Messages in this thread | | | Date | Mon, 21 Feb 2022 15:14:57 +0100 | Subject | Re: [PATCH v4 06/15] crypto: dh - introduce common code for built-in safe-prime group support | From | Hannes Reinecke <> |
| |
On 2/21/22 13:10, Nicolai Stange wrote: > Recent work on NVME in-band authentication support ([1]) needs to invoke > the "dh" KPP with the FFDHE safe-prime group parameters as specified in > RFC 7919 and generate ephemeral keys suitable for the respective group. By > coincidence, the requirements from NIST SP800-56Arev3, > sec. 5.5.2 ("Assurance of Domain-Parameter Validity") basically boil down > to disallowing any group parameters not among the approved safe-prime > groups specified in either RFC 7919 or RFC 3526 in FIPS mode. Furthermore, > SP800-56Arev3 specifies the respective security strength for each of the > approved safe-prime groups, which has a direct impact on the minimum key > lengths. > > In this light, it's desirable to introduce built-in support for the > RFC 7919 safe-prime groups to the kernel's DH implementation, provide a > SP800-56Arev3 conforming key generation primitive for those and render > non-approved group parameters unusable in FIPS mode on the way. > > As suggested ([2]) in the course of discussion to previous iterations of > this patchset, the built-in support for ffdhe groups would be best made > available in the form of templates wrapping the existing "dh" > implementation, one for each group specified by RFC 7919: ffdhe2048(dh), > ffdhe3072(dh), ffdhe4096(dh), ffdhe6144(dh) and ffdhe8192(dh). As these > templates differ only in the safe-prime constants they'd configure the > inner "dh" transforms with, they can share almost all of their > "dh"-wrapping template implementation code. > > Introduce this common code to dh_generic. The actual dump of the RFC 7919 > safe-prime constants will be deferred to the next patch in order to > facilitate review. The ephemeral key generation primitive mentioned above > likewise deserves a patch on its own, as does the mechanism by which > unapproved groups are rendered unusable in FIPS mode. > > Define a struct dh_safe_prime container for specifying the individual > templates' associated safe-prime group constants. All ffdheXYZ(dh) template > instances will store a pointer to such a dh_safe_prime in their context > areas each. Implement the common __dh_safe_prime_create() template > instantiation helper. The intention is that the individual ffdheXYZ(dh) > crypto_templates' ->create() implementations will simply forward any calls > to __dh_safe_prime_create(), passing a suitable dh_safe_prime in addition > to the received ->create() arguments. __dh_safe_prime_create() would then > create and register a kpp_instance as appropriate, storing the given > dh_safe_prime pointer alongside a crypto_kpp_spawn for the inner "dh" > kpp_alg in the context area. > > As the ffdheXYZ(dh) kpp_instances are supposed to act as proxies to the > inner "dh" kpp_alg, make each of their associated crypto_kpp transforms to > in turn own an inner "dh" transform, a pointer to which gets stored in the > context area. Setup and teardown are getting handled from the outer > ->init_tfm() and ->exit_tfm() respectively. > > In order to achieve the overall goal and let the ffdheXYZ(dh) kpp_instances > configure the inner "dh" transforms with the respective group parameters, > make their common ->set_secret(), the new dh_safe_prime_set_secret(), fill > in the P and G values before forwarding the call to the inner "dh"'s > ->set_secret(). Note that the outer ->set_secret() can obtain the P value > associated with the given ffdheXYZ(dh) kpp_instance by means of the > dh_safe_prime referenced from the latter's context. The value of G OTOH > always equals constant 2 for the safe-prime groups. > > Finally, make the remaining two kpp_alg primitives both operating on > kpp_requests, i.e. ->generate_public_key() and ->compute_shared_secret(), > to merely forward any request to the inner "dh" implementation. However, a > kpp_request instance received from the outside cannot get simply passed > on as-is, because its associated transform (crypto_kpp_reqtfm()) will have > been set to the outer ffdheXYZ(dh) one. In order to handle this, reserve > some space in the outer ffdheXYZ(dh) kpp_requests' context areas for in > turn storing an inner kpp_request suitable for "dh" each. Make the outer > ->generate_public_key() and ->compute_shared_secret() respectively to setup > this inner kpp_request by means of the new dh_safe_prime_prepare_dh_req() > helper before handing it over to the "dh" implementation for further > processing. dh_safe_prime_prepare_dh_req() basically copies the outer > kpp_request received from the outside over to the inner one, but installs > the inner transform and its own ->complete() proxy callback therein. This > completion callback, the new dh_safe_prime_complete_req(), doesn't do > anything beyond completing the outer request. Note that there exist some > examples in crypto/, which would simply install the completion handler > from the outer request at the inner one in similar setups, e.g. seqiv. > However, this would mean that the user-provided completion handler won't > get called with the address of the outer kpp_request initially submitted > and the handler might not be prepared for this. Users could certainly work > around this by setting the callback ->data properly, but IMO it's cleaner > this way. Furthermore, it might make sense to extend > dh_safe_prime_complete_req() in the future and move e.g. those > post-computation FIPS checks from the generic "dh" implementation to the > ffdheXYZ(dh) templates. > > [1] https://lore.kernel.org/r/20211202152358.60116-1-hare@suse.de > [2] https://lore.kernel.org/r/20211217055227.GA20698@gondor.apana.org.au > > Signed-off-by: Nicolai Stange <nstange@suse.de> > --- > crypto/dh.c | 208 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 208 insertions(+) > Reviewed-by: Hannes Reinecke <hare@suse.de>
Cheers,
Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
| |