Diffie-Hellman parameter generation based on Lim-Lee primes.

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+/* -*-c-*-
+ *
+ * $Id: dh-limlee.c,v 1.1 2000/07/29 10:01:31 mdw Exp $
+ *
+ * Generate Diffie-Hellman parameters from Lim-Lee primes
+ *
+ * (c) 2000 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.
+ */
+
+/*----- Revision history --------------------------------------------------* 
+ *
+ * $Log: dh-limlee.c,v $
+ * Revision 1.1  2000/07/29 10:01:31  mdw
+ * Diffie-Hellman parameter generation based on Lim-Lee primes.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "dh.h"
+#include "limlee.h"
+#include "mpmont.h"
+#include "prim.h"
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- @dh_limlee@ --- *
+ *
+ * Arguments:  @dh_param *dp@ = pointer to output parameter block
+ *             @unsigned ql@ = length of smallest factor of %$(p - 1)/2$%
+ *             @unsigned pl@ = length of %$p$% in bits
+ *             @unsigned flags@ = other generation flags
+ *             @unsigned steps@ = number of steps to go
+ *             @grand *r@ = random number source
+ *              @pgen_proc *oev@ = outer event handler function
+ *              @void *oec@ = argument for the outer event handler
+ *              @pgen_proc *iev@ = inner event handler function
+ *              @void *iec@ = argument for the inner event handler
+ *              @size_t *nf@, @mp ***f@ = output array for factors
+ *
+ * Returns:    @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it didn't.
+ *
+ * Use:                Generates Diffie-Hellman parameters based on a Lim-Lee prime.
+ *
+ *             The modulus is a large prime %$p = 2 \prod q_i + 1$%, @pl@
+ *             bits long, where the %$q_i$% are smaller primes each at least
+ *             @ql@ bits long.  It is safe to set @nf@ and @f@ to zero if
+ *             you're not interested in the factor values.
+ *
+ *             The returned %$g$% generates a subgroup of order %$q_0$% (the
+ *             first factor, returned as @f[0]@), if the flag @DH_SUBGROUP@
+ *             is set on entry; otherwise %$g$% will have order
+ *             %$(p - 1)/2$%.
+ */
+
+int dh_limlee(dh_param *dp, unsigned ql, unsigned pl,
+             unsigned flags, unsigned steps, grand *r,
+             pgen_proc *oev, void *oec, pgen_proc *iev,
+             void *iec, size_t *nf, mp ***f)
+{
+  mp **ff;
+  size_t nff;
+  prim_ctx pc;
+  size_t i;
+  int j;
+  mp *pp;
+
+  /* --- Generate the Lim-Lee prime --- */
+
+  if ((dp->p = limlee("p", MP_NEW, MP_NEW, ql, pl,
+                     r, steps, oev, oec, iev, iec, &nff, &ff)) == 0)
+    return (PGEN_FAIL);
+  dp->q = mp_copy(ff[0]);
+
+  /* --- Now find a primitive element --- */
+
+  mpmont_create(&pc.mm, dp->p);
+  pp = mp_sub(MP_NEW, dp->p, MP_ONE);
+  if (flags & DH_SUBGROUP) {
+    pc.exp = MP_NEW;
+    mp_div(&pc.exp, 0, pp, dp->q);
+    pc.n = 0;
+    pc.f = 0;
+  } else {
+    pc.exp = MP_TWO;
+    pc.n = nff;
+    pc.f = xmalloc(nff * sizeof(mp *));
+    for (i = 0; i < nff; i++) {
+      pc.f[i] = MP_NEW;
+      mp_div(&pc.f[i], 0, pp, ff[i]);
+    }
+  }
+
+  j = 0;
+  dp->g = pgen("g", MP_NEW, MP_NEW, oev, oec,
+              0, prim_step, &j, 1, prim_test, &pc);
+
+  mp_drop(pp);
+  if (pc.f) {
+    for (i = 0; i < pc.n; i++)
+      mp_drop(pc.f[i]);
+    xfree(pc.f);
+  }
+  mpmont_destroy(&pc.mm);
+
+  /* --- Do something sensible with the list of primes --- */
+
+  if (dp->g && f) {
+    *f = ff;
+    *nf = nff;
+  } else {
+    for (i = 0; i < nff; i++)
+      mp_drop(ff[i]);
+    xfree(ff);
+  }
+
+  /* --- Tidy up and return --- */
+
+  if (!dp->g) {
+    mp_drop(dp->p);
+    mp_drop(dp->q);
+    return (PGEN_FAIL);
+  }
+  return (PGEN_DONE);
+}
+
+/*----- That's all, folks -------------------------------------------------*/