Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 15 Jan 2021 17:43:23 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     "Dey, Megha" <megha.dey@intel.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ravi.v.shankar@intel.com, tim.c.chen@intel.com,
        andi.kleen@intel.com, dave.hansen@intel.com,
        wajdi.k.feghali@intel.com, greg.b.tucker@intel.com,
        robert.a.kasten@intel.com, rajendrakumar.chinnaiyan@intel.com,
        tomasz.kantecki@intel.com, ryan.d.saffores@intel.com,
        ilya.albrekht@intel.com, kyung.min.park@intel.com,
        Tony Luck <tony.luck@intel.com>, ira.weiny@intel.com
Subject: Re: [RFC V1 3/7] crypto: ghash - Optimized GHASH computations
Message-ID: <YAJEu1esw0zPA7Qh@gmail.com>
References: <1608325864-4033-1-git-send-email-megha.dey@intel.com>
 <1608325864-4033-4-git-send-email-megha.dey@intel.com>
 <CAMj1kXGhGopfg19at5N_9q89-UA4irSgMULyDXg+dKhnbRrCZQ@mail.gmail.com>
 <dfb5f2e0-027d-2b9c-aec7-313ff0275381@intel.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <dfb5f2e0-027d-2b9c-aec7-313ff0275381@intel.com>
Precedence: bulk

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