-/* crypto/bn/bn_gcd.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
* All rights reserved.
*
* This package is an SSL implementation written
* by Eric Young (eay@cryptsoft.com).
* The implementation was written so as to conform with Netscapes SSL.
- *
+ *
* This library is free for commercial and non-commercial use as long as
* the following conditions are aheared to. The following conditions
* apply to all code found in this distribution, be it the RC4, RSA,
* lhash, DES, etc., code; not just the SSL code. The SSL documentation
* included with this distribution is covered by the same copyright terms
* except that the holder is Tim Hudson (tjh@cryptsoft.com).
- *
+ *
* Copyright remains Eric Young's, and as such any Copyright notices in
* the code are not to be removed.
* If this package is used in a product, Eric Young should be given attribution
* as the author of the parts of the library used.
* This can be in the form of a textual message at program startup or
* in documentation (online or textual) provided with the package.
- *
+ *
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* Eric Young (eay@cryptsoft.com)"
* The word 'cryptographic' can be left out if the rouines from the library
* being used are not cryptographic related :-).
- * 4. If you include any Windows specific code (or a derivative thereof) from
+ * 4. If you include any Windows specific code (or a derivative thereof) from
* the apps directory (application code) you must include an acknowledgement:
* "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
- *
+ *
* THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
- *
+ *
* The licence and distribution terms for any publically available version or
* derivative of this code cannot be changed. i.e. this code cannot simply be
* copied and put under another distribution licence
* [including the GNU Public Licence.]
*/
/* ====================================================================
- * Copyright (c) 1998-2000 The OpenSSL Project. All rights reserved.
+ * Copyright (c) 1998-2001 The OpenSSL Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
+ * notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
*
*/
-#include "cryptlib.h"
+#include "internal/cryptlib.h"
#include "bn_lcl.h"
static BIGNUM *euclid(BIGNUM *a, BIGNUM *b);
int BN_gcd(BIGNUM *r, const BIGNUM *in_a, const BIGNUM *in_b, BN_CTX *ctx)
- {
- BIGNUM *a,*b,*t;
- int ret=0;
-
- bn_check_top(in_a);
- bn_check_top(in_b);
-
- BN_CTX_start(ctx);
- a = BN_CTX_get(ctx);
- b = BN_CTX_get(ctx);
- if (a == NULL || b == NULL) goto err;
-
- if (BN_copy(a,in_a) == NULL) goto err;
- if (BN_copy(b,in_b) == NULL) goto err;
- a->neg = 0;
- b->neg = 0;
-
- if (BN_cmp(a,b) < 0) { t=a; a=b; b=t; }
- t=euclid(a,b);
- if (t == NULL) goto err;
-
- if (BN_copy(r,t) == NULL) goto err;
- ret=1;
-err:
- BN_CTX_end(ctx);
- return(ret);
- }
+{
+ BIGNUM *a, *b, *t;
+ int ret = 0;
+
+ bn_check_top(in_a);
+ bn_check_top(in_b);
+
+ BN_CTX_start(ctx);
+ a = BN_CTX_get(ctx);
+ b = BN_CTX_get(ctx);
+ if (a == NULL || b == NULL)
+ goto err;
