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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 2198be3)

Conflicts:

	CHANGES
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snhenson committed Mar 12, 2014
1 parent e0660c6 commit 4b7a4ba29cafa432fc4266fe6e59e60bc1c96332
Showing with 88 additions and 11 deletions.
  1. +9 −0 CHANGES
  2. +11 −0 crypto/bn/bn.h
  3. +52 −0 crypto/bn/bn_lib.c
  4. +16 −11 crypto/ec/ec2_mult.c
@@ -4,6 +4,15 @@

Changes between 1.0.1f and 1.0.1g [xx XXX xxxx]

*) 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 (CVE-2014-0076)
[Yuval Yarom and Naomi Benger]

*) TLS pad extension: draft-agl-tls-padding-02

Workaround for the "TLS hang bug" (see FAQ and PR#2771): if the
@@ -538,6 +538,8 @@ BIGNUM *BN_mod_inverse(BIGNUM *ret,
BIGNUM *BN_mod_sqrt(BIGNUM *ret,
const BIGNUM *a, const BIGNUM *n,BN_CTX *ctx);

void BN_consttime_swap(BN_ULONG swap, BIGNUM *a, BIGNUM *b, int nwords);

/* Deprecated versions */
#ifndef OPENSSL_NO_DEPRECATED
BIGNUM *BN_generate_prime(BIGNUM *ret,int bits,int safe,
@@ -774,11 +776,20 @@ int RAND_pseudo_bytes(unsigned char *buf,int num);

#define bn_fix_top(a) bn_check_top(a)

#define bn_check_size(bn, bits) bn_wcheck_size(bn, ((bits+BN_BITS2-1))/BN_BITS2)
#define bn_wcheck_size(bn, words) \
do { \
const BIGNUM *_bnum2 = (bn); \
assert(words <= (_bnum2)->dmax && words >= (_bnum2)->top); \
} while(0)

#else /* !BN_DEBUG */

#define bn_pollute(a)
#define bn_check_top(a)
#define bn_fix_top(a) bn_correct_top(a)
#define bn_check_size(bn, bits)
#define bn_wcheck_size(bn, words)

#endif

@@ -824,3 +824,55 @@ int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b,
}
return bn_cmp_words(a,b,cl);
}

/*
* Constant-time conditional swap of a and b.
* a and b are swapped if condition is not 0. The code assumes that at most one bit of condition is set.
* nwords is the number of words to swap. The code assumes that at least nwords are allocated in both a and b,
* and that no more than nwords are used by either a or b.
* a and b cannot be the same number
*/
void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
{
BN_ULONG t;
int i;

bn_wcheck_size(a, nwords);
bn_wcheck_size(b, nwords);

assert(a != b);
assert((condition & (condition - 1)) == 0);
assert(sizeof(BN_ULONG) >= sizeof(int));

condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;

t = (a->top^b->top) & condition;
a->top ^= t;
b->top ^= t;

#define BN_CONSTTIME_SWAP(ind) \
do { \
t = (a->d[ind] ^ b->d[ind]) & condition; \
a->d[ind] ^= t; \
b->d[ind] ^= t; \
} while (0)


switch (nwords) {
default:
for (i = 10; i < nwords; i++)
BN_CONSTTIME_SWAP(i);
/* Fallthrough */
case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */
case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */
case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */
case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */
case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */
case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */
case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */
case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */
case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */
case 1: BN_CONSTTIME_SWAP(0);
}
#undef BN_CONSTTIME_SWAP
}
@@ -208,11 +208,15 @@ 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)
@@ -246,6 +250,11 @@ 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 */
@@ -270,16 +279,12 @@ 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;

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