linux-kernel - Re: [PATCH v2 12/15] crypto: arm64/sm4 - add CE implementation for ESSIV mode

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Message-ID: <Y1dyNWSdCesQlWm8@sol.localdomain>
Date:   Mon, 24 Oct 2022 22:20:53 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Jussi Kivilinna <jussi.kivilinna@....fi>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 12/15] crypto: arm64/sm4 - add CE implementation for
 ESSIV mode

On Fri, Oct 21, 2022 at 10:47:14AM +0800, Tianjia Zhang wrote:
> Hi Eric,
> 
> On 10/20/22 11:58 AM, Eric Biggers wrote:
> > On Tue, Oct 18, 2022 at 03:10:03PM +0800, Tianjia Zhang wrote:
> > > This patch is a CE-optimized assembly implementation for ESSIV mode.
> > > The assembly part is realized by reusing the CBC mode.
> > > 
> > > Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> > 
> > Is there still a use case for CBC-ESSIV mode these days, now that everyone is
> > using XTS instead?
> > 
> > - Eric
> 
> The mainstream is already using XTS, but CBC-ESSIV is still an optional
> backup algorithm, especially in block crypto and fscrypto, I'm currently
> working on supporting the SM4 algorithm for these subsystems.
> 

The only reason that AES-CBC-ESSIV support was added to fs/crypto/ was because
someone had a low-power embedded device with a hardware crypto accelerator that
only supported AES-CBC.

Nothing like that is relevant here, as this is just a software implementation.

Please just don't include ESSIV.  There's no need to implement random useless
algorithms.  It could always be added later if a use case actually arises.

- Eric