linux-kernel - Re: [PATCH v2 18/18] crypto: dh - accept only approved safe-prime groups in FIPS mode

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Message-ID: <e44987d3-d838-38bc-d744-48d6010e2c59@suse.de>
Date:   Fri, 10 Dec 2021 12:37:45 +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 v2 18/18] crypto: dh - accept only approved safe-prime
 groups in FIPS mode

On 12/9/21 10:03 AM, 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.
> 
> Make the dh implementations reject any domain parameters which don't
> correspond to any of the approved safe-prime groups in FIPS mode. The
> approved safe-prime groups are the ones specified in RFC 7919 and RFC 3526,
> and given that all possible values of enum dh_group_id correspond to
> either groups from these RFCs or to DH_GROUP_ID_UNKNOWN, it suffices to
> make crypto_dh_decode_key() to reject any parameter set where
> ->group_id == DH_GROUP_ID_UNKNOWN.
> 
> As this change will effectively render the dh implementation unusable in
> FIPS mode if neither of the CRYPTO_DH_GROUPS_RFC7919 or
> CRYPTO_DH_GROUPS_RFC3526 Kconfig options enabled, make CRYPTO_DH imply
> these two if CRYPTO_FIPS is set.
> 
> Signed-off-by: Nicolai Stange <nstange@...e.de>
> ---
>  crypto/Kconfig     | 2 ++
>  crypto/dh_helper.c | 4 ++++
>  2 files changed, 6 insertions(+)
> 
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