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authorAndy Polyakov <appro@openssl.org>2018-07-06 15:55:34 +0200
committerAndy Polyakov <appro@openssl.org>2018-07-18 16:08:59 +0200
commit3fc7a9b96cbed0c3da6f53c08e34d8d0c982745f (patch)
tree47fd1b4a09f2482d51d461450f1cc21b6cb970f0 /crypto/ec/ecdsa_ossl.c
parent83e034379fa3f6f0d308ec75fbcb137e26154aec (diff)
downloadopenssl-new-3fc7a9b96cbed0c3da6f53c08e34d8d0c982745f.tar.gz
ec/ecdsa_ossl.c: revert blinding in ECDSA signature.
Originally suggested solution for "Return Of the Hidden Number Problem" is arguably too expensive. While it has marginal impact on slower curves, none to ~6%, optimized implementations suffer real penalties. Most notably sign with P-256 went more than 2 times[!] slower. Instead, just implement constant-time BN_mod_add_quick. Reviewed-by: Rich Salz <rsalz@openssl.org> Reviewed-by: David Benjamin <davidben@google.com> (Merged from https://github.com/openssl/openssl/pull/6664)
Diffstat (limited to 'crypto/ec/ecdsa_ossl.c')
-rw-r--r--crypto/ec/ecdsa_ossl.c71
1 files changed, 7 insertions, 64 deletions
diff --git a/crypto/ec/ecdsa_ossl.c b/crypto/ec/ecdsa_ossl.c
index dfb0d192d9..18af4a57f5 100644
--- a/crypto/ec/ecdsa_ossl.c
+++ b/crypto/ec/ecdsa_ossl.c
@@ -172,8 +172,7 @@ ECDSA_SIG *ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
EC_KEY *eckey)
{
int ok = 0, i;
- BIGNUM *kinv = NULL, *s, *m = NULL, *tmp = NULL, *blind = NULL;
- BIGNUM *blindm = NULL;
+ BIGNUM *kinv = NULL, *s, *m = NULL, *tmp = NULL;
const BIGNUM *order, *ckinv;
BN_CTX *ctx = NULL;
const EC_GROUP *group;
@@ -206,18 +205,8 @@ ECDSA_SIG *ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
}
s = ret->s;
- ctx = BN_CTX_secure_new();
- if (ctx == NULL) {
- ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_MALLOC_FAILURE);
- goto err;
- }
-
- BN_CTX_start(ctx);
- tmp = BN_CTX_get(ctx);
- m = BN_CTX_get(ctx);
- blind = BN_CTX_get(ctx);
- blindm = BN_CTX_get(ctx);
- if (blindm == NULL) {
+ if ((ctx = BN_CTX_new()) == NULL ||
+ (tmp = BN_new()) == NULL || (m = BN_new()) == NULL) {
ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_MALLOC_FAILURE);
goto err;
}
@@ -257,64 +246,18 @@ ECDSA_SIG *ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
}
}
- /*
- * The normal signature calculation is:
- *
- * s := k^-1 * (m + r * priv_key) mod order
- *
- * We will blind this to protect against side channel attacks
- *
- * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod order
- */
-
- /* Generate a blinding value */
- do {
- if (!BN_priv_rand(blind, BN_num_bits(order) - 1,
- BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
- goto err;
- } while (BN_is_zero(blind));
- BN_set_flags(blind, BN_FLG_CONSTTIME);
- BN_set_flags(blindm, BN_FLG_CONSTTIME);
- BN_set_flags(tmp, BN_FLG_CONSTTIME);
-
- /* tmp := blind * priv_key * r mod order */
- if (!BN_mod_mul(tmp, blind, priv_key, order, ctx)) {
- ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
- goto err;
- }
- if (!BN_mod_mul(tmp, tmp, ret->r, order, ctx)) {
- ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
- goto err;
- }
-
- /* blindm := blind * m mod order */
- if (!BN_mod_mul(blindm, blind, m, order, ctx)) {
+ if (!BN_mod_mul(tmp, priv_key, ret->r, order, ctx)) {
ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
goto err;
}
-
- /* s : = (blind * priv_key * r) + (blind * m) mod order */
- if (!BN_mod_add_quick(s, tmp, blindm, order)) {
+ if (!BN_mod_add_quick(s, tmp, m, order)) {
ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
goto err;
}
-
- /* s := s * k^-1 mod order */
if (!BN_mod_mul(s, s, ckinv, order, ctx)) {
ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
goto err;
}
-
- /* s:= s * blind^-1 mod order */
- if (BN_mod_inverse(blind, blind, order, ctx) == NULL) {
- ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
- goto err;
- }
- if (!BN_mod_mul(s, s, blind, order, ctx)) {
- ECerr(EC_F_OSSL_ECDSA_SIGN_SIG, ERR_R_BN_LIB);
- goto err;
- }
-
if (BN_is_zero(s)) {
/*
* if kinv and r have been supplied by the caller, don't
@@ -336,9 +279,9 @@ ECDSA_SIG *ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len,
ECDSA_SIG_free(ret);
ret = NULL;
}
- if (ctx != NULL)
- BN_CTX_end(ctx);
BN_CTX_free(ctx);
+ BN_clear_free(m);
+ BN_clear_free(tmp);
BN_clear_free(kinv);
return ret;
}