From: Andy Polyakov Date: Fri, 6 Jul 2018 13:55:34 +0000 (+0200) Subject: ec/ecdsa_ossl.c: revert blinding in ECDSA signature. X-Git-Tag: OpenSSL_1_1_0i~26 X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=6040bd3f7109dcae508c3194232e7b8ee8654dc0;p=oweals%2Fopenssl.git 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 (Merged from https://github.com/openssl/openssl/pull/6796) (cherry picked from commit 3fc7a9b96cbed0c3da6f53c08e34d8d0c982745f) Resolved conflicts: crypto/ec/ecdsa_ossl.c --- diff --git a/crypto/bn/bn_mod.c b/crypto/bn/bn_mod.c index 13b583f76c..99929f9278 100644 --- a/crypto/bn/bn_mod.c +++ b/crypto/bn/bn_mod.c @@ -35,18 +35,72 @@ int BN_mod_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m, /* * BN_mod_add variant that may be used if both a and b are non-negative and - * less than m + * less than m. The original algorithm was + * + * if (!BN_uadd(r, a, b)) + * return 0; + * if (BN_ucmp(r, m) >= 0) + * return BN_usub(r, r, m); + * + * which is replaced with addition, subtracting modulus, and conditional + * move depending on whether or not subtraction borrowed. */ -int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, - const BIGNUM *m) +int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, + const BIGNUM *m) { - if (!BN_uadd(r, a, b)) + size_t i, ai, bi, mtop = m->top; + BN_ULONG storage[1024 / BN_BITS2]; + BN_ULONG carry, temp, mask, *rp, *tp = storage; + const BN_ULONG *ap, *bp; + + if (bn_wexpand(r, mtop) == NULL) return 0; - if (BN_ucmp(r, m) >= 0) - return BN_usub(r, r, m); + + if (mtop > sizeof(storage) / sizeof(storage[0]) + && (tp = OPENSSL_malloc(mtop * sizeof(BN_ULONG))) == NULL) + return 0; + + ap = a->d != NULL ? a->d : tp; + bp = b->d != NULL ? b->d : tp; + + for (i = 0, ai = 0, bi = 0, carry = 0; i < mtop;) { + mask = (BN_ULONG)0 - ((i - a->top) >> (8 * sizeof(i) - 1)); + temp = ((ap[ai] & mask) + carry) & BN_MASK2; + carry = (temp < carry); + + mask = (BN_ULONG)0 - ((i - b->top) >> (8 * sizeof(i) - 1)); + tp[i] = ((bp[bi] & mask) + temp) & BN_MASK2; + carry += (tp[i] < temp); + + i++; + ai += (i - a->dmax) >> (8 * sizeof(i) - 1); + bi += (i - b->dmax) >> (8 * sizeof(i) - 1); + } + rp = r->d; + carry -= bn_sub_words(rp, tp, m->d, mtop); + for (i = 0; i < mtop; i++) { + rp[i] = (carry & tp[i]) | (~carry & rp[i]); + ((volatile BN_ULONG *)tp)[i] = 0; + } + r->top = mtop; + + if (tp != storage) + OPENSSL_free(tp); + return 1; } +int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, + const BIGNUM *m) +{ + int ret = bn_mod_add_fixed_top(r, a, b, m); + + if (ret) + bn_correct_top(r); + + return ret; +} + int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m, BN_CTX *ctx) { diff --git a/crypto/ec/ecdsa_ossl.c b/crypto/ec/ecdsa_ossl.c index c103917e76..72e2f0f28b 100644 --- a/crypto/ec/ecdsa_ossl.c +++ b/crypto/ec/ecdsa_ossl.c @@ -210,8 +210,7 @@ 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; @@ -244,18 +243,8 @@ 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; } @@ -295,64 +284,18 @@ 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_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)) { + if (!BN_mod_mul(tmp, priv_key, ret->r, 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)) { + if (!BN_mod_add_quick(s, tmp, m, order)) { 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)) { - 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)) { - 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 to @@ -374,8 +317,9 @@ ECDSA_SIG *ossl_ecdsa_sign_sig(const unsigned char *dgst, int dgst_len, ECDSA_SIG_free(ret); ret = NULL; } - BN_CTX_end(ctx); BN_CTX_free(ctx); + BN_clear_free(m); + BN_clear_free(tmp); BN_clear_free(kinv); return ret; } diff --git a/crypto/include/internal/bn_int.h b/crypto/include/internal/bn_int.h index 3501ffb3b4..32eb581d09 100644 --- a/crypto/include/internal/bn_int.h +++ b/crypto/include/internal/bn_int.h @@ -85,6 +85,8 @@ int bn_mul_mont_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_MONT_CTX *mont, BN_CTX *ctx); int bn_to_mont_fixed_top(BIGNUM *r, const BIGNUM *a, BN_MONT_CTX *mont, BN_CTX *ctx); +int bn_mod_add_fixed_top(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, + const BIGNUM *m); #ifdef __cplusplus }