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crypto: dh - calculate Q from P for the full public key verification

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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@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Nicolai Stange 2022-02-21 13:11:01 +01:00 committed by Herbert Xu
parent 81771ff241
commit 35d2bf2068
1 changed files with 29 additions and 11 deletions
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40
crypto/dh.c
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@ -15,7 +15,6 @@
struct dh_ctx {
MPI p; /* Value is guaranteed to be set. */
MPI q; /* Value is optional. */
MPI g; /* Value is guaranteed to be set. */
MPI xa; /* Value is guaranteed to be set. */
};
@ -23,7 +22,6 @@ struct dh_ctx {
static void dh_clear_ctx(struct dh_ctx *ctx)
{
mpi_free(ctx->p);
mpi_free(ctx->q);
mpi_free(ctx->g);
mpi_free(ctx->xa);
memset(ctx, 0, sizeof(*ctx));
@ -99,11 +97,12 @@ err_clear_ctx:
/*
* SP800-56A public key verification:
*
* * If Q is provided as part of the domain paramenters, a full validation
* according to SP800-56A section 5.6.2.3.1 is performed.
* * For the safe-prime groups in FIPS mode, Q can be computed
* trivially from P and a full validation according to SP800-56A
* section 5.6.2.3.1 is performed.
*
* * If Q is not provided, a partial validation according to SP800-56A section
* 5.6.2.3.2 is performed.
* * For all other sets of group parameters, only a partial validation
* according to SP800-56A section 5.6.2.3.2 is performed.
*/
static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
{
@ -114,21 +113,40 @@ static int dh_is_pubkey_valid(struct dh_ctx *ctx, MPI y)
* Step 1: Verify that 2 <= y <= p - 2.
*
* The upper limit check is actually y < p instead of y < p - 1
* as the mpi_sub_ui function is yet missing.
* in order to save one mpi_sub_ui() invocation here. Note that
* p - 1 is the non-trivial element of the subgroup of order 2 and
* thus, the check on y^q below would fail if y == p - 1.
*/
if (mpi_cmp_ui(y, 1) < 1 || mpi_cmp(y, ctx->p) >= 0)
return -EINVAL;
/* Step 2: Verify that 1 = y^q mod p */
if (ctx->q) {
MPI val = mpi_alloc(0);
/*
* Step 2: Verify that 1 = y^q mod p
*
* For the safe-prime groups q = (p - 1)/2.
*/
if (fips_enabled) {
MPI val, q;
int ret;
val = mpi_alloc(0);
if (!val)
return -ENOMEM;
ret = mpi_powm(val, y, ctx->q, ctx->p);
q = mpi_alloc(mpi_get_nlimbs(ctx->p));
if (!q) {
mpi_free(val);
return -ENOMEM;
}
/*
* ->p is odd, so no need to explicitly subtract one
* from it before shifting to the right.
*/
mpi_rshift(q, ctx->p, 1);
ret = mpi_powm(val, y, q, ctx->p);
mpi_free(q);
if (ret) {
mpi_free(val);
return ret;