+
+ if (BN_copy(a, in_a) == NULL)
+ goto err;
+ if (BN_copy(b, in_b) == NULL)
+ goto err;
+ a->neg = 0;
+ b->neg = 0;
+
+ if (BN_cmp(a, b) < 0) {
+ t = a;
+ a = b;
+ b = t;
+ }
+ t = euclid(a, b);
+ if (t == NULL)
+ goto err;
+
+ if (BN_copy(r, t) == NULL)
+ goto err;
+ ret = 1;
+ err:
+ BN_CTX_end(ctx);
+ bn_check_top(r);
+ return (ret);
+}
static BIGNUM *euclid(BIGNUM *a, BIGNUM *b)
- {
- BIGNUM *t;
- int shifts=0;
-
- bn_check_top(a);
- bn_check_top(b);
-
- /* 0 <= b <= a */
- while (!BN_is_zero(b))
- {
- /* 0 < b <= a */
-
- if (BN_is_odd(a))
- {
- if (BN_is_odd(b))
- {
- if (!BN_sub(a,a,b)) goto err;
- if (!BN_rshift1(a,a)) goto err;
- if (BN_cmp(a,b) < 0)
- { t=a; a=b; b=t; }
- }
- else /* a odd - b even */
- {
- if (!BN_rshift1(b,b)) goto err;
- if (BN_cmp(a,b) < 0)
- { t=a; a=b; b=t; }
- }
- }
- else /* a is even */
- {
- if (BN_is_odd(b))
- {
- if (!BN_rshift1(a,a)) goto err;
- if (BN_cmp(a,b) < 0)
- { t=a; a=b; b=t; }
- }
- else /* a even - b even */
- {
- if (!BN_rshift1(a,a)) goto err;
- if (!BN_rshift1(b,b)) goto err;
- shifts++;
- }
- }
- /* 0 <= b <= a */
- }
-
- if (shifts)
- {
- if (!BN_lshift(a,a,shifts)) goto err;
- }
- return(a);
-err:
- return(NULL);
- }
+{
+ BIGNUM *t;
+ int shifts = 0;
+
+ bn_check_top(a);
+ bn_check_top(b);
+
+ /* 0 <= b <= a */
+ while (!BN_is_zero(b)) {
+ /* 0 < b <= a */
+
+ if (BN_is_odd(a)) {
+ if (BN_is_odd(b)) {
+ if (!BN_sub(a, a, b))
+ goto err;
+ if (!BN_rshift1(a, a))
+ goto err;
+ if (BN_cmp(a, b) < 0) {
+ t = a;
+ a = b;
+ b = t;
+ }
+ } else { /* a odd - b even */
+
+ if (!BN_rshift1(b, b))
+ goto err;
+ if (BN_cmp(a, b) < 0) {
+ t = a;
+ a = b;
+ b = t;
+ }
+ }
+ } else { /* a is even */
+
+ if (BN_is_odd(b)) {
+ if (!BN_rshift1(a, a))
+ goto err;
+ if (BN_cmp(a, b) < 0) {
+ t = a;
+ a = b;
+ b = t;
+ }
+ } else { /* a even - b even */
+ if (!BN_rshift1(a, a))
+ goto err;
+ if (!BN_rshift1(b, b))
+ goto err;
+ shifts++;
+ }
+ }
+ /* 0 <= b <= a */
+ }
+
+ if (shifts) {
+ if (!BN_lshift(a, a, shifts))
+ goto err;
+ }
+ bn_check_top(a);
+ return (a);
+ err:
+ return (NULL);
+}
/* solves ax == 1 (mod n) */
+static BIGNUM *BN_mod_inverse_no_branch(BIGNUM *in,
+ const BIGNUM *a, const BIGNUM *n,
+ BN_CTX *ctx);
+
BIGNUM *BN_mod_inverse(BIGNUM *in,
- const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
- {
- BIGNUM *A,*B,*X,*Y,*M,*D,*T,*R=NULL;
- BIGNUM *ret=NULL;
- int sign;
-
- bn_check_top(a);
- bn_check_top(n);
-
- 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;
-
- if (in == NULL)
- R=BN_new();
- else
- R=in;
- if (R == NULL) goto err;
-
- BN_one(X);
- BN_zero(Y);
- if (BN_copy(B,a) == NULL) goto err;
- if (BN_copy(A,n) == NULL) goto err;
- A->neg = 0;
- if (B->neg || (BN_ucmp(B, A) >= 0))
- {
- if (!BN_nnmod(B, B, A, ctx)) goto err;
- }
- sign = -1;
- /* From B = a mod |n|, A = |n| it follows that
- *
- * 0 <= B < A,
- * X*a == B (mod |n|),
- * -sign*Y*a == A (mod |n|).
- */
-
- while (!BN_is_zero(B))
- {
- BIGNUM *tmp;
-
- /*
- * 0 < B < A,
- * (*) 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
- * X*a == A (mod |n|).
