--- /dev/null
+/* -*-c-*-
+ *
+ * Generate Diffie-Hellman parameters
+ *
+ * (c) 1999 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------*
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/macros.h>
+
+#include "dh.h"
+#include "grand.h"
+#include "mp.h"
+#include "mpmont.h"
+#include "mprand.h"
+#include "pfilt.h"
+#include "pgen.h"
+#include "prim.h"
+#include "rabin.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @dh_gen@ --- *
+ *
+ * Arguments: @dh_param *dp@ = pointer to output parameter block
+ * @unsigned ql@ = length of %$q$% in bits, or zero
+ * @unsigned pl@ = length of %$p$% in bits
+ * @unsigned steps@ = number of steps to go
+ * @grand *r@ = random number source
+ * @pgen_proc *event@ = event handler function
+ * @void *ectx@ = argument for the event handler
+ *
+ * Returns: @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it didn't.
+ *
+ * Use: Generates Diffie-Hellman parameters.
+ *
+ * The parameters are a prime %$q$%, relatively small, and a
+ * large prime %$p = kq + 1$% for some %$k$%, together with a
+ * generator %$g$% of the cyclic subgroup of order %$q$%. These
+ * are actually the same as the DSA parameter set, but the
+ * generation algorithm is different. Also, if @ql@ is zero,
+ * this algorithm forces %$k = 2$%, and chooses %$g = 4$%. Make
+ * sure you have something interesting to do if you choose this
+ * option.
+ */
+
+int dh_gen(dh_param *dp, unsigned ql, unsigned pl, unsigned steps, grand *r,
+ pgen_proc *event, void *ectx)
+{
+ /* --- If @ql@ is zero, do the time consuming safe-prime thing --- */
+
+ if (!ql) {
+ pgen_simulprime sp[2];
+ pgen_simulctx ss;
+
+ mp *m = mprand(MP_NEW, pl - 1, r, 1);
+ ss.step = MP_TWO;
+ sp[0].mul = MP_ONE; sp[0].add = MP_ZERO; sp[0].f = 0;
+ sp[1].mul = MP_TWO; sp[1].add = MP_ONE; sp[1].f = PGENF_KEEP;
+ ss.v = sp; ss.n = N(sp);
+ dp->q = pgen("p", MP_NEW, m, event, ectx, steps, pgen_simulstep, &ss,
+ rabin_iters(pl), pgen_simultest, &ss);
+ mp_drop(m);
+ if (!dp->q) {
+ mp_drop(sp[1].u.x);
+ return (PGEN_ABORT);
+ }
+ dp->p = sp[1].u.x;
+ dp->g = MP_FOUR;
+ return (PGEN_DONE);
+ }
+
+ /* --- Otherwise the job is much simpler --- *
+ *
+ * But doesn't look it...
+ */
+
+ else {
+ pgen_filterctx c;
+ pgen_jumpctx j;
+ rabin rb;
+ prim_ctx p;
+ int i;
+ mp *m = MP_NEW;
+ mp *x, *y;
+
+ /* --- Generate @q@ first --- */
+
+ c.step = 2;
+ m = mprand(MP_NEW, ql, r, 1);
+ dp->q = pgen("q", MP_NEW, m, event, ectx, steps, pgen_filter, &c,
+ rabin_iters(ql), pgen_test, &rb);
+ if (!dp->q)
+ goto fail_q;
+
+ /* --- Now pick a suitable @p@ --- */
+
+ m = mp_lsl(m, dp->q, 1);
+ x = mprand(MP_NEW, pl, r, 0);
+ y = MP_NEW; mp_div(0, &y, x, m);
+ x = mp_sub(x, x, y);
+ x = mp_add(x, x, MP_ONE);
+ mp_drop(y);
+ pfilt_create(&c.f, m);
+ j.j = &c.f;
+ dp->p = pgen("p", MP_NEW, x, event, ectx, steps, pgen_jump, &j,
+ rabin_iters(pl), pgen_test, &rb);
+ pfilt_destroy(&c.f);
+ mp_drop(x);
+ if (!dp->p)
+ goto fail_p;
+
+ /* --- And finally a suitable @g@ --- */
+
+ mpmont_create(&p.mm, dp->p);
+ mp_div(&m, 0, dp->p, dp->q);
+ i = 0;
+ p.exp = m;
+ p.n = 0;
+ dp->g = pgen("g", MP_NEW, MP_NEW, event, ectx, 0, prim_step, &i,
+ 1, prim_test, &p);
+ mpmont_destroy(&p.mm);
+ if (!dp->g)
+ goto fail_g;
+ mp_drop(m);
+ return (PGEN_DONE);
+
+ /* --- Tidy up --- */
+
+ fail_g:
+ mp_drop(dp->q);
+ fail_q:
+ mp_drop(dp->p);
+ fail_p:
+ mp_drop(m);
+ return (PGEN_ABORT);
+ }
+}
+
+/*----- That's all, folks -------------------------------------------------*/