5 * Modular exponentiation with Montgomery reduction
7 * (c) 2004 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
14 * Catacomb is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
19 * Catacomb is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
24 * You should have received a copy of the GNU Library General Public
25 * License along with Catacomb; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
30 /*----- Header files ------------------------------------------------------*/
34 #include "mpmont-exp.h"
36 /*----- Exponentiation ----------------------------------------------------*/
38 /* --- @mpmont_expr@ --- *
40 * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context
41 * @mp *d@ = fake destination
45 * Returns: Result, %$(a R^{-1})^e R \bmod m$%.
48 mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
50 mp *x = MP_COPY(mm->r);
51 mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
59 a = mpmont_reduce(mm, a, a);
60 a = mp_modinv(a, a, mm->m);
61 a = mpmont_mul(mm, a, a, mm->r2);
63 if (MP_LEN(e) < EXP_THRESH)
74 /* --- @mpmont_exp@ --- *
76 * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context
77 * @mp *d@ = fake destination
81 * Returns: Result, %$a^e \bmod m$%.
84 mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e)
87 d = mpmont_mul(mm, d, a, mm->r2);
88 d = mpmont_expr(mm, d, d, e);
89 d = mpmont_reduce(mm, d, d);
94 /*----- Test rig ----------------------------------------------------------*/
98 static int texp(dstr *v)
100 mp *m = *(mp **)v[0].buf;
101 mp *a = *(mp **)v[1].buf;
102 mp *b = *(mp **)v[2].buf;
103 mp *r = *(mp **)v[3].buf;
108 mpmont_create(&mm, m);
110 mr = mpmont_exp(&mm, MP_NEW, a, b);
113 fputs("\n*** montgomery modexp failed", stderr);
114 fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
115 fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
116 fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
117 fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
118 fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
129 assert(mparena_count(MPARENA_GLOBAL) == 0);
133 static test_chunk tests[] = {
134 { "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
138 int main(int argc, char *argv[])
141 test_run(argc, argv, tests, SRCDIR "/tests/mpmont");
147 /*----- That's all, folks -------------------------------------------------*/