- *
- * Thus,
- * -sign*Y*a - D*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
- * 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;
- }
-
- /*
- * The while loop 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|). */
-
-
- if (BN_is_one(A))
- {
- /* Y*a == 1 (mod |n|) */
- if (BN_ucmp(Y,n) < 0)
- if (!BN_copy(R,Y)) goto err;
- else
- if (!BN_nnmod(R,Y,n,ctx)) goto err;
- }
- else
- {
- BNerr(BN_F_BN_MOD_INVERSE,BN_R_NO_INVERSE);
- goto err;
- }
- ret=R;
-err:
- if ((ret == NULL) && (in == NULL)) BN_free(R);
- BN_CTX_end(ctx);
- return(ret);
- }
+ const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx)
+{
+ BIGNUM *rv;
+ int noinv;
+ rv = int_bn_mod_inverse(in, a, n, ctx, &noinv);
+ if (noinv)
+ BNerr(BN_F_BN_MOD_INVERSE, BN_R_NO_INVERSE);
+ return rv;
+}
+
+BIGNUM *int_bn_mod_inverse(BIGNUM *in,
+ const BIGNUM *a, const BIGNUM *n, BN_CTX *ctx,
+ int *pnoinv)
+{
+ BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
+ BIGNUM *ret = NULL;
+ int sign;
+
+ if (pnoinv)
+ *pnoinv = 0;
+
+ if ((BN_get_flags(a, BN_FLG_CONSTTIME) != 0)
+ || (BN_get_flags(n, BN_FLG_CONSTTIME) != 0)) {
+ return BN_mod_inverse_no_branch(in, a, n, ctx);
+ }
+
+ bn_check_top(a);
+ bn_check_top(n);
+
+ 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;
+
+ if (in == NULL)
+ R = BN_new();
+ else
+ R = in;
+ if (R == NULL)
+ goto err;
+
+ BN_one(X);
+ BN_zero(Y);
+ if (BN_copy(B, a) == NULL)
+ goto err;
+ if (BN_copy(A, n) == NULL)
+ goto err;
+ A->neg = 0;
+ if (B->neg || (BN_ucmp(B, A) >= 0)) {
+ if (!BN_nnmod(B, B, A, ctx))
+ goto err;
+ }
+ 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|).
+ */
+
+ if (BN_is_odd(n) && (BN_num_bits(n) <= 2048)) {
+ /*
+ * Binary inversion algorithm; requires odd modulus. This is faster
+ * than the general algorithm if the modulus is sufficiently small
+ * (about 400 .. 500 bits on 32-bit sytems, but much more on 64-bit
+ * systems)
+ */
+ int shift;
+
+ while (!BN_is_zero(B)) {
+ /*-
+ * 0 < B < |n|,
+ * 0 < A <= |n|,
+ * (1) -sign*X*a == B (mod |n|),
+ * (2) sign*Y*a == A (mod |n|)
+ */
+
+ /*
+ * Now divide B by the maximum possible power of two in the
+ * integers, and divide X by the same value mod |n|. When we're
+ * done, (1) still holds.
+ */
+ shift = 0;
+ while (!BN_is_bit_set(B, shift)) { /* note that 0 < B */
+ shift++;
+
+ if (BN_is_odd(X)) {
+ if (!BN_uadd(X, X, n))
+ goto err;
+ }
+ /*
+ * now X is even, so we can easily divide it by two
+ */
+ if (!BN_rshift1(X, X))
+ goto err;
+ }
+ if (shift > 0) {
+ if (!BN_rshift(B, B, shift))
+ goto err;
+ }
+
+ /*
+ * Same for A and Y. Afterwards, (2) still holds.
+ */
+ shift = 0;
+ while (!BN_is_bit_set(A, shift)) { /* note that 0 < A */
+ shift++;
+
+ if (BN_is_odd(Y)) {
+ if (!BN_uadd(Y, Y, n))
+ goto err;
+ }
+ /* now Y is even */
+ if (!BN_rshift1(Y, Y))
+ goto err;
+ }
+ if (shift > 0) {
+ if (!BN_rshift(A, A, shift))
+ goto err;
+ }
+
+ /*-
+ * We still have (1) and (2).
