From f4675379275c304dbfa593cc573b4e4c4eb54bd4 Mon Sep 17 00:00:00 2001 From: Nicola Tuveri Date: Fri, 20 Apr 2018 11:02:52 +0000 Subject: [PATCH] Pass through Reviewed-by: Andy Polyakov Reviewed-by: Matt Caswell (Merged from https://github.com/openssl/openssl/pull/6009) --- crypto/ec/ec_mult.c | 57 ++++++++++++++++++++++++--------------------- 1 file changed, 30 insertions(+), 27 deletions(-) diff --git a/crypto/ec/ec_mult.c b/crypto/ec/ec_mult.c index 2da6ceba7b..801726f9f5 100644 --- a/crypto/ec/ec_mult.c +++ b/crypto/ec/ec_mult.c @@ -107,7 +107,7 @@ void EC_ec_pre_comp_free(EC_PRE_COMP *pre) BN_set_flags((P)->Z, (flags)); \ } while(0) -/* +/*- * This functions computes (in constant time) a point multiplication over the * EC group. * @@ -128,8 +128,9 @@ void EC_ec_pre_comp_free(EC_PRE_COMP *pre) * * Returns 1 on success, 0 otherwise. */ -static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, - const EC_POINT *point, BN_CTX *ctx) +static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, + const BIGNUM *scalar, const EC_POINT *point, + BN_CTX *ctx) { int i, order_bits, group_top, kbit, pbit, Z_is_one; EC_POINT *s = NULL; @@ -185,11 +186,11 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, const BIGNUM *sc BN_set_flags(k, BN_FLG_CONSTTIME); if ((BN_num_bits(k) > order_bits) || (BN_is_negative(k))) { - /* + /*- * this is an unusual input, and we don't guarantee * constant-timeness */ - if(!BN_nnmod(k, k, group->order, ctx)) + if (!BN_nnmod(k, k, group->order, ctx)) goto err; } @@ -234,7 +235,7 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, const BIGNUM *sc (b)->Z_is_one ^= (t); \ } while(0) - /* + /*- * The ladder step, with branches, is * * k[i] == 0: S = add(R, S), R = dbl(R) @@ -283,11 +284,11 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, const BIGNUM *sc * So instead of two contiguous swaps, you can merge the condition * bits and do a single swap. * - * k[i]    k[i-1]    Outcome - * 0       0         No Swap - * 0       1         Swap - * 1       0         Swap - * 1       1         No Swap + * k[i] k[i-1] Outcome + * 0 0 No Swap + * 0 1 Swap + * 1 0 Swap + * 1 1 No Swap * * This is XOR. pbit tracks the previous bit of k. */ @@ -311,13 +312,14 @@ static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r, const BIGNUM *sc ret = 1; -err: + err: EC_POINT_free(s); BN_CTX_end(ctx); BN_CTX_free(new_ctx); return ret; } + #undef EC_POINT_BN_set_flags /* @@ -370,31 +372,32 @@ int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, * precomputation is not available */ int ret = 0; - /* Handle the common cases where the scalar is secret, enforcing a - * constant time scalar multiplication algorithm. + /*- + * Handle the common cases where the scalar is secret, enforcing a constant + * time scalar multiplication algorithm. */ if ((scalar != NULL) && (num == 0)) { - /* In this case we want to compute scalar * GeneratorPoint: - * this codepath is reached most prominently by (ephemeral) key - * generation of EC cryptosystems (i.e. ECDSA keygen and sign setup, - * ECDH keygen/first half), where the scalar is always secret. - * This is why we ignore if BN_FLG_CONSTTIME is actually set and we - * always call the constant time version. + /*- + * In this case we want to compute scalar * GeneratorPoint: this + * codepath is reached most prominently by (ephemeral) key generation + * of EC cryptosystems (i.e. ECDSA keygen and sign setup, ECDH + * keygen/first half), where the scalar is always secret. This is why + * we ignore if BN_FLG_CONSTTIME is actually set and we always call the + * constant time version. */ return ec_mul_consttime(group, r, scalar, NULL, ctx); } if ((scalar == NULL) && (num == 1)) { - /* In this case we want to compute scalar * GenericPoint: - * this codepath is reached most prominently by the second half of - * ECDH, where the secret scalar is multiplied by the peer's public - * point. - * To protect the secret scalar, we ignore if BN_FLG_CONSTTIME is - * actually set and we always call the constant time version. + /*- + * In this case we want to compute scalar * GenericPoint: this codepath + * is reached most prominently by the second half of ECDH, where the + * secret scalar is multiplied by the peer's public point. To protect + * the secret scalar, we ignore if BN_FLG_CONSTTIME is actually set and + * we always call the constant time version. */ return ec_mul_consttime(group, r, scalars[0], points[0], ctx); } - if (group->meth != r->meth) { ECerr(EC_F_EC_WNAF_MUL, EC_R_INCOMPATIBLE_OBJECTS); return 0; -- 2.25.1