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

[Hannes Reinecke]

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@xxxxxxx>
> ---
>  crypto/Kconfig     | 2 ++
>  crypto/dh_helper.c | 4 ++++
>  2 files changed, 6 insertions(+)
> 
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>

Cheers,

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