Re: [http-auth] I-D Action: draft-ietf-httpauth-scram-auth-10.txt

[Alexey Melnikov <[e-mail]>]

Hi Tony,

On 19/11/2015 15:52, Tony Hansen wrote:
> On 11/19/15 8:46 AM, Alexey Melnikov wrote:
>> On 19/11/2015 13:43, [e-mail] wrote:
>>> The IETF datatracker status page for this draft is:
>>> https://datatracker.ietf.org/doc/draft-ietf-httpauth-scram-auth/
>>>
>>> There's also a htmlized version available at:
>>> https://tools.ietf.org/html/draft-ietf-httpauth-scram-auth-10
>>>
>>> A diff from the previous version is available at:
>>> https://www.ietf.org/rfcdiff?url2=draft-ietf-httpauth-scram-auth-10
>> This version fixes a few typos spotted by people, changes examples
>> from using "host.com" to "example.com" (thank you Tony) and fixes more
>> things in examples (again, thank you Tony).
>
> I've been thinking about re-authentication and the question about having
> a counter that changes to make each sr= unique. Unless I'm mistaken, I
> THINK without it, what is there now could allow replay attacks and MITM
> attacks.
Yes, until ttl expires. That is why I had this comment in the draft :-).
> It might be better to make sr= a base64-encoded block that includes both
> the s-nonce and the i value. The s-nonce would be what was in the
> earlier response, but uses a higher i= value, such as 4097, 4098, etc.
> The i value is ALREADY a counter that can be used to make things unique.
> And this should be easy for both sides to calculate because it can use
> the earlier result and just do another round of hashing.
I think I like your idea of reusing the "i" value as the starting 
counter. I am about to post a version of the draft with this change.