--- /dev/null
+/* -*-c-*-
+ *
+ * Generate KCDSA prime groups
+ *
+ * (c) 2006 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 "mprand.h"
+#include "pgen.h"
+#include "prim.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @dh_kcdsagen@ --- *
+ *
+ * Arguments: @dh_param *dp@ = pointer to output parameter block
+ * @unsigned ql@ = size of small factor of %$(p - 1)/2$%
+ * @unsigned pl@ = size of %$p$% in bits
+ * @unsigned flags@ = other generation flags
+ * @unsigned steps@ = number of steps to go
+ * @grand *r@ = random number source
+ * @pgen_proc *ev@ = event handler function
+ * @void *ec@ = context for the event handler
+ *
+ * Returns: @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it failed.
+ *
+ * Use: Generates a KCDSA prime group. That is, it chooses a prime
+ * %$p$%, such that $%p = 2 q v + 1$%, for primes %$q$% and
+ * %$v$%. The actual group of interest is the subgroup of order
+ * %$q$%.
+ */
+
+int dh_kcdsagen(dh_param *dp, unsigned ql, unsigned pl,
+ unsigned flags, unsigned steps, grand *r,
+ pgen_proc *ev, void *ec)
+{
+ pgen_filterctx pf;
+ pgen_simulprime sp[2];
+ pgen_simulctx ss;
+ prim_ctx pc;
+ rabin rb;
+ int rc = PGEN_ABORT;
+ int i;
+ mp *x;
+
+ /* --- First trick: find %$q$% --- */
+
+ pf.step = 2;
+ x = mprand(MP_NEW, pl - ql, r, 1);
+ x = pgen("v", x, x, ev, ec,
+ steps, pgen_filter, &pf,
+ rabin_iters(pl - ql), pgen_test, &rb);
+ if (!x)
+ goto fail_0;
+
+ /* --- Second trick: find %$p$% and %$v$% --- */
+
+ x = mp_lsl(x, x, 1);
+ sp[0].add = MP_ZERO; sp[0].mul = MP_ONE; sp[0].f = 0;
+ sp[1].add = MP_ONE; sp[1].mul = x; sp[1].f = PGENF_KEEP;
+ ss.step = MP_TWO; ss.v = sp; ss.n = N(sp);
+ x = mprand(MP_NEW, ql, r, 1);
+ dp->q = pgen("p", MP_NEW, x, ev, ec,
+ steps, pgen_simulstep, &ss,
+ rabin_iters(ql), pgen_simultest, &ss);
+ mp_drop(sp[0].mul);
+ if (!dp->q)
+ goto fail_1;
+ dp->p = sp[1].u.x;
+
+ /* --- Third trick: find a generator --- */
+
+ mpmont_create(&pc.mm, dp->p);
+ mp_div(&x, 0, dp->p, dp->q);
+ i = 0;
+ pc.exp = x;
+ pc.n = 0;
+ dp->g = pgen("g", MP_NEW, MP_NEW, ev, ec,
+ 0, prim_step, &i, 1, prim_test, &pc);
+ mpmont_destroy(&pc.mm);
+ if (!dp->g)
+ goto fail_2;
+
+ rc = PGEN_DONE;
+ goto done;
+
+ /* --- Tidying up and going home --- */
+
+fail_2:
+ mp_drop(dp->p);
+fail_1:
+fail_0:
+done:
+ mp_drop(x);
+ return (rc);
+}
+
+/*----- That's all, folks -------------------------------------------------*/