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53 lines
1.9 KiB
Diff
53 lines
1.9 KiB
Diff
From 00a6cc73da61b03c146b6c341d0d1e572bcef432 Mon Sep 17 00:00:00 2001
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From: Jouni Malinen <j@w1.fi>
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Date: Mon, 24 Jun 2019 23:02:51 +0300
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Subject: [PATCH 5/6] EAP-pwd: Run through prf result processing even if it >=
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prime
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This reduces differences in timing and memory access within the
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hunting-and-pecking loop for ECC groups that have a prime that is not
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close to a power of two (e.g., Brainpool curves).
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Signed-off-by: Jouni Malinen <j@w1.fi>
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(cherry picked from commit cd803299ca485eb857e37c88f973fccfbb8600e5)
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---
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src/eap_common/eap_pwd_common.c | 13 ++++++++++---
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1 file changed, 10 insertions(+), 3 deletions(-)
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--- a/src/eap_common/eap_pwd_common.c
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+++ b/src/eap_common/eap_pwd_common.c
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@@ -155,6 +155,8 @@ int compute_password_element(EAP_PWD_gro
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struct crypto_bignum *x_candidate = NULL;
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const struct crypto_bignum *prime;
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u8 mask, found_ctr = 0, is_odd = 0;
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+ int cmp_prime;
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+ unsigned int in_range;
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if (grp->pwe)
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return -1;
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@@ -241,8 +243,13 @@ int compute_password_element(EAP_PWD_gro
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if (primebitlen % 8)
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buf_shift_right(prfbuf, primebytelen,
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8 - primebitlen % 8);
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- if (const_time_memcmp(prfbuf, prime_bin, primebytelen) >= 0)
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- continue;
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+ cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen);
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+ /* Create a const_time mask for selection based on prf result
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+ * being smaller than prime. */
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+ in_range = const_time_fill_msb((unsigned int) cmp_prime);
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+ /* The algorithm description would skip the next steps if
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+ * cmp_prime >= 0, but go through them regardless to minimize
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+ * externally observable differences in behavior. */
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crypto_bignum_deinit(x_candidate, 1);
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x_candidate = crypto_bignum_init_set(prfbuf, primebytelen);
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@@ -306,7 +313,7 @@ int compute_password_element(EAP_PWD_gro
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goto fail;
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mask = const_time_eq(res, check);
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found_ctr = const_time_select_u8(found, found_ctr, ctr);
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- found |= mask;
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+ found |= mask & in_range;
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}
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if (found == 0) {
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wpa_printf(MSG_INFO,
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