mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-28 20:02:17 +00:00
144 lines
3.3 KiB
C
144 lines
3.3 KiB
C
![]() |
/* mpi-inv.c - MPI functions
|
||
|
* Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
|
||
|
*
|
||
|
* This file is part of Libgcrypt.
|
||
|
*
|
||
|
* Libgcrypt is free software; you can redistribute it and/or modify
|
||
|
* it under the terms of the GNU Lesser General Public License as
|
||
|
* published by the Free Software Foundation; either version 2.1 of
|
||
|
* the License, or (at your option) any later version.
|
||
|
*
|
||
|
* Libgcrypt is distributed in the hope that it will be useful,
|
||
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
|
* GNU Lesser General Public License for more details.
|
||
|
*
|
||
|
* You should have received a copy of the GNU Lesser General Public
|
||
|
* License along with this program; if not, see <http://www.gnu.org/licenses/>.
|
||
|
*/
|
||
|
|
||
|
#include "mpi-internal.h"
|
||
|
|
||
|
/****************
|
||
|
* Calculate the multiplicative inverse X of A mod N
|
||
|
* That is: Find the solution x for
|
||
|
* 1 = (a*x) mod n
|
||
|
*/
|
||
|
int mpi_invm(MPI x, MPI a, MPI n)
|
||
|
{
|
||
|
/* Extended Euclid's algorithm (See TAOCP Vol II, 4.5.2, Alg X)
|
||
|
* modified according to Michael Penk's solution for Exercise 35
|
||
|
* with further enhancement
|
||
|
*/
|
||
|
MPI u, v, u1, u2 = NULL, u3, v1, v2 = NULL, v3, t1, t2 = NULL, t3;
|
||
|
unsigned int k;
|
||
|
int sign;
|
||
|
int odd;
|
||
|
|
||
|
if (!mpi_cmp_ui(a, 0))
|
||
|
return 0; /* Inverse does not exists. */
|
||
|
if (!mpi_cmp_ui(n, 1))
|
||
|
return 0; /* Inverse does not exists. */
|
||
|
|
||
|
u = mpi_copy(a);
|
||
|
v = mpi_copy(n);
|
||
|
|
||
|
for (k = 0; !mpi_test_bit(u, 0) && !mpi_test_bit(v, 0); k++) {
|
||
|
mpi_rshift(u, u, 1);
|
||
|
mpi_rshift(v, v, 1);
|
||
|
}
|
||
|
odd = mpi_test_bit(v, 0);
|
||
|
|
||
|
u1 = mpi_alloc_set_ui(1);
|
||
|
if (!odd)
|
||
|
u2 = mpi_alloc_set_ui(0);
|
||
|
u3 = mpi_copy(u);
|
||
|
v1 = mpi_copy(v);
|
||
|
if (!odd) {
|
||
|
v2 = mpi_alloc(mpi_get_nlimbs(u));
|
||
|
mpi_sub(v2, u1, u); /* U is used as const 1 */
|
||
|
}
|
||
|
v3 = mpi_copy(v);
|
||
|
if (mpi_test_bit(u, 0)) { /* u is odd */
|
||
|
t1 = mpi_alloc_set_ui(0);
|
||
|
if (!odd) {
|
||
|
t2 = mpi_alloc_set_ui(1);
|
||
|
t2->sign = 1;
|
||
|
}
|
||
|
t3 = mpi_copy(v);
|
||
|
t3->sign = !t3->sign;
|
||
|
goto Y4;
|
||
|
} else {
|
||
|
t1 = mpi_alloc_set_ui(1);
|
||
|
if (!odd)
|
||
|
t2 = mpi_alloc_set_ui(0);
|
||
|
t3 = mpi_copy(u);
|
||
|
}
|
||
|
|
||
|
do {
|
||
|
do {
|
||
|
if (!odd) {
|
||
|
if (mpi_test_bit(t1, 0) || mpi_test_bit(t2, 0)) {
|
||
|
/* one is odd */
|
||
|
mpi_add(t1, t1, v);
|
||
|
mpi_sub(t2, t2, u);
|
||
|
}
|
||
|
mpi_rshift(t1, t1, 1);
|
||
|
mpi_rshift(t2, t2, 1);
|
||
|
mpi_rshift(t3, t3, 1);
|
||
|
} else {
|
||
|
if (mpi_test_bit(t1, 0))
|
||
|
mpi_add(t1, t1, v);
|
||
|
mpi_rshift(t1, t1, 1);
|
||
|
mpi_rshift(t3, t3, 1);
|
||
|
}
|
||
|
Y4:
|
||
|
;
|
||
|
} while (!mpi_test_bit(t3, 0)); /* while t3 is even */
|
||
|
|
||
|
if (!t3->sign) {
|
||
|
mpi_set(u1, t1);
|
||
|
if (!odd)
|
||
|
mpi_set(u2, t2);
|
||
|
mpi_set(u3, t3);
|
||
|
} else {
|
||
|
mpi_sub(v1, v, t1);
|
||
|
sign = u->sign; u->sign = !u->sign;
|
||
|
if (!odd)
|
||
|
mpi_sub(v2, u, t2);
|
||
|
u->sign = sign;
|
||
|
sign = t3->sign; t3->sign = !t3->sign;
|
||
|
mpi_set(v3, t3);
|
||
|
t3->sign = sign;
|
||
|
}
|
||
|
mpi_sub(t1, u1, v1);
|
||
|
if (!odd)
|
||
|
mpi_sub(t2, u2, v2);
|
||
|
mpi_sub(t3, u3, v3);
|
||
|
if (t1->sign) {
|
||
|
mpi_add(t1, t1, v);
|
||
|
if (!odd)
|
||
|
mpi_sub(t2, t2, u);
|
||
|
}
|
||
|
} while (mpi_cmp_ui(t3, 0)); /* while t3 != 0 */
|
||
|
/* mpi_lshift( u3, k ); */
|
||
|
mpi_set(x, u1);
|
||
|
|
||
|
mpi_free(u1);
|
||
|
mpi_free(v1);
|
||
|
mpi_free(t1);
|
||
|
if (!odd) {
|
||
|
mpi_free(u2);
|
||
|
mpi_free(v2);
|
||
|
mpi_free(t2);
|
||
|
}
|
||
|
mpi_free(u3);
|
||
|
mpi_free(v3);
|
||
|
mpi_free(t3);
|
||
|
|
||
|
mpi_free(u);
|
||
|
mpi_free(v);
|
||
|
return 1;
|
||
|
}
|
||
|
EXPORT_SYMBOL_GPL(mpi_invm);
|