Subject: Re: your mail

From: "Massimiliano Pala" <[email-masked]>
Date: Thu, 29 Apr 2004 17:13:48 +0200 (CEST)

Dear List,

I have a doubt about the nonce in a TSP request. In section 2.4.1 at page 5
it is written that:

  "The nonce, if included, allows the client to verify the timeliness of
   the response when no local clock is available.  The nonce is a large
   random number with a high probability that the client generates it
   only once (e.g., a 64 bit integer).  In such a case the same nonce
   value MUST be included in the response, otherwise the response shall
   be rejected."

Anyway there is no indication of an upper limit to the nonce (in terms
of bits). This could allow rfc-compliant requests having very long nonce
thus allowing for a DoS or other type of attacks (in the server responses'
the same huge nonce MUST be present). A solution to this problem could be
not accepting requests bigger than a certain limit in size, but I guess
a fix is needed here anyway.

Does someone share my vision or am I missing something ?

    --- Massimiliano Pala

---

From: Jack Lloyd <[email-masked]>
Date: Thu, 29 Apr 2004 12:34:38 -0400

It is a potential DoS, but ones of this type (where the attacker has to use up
an amount of bandwidth at the same rate as what his target takes) is not
considered serious. That's because there really isn't much of a way to stop
this type of attack.

Anyway, there are much easier ways to kill TCP-based systems then drown them
in requests. :)

-Jack

---

From: [email-masked] (Peter Gutmann)
Date: Fri, 30 Apr 2004 05:19:36 +1200

"Massimiliano Pala" <[email-masked]> writes:

>Anyway there is no indication of an upper limit to the nonce (in terms of
>bits). This could allow rfc-compliant requests having very long nonce thus
>allowing for a DoS or other type of attacks (in the server responses' the
>same huge nonce MUST be present). A solution to this problem could be not
>accepting requests bigger than a certain limit in size, but I guess a fix is
>needed here anyway.

Most protocols never specify these things, leaving it up to implementors to
choose some suitable value.  I once crashed one vendor's server when I
included a huge nonce just to see what would happen :-).

Peter.

---

From: "Miguel Rodriguez" <[email-masked]>
Date: Thu, 29 Apr 2004 12:38:31 -0500

I agree with you, there's no upper limit to its size. My guess is that
most implementations are using 64 bit nonces (the lower bound).

Miguel A Rodriguez
SeguriData

> -----Original Message-----
> From: [email-masked] 
> [mailto:[email-masked]] On Behalf Of Massimiliano Pala
> Sent: Thursday, April 29, 2004 10:14 AM
> To: [email-masked]
> Subject: 
> 
> 
> 
> Dear List,
>