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| author | NIIBE Yutaka <gniibe@fsij.org> | 2015-11-25 10:52:57 +0900 |
|---|---|---|
| committer | NIIBE Yutaka <gniibe@fsij.org> | 2015-11-25 11:35:30 +0900 |
| commit | 8ad682c412047d3b9196950709dbd7bd14ac8732 (patch) | |
| tree | 6abc09e99c0fc453d1be531e7269f0f451074ac6 | |
| parent | 295b1c3540752af4fc5e6f41480e6db215222fba (diff) | |
| download | libgcrypt-8ad682c412047d3b9196950709dbd7bd14ac8732.tar.gz | |
mpi: Fix mpi_set_cond and mpi_swap_cond .
* mpi/mpiutil.c (_gcry_mpi_set_cond, _gcry_mpi_swap_cond): Don't use
the operator of !!, but assume SET/SWAP is 0 or 1.
--
If the code for !! would include a branch, it spoils the purpose of
mpi_set_cond/mpi_swap_cond at all. It's better to make sure the use
of this function to be called with 0 or 1 for SET/SWAP. Note that it
conforms when SET/SWAP is the result of conditional expression of
mpi_test_bit.
Reported-by: Taylor R Campbell.
| -rw-r--r-- | mpi/mpiutil.c | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/mpi/mpiutil.c b/mpi/mpiutil.c index 71b3f1c3..d3264c72 100644 --- a/mpi/mpiutil.c +++ b/mpi/mpiutil.c @@ -483,12 +483,17 @@ _gcry_mpi_set (gcry_mpi_t w, gcry_mpi_t u) return w; } +/**************** + * Set the value of W by the one of U, when SET is 1. + * Leave the value when SET is 0. + * This implementation should be constant-time regardless of SET. + */ gcry_mpi_t _gcry_mpi_set_cond (gcry_mpi_t w, const gcry_mpi_t u, unsigned long set) { mpi_size_t i; mpi_size_t nlimbs = u->alloced; - mpi_limb_t mask = ((mpi_limb_t)0) - !!set; + mpi_limb_t mask = ((mpi_limb_t)0) - set; mpi_limb_t x; if (w->alloced != u->alloced) @@ -568,12 +573,17 @@ _gcry_mpi_swap (gcry_mpi_t a, gcry_mpi_t b) } +/**************** + * Swap the value of A and B, when SWAP is 1. + * Leave the value when SWAP is 0. + * This implementation should be constant-time regardless of SWAP. + */ void _gcry_mpi_swap_cond (gcry_mpi_t a, gcry_mpi_t b, unsigned long swap) { mpi_size_t i; mpi_size_t nlimbs = a->alloced; - mpi_limb_t mask = ((mpi_limb_t)0) - !!swap; + mpi_limb_t mask = ((mpi_limb_t)0) - swap; mpi_limb_t x; if (a->alloced != b->alloced) |