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Re: [TLS] Working Group Last Call for draft-ietf-tls-pwd

Joseph Birr-Pixton <jpixton@gmail.com> Fri, 06 December 2013 23:25 UTC

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Date: Fri, 06 Dec 2013 23:25:44 +0000
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From: Joseph Birr-Pixton <jpixton@gmail.com>
To: tls@ietf.org, dharkins@lounge.org
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Subject: Re: [TLS] Working Group Last Call for draft-ietf-tls-pwd
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On 6 December 2013 20:00,  <tls-request@ietf.org> wrote:
> From: "Dan Harkins" <dharkins@lounge.org>
> To: "CodesInChaos" <codesinchaos@gmail.com>
> Cc: "tls@ietf.org" <tls@ietf.org>
> Date: Fri, 6 Dec 2013 10:29:22 -0800 (PST)
> Subject: Re: [TLS] Working Group Last Call for draft-ietf-tls-pwd
>
> On Fri, December 6, 2013 3:14 am, CodesInChaos wrote:
>> Database compromises happen all the time, and forcing the server to
>> store a weakly hashed password
>> isn't acceptable IMO.
>
>   You're absolutely right, that would not be acceptable.
>
>   TLS-pwd uses HMAC-SHA256 with a 32 byte random key (salt) to
> hash passwords that the server stores.

How does this not constitute an immensely fast password oracle?

If the server stores (username, base, salt) per user with base :=
HMAC-SHA256(salt, username || password) you'd only need to compute
about 3 SHA256 blocks to check each candidate password.

Cheers,
Joe

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