Re: [TLS] New cipher suites for SRP

Schmidt, Jörn-Marc <Joern-Marc.Schmidt@secunet.com> Mon, 20 July 2015 11:59 UTC

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From: =?Windows-1252?Q?Schmidt=2C_J=F6rn-Marc?= <Joern-Marc.Schmidt@secunet.com>
To: Geoff Keating <geoffk@geoffk.org>
Thread-Topic: [TLS] New cipher suites for SRP
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Date: Mon, 20 Jul 2015 11:58:55 +0000
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Subject: Re: [TLS] New cipher suites for SRP
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>> TLS-pwd already supports both of these. It also supports ECC too,
>> which is problematic with the current SRP protocol.

>In the language of the CFRG draft, TLS-pwd is “balanced” where SRP is
“augmented”,
>so they’re not really equivalent, correct?

Correct.


>This is possible, but you’d need to have the client and server negotiate
based on
>what they have.  For example, if the server has a SRP verifier from the
current
>protocol, but the client has a stored PBKDF2 hash of the password for that
server,
>they cannot communicate and would need to pick a different cipher suite.  I
am not
>sure how you can do this without revealing the existence of an account
under some
>circumstances.  So this might be a situation where fewer protocol options
is better.

Of course both sides have to agree on  common protocol details: You could do
this by specifying that you want to use PAKE and refine in an extension a
set of schemes that you are capable of. 
I think there are many flavors out there that may be beneficial in specific
use-cases. I envision that e.g. in the context of the IoT with very
constrained devices (specific) PAKE schemes might be helpful. Having an
ExtensionType & corresponding CipherSuites for each of them would be way too
much. 

Best,

Jörn