Re: [PATCH 18/18] signed push: final protocol update
On Thu, Sep 4, 2014 at 4:57 PM, Junio C Hamano <gitster@pobox.com> wrote:
Show 22 quoted lines
> Shawn Pearce <spearce@spearce.org> writes:
>
>> As you know, the stateless HTTP thing doesn't allow the nonce on the
>> server to be carried from the initial ref advertisement into the final
>> receive-pack. We would either need to write the nonce to disk and load
>> it back up later (ick), or use some sort of stateless nonce.
>>
>> A stateless nonce could look like:
>>
>> nonce = HMAC_SHA1( SHA1(site+path) + '.' + now, site_key )
>>
>> where site_key is a private key known to the server. It doesn't have
>> to be per-repo.
>
> Doing the above naively will force you to check 600 HMAC if your
> slack is for 10 minutes. You could just instead use
>
> nonce = now '-' HMAC_SHA1(path + '.' + now, site_key)
>
> and the validation side can make sure the same site_key was used,
> and also "now" readable from the plaintext part is fresh enough,
> with a single HMAC.
Argh. Yes, thank you. This is what I meant but did not write. :(
> I may be missing something, but with this, we can always validate
> that "nonce" is what the repository issued (whether "stateless" is
> used or not). The hook script can decide if "now" is recent enough
> or not without bothering receive-pack at all.
Shawn Pearce <spearce@spearce.org>