Always use the "no_branch" inversion algorithm for even moduli.
This eliminates duplicate logic. Change-Id: I283273ae152f3644df4384558ee4a021f8c2d454 Reviewed-on: https://boringssl-review.googlesource.com/9104 Reviewed-by: David Benjamin <davidben@google.com> CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Commit-Queue: David Benjamin <davidben@google.com>
This commit is contained in:
Brian Smith
CQ bot account: commit-bot@chromium.org
parent
a432757acb
commit
253c05e16b
235
crypto/bn/gcd.c
235
crypto/bn/gcd.c
@ -225,9 +225,9 @@ err:
|
||||
}
|
||||
|
||||
/* solves ax == 1 (mod n) */
|
||||
static int 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_general(BIGNUM *out, int *out_no_inverse,
|
||||
const BIGNUM *a, const BIGNUM *n,
|
||||
BN_CTX *ctx);
|
||||
|
||||
int BN_mod_inverse_odd(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
|
||||
const BIGNUM *n, BN_CTX *ctx) {
|
||||
@ -397,216 +397,6 @@ err:
|
||||
return ret;
|
||||
}
|
||||
|
||||
static int bn_mod_inverse_general(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;
|
||||
|
||||
BN_CTX_start(ctx);
|
||||
A = BN_CTX_get(ctx);
|
||||
B = BN_CTX_get(ctx);
|
||||
X = BN_CTX_get(ctx);
|
||||
D = BN_CTX_get(ctx);
|
||||
M = BN_CTX_get(ctx);
|
||||
Y = BN_CTX_get(ctx);
|
||||
T = BN_CTX_get(ctx);
|
||||
if (T == NULL) {
|
||||
goto err;
|
||||
}
|
||||
|
||||
BIGNUM *R = out;
|
||||
|
||||
BN_zero(Y);
|
||||
if (!BN_one(X) || BN_copy(B, a) == NULL || BN_copy(A, n) == NULL) {
|
||||
goto err;
|
||||
}
|
||||
A->neg = 0;
|
||||
sign = -1;
|
||||
/* From B = a mod |n|, A = |n| it follows that
|
||||
*
|
||||
* 0 <= B < A,
|
||||
* -sign*X*a == B (mod |n|),
|
||||
* sign*Y*a == A (mod |n|).
|
||||
*/
|
||||
|
||||
/* general inversion algorithm */
|
||||
|
||||
while (!BN_is_zero(B)) {
|
||||
BIGNUM *tmp;
|
||||
|
||||
/*
|
||||
* 0 < B < A,
|
||||
* (*) -sign*X*a == B (mod |n|),
|
||||
* sign*Y*a == A (mod |n|) */
|
||||
|
||||
/* (D, M) := (A/B, A%B) ... */
|
||||
if (BN_num_bits(A) == BN_num_bits(B)) {
|
||||
if (!BN_one(D)) {
|
||||
goto err;
|
||||
}
|
||||
if (!BN_sub(M, A, B)) {
|
||||
goto err;
|
||||
}
|
||||
} else if (BN_num_bits(A) == BN_num_bits(B) + 1) {
|
||||
/* A/B is 1, 2, or 3 */
|
||||
if (!BN_lshift1(T, B)) {
|
||||
goto err;
|
||||
}
|
||||
if (BN_ucmp(A, T) < 0) {
|
||||
/* A < 2*B, so D=1 */
|
||||
if (!BN_one(D)) {
|
||||
goto err;
|
||||
}
|
||||
if (!BN_sub(M, A, B)) {
|
||||
goto err;
|
||||
}
|
||||
} else {
|
||||
/* A >= 2*B, so D=2 or D=3 */
|
||||
if (!BN_sub(M, A, T)) {
|
||||
goto err;
|
||||
}
|
||||
if (!BN_add(D, T, B)) {
|
||||
goto err; /* use D (:= 3*B) as temp */
|
||||
}
|
||||
if (BN_ucmp(A, D) < 0) {
|
||||
/* A < 3*B, so D=2 */
|
||||
if (!BN_set_word(D, 2)) {
|
||||
goto err;
|
||||
}
|
||||
/* M (= A - 2*B) already has the correct value */
|
||||
} else {
|
||||
/* only D=3 remains */
|
||||
if (!BN_set_word(D, 3)) {
|
||||
goto err;
|
||||
}
|
||||
/* currently M = A - 2*B, but we need M = A - 3*B */
|
||||
if (!BN_sub(M, M, B)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
}
|
||||
} else {
|
||||
if (!BN_div(D, M, A, B, ctx)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
|
||||
/* Now
|
||||
* A = D*B + M;
|
||||
* thus we have
|
||||
* (**) sign*Y*a == D*B + M (mod |n|). */
|
||||
|
||||
tmp = A; /* keep the BIGNUM object, the value does not matter */
|
||||
|
||||
/* (A, B) := (B, A mod B) ... */
|
||||
A = B;
|
||||
B = M;
|
||||
/* ... so we have 0 <= B < A again */
|
||||
|
||||
/* Since the former M is now B and the former B is now A,
|
||||
* (**) translates into
|
||||
* sign*Y*a == D*A + B (mod |n|),
|
||||
* i.e.
|
||||
* sign*Y*a - D*A == B (mod |n|).
|
||||
* Similarly, (*) translates into
|
||||
* -sign*X*a == A (mod |n|).
