From: Richard Henderson <richard.henderson@linaro.org>
To: Ard Biesheuvel <ardb@kernel.org>, qemu-devel@nongnu.org
Cc: "Philippe Mathieu-Daudé" <philmd@linaro.org>,
"Zewen Ye" <lustrew@foxmail.com>,
"Weiwei Li" <liweiwei@iscas.ac.cn>,
"Junqiang Wang" <wangjunqiang@iscas.ac.cn>
Subject: Re: [PATCH v2] target/riscv: Use existing lookup tables for MixColumns
Date: Mon, 31 Jul 2023 08:16:02 -0700 [thread overview]
Message-ID: <db4d8cd1-a214-5991-0169-a66147816f72@linaro.org> (raw)
In-Reply-To: <20230731084043.1791984-1-ardb@kernel.org>
On 7/31/23 01:40, Ard Biesheuvel wrote:
> The AES MixColumns and InvMixColumns operations are relatively
> expensive 4x4 matrix multiplications in GF(2^8), which is why C
> implementations usually rely on precomputed lookup tables rather than
> performing the calculations on demand.
>
> Given that we already carry those tables in QEMU, we can just grab the
> right value in the implementation of the RISC-V AES32 instructions. Note
> that the tables in question are permuted according to the respective
> Sbox, so we can omit the Sbox lookup as well in this case.
>
> Cc: Richard Henderson<richard.henderson@linaro.org>
> Cc: Philippe Mathieu-Daudé<philmd@linaro.org>
> Cc: Zewen Ye<lustrew@foxmail.com>
> Cc: Weiwei Li<liweiwei@iscas.ac.cn>
> Cc: Junqiang Wang<wangjunqiang@iscas.ac.cn>
> Signed-off-by: Ard Biesheuvel<ardb@kernel.org>
> ---
> v2:
> - ignore host endianness and use be32_to_cpu() unconditionally
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
next prev parent reply other threads:[~2023-07-31 15:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-31 8:40 [PATCH v2] target/riscv: Use existing lookup tables for MixColumns Ard Biesheuvel
2023-07-31 15:16 ` Richard Henderson [this message]
2023-08-02 13:41 ` Alistair Francis
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