linux-kernel - Re: [RFC V1 3/7] crypto: ghash - Optimized GHASH computations

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Date:   Fri, 15 Jan 2021 17:43:23 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Dey, Megha" <megha.dey@...el.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ravi.v.shankar@...el.com, tim.c.chen@...el.com,
        andi.kleen@...el.com, dave.hansen@...el.com,
        wajdi.k.feghali@...el.com, greg.b.tucker@...el.com,
        robert.a.kasten@...el.com, rajendrakumar.chinnaiyan@...el.com,
        tomasz.kantecki@...el.com, ryan.d.saffores@...el.com,
        ilya.albrekht@...el.com, kyung.min.park@...el.com,
        Tony Luck <tony.luck@...el.com>, ira.weiny@...el.com
Subject: Re: [RFC V1 3/7] crypto: ghash - Optimized GHASH computations

On Fri, Jan 15, 2021 at 04:14:40PM -0800, Dey, Megha wrote:
> > Hello Megha,
> > 
> > What is the purpose of this separate GHASH module? GHASH is only used
> > in combination with AES-CTR to produce GCM, and this series already
> > contains a GCM driver.
> > 
> > Do cores exist that implement PCLMULQDQ but not AES-NI?
> > 
> > If not, I think we should be able to drop this patch (and remove the
> > existing PCLMULQDQ GHASH driver as well)
> 
> AFAIK, dm-verity (authenticated but not encrypted file system) is one use
> case for authentication only.
> 
> Although I am not sure if GHASH is specifically used for this or SHA?
> 
> Also, I do not know of any cores that implement PCLMULQDQ and not AES-NI.
> 

dm-verity only uses unkeyed hash algorithms.  So no, it doesn't use GHASH.

- Eric