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- From a25b48118d75f3c2d7cb1b2c3b4cffb13091a34c Mon Sep 17 00:00:00 2001
- From: Jouni Malinen <[email protected]>
- Date: Mon, 24 Jun 2019 23:01:06 +0300
- Subject: [PATCH 4/6] 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 <[email protected]>
- (cherry picked from commit 147bf7b88a9c231322b5b574263071ca6dbb0503)
- ---
- src/common/sae.c | 15 ++++++++++++---
- 1 file changed, 12 insertions(+), 3 deletions(-)
- --- a/src/common/sae.c
- +++ b/src/common/sae.c
- @@ -304,6 +304,8 @@ static int sae_test_pwd_seed_ecc(struct
- 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);
-
- @@ -317,8 +319,13 @@ static int sae_test_pwd_seed_ecc(struct
- 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)
- @@ -330,7 +337,9 @@ static int sae_test_pwd_seed_ecc(struct
-
- res = is_quadratic_residue_blind(sae, prime, bits, 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);
- }
-
-
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