3 * $Id: dh-limlee.c,v 1.2 2000/07/29 17:02:00 mdw Exp $
5 * Generate Diffie-Hellman parameters from Lim-Lee primes
7 * (c) 2000 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 --------------------------------------------------*
32 * $Log: dh-limlee.c,v $
33 * Revision 1.2 2000/07/29 17:02:00 mdw
34 * (dh_limlee): Bug fix. Return @dp->q@ as the subgroup order, which isn't
35 * necessarily the first factor.
37 * Revision 1.1 2000/07/29 10:01:31 mdw
38 * Diffie-Hellman parameter generation based on Lim-Lee primes.
42 /*----- Header files ------------------------------------------------------*/
49 /*----- Main code ---------------------------------------------------------*/
51 /* --- @dh_limlee@ --- *
53 * Arguments: @dh_param *dp@ = pointer to output parameter block
54 * @unsigned ql@ = length of smallest factor of %$(p - 1)/2$%
55 * @unsigned pl@ = length of %$p$% in bits
56 * @unsigned flags@ = other generation flags
57 * @unsigned steps@ = number of steps to go
58 * @grand *r@ = random number source
59 * @pgen_proc *oev@ = outer event handler function
60 * @void *oec@ = argument for the outer event handler
61 * @pgen_proc *iev@ = inner event handler function
62 * @void *iec@ = argument for the inner event handler
63 * @size_t *nf@, @mp ***f@ = output array for factors
65 * Returns: @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it didn't.
67 * Use: Generates Diffie-Hellman parameters based on a Lim-Lee prime.
69 * The modulus is a large prime %$p = 2 \prod q_i + 1$%, @pl@
70 * bits long, where the %$q_i$% are smaller primes each at least
71 * @ql@ bits long. It is safe to set @nf@ and @f@ to zero if
72 * you're not interested in the factor values.
74 * The returned %$g$% generates a subgroup of order %$q_0$% (the
75 * first factor, returned as @f[0]@), if the flag @DH_SUBGROUP@
76 * is set on entry; otherwise %$g$% will have order
80 int dh_limlee(dh_param *dp, unsigned ql, unsigned pl,
81 unsigned flags, unsigned steps, grand *r,
82 pgen_proc *oev, void *oec, pgen_proc *iev,
83 void *iec, size_t *nf, mp ***f)
92 /* --- Generate the Lim-Lee prime --- */
94 if ((dp->p = limlee("p", MP_NEW, MP_NEW, ql, pl,
95 r, steps, oev, oec, iev, iec, &nff, &ff)) == 0)
98 /* --- Now find a primitive element --- */
100 mpmont_create(&pc.mm, dp->p);
101 pp = mp_sub(MP_NEW, dp->p, MP_ONE);
102 if (flags & DH_SUBGROUP) {
103 dp->q = mp_copy(ff[0]);
105 mp_div(&pc.exp, 0, pp, dp->q);
109 dp->q = mp_lsr(MP_NEW, dp->p, 1);
112 pc.f = xmalloc(nff * sizeof(mp *));
113 for (i = 0; i < nff; i++) {
115 mp_div(&pc.f[i], 0, pp, ff[i]);
120 dp->g = pgen("g", MP_NEW, MP_NEW, oev, oec,
121 0, prim_step, &j, 1, prim_test, &pc);
125 for (i = 0; i < pc.n; i++)
129 mpmont_destroy(&pc.mm);
131 /* --- Do something sensible with the list of primes --- */
137 for (i = 0; i < nff; i++)
142 /* --- Tidy up and return --- */
152 /*----- That's all, folks -------------------------------------------------*/