diff options
author | Dr. Stephen Henson <steve@openssl.org> | 2014-03-12 14:16:19 +0000 |
---|---|---|
committer | Dr. Stephen Henson <steve@openssl.org> | 2014-03-12 14:29:43 +0000 |
commit | f9b6c0ba4c02497782f801e3c45688f3efaac55c (patch) | |
tree | e6fe7fd8427a6f1c8067ad5e5159109e30c137c5 /crypto/ec/ec2_mult.c | |
parent | a029788b0e0c19cee4007cc1f73201cf2c13addf (diff) |
Fix for CVE-2014-0076
Fix for the attack described in the paper "Recovering OpenSSL
ECDSA Nonces Using the FLUSH+RELOAD Cache Side-channel Attack"
by Yuval Yarom and Naomi Benger. Details can be obtained from:
http://eprint.iacr.org/2014/140
Thanks to Yuval Yarom and Naomi Benger for discovering this
flaw and to Yuval Yarom for supplying a fix.
(cherry picked from commit 2198be3483259de374f91e57d247d0fc667aef29)
Conflicts:
CHANGES
Diffstat (limited to 'crypto/ec/ec2_mult.c')
-rw-r--r-- | crypto/ec/ec2_mult.c | 27 |
1 files changed, 16 insertions, 11 deletions
diff --git a/crypto/ec/ec2_mult.c b/crypto/ec/ec2_mult.c index f41665ac10..06405d0716 100644 --- a/crypto/ec/ec2_mult.c +++ b/crypto/ec/ec2_mult.c @@ -210,11 +210,15 @@ static int gf2m_Mxy(const EC_GROUP *group, const BIGNUM *x, const BIGNUM *y, BIG return ret; } + /* Computes scalar*point and stores the result in r. * point can not equal r. - * Uses algorithm 2P of + * Uses a modified algorithm 2P of * Lopez, J. and Dahab, R. "Fast multiplication on elliptic curves over * GF(2^m) without precomputation" (CHES '99, LNCS 1717). + * + * To protect against side-channel attack the function uses constant time swap, + * avoiding conditional branches. */ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, const EC_POINT *point, BN_CTX *ctx) @@ -248,6 +252,11 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, x2 = &r->X; z2 = &r->Y; + bn_wexpand(x1, group->field.top); + bn_wexpand(z1, group->field.top); + bn_wexpand(x2, group->field.top); + bn_wexpand(z2, group->field.top); + if (!BN_GF2m_mod_arr(x1, &point->X, group->poly)) goto err; /* x1 = x */ if (!BN_one(z1)) goto err; /* z1 = 1 */ if (!group->meth->field_sqr(group, z2, x1, ctx)) goto err; /* z2 = x1^2 = x^2 */ @@ -272,16 +281,12 @@ static int ec_GF2m_montgomery_point_multiply(const EC_GROUP *group, EC_POINT *r, word = scalar->d[i]; while (mask) { - if (word & mask) - { - if (!gf2m_Madd(group, &point->X, x1, z1, x2, z2, ctx)) goto err; - if (!gf2m_Mdouble(group, x2, z2, ctx)) goto err; - } - else - { - if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err; - if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err; - } + BN_consttime_swap(word & mask, x1, x2, group->field.top); + BN_consttime_swap(word & mask, z1, z2, group->field.top); + if (!gf2m_Madd(group, &point->X, x2, z2, x1, z1, ctx)) goto err; + if (!gf2m_Mdouble(group, x1, z1, ctx)) goto err; + BN_consttime_swap(word & mask, x1, x2, group->field.top); + BN_consttime_swap(word & mask, z1, z2, group->field.top); mask >>= 1; } mask = BN_TBIT; |