 Dec 1997, Scott Lawrence wrote:
>
>> John Franks:
>
>> It is the client who must be concerned about reused nonces to avoid
>> a replay attack. To avoid a replay attack the client would have to
>> keep a data base of all previous nonces and make sure they are not
>> reused.
>
> No - it only needs to keep the nonce it used for the outstanding
> request; if that does not produce the correct digest then it is not
> valid even if it would have been valid for some earlier request.
>
Maybe I am not understanding you. It seems to me that if a client,
for example, regularly places an order and receives and acknowledgement
there is a possible replay attack.
If an intermediary attacker intercepts the order he can impersonate
the server and offer a nonce from a previous transaction. The client
then submits the order which is grabbed by the attacker and then the
attacker replays a previous acknowledgement with the dates changed. A
similar attack might involve sending a fake 304 when in fact the
resource has changed. This is what hash dates is supposed to prevent.
Am I missing something.
John Franks
john@math.nwu.edu