git.librecmc.org Git - librecmc/librecmc.git/blob

   1 From 00a6cc73da61b03c146b6c341d0d1e572bcef432 Mon Sep 17 00:00:00 2001
   2 From: Jouni Malinen <j@w1.fi>
   3 Date: Mon, 24 Jun 2019 23:02:51 +0300
   4 Subject: [PATCH 5/6] EAP-pwd: Run through prf result processing even if it >=
   5  prime
   6
   7 This reduces differences in timing and memory access within the
   8 hunting-and-pecking loop for ECC groups that have a prime that is not
   9 close to a power of two (e.g., Brainpool curves).
  10
  11 Signed-off-by: Jouni Malinen <j@w1.fi>
  12 (cherry picked from commit cd803299ca485eb857e37c88f973fccfbb8600e5)
  13 ---
  14  src/eap_common/eap_pwd_common.c | 13 ++++++++++---
  15  1 file changed, 10 insertions(+), 3 deletions(-)
  16
  17 --- a/src/eap_common/eap_pwd_common.c
  18 +++ b/src/eap_common/eap_pwd_common.c
  19 @@ -155,6 +155,8 @@ int compute_password_element(EAP_PWD_gro
  20         struct crypto_bignum *x_candidate = NULL;
  21         const struct crypto_bignum *prime;
  22         u8 mask, found_ctr = 0, is_odd = 0;
  23 +       int cmp_prime;
  24 +       unsigned int in_range;
  25
  26         if (grp->pwe)
  27                 return -1;
  28 @@ -241,8 +243,13 @@ int compute_password_element(EAP_PWD_gro
  29                 if (primebitlen % 8)
  30                         buf_shift_right(prfbuf, primebytelen,
  31                                         8 - primebitlen % 8);
  32 -               if (const_time_memcmp(prfbuf, prime_bin, primebytelen) >= 0)
  33 -                       continue;
  34 +               cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen);
  35 +               /* Create a const_time mask for selection based on prf result
  36 +                * being smaller than prime. */
  37 +               in_range = const_time_fill_msb((unsigned int) cmp_prime);
  38 +               /* The algorithm description would skip the next steps if
  39 +                * cmp_prime >= 0, but go through them regardless to minimize
  40 +                * externally observable differences in behavior. */
  41
  42                 crypto_bignum_deinit(x_candidate, 1);
  43                 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen);
  44 @@ -306,7 +313,7 @@ int compute_password_element(EAP_PWD_gro
  45                         goto fail;
  46                 mask = const_time_eq(res, check);
  47                 found_ctr = const_time_select_u8(found, found_ctr, ctr);
  48 -               found |= mask;
  49 +               found |= mask & in_range;
  50         }
  51         if (found == 0) {
  52                 wpa_printf(MSG_INFO,