cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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mpi-inv.c (3334B)

      1/* mpi-inv.c  -  MPI functions
      2 *	Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
      3 *
      4 * This file is part of Libgcrypt.
      5 *
      6 * Libgcrypt is free software; you can redistribute it and/or modify
      7 * it under the terms of the GNU Lesser General Public License as
      8 * published by the Free Software Foundation; either version 2.1 of
      9 * the License, or (at your option) any later version.
     10 *
     11 * Libgcrypt is distributed in the hope that it will be useful,
     12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
     13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     14 * GNU Lesser General Public License for more details.
     15 *
     16 * You should have received a copy of the GNU Lesser General Public
     17 * License along with this program; if not, see <http://www.gnu.org/licenses/>.
     18 */
     19
     20#include "mpi-internal.h"
     21
     22/****************
     23 * Calculate the multiplicative inverse X of A mod N
     24 * That is: Find the solution x for
     25 *		1 = (a*x) mod n
     26 */
     27int mpi_invm(MPI x, MPI a, MPI n)
     28{
     29	/* Extended Euclid's algorithm (See TAOCP Vol II, 4.5.2, Alg X)
     30	 * modified according to Michael Penk's solution for Exercise 35
     31	 * with further enhancement
     32	 */
     33	MPI u, v, u1, u2 = NULL, u3, v1, v2 = NULL, v3, t1, t2 = NULL, t3;
     34	unsigned int k;
     35	int sign;
     36	int odd;
     37
     38	if (!mpi_cmp_ui(a, 0))
     39		return 0; /* Inverse does not exists.  */
     40	if (!mpi_cmp_ui(n, 1))
     41		return 0; /* Inverse does not exists.  */
     42
     43	u = mpi_copy(a);
     44	v = mpi_copy(n);
     45
     46	for (k = 0; !mpi_test_bit(u, 0) && !mpi_test_bit(v, 0); k++) {
     47		mpi_rshift(u, u, 1);
     48		mpi_rshift(v, v, 1);
     49	}
     50	odd = mpi_test_bit(v, 0);
     51
     52	u1 = mpi_alloc_set_ui(1);
     53	if (!odd)
     54		u2 = mpi_alloc_set_ui(0);
     55	u3 = mpi_copy(u);
     56	v1 = mpi_copy(v);
     57	if (!odd) {
     58		v2 = mpi_alloc(mpi_get_nlimbs(u));
     59		mpi_sub(v2, u1, u); /* U is used as const 1 */
     60	}
     61	v3 = mpi_copy(v);
     62	if (mpi_test_bit(u, 0)) { /* u is odd */
     63		t1 = mpi_alloc_set_ui(0);
     64		if (!odd) {
     65			t2 = mpi_alloc_set_ui(1);
     66			t2->sign = 1;
     67		}
     68		t3 = mpi_copy(v);
     69		t3->sign = !t3->sign;
     70		goto Y4;
     71	} else {
     72		t1 = mpi_alloc_set_ui(1);
     73		if (!odd)
     74			t2 = mpi_alloc_set_ui(0);
     75		t3 = mpi_copy(u);
     76	}
     77
     78	do {
     79		do {
     80			if (!odd) {
     81				if (mpi_test_bit(t1, 0) || mpi_test_bit(t2, 0)) {
     82					/* one is odd */
     83					mpi_add(t1, t1, v);
     84					mpi_sub(t2, t2, u);
     85				}
     86				mpi_rshift(t1, t1, 1);
     87				mpi_rshift(t2, t2, 1);
     88				mpi_rshift(t3, t3, 1);
     89			} else {
     90				if (mpi_test_bit(t1, 0))
     91					mpi_add(t1, t1, v);
     92				mpi_rshift(t1, t1, 1);
     93				mpi_rshift(t3, t3, 1);
     94			}
     95Y4:
     96			;
     97		} while (!mpi_test_bit(t3, 0)); /* while t3 is even */
     98
     99		if (!t3->sign) {
    100			mpi_set(u1, t1);
    101			if (!odd)
    102				mpi_set(u2, t2);
    103			mpi_set(u3, t3);
    104		} else {
    105			mpi_sub(v1, v, t1);
    106			sign = u->sign; u->sign = !u->sign;
    107			if (!odd)
    108				mpi_sub(v2, u, t2);
    109			u->sign = sign;
    110			sign = t3->sign; t3->sign = !t3->sign;
    111			mpi_set(v3, t3);
    112			t3->sign = sign;
    113		}
    114		mpi_sub(t1, u1, v1);
    115		if (!odd)
    116			mpi_sub(t2, u2, v2);
    117		mpi_sub(t3, u3, v3);
    118		if (t1->sign) {
    119			mpi_add(t1, t1, v);
    120			if (!odd)
    121				mpi_sub(t2, t2, u);
    122		}
    123	} while (mpi_cmp_ui(t3, 0)); /* while t3 != 0 */
    124	/* mpi_lshift( u3, k ); */
    125	mpi_set(x, u1);
    126
    127	mpi_free(u1);
    128	mpi_free(v1);
    129	mpi_free(t1);
    130	if (!odd) {
    131		mpi_free(u2);
    132		mpi_free(v2);
    133		mpi_free(t2);
    134	}
    135	mpi_free(u3);
    136	mpi_free(v3);
    137	mpi_free(t3);
    138
    139	mpi_free(u);
    140	mpi_free(v);
    141	return 1;
    142}
    143EXPORT_SYMBOL_GPL(mpi_invm);