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

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Date:   Mon, 10 Feb 2020 12:39:20 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     "Van Leeuwen, Pascal" <pvanleeuwen@...bus.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Ken Goldman <kgold@...ux.ibm.com>,
        Eric Biggers <ebiggers@...nel.org>,
        Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dmitry.kasatkin@...il.com" <dmitry.kasatkin@...il.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...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 17:01 +0000, Van Leeuwen, Pascal wrote:
> > -----Original Message-----
> > From: linux-crypto-owner@...r.kernel.org <linux-crypto-owner@...r.kernel.org> On Behalf Of James Bottomley
> > Sent: Monday, February 10, 2020 5:40 PM
> > 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
> >
> > <<< External Email >>>
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the
> > sender/sender address and know the content is safe.
> >
> >
> > 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://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fid%2Fdraft-oscca-cfrg-sm3-
> > 01.html&amp;data=01%7C01%7Cpvanleeuwen%40verimatrix.com%7C3a51d0c133dd4b00fd9a08d7ae47d6d6%7Cdcb260f9022d449586
> > 02eae51035a0d0%7C0&amp;sdata=0nQ6tWMdVR5uB0MTCgdMXiOmkvTvGEKDTLcMXdzyZpg%3D&amp;reserved=0
> > > > ,
> > > > 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.
> >
> Well, the current specification surely doesn't define anything else and is
> already over a decade old. So what would be the odds that they add a
> different blocksize variant _now_ AND still call that SM3-something?
> 
> > >   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:
> >
> SM3 is based on 512 bit input blocks, like _SHA-2_.
> The SHA-3 variants use block sizes between 576 and 1152 bits,
> depending on the output (digest) size.
> 
> The -xxx is referring to output (digest) size, not block size by the way.
> And SHA-3 is indeed defined for 512 bit output size, amongst others.
> 
> > https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Farchive%2Fid%2Fdraft-sca-cfrg-sm3-
> > 02.txt&amp;data=01%7C01%7Cpvanleeuwen%40verimatrix.com%7C3a51d0c133dd4b00fd9a08d7ae47d6d6%7Cdcb260f9022d44958602
> > eae51035a0d0%7C0&amp;sdata=9pfgM0bG%2Bp0zUavsknwn9vquWqPsqzPENV2okmgCOqE%3D&amp;reserved=0
> >
> > Currently only defines a 256 output (via compression from the final 512
> > bit output).
> >
> Yes. Although that is not the original (Chinese) specification.
> 
> > In theory, like SHA-3, SM3 could support 384 and 512
> > output variants.  However, there's no evidence anyone is working on
> > adding this.
> >
> Hmm ... not without changing the word width (as for SHA-512) and/or
> increasing the number of rounds plus other tweaking, I would say.
> It's not as straightforward as you are suggesting (crypto rarely is).
> I would even go as far as saying that is highly unlikely to happen.

So in terms of this discussion, does this mean you don't see a problem
with renaming "sm3-256" to "sm3" in crypto/hash_info.c?  If that's the
case, please add your Reviewed-by tag to the 1/2.

thanks,

Mimi