diff options
author | Dr. Stephen Henson <steve@openssl.org> | 2014-03-12 14:16:19 +0000 |
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committer | Dr. Stephen Henson <steve@openssl.org> | 2014-03-12 14:23:21 +0000 |
commit | 0a9f7780e51b2bed69f4d9347da618fc069b9900 (patch) | |
tree | 3de171cdff1af181b591ddbdb4382870fb256997 /crypto/bn | |
parent | 44f7e399d342f0fbb90be023c2b9828a866fc8d1 (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/bn')
-rw-r--r-- | crypto/bn/bn.h | 11 | ||||
-rw-r--r-- | crypto/bn/bn_lib.c | 52 |
2 files changed, 63 insertions, 0 deletions
diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h index 5897d2b314..2e3fab98db 100644 --- a/crypto/bn/bn.h +++ b/crypto/bn/bn.h @@ -520,6 +520,8 @@ 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, @@ -756,11 +758,20 @@ 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 diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c index 7a5676de69..5461e6ee7d 100644 --- a/crypto/bn/bn_lib.c +++ b/crypto/bn/bn_lib.c @@ -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 +} |