Re: [saag] Improving the CHAP protocol

Kathleen Moriarty <> Wed, 18 September 2019 16:23 UTC

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From: Kathleen Moriarty <>
Date: Wed, 18 Sep 2019 12:22:29 -0400
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To: "Mark D. Baushke" <>
Cc: Maurizio Lombardi <>,
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Subject: Re: [saag] Improving the CHAP protocol
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This is the right place to start the discussion.  If you pull together a
draft before the deadline and want a slot to present at SecDispatch, send a
message there as well.  SecDispatch will help find a home for the draft,
even if that is an AD sponsored draft (if there's not WG that is a fit).

Best regards,

On Wed, Sep 18, 2019 at 11:48 AM Mark D. Baushke <mdb=>; wrote:

> Hi Maurizio,
> Summary: SHA2-512/256 looks good to me. You may also wish to consider
>          SHAKE128(M,256) or SHAKE256(M,256) generating 256 bits.
> Long reply:
> See "Comparing Hardware Performance of Round 3 SHA-3 Candidates using
> Multiple Hardware Architectures in Xilinx and Altera FPGAs"
> and look for Keecak vs SHA-2 results.
> Doing SHA3 in hardware is going to be faster than doing SHA2 in
> hardware.
> Doing SHA3 in software is going to be much slower than doing SHA2 in
> software.
> Comparing SHA2-256 to SHA2-512/256 in software depends on the native
> size of a CPU word.
> On a 64bit CPU, I beleve that doing a SHA2-256 will be slower than
> doing a SHA2-512/256 on the order of 30% (best to run your own
> benchmarks using something like 'openssl speed').
> Per FIPS Publication 202, for SHA3, to get 256-bits of hash, there are
> alternatives: SHA3-256, and the two Extendable-Output Functions (XOF):
> SHAKE128 and SHAKE256. (There is no definition for SHA3-512/256.)
> I have not done any software performance analysis of SHA3 functionality,
> however, the shows that using
> the XOF functions are on performance part with SHA-2 on common
> processors.
> Considering longer term safety of the 256-bit hashes...
> The SHA2-512/256 keeps an internal state of 1024 bits and displays only
> 256 bits of the finished hash. While SHA2-256 keeps an internal state of
> 512 bits and displays half of it (256 bits), so from a data hiding point
> of view is should be more secure to use SH2-512/256.
> As the intention is cryptographic agility, I think that adding
> SHA2-512/256 is a good idea.
> It may also be desirable to consult with your FIPS experts to determine
> if SHAKE{128,256} is acceptable to generate the 256-bits needed and be
> FIPS 140-2 compliant.
>         -- Mark
> _______________________________________________
> saag mailing list


Best regards,