linux-kernel - Re: [PATCH v4 11/12] crypto: asymmetric_keys - Adjust signature size calculation for NIST P521

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Date: Sun, 3 Mar 2024 19:47:45 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Stefan Berger <stefanb@...ux.ibm.com>
Cc: keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
	herbert@...dor.apana.org.au, davem@...emloft.net,
	linux-kernel@...r.kernel.org, saulo.alessandre@....jus.br
Subject: Re: [PATCH v4 11/12] crypto: asymmetric_keys - Adjust signature size
 calculation for NIST P521

On Thu, Feb 29, 2024 at 09:20:06PM -0500, Stefan Berger wrote:
> Adjust the calculation of the maximum signature size for support of
> NIST P521. While existing curves may prepend a 0 byte to their coordinates
> (to make the number positive), NIST P521 will not do this since only the
> first bit in the most significant byte is used.
> 
> If the encoding of the x & y coordinates requires more than 128 bytes then
> an additional byte is needed for the encoding of the length. Take this into
> account when calculating the maximum signature size.
> 
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>

Reviewed-by: Lukas Wunner <lukas@...ner.de>