+ * Both A and B are odd.
+ * The following computations ensure that
+ *
+ * 0 <= B < |n|,
+ * 0 < A < |n|,
+ * (1) -sign*X*a == B (mod |n|),
+ * (2) sign*Y*a == A (mod |n|),
+ *
+ * and that either A or B is even in the next iteration.
+ */
+ if (BN_ucmp(B, A) >= 0) {
+ /* -sign*(X + Y)*a == B - A (mod |n|) */
+ if (!BN_uadd(X, X, Y))
+ goto err;
+ /*
+ * NB: we could use BN_mod_add_quick(X, X, Y, n), but that
+ * actually makes the algorithm slower
+ */
+ if (!BN_usub(B, B, A))
+ goto err;
+ } else {
+ /* sign*(X + Y)*a == A - B (mod |n|) */
+ if (!BN_uadd(Y, Y, X))
+ goto err;
+ /*
+ * as above, BN_mod_add_quick(Y, Y, X, n) would slow things
+ * down
+ */
+ if (!BN_usub(A, A, B))
+ goto err;
+ }
+ }
+ } else {
+ /* 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;
+ }
+ }
+
+ /*-
+ * 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|). */
+
+ if (BN_is_one(A)) {
+ /* 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;
+ }
+ } else {
+ if (pnoinv)
+ *pnoinv = 1;
+ goto err;
+ }
+ ret = R;
+ err:
+ if ((ret == NULL) && (in == NULL))
+ BN_free(R);
+ BN_CTX_end(ctx);
+ bn_check_top(ret);
+ 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 BIGNUM *BN_mod_inverse_no_branch(BIGNUM *in,
+ const BIGNUM *a, const BIGNUM *n,
+ BN_CTX *ctx)
+{
+ BIGNUM *A, *B, *X, *Y, *M, *D, *T, *R = NULL;
+ BIGNUM *ret = NULL;
+ int sign;
+
+ bn_check_top(a);
+ bn_check_top(n);
+
+ 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;
+
+ if (in == NULL)
+ R = BN_new();
+ else
+ R = in;
+ if (R == NULL)
+ goto err;
+
+ BN_one(X);
+ BN_zero(Y);
+ if (BN_copy(B, a) == NULL)
+ goto err;
+ if (BN_copy(A, n) == NULL)
+ goto err;
+ 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.
+ */
+ {
+ BIGNUM local_B;
+ bn_init(&local_B);
+ BN_with_flags(&local_B, B, BN_FLG_CONSTTIME);
+ if (!BN_nnmod(B, &local_B, A, ctx))
+ goto err;
+ /* Ensure local_B goes out of scope before any further use of B */
+ }
+ }
+ 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|).
+ */
+
+ while (!BN_is_zero(B)) {
+ BIGNUM *tmp;
+
+ /*-
+ * 0 < B < A,
+ * (*) -sign*X*a == B (mod |n|),
+ * sign*Y*a == A (mod |n|)
+ */
+
+ /*
+ * Turn BN_FLG_CONSTTIME flag on, so that when BN_div is invoked,
+ * BN_div_no_branch will be called eventually.
+ */
+ {
+ BIGNUM local_A;
+ bn_init(&local_A);
+ BN_with_flags(&local_A, A, BN_FLG_CONSTTIME);
+
+ /* (D, M) := (A/B, A%B) ... */
+ if (!BN_div(D, M, &local_A, B, ctx))
+ goto err;
+ /* Ensure local_A goes out of scope before any further use of A */
+ }
+
+ /*-
+ * 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.
+ */
+
+ 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;
+ }
+
+ /*-
+ * 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|). */
+ if (BN_is_one(A)) {
+ /* 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;
+ }
+ } else {
+ BNerr(BN_F_BN_MOD_INVERSE_NO_BRANCH, BN_R_NO_INVERSE);
+ goto err;
+ }
+ ret = R;
+ err:
+ if ((ret == NULL) && (in == NULL))
+ BN_free(R);
+ BN_CTX_end(ctx);
+ bn_check_top(ret);
+ return (ret);
+}
projects / openssl.git / blobdiff