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Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6009)
This commit is contained in:
Nicola Tuveri 2018-04-20 11:02:52 +00:00 committed by Matt Caswell
parent a067a8705a
commit f467537927
1 changed files with 30 additions and 27 deletions
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57
crypto/ec/ec_mult.c
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@ -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;