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Date:   Mon, 12 Jun 2023 20:02:16 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Heiko Stuebner <heiko@sntech.de>
Cc:     palmer@dabbelt.com, paul.walmsley@sifive.com,
        aou@eecs.berkeley.edu, herbert@gondor.apana.org.au,
        davem@davemloft.net, conor.dooley@microchip.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-crypto@vger.kernel.org, christoph.muellner@vrull.eu,
        Heiko Stuebner <heiko.stuebner@vrull.eu>
Subject: Re: [PATCH v5 0/4] Implement GCM ghash using Zbc and Zbkb extensions
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References: <20230612210442.1805962-1-heiko.stuebner@vrull.eu>
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Hi Heiko,

On Mon, Jun 12, 2023 at 11:04:38PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@vrull.eu>
> 
> This was originally part of my vector crypto series, but was part
> of a separate openssl merge request implementing GCM ghash as using
> non-vector extensions.
> 
> As that pull-request
>     https://github.com/openssl/openssl/pull/20078
> got merged recently into openssl, we could also check if this could
> go into the kernel as well and provide a base for further accelerated
> cryptographic support.

I'm still a bit skeptical of the usefulness of a standalone "ghash"
implementation, when in practice it will only be used as part of "gcm(aes)".
Directly implementing "gcm(aes)" (instead of relying on crypto/gcm.c to compose
"ghash" and "ctr(aes)") also allows some performance optimizations.

I asked about this on v4
(https://lore.kernel.org/linux-crypto/ZCSG71bRuTzVutdm@gmail.com/),
but I didn't receive a response.

Any thoughts on this?

- Eric