3 * Generate Diffie-Hellman parameters
5 * (c) 1999 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
12 * Catacomb is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * Catacomb is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with Catacomb; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
30 #include <mLib/macros.h>
42 /*----- Main code ---------------------------------------------------------*/
46 * Arguments: @dh_param *dp@ = pointer to output parameter block
47 * @unsigned ql@ = length of %$q$% in bits, or zero
48 * @unsigned pl@ = length of %$p$% in bits
49 * @unsigned steps@ = number of steps to go
50 * @grand *r@ = random number source
51 * @pgen_proc *event@ = event handler function
52 * @void *ectx@ = argument for the event handler
54 * Returns: @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it didn't.
56 * Use: Generates Diffie-Hellman parameters.
58 * The parameters are a prime %$q$%, relatively small, and a
59 * large prime %$p = kq + 1$% for some %$k$%, together with a
60 * generator %$g$% of the cyclic subgroup of order %$q$%. These
61 * are actually the same as the DSA parameter set, but the
62 * generation algorithm is different. Also, if @ql@ is zero,
63 * this algorithm forces %$k = 2$%, and chooses %$g = 4$%. Make
64 * sure you have something interesting to do if you choose this
68 int dh_gen(dh_param *dp, unsigned ql, unsigned pl, unsigned steps, grand *r,
69 pgen_proc *event, void *ectx)
71 /* --- If @ql@ is zero, do the time consuming safe-prime thing --- */
74 pgen_simulprime sp[2];
77 mp *m = mprand(MP_NEW, pl - 1, r, 1);
79 sp[0].mul = MP_ONE; sp[0].add = MP_ZERO; sp[0].f = 0;
80 sp[1].mul = MP_TWO; sp[1].add = MP_ONE; sp[1].f = PGENF_KEEP;
81 ss.v = sp; ss.n = N(sp);
82 dp->q = pgen("p", MP_NEW, m, event, ectx, steps, pgen_simulstep, &ss,
83 rabin_iters(pl), pgen_simultest, &ss);
94 /* --- Otherwise the job is much simpler --- *
96 * But doesn't look it...
108 /* --- Generate @q@ first --- */
111 m = mprand(MP_NEW, ql, r, 1);
112 dp->q = pgen("q", MP_NEW, m, event, ectx, steps, pgen_filter, &c,
113 rabin_iters(ql), pgen_test, &rb);
117 /* --- Now pick a suitable @p@ --- */
119 m = mp_lsl(m, dp->q, 1);
120 x = mprand(MP_NEW, pl, r, 0);
121 y = MP_NEW; mp_div(0, &y, x, m);
123 x = mp_add(x, x, MP_ONE);
125 pfilt_create(&c.f, m);
127 dp->p = pgen("p", MP_NEW, x, event, ectx, steps, pgen_jump, &j,
128 rabin_iters(pl), pgen_test, &rb);
134 /* --- And finally a suitable @g@ --- */
136 mpmont_create(&p.mm, dp->p);
137 mp_div(&m, 0, dp->p, dp->q);
141 dp->g = pgen("g", MP_NEW, MP_NEW, event, ectx, 0, prim_step, &i,
143 mpmont_destroy(&p.mm);
149 /* --- Tidy up --- */
161 /*----- That's all, folks -------------------------------------------------*/