Re: [xmpp] IQ Handling vulnerabilities

[Alexander Holler <[e-mail]>]

Am 11.02.2014 16:33, schrieb Thijs Alkemade:
>
> On 11 feb. 2014, at 16:14, Alexander Holler <[e-mail]> wrote:
>
>> Am 11.02.2014 13:29, schrieb Dave Cridland:
>>> On Tue, Feb 11, 2014 at 12:23 PM, Alexander Holler <[e-mail]>wrote:
>>>
>>>> Hmm, in all these mails it was never be mentioned that IDs still have to
>>>> be unique over some time for one session. I'm not sure if such is given
>>>> with the above constructs. It might be very unlikely that the same ID will
>>>> appear twice, but someone has to take a deeper look at it when using such
>>>> constructs like above. Of course, in reality the window in time IDs must be
>>>> unique is rather small, but ...
>>>>
>>>
>>> You'd need random collisions amongst cryptographically secure hashes.
>>> You're pretty safe.
>>
>> I don't aggree. You are safe if you use the hash as intendend, but not
>> if you just use some part of the hash(-number) or hashes of hashes. I'm
>> not sure about how safe it is (in regard to collisions) if you look at
>> consequent hashes of hashes. I would assume that is not what
>> cryptographers do look for (primarily).
>>
>> At least I can't remember to have seen some discussion if the series of
>> hash(hash(hash(...))) is collision free (that is imho quiet different
>> than hash(random); hash(random)). Of course, I'm not looking that often
>> at cryptographic papers, I usually prefer if cryptographers do such. ;)
>
> You're not going to stumble upon a SHA-1 collision by accident. Even if you do
> "hashes of hashes". The esitmated cost of an intentional SHA-1 collision is
> still at least $1M:
> https://www.schneier.com/blog/archives/2012/10/when_will_we_se.html
>
> If you do happen to find one, congratulations, you are now famous. Nobody has
> published a SHA-1 collision yet.

Sorry, but you haven't understood what I've written.

Alexander Holler