Re: IQ Handling vulnerabilities

Thijs Alkemade <[email protected]> Mon, 10 Feb 2014 20:25:36 +0100

Newsgroups	gmane.ietf.xmpp
Message-ID	<[email protected]>

On 10 feb. 2014, at 18:15, Joe Hildebrand (jhildebr) <[email protected]> wrote:

> On 2/7/14 8:13 AM, "Joe Hildebrand (jhildebr)" <[email protected]> wrote:
> 
>> I have a couple of ludicrous s2s attacks on mind, but more important I
>> think is doing what
>> 
>> Mobile/terse. DYAC.
> 
> Yes, well that was even more terse than normal.  I was going to say
> something about generating less-guessable IDs that don't eat up much
> entropy.  For example:
> 
> start = sha1(crytpo_rand())
> start+1 = sha1(start)
> 
> would probably do nicely.

Uhm. Maybe this email is missing a line again, but if you use those values as
'id's directly, they will not be unpredictable at all, as anyone who receives
an <iq/> can generate the rest of the chain.

However, if you make sure the 'id' values are only half the hashes, it should
be unpredictable unless an attacker is willing to spend an insane amount of
work.

So:

start = sha1(crytpo_rand())
start+1 = sha1(start)
...

id1 = start[0:10]
id2 = start+1[0:10]
…

Thijs

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