linux-kernel - Re: [PATCH v4 13/15] crypto: dh - disallow plain "dh" usage in FIPS mode

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Message-ID: <23740a5b-5c3b-d685-c1fa-99f97d5211ea@suse.de>
Date:   Mon, 21 Feb 2022 15:19:49 +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 13/15] crypto: dh - disallow plain "dh" usage in FIPS
 mode

On 2/21/22 13:10, Nicolai Stange wrote:
> SP800-56Arev3, sec. 5.5.2 ("Assurance of Domain-Parameter Validity")
> asserts that an implementation needs to verify domain paramtere validity,
> which boils down to either
> - the domain parameters corresponding to some known safe-prime group
>    explicitly listed to be approved in the document or
> - for parameters conforming to a "FIPS 186-type parameter-size set",
>    that the implementation needs to perform an explicit domain parameter
>    verification, which would require access to the "seed" and "counter"
>    values used in their generation.
> 
> The latter is not easily feasible and moreover, SP800-56Arev3 states that
> safe-prime groups are preferred and that FIPS 186-type parameter sets
> should only be supported for backward compatibility, if it all.
> 
> Mark "dh" as not fips_allowed in testmgr. Note that the safe-prime
> ffdheXYZ(dh) wrappers are not affected by this change: as these enforce
> some approved safe-prime group each, their usage is still allowed in FIPS
> mode.
> 
> This change will effectively render the keyctl(KEYCTL_DH_COMPUTE) syscall
> unusable in FIPS mode, but it has been brought up that this might even be
> a good thing ([1]).
> 
> [1] https://lore.kernel.org/r/20211217055227.GA20698@gondor.apana.org.au
> 
> Signed-off-by: Nicolai Stange <nstange@...e.de>
> ---
>   crypto/testmgr.c | 1 -
>   1 file changed, 1 deletion(-)
> 
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