|
||||
*
|
||||
* Thus,
|
||||
* sign*Y*a + D*sign*X*a == B (mod |n|),
|
||||
* i.e.
|
||||
* sign*(Y + D*X)*a == B (mod |n|).
|
||||
*
|
||||
* So if we set (X, Y, sign) := (Y + D*X, X, -sign), we arrive back at
|
||||
* -sign*X*a == B (mod |n|),
|
||||
* sign*Y*a == A (mod |n|).
|
||||
* Note that X and Y stay non-negative all the time. */
|
||||
|
||||
/* most of the time D is very small, so we can optimize tmp := D*X+Y */
|
||||
if (BN_is_one(D)) {
|
||||
if (!BN_add(tmp, X, Y)) {
|
||||
goto err;
|
||||
}
|
||||
} else {
|
||||
if (BN_is_word(D, 2)) {
|
||||
if (!BN_lshift1(tmp, X)) {
|
||||
goto err;
|
||||
}
|
||||
} else if (BN_is_word(D, 4)) {
|
||||
if (!BN_lshift(tmp, X, 2)) {
|
||||
goto err;
|
||||
}
|
||||
} else if (D->top == 1) {
|
||||
if (!BN_copy(tmp, X)) {
|
||||
goto err;
|
||||
}
|
||||
if (!BN_mul_word(tmp, D->d[0])) {
|
||||
goto err;
|
||||
}
|
||||
} else {
|
||||
if (!BN_mul(tmp, D, X, ctx)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
if (!BN_add(tmp, tmp, Y)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
|
||||
M = Y; /* keep the BIGNUM object, the value does not matter */
|
||||
Y = X;
|
||||
X = tmp;
|
||||
sign = -sign;
|
||||
}
|
||||
|
||||
if (!BN_is_one(A)) {
|
||||
*out_no_inverse = 1;
|
||||
OPENSSL_PUT_ERROR(BN, BN_R_NO_INVERSE);
|
||||
goto err;
|
||||
}
|
||||
|
||||
/* The while loop (Euclid's algorithm) ends when
|
||||
* A == gcd(a,n);
|
||||
* we have
|
||||
* sign*Y*a == A (mod |n|),
|
||||
* where Y is non-negative. */
|
||||
|
||||
if (sign < 0) {
|
||||
if (!BN_sub(Y, n, Y)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
/* Now Y*a == A (mod |n|). */
|
||||
|
||||
/* Y*a == 1 (mod |n|) */
|
||||
if (!Y->neg && BN_ucmp(Y, n) < 0) {
|
||||
if (!BN_copy(R, Y)) {
|
||||
goto err;
|
||||
}
|
||||
} else {
|
||||
if (!BN_nnmod(R, Y, n, ctx)) {
|
||||
goto err;
|
||||
}
|
||||
}
|
||||
|
||||
ret = 1;
|
||||
|
||||
err:
|
||||
BN_CTX_end(ctx);
|
||||
return ret;
|
||||
}
|
||||
|
||||
static int bn_mod_inverse_ex(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
|
||||
const BIGNUM *n, BN_CTX *ctx) {
|
||||
if (BN_is_odd(n) && (BN_num_bits(n) <= (BN_BITS2 <= 32 ? 450 : 2048))) {
|
||||
return BN_mod_inverse_odd(out, out_no_inverse, a, n, ctx);
|
||||
}
|
||||
return bn_mod_inverse_general(out, out_no_inverse, a, n, ctx);
|
||||
}
|
||||
|
||||
BIGNUM *BN_mod_inverse(BIGNUM *out, const BIGNUM *a, const BIGNUM *n,
|
||||
BN_CTX *ctx) {
|
||||
int no_inverse;
|
||||
@ -642,12 +432,12 @@ BIGNUM *BN_mod_inverse(BIGNUM *out, const BIGNUM *a, const BIGNUM *n,
|
||||
a = a_reduced;
|
||||
}
|
||||
|
||||
if (no_branch) {
|
||||
if (!bn_mod_inverse_no_branch(out, &no_inverse, a, n, ctx)) {
|
||||
if (no_branch || !BN_is_odd(n)) {
|
||||
if (!bn_mod_inverse_general(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)) {
|
||||
} else if (!BN_mod_inverse_odd(out, &no_inverse, a, n, ctx)) {
|
||||
OPENSSL_PUT_ERROR(BN, ERR_R_INTERNAL_ERROR);
|
||||
goto err;
|
||||
}
|
||||
@ -691,11 +481,14 @@ err:
|
||||
return ret;
|
||||
}
|
||||
|
||||
/* BN_mod_inverse_no_branch is a special version of BN_mod_inverse.
|
||||
* It does not contain branches that may leak sensitive information. */
|
||||
static int bn_mod_inverse_no_branch(BIGNUM *out, int *out_no_inverse,
|
||||
const BIGNUM *a, const BIGNUM *n,
|
||||
BN_CTX *ctx) {
|
||||
/* bn_mod_inverse_general is the general inversion algorithm that works for
|
||||
* both even and odd |n|. It was specifically designed to contain fewer
|
||||
* branches that may leak sensitive information. See "New Branch Prediction
|
||||
* Vulnerabilities in OpenSSL and Necessary Software Countermeasures" by
|
||||
* Onur Acıçmez, Shay Gueron, and Jean-Pierre Seifert. */
|
||||
static int bn_mod_inverse_general(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;
|
||||
|
||||
Loading…
Reference in New Issue
Block a user