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Factor out common logic in bn_mod_inverse_*.

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This is in preparation for factoring out the binary Euclidean
implementation (the one used for odd numbers that aren't too big) for
direct use from outside of crypto/bn/gcd.c. The goal is to make the
resultant |BN_mod_inverse_odd|'s signature similar to
|BN_mod_inverse_blinded|. Thus, the logic for reducing the final result
isn't factored out because that yet-to-be-created |BN_mod_inverse_odd|
will need to do it itself.

Change-Id: Iaecb79fb17d13c774c4fb6ade8742937780b0006
Reviewed-on: https://boringssl-review.googlesource.com/9100
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
This commit is contained in:
Brian Smith 2016-08-02 16:18:00 -10:00 committed by CQ bot account: commit-bot@chromium.org
parent 22edd87755
commit 10b09ad28e
1 changed files with 60 additions and 64 deletions
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124
crypto/bn/gcd.c
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@ -223,15 +223,14 @@ err:
}
/* solves ax == 1 (mod n) */
static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx);
static int bn_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx);
static BIGNUM *bn_mod_inverse_ex(BIGNUM *out, int *out_no_inverse,
const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx) {
BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
BIGNUM *ret = NULL;
static int bn_mod_inverse_ex(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
const BIGNUM *n, BN_CTX *ctx) {
BIGNUM *A, *B, *X, *Y, *M, *D, *T;
int ret = 0;
int sign;
*out_no_inverse = 0;
@ -248,14 +247,7 @@ static BIGNUM *bn_mod_inverse_ex(BIGNUM *out, int *out_no_inverse,
goto err;
}
if (out == NULL) {
R = BN_new();
} else {
R = out;
}
if (R == NULL) {
goto err;
}
BIGNUM *R = out;
BN_zero(Y);
if (!BN_one(X) || BN_copy(B, a) == NULL || BN_copy(A, n) == NULL) {
@ -521,12 +513,9 @@ static BIGNUM *bn_mod_inverse_ex(BIGNUM *out, int *out_no_inverse,
}
}
ret = R;
ret = 1;
err:
if (ret == NULL && out == NULL) {
BN_free(R);
}
BN_CTX_end(ctx);
return ret;
}
@ -535,28 +524,56 @@ BIGNUM *BN_mod_inverse(BIGNUM *out, const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx) {
int no_inverse;
if ((a->flags & BN_FLG_CONSTTIME) != 0 ||
(n->flags & BN_FLG_CONSTTIME) != 0) {
return BN_mod_inverse_no_branch(out, &no_inverse, a, n, ctx);
BIGNUM *a_reduced = NULL;
BIGNUM *new_out = NULL;
if (out == NULL) {
new_out = BN_new();
if (new_out == NULL) {
OPENSSL_PUT_ERROR(BN, ERR_R_MALLOC_FAILURE);
return NULL;
}
out = new_out;
}
if (!a->neg && BN_ucmp(a, n) < 0) {
return bn_mod_inverse_ex(out, &no_inverse, a, n, ctx);
int ok = 0;
int no_branch =
(a->flags & BN_FLG_CONSTTIME) != 0 || (n->flags & BN_FLG_CONSTTIME) != 0;
if (a->neg || BN_ucmp(a, n) >= 0) {
a_reduced = BN_dup(a);
if (a_reduced == NULL) {
goto err;
}
if (no_branch) {
BN_set_flags(a_reduced, BN_FLG_CONSTTIME);
}
if (!BN_nnmod(a_reduced, a_reduced, n, ctx)) {
goto err;
}
a = a_reduced;
}
BIGNUM a_reduced;
BN_init(&a_reduced);
BIGNUM *ret = NULL;
if (!BN_nnmod(&a_reduced, a, n, ctx)) {
if (no_branch) {
if (!bn_mod_inverse_no_branch(out, &no_inverse, a, n, ctx)) {
OPENSSL_PUT_ERROR(BN, ERR_R_INTERNAL_ERROR);
goto err;
}
} else if (!bn_mod_inverse_ex(out, &no_inverse, a, n, ctx)) {
OPENSSL_PUT_ERROR(BN, ERR_R_INTERNAL_ERROR);
goto err;
}
ret = bn_mod_inverse_ex(out, &no_inverse, &a_reduced, n, ctx);
ok = 1;
err:
BN_free(&a_reduced);
return ret;
if (!ok) {
BN_free(new_out);
out = NULL;
}
BN_free(a_reduced);
return out;
}
int BN_mod_inverse_blinded(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
@ -574,7 +591,7 @@ int BN_mod_inverse_blinded(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
if (!BN_rand_range_ex(&blinding_factor, 1, &mont->N) ||
!BN_mod_mul_montgomery(out, &blinding_factor, a, mont, ctx) ||
bn_mod_inverse_ex(out, out_no_inverse, out, &mont->N, ctx) == NULL ||
!bn_mod_inverse_ex(out, out_no_inverse, out, &mont->N, ctx) ||
!BN_mod_mul_montgomery(out, &blinding_factor, out, mont, ctx)) {
OPENSSL_PUT_ERROR(BN, ERR_R_BN_LIB);
goto err;
@ -589,13 +606,13 @@ err:
/* BN_mod_inverse_no_branch is a special version of BN_mod_inverse.
* It does not contain branches that may leak sensitive information. */
static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx) {
BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
BIGNUM local_A, local_B;
BIGNUM *pA, *pB;
BIGNUM *ret = NULL;
static int bn_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx) {
BIGNUM *A, *B, *X, *Y, *M, *D, *T;
BIGNUM local_A;
BIGNUM *pA;
int ret = 0;
int sign;
*out_no_inverse = 0;
@ -612,14 +629,7 @@ static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
goto err;
}
if (out == NULL) {
R = BN_new();
} else {
R = out;
}
if (R == NULL) {
goto err;
}
BIGNUM *R = out;
BN_zero(Y);
if (!BN_one(X) || BN_copy(B, a) == NULL || BN_copy(A, n) == NULL) {
@ -627,16 +637,6 @@ static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
}
A->neg = 0;
if (B->neg || (BN_ucmp(B, A) >= 0)) {
/* Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
* BN_div_no_branch will be called eventually.
*/
pB = &local_B;
BN_with_flags(pB, B, BN_FLG_CONSTTIME);
if (!BN_nnmod(B, pB, A, ctx)) {
goto err;
}
}
sign = -1;
/* From B = a mod |n|, A = |n| it follows that
*
@ -742,13 +742,9 @@ static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
}
}
ret = R;
ret = 1;
err:
if (ret == NULL && out == NULL) {
BN_free(R);
}
BN_CTX_end(ctx);
return ret;
}