linux-kernel - Re: [PATCH 1/2] crypto: sm3 - add a new alias name sm3-256

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Date:   Mon, 10 Feb 2020 08:39:37 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Ken Goldman <kgold@...ux.ibm.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        zohar@...ux.ibm.com, dmitry.kasatkin@...il.com, jmorris@...ei.org,
        serge@...lyn.com, linux-crypto@...r.kernel.org,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] crypto: sm3 - add a new alias name sm3-256

On Mon, 2020-02-10 at 11:30 -0500, Ken Goldman wrote:
> On 2/9/2020 10:17 PM, Eric Biggers wrote:
> > According to https://tools.ietf.org/id/draft-oscca-cfrg-sm3-01.html
> > ,
> > SM3 always produces a 256-bit hash value.  E.g., it says:
> > 
> > 	"SM3 produces an output hash value of 256 bits long"
> > 
> > and
> > 
> > 	"SM3 is a hash function that generates a 256-bit hash value."
> > 
> > I don't see any mention of "SM3-256".
> > 
> > So why not just keep it as "sm3" and change hash_info.c instead?
> > Since the name there is currently wrong, no one can be using it
> > yet.
> 
> Question:  Is 256 bits fundamental to SM3?

No.

>   Could there ever be a 
> variant in the future that's e.g., 512 bits?

Yes, SM3 like SHA-3 is based on a 512  bit input blocks.  However,
what's left of the standard:

https://www.ietf.org/archive/id/draft-sca-cfrg-sm3-02.txt

Currently only defines a 256 output (via compression from the final 512
bit output).  In theory, like SHA-3, SM3 could support 384 and 512
output variants.  However, there's no evidence anyone is working on
adding this.

James