diff options
| author | Jouni Malinen <j@w1.fi> | 2019-06-24 23:01:06 +0300 |
|---|---|---|
| committer | Jouni Malinen <j@w1.fi> | 2019-07-02 22:19:27 +0300 |
| commit | 147bf7b88a9c231322b5b574263071ca6dbb0503 (patch) | |
| tree | 64313fee030b177a725305fb84210cee4c57ca49 | |
| parent | 91b6eba7732354ed3dfe0aa9715dc4c0746e3336 (diff) | |
SAE: Run through prf result processing even if it >= prime
This reduces differences in timing and memory access within the
hunting-and-pecking loop for ECC groups that have a prime that is not
close to a power of two (e.g., Brainpool curves).
Signed-off-by: Jouni Malinen <j@w1.fi>
| -rw-r--r-- | src/common/sae.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/src/common/sae.c b/src/common/sae.c index c1c80710c..0da7145e2 100644 --- a/src/common/sae.c +++ b/src/common/sae.c @@ -142,6 +142,8 @@ static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed, struct crypto_bignum *y_sqr, *x_cand; int res; size_t bits; + int cmp_prime; + unsigned int in_range; wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, SHA256_MAC_LEN); @@ -155,8 +157,13 @@ static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed, wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-value", pwd_value, sae->tmp->prime_len); - if (const_time_memcmp(pwd_value, prime, sae->tmp->prime_len) >= 0) - return 0; + cmp_prime = const_time_memcmp(pwd_value, prime, sae->tmp->prime_len); + /* Create a const_time mask for selection based on prf result + * being smaller than prime. */ + in_range = const_time_fill_msb((unsigned int) cmp_prime); + /* The algorithm description would skip the next steps if + * cmp_prime >= 0 (reutnr 0 here), but go through them regardless to + * minimize externally observable differences in behavior. */ x_cand = crypto_bignum_init_set(pwd_value, sae->tmp->prime_len); if (!x_cand) @@ -169,7 +176,9 @@ static int sae_test_pwd_seed_ecc(struct sae_data *sae, const u8 *pwd_seed, res = dragonfly_is_quadratic_residue_blind(sae->tmp->ec, qr, qnr, y_sqr); crypto_bignum_deinit(y_sqr, 1); - return res; + if (res < 0) + return res; + return const_time_select_int(in_range, res, 0); } |
