3 * $Id: rabin.c,v 1.3 1999/12/22 15:50:29 mdw Exp $
5 * Miller-Rabin primality test
7 * (c) 1999 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 /*----- Revision history --------------------------------------------------*
33 * Revision 1.3 1999/12/22 15:50:29 mdw
34 * Reworking for new prime-search system. Add function for working out how
35 * many iterations to use for a particular number.
37 * Revision 1.2 1999/12/10 23:29:48 mdw
38 * Change header file guard names.
40 * Revision 1.1 1999/11/19 13:17:57 mdw
41 * Prime number generator and tester.
45 /*----- Header files ------------------------------------------------------*/
48 #include "mpbarrett.h"
53 /*----- Main code ---------------------------------------------------------*/
55 /* --- @rabin_create@ --- *
57 * Arguments: @rabin *r@ = pointer to Rabin-Miller context
58 * @mp *m@ = pointer to number to test
62 * Use: Precomputes some useful values for performing the
63 * Miller-Rabin probabilistic primality test.
66 void rabin_create(rabin
*r
, mp
*m
)
68 mp
*m1
= mp_sub(MP_NEW
, m
, MP_ONE
);
72 /* --- Find @r@ and @s@ --- */
74 mpmont_create(&r
->mm
, m
);
77 while (mp_step(&sc
)) {
83 r
->r
= mp_lsr(MP_NEW
, m1
, s
);
85 /* --- Compute %$(m - 1)R \bmod m$% --- */
87 r
->m1
= mp_sub(MP_NEW
, m
, r
->mm
.r
);
91 /* --- @rabin_destroy@ --- *
93 * Arguments: @rabin *r@ = pointer to Rabin-Miller context
97 * Use: Disposes of a Rabin-Miller context when it's no longer
101 void rabin_destroy(rabin
*r
)
105 mpmont_destroy(&r
->mm
);
108 /* --- @rabin_test@ --- *
110 * Arguments: @rabin *r@ = pointer to Rabin-Miller context
111 * @mp *g@ = base to test the number against
113 * Returns: Either @PGEN_FAIL@ if the test failed, or @PGEN_PASS@
116 * Use: Performs a single iteration of the Rabin-Miller primality
120 int rabin_test(rabin
*r
, mp
*g
)
123 mp
*dd
, *spare
= MP_NEW
;
127 /* --- Calculate %$y R = g^r R \bmod m$% --- *
129 * If %$y = 1$% or %$y = m - 1$% then %$m$% is prime. If course, note that
130 * @y@ here has an extra factor of %$R$%.
133 y
= mpmont_expr(&r
->mm
, MP_NEW
, g
, r
->r
);
134 if (MP_CMP(y
, ==, r
->mm
.r
) || MP_CMP(y
, ==, r
->m1
)) {
139 /* --- Now for the main loop --- *
141 * If %$y^{2^j} \ne m - 1$% for any %$0 \le j < s$% then %$m$% is
142 * composite. Of course, %$j = 0$% has already been tested.
145 for (j
= 1; j
< r
->s
; j
++) {
146 dd
= mp_sqr(spare
, y
);
147 dd
= mpmont_reduce(&r
->mm
, dd
, dd
);
149 if (MP_CMP(y
, ==, r
->mm
.r
))
151 if (MP_CMP(y
, ==, r
->m1
)) {
166 /* --- @rabin_iters@ --- *
168 * Arguments: @unsigned len@ = number of bits in value
170 * Returns: Number of iterations recommended.
172 * Use: Returns the recommended number of iterations to ensure that a
173 * number with @len@ bits is really prime.
176 int rabin_iters(unsigned len
)
198 /* --- Binary search through the table --- */
201 q
= tab
+ (sizeof(tab
)/sizeof(tab
[0]));
206 if (len
>= p
[i
].b
&& len
< p
[i
+ 1].b
)
216 /*----- That's all, folks -------------------------------------------------*/