+++ /dev/null
-From cff138b0747fa39765cbc641b66cfa5d7f1735d1 Mon Sep 17 00:00:00 2001
-From: Jouni Malinen <jouni@codeaurora.org>
-Date: Sat, 2 Mar 2019 16:05:56 +0200
-Subject: [PATCH 09/14] SAE: Use constant time operations in
- sae_test_pwd_seed_ffc()
-
-Try to avoid showing externally visible timing or memory access
-differences regardless of whether the derived pwd-value is smaller than
-the group prime.
-
-This is related to CVE-2019-9494.
-
-Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
----
- src/common/sae.c | 75 ++++++++++++++++++++++++++++++++++----------------------
- 1 file changed, 46 insertions(+), 29 deletions(-)
-
---- a/src/common/sae.c
-+++ b/src/common/sae.c
-@@ -311,14 +311,17 @@ static int sae_test_pwd_seed_ecc(struct
- }
-
-
-+/* Returns -1 on fatal failure, 0 if PWE cannot be derived from the provided
-+ * pwd-seed, or 1 if a valid PWE was derived from pwd-seed. */
- static int sae_test_pwd_seed_ffc(struct sae_data *sae, const u8 *pwd_seed,
- struct crypto_bignum *pwe)
- {
- u8 pwd_value[SAE_MAX_PRIME_LEN];
- size_t bits = sae->tmp->prime_len * 8;
- u8 exp[1];
-- struct crypto_bignum *a, *b;
-- int res;
-+ struct crypto_bignum *a, *b = NULL;
-+ int res, is_val;
-+ u8 pwd_value_valid;
-
- wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-seed", pwd_seed, SHA256_MAC_LEN);
-
-@@ -330,16 +333,29 @@ static int sae_test_pwd_seed_ffc(struct
- wpa_hexdump_key(MSG_DEBUG, "SAE: pwd-value", pwd_value,
- sae->tmp->prime_len);
-
-- if (os_memcmp(pwd_value, sae->tmp->dh->prime, sae->tmp->prime_len) >= 0)
-- {
-- wpa_printf(MSG_DEBUG, "SAE: pwd-value >= p");
-- return 0;
-- }
-+ /* Check whether pwd-value < p */
-+ res = const_time_memcmp(pwd_value, sae->tmp->dh->prime,
-+ sae->tmp->prime_len);
-+ /* pwd-value >= p is invalid, so res is < 0 for the valid cases and
-+ * the negative sign can be used to fill the mask for constant time
-+ * selection */
-+ pwd_value_valid = const_time_fill_msb(res);
-+
-+ /* If pwd-value >= p, force pwd-value to be < p and perform the
-+ * calculations anyway to hide timing difference. The derived PWE will
-+ * be ignored in that case. */
-+ pwd_value[0] = const_time_select_u8(pwd_value_valid, pwd_value[0], 0);
-
- /* PWE = pwd-value^((p-1)/r) modulo p */
-
-+ res = -1;
- a = crypto_bignum_init_set(pwd_value, sae->tmp->prime_len);
-+ if (!a)
-+ goto fail;
-
-+ /* This is an optimization based on the used group that does not depend
-+ * on the password in any way, so it is fine to use separate branches
-+ * for this step without constant time operations. */
- if (sae->tmp->dh->safe_prime) {
- /*
- * r = (p-1)/2 for the group used here, so this becomes:
-@@ -353,33 +369,34 @@ static int sae_test_pwd_seed_ffc(struct
- b = crypto_bignum_init_set(exp, sizeof(exp));
- if (b == NULL ||
- crypto_bignum_sub(sae->tmp->prime, b, b) < 0 ||
-- crypto_bignum_div(b, sae->tmp->order, b) < 0) {
-- crypto_bignum_deinit(b, 0);
-- b = NULL;
-- }
-+ crypto_bignum_div(b, sae->tmp->order, b) < 0)
-+ goto fail;
- }
-
-- if (a == NULL || b == NULL)
-- res = -1;
-- else
-- res = crypto_bignum_exptmod(a, b, sae->tmp->prime, pwe);
--
-- crypto_bignum_deinit(a, 0);
-- crypto_bignum_deinit(b, 0);
--
-- if (res < 0) {
-- wpa_printf(MSG_DEBUG, "SAE: Failed to calculate PWE");
-- return -1;
-- }
--
-- /* if (PWE > 1) --> found */
-- if (crypto_bignum_is_zero(pwe) || crypto_bignum_is_one(pwe)) {
-- wpa_printf(MSG_DEBUG, "SAE: PWE <= 1");
-- return 0;
-- }
-+ if (!b)
-+ goto fail;
-
-- wpa_printf(MSG_DEBUG, "SAE: PWE found");
-- return 1;
-+ res = crypto_bignum_exptmod(a, b, sae->tmp->prime, pwe);
-+ if (res < 0)
-+ goto fail;
-+
-+ /* There were no fatal errors in calculations, so determine the return
-+ * value using constant time operations. We get here for number of
-+ * invalid cases which are cleared here after having performed all the
-+ * computation. PWE is valid if pwd-value was less than prime and
-+ * PWE > 1. Start with pwd-value check first and then use constant time
-+ * operations to clear res to 0 if PWE is 0 or 1.
-+ */
-+ res = const_time_select_u8(pwd_value_valid, 1, 0);
-+ is_val = crypto_bignum_is_zero(pwe);
-+ res = const_time_select_u8(const_time_is_zero(is_val), res, 0);
-+ is_val = crypto_bignum_is_one(pwe);
-+ res = const_time_select_u8(const_time_is_zero(is_val), res, 0);
-+
-+fail:
-+ crypto_bignum_deinit(a, 1);
-+ crypto_bignum_deinit(b, 1);
-+ return res;
- }
-
-
projects / openwrt / staging / chunkeey.git / blobdiff