Module Name: src
Committed By: christos
Date: Thu Aug 8 09:56:10 UTC 2019
Modified Files:
src/external/bsd/wpa/dist/src/common: sae.c
Log Message:
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>
(cherry picked from commit 147bf7b88a9c231322b5b574263071ca6dbb0503)
To generate a diff of this commit:
cvs rdiff -u -r1.8 -r1.9 src/external/bsd/wpa/dist/src/common/sae.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/external/bsd/wpa/dist/src/common/sae.c
diff -u src/external/bsd/wpa/dist/src/common/sae.c:1.8 src/external/bsd/wpa/dist/src/common/sae.c:1.9
--- src/external/bsd/wpa/dist/src/common/sae.c:1.8 Thu Aug 8 04:55:48 2019
+++ src/external/bsd/wpa/dist/src/common/sae.c Thu Aug 8 05:56:10 2019
@@ -281,6 +281,8 @@ 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);
@@ -294,8 +296,13 @@ 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)
@@ -307,7 +314,9 @@ 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);
}
