linux-kernel - Re: [PATCH 16/18] crypto: dh - calculate Q from P for the full public key verification

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Date:   Wed, 1 Dec 2021 08:33:28 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Nicolai Stange <nstange@...e.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Stephan Müller <smueller@...onox.de>,
        Torsten Duwe <duwe@...e.de>, Zaibo Xu <xuzaibo@...wei.com>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        qat-linux@...el.com, keyrings@...r.kernel.org
Subject: Re: [PATCH 16/18] crypto: dh - calculate Q from P for the full public
 key verification

On 12/1/21 1:48 AM, Nicolai Stange wrote:
> As the ->q in struct dh_ctx gets never set anywhere, the code
> in dh_is_pubkey_valid() for doing the full public key validation in
> accordance to SP800-56Arev3 is effectively dead.
> 
> However, for safe-prime groups, Q = (P - 1)/2 by definition and this
> enables dh_is_pubkey_valid() to calculate Q on the fly for these groups.
> Implement this.
> 
> With this change, the last code accessing struct dh_ctx's ->q is now gone.
> Remove this member from struct dh_ctx.
> 
> Signed-off-by: Nicolai Stange <nstange@...e.de>
> ---
>   crypto/dh.c | 40 +++++++++++++++++++++++++++++-----------
>   1 file changed, 29 insertions(+), 11 deletions(-)
> Reviewed-by: Hannes Reinecke <hare@...e.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
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