Re: [saag] Improving the CHAP protocol

Yoav Nir <ynir.ietf@gmail.com> Sat, 21 September 2019 17:56 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
In-Reply-To: <1569087342890.52733@cs.auckland.ac.nz>
Date: Sat, 21 Sep 2019 20:56:11 +0300
Cc: Maurizio Lombardi <mlombard@redhat.com>, Security Area Advisory Group <saag@ietf.org>
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To: Peter Gutmann <pgut001@cs.auckland.ac.nz>
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Subject: Re: [saag] Improving the CHAP protocol
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FIPS is one advantage. The other is that MD5 is getting scarce in crypto libraries, while SHA-256 is everywhere.  Not everything is devices — there’s still software out there.

But yes, it’s still CHAP.

> On 21 Sep 2019, at 20:35, Peter Gutmann <pgut001@cs.auckland.ac.nz>; wrote:
> 
> I think many people in this thread are missing the purpose of the exercise.
> CHAP is used because umpteen bajillion devices and systems need it, not
> because it's a very good protocol.  It's insecure because it's CHAP, not
> because it uses MD5.  Since it needs a one-way function, not a collision-
> resistant function, any hash function is as good - or bad since CHAP isn't
> very secure - as any other.  Switching from MD5 to polyquantumresistantind-
> ccaprovable2048bithash will make no difference whatsoever to its security.
> 
> What the original poster asked for is something FIPS compliant.  If you want
> to convince said umpteen bajillion devices to switch, you'd better use the
> universal-standard FIPS-compliant hash algorithm that everything supports,
> which is SHA-256, not a bunch of wierdo fashion-statement algorithms that
> nothing supports, which is most of the other stuff that's been suggested.
> 
> Having said that, you'll have to accept that the vast majority of users will
> keep going with MD5 more or less forever since there's no motive apart from
> FIPS to change, so perhaps it'd be best to pitch the update RFC as "FIPS
> compliance for CHAP" or something similar.
> 
> Peter.
> 
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