On 24.01.19 16:20, Evgeny wrote:
> On Thu, Jan 24, 2019 at 6:11 PM, Florian Schmaus <[email protected]> wrote:
>> Then you can't authenticate unless the server also stores the
>> authentication data for SCRAM-SHA1. I guess that is your point. What is
>> wrong with the server storing the required data to authenticate clients
>> with eg. SCRAM-SHA1 or SCRAM-SHA256 (besides the implementation overhead
>> argument)? Maybe I am missing something?
> 
> I am not sure what you mean. I can only do that on the server
> if I get plain password from the client which is something SCRAM
> was designed to prevent if I understand it correctly.

I don't think that SCRAM was designed to prevent handing over the
plaintext password *on account creation*. Although reducing the exposure
of the plaintext password is always a good idea.

That is why modern challenge response authentication mechanism do not
require the server to *store* the password in plaintext. That was/is one
design goal of SCRAM. Happy to stand corrected.

> Also, the problem still remains with upgrading existing
> SHA-1 to SHA-256/384/512/whatever and if I don't upgrade it there
> is possibility to create interop problem again, unless a client
> 1) supports all previous SHA versions
> 2) doesn't treat previous SHA versions as a downgrade attack

I agree that a few words about future interoperability would be nice.
Although I think that there is possibly not much to say about it,
besides that servers are encouraged to support both mechanisms for a
certain time period.

I am not sure if the XSF is the right venue, since it is an IETF
standard and other protocols using SASL should also be affected. May I
suggest to ask for opinions on this on the kitten WG [1] mailing list?

- Florian

1: https://datatracker.ietf.org/wg/kitten/about/

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