linux-kernel - Re: [PATCH v4 15/15] crypto: dh - calculate Q from P for the full public key verification

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Message-ID: <8576d112-c898-410c-6444-56c14bd8607c@suse.de>
Date:   Mon, 21 Feb 2022 15:20:20 +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>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        keyrings@...r.kernel.org
Subject: Re: [PATCH v4 15/15] crypto: dh - calculate Q from P for the full
 public key verification

On 2/21/22 13:11, 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
> as the safe-prime groups are the only possible groups in FIPS mode (via
> those ffdheXYZ() templates), this enables dh_is_pubkey_valid() to calculate
> Q on the fly for these.
> 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
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer