--- /dev/null
+/* -*-c-*-
+ *
+ * $Id: mpmont-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
+ *
+ * Modular exponentiation with Montgomery reduction
+ *
+ * (c) 2004 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: mpmont-exp.c,v $
+ * Revision 1.1 2004/04/01 12:50:09 mdw
+ * Add cyclic group abstraction, with test code. Separate off exponentation
+ * functions for better static linking. Fix a buttload of bugs on the way.
+ * Generally ensure that negative exponents do inversion correctly. Add
+ * table of standard prime-field subgroups. (Binary field subgroups are
+ * currently unimplemented but easy to add if anyone ever finds a good one.)
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "mp.h"
+#include "mpmont.h"
+#include "mpmont-exp.h"
+
+/*----- Exponentiation ----------------------------------------------------*/
+
+/* --- @mpmont_expr@ --- *
+ *
+ * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context
+ * @mp *d@ = fake destination
+ * @mp *a@ = base
+ * @mp *e@ = exponent
+ *
+ * Returns: Result, %$(a R^{-1})^e R \bmod m$%.
+ */
+
+mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
+{
+ mp *x = MP_COPY(mm->r);
+ mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
+
+ MP_COPY(a);
+ MP_SHRINK(e);
+ if (e->f & MP_NEG) {
+ mp *g = MP_NEW;
+ a = mpmont_reduce(mm, a, a);
+ mp_gcd(&g, 0, &a, mm->m, a);
+ assert(MP_EQ(g, MP_ONE));
+ a = mpmont_mul(mm, a, a, mm->r2);
+ mp_drop(g);
+ }
+ if (MP_LEN(e) == 0)
+ ;
+ else if (MP_LEN(e) < EXP_THRESH)
+ EXP_SIMPLE(x, a, e);
+ else
+ EXP_WINDOW(x, a, e);
+ mp_drop(d);
+ mp_drop(spare);
+ mp_drop(a);
+ return (x);
+}
+
+/* --- @mpmont_exp@ --- *
+ *
+ * Arguments: @mpmont *mm@ = pointer to Montgomery reduction context
+ * @mp *d@ = fake destination
+ * @mp *a@ = base
+ * @mp *e@ = exponent
+ *
+ * Returns: Result, %$a^e \bmod m$%.
+ */
+
+mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e)
+{
+ e = MP_COPY(e);
+ d = mpmont_mul(mm, d, a, mm->r2);
+ d = mpmont_expr(mm, d, d, e);
+ d = mpmont_reduce(mm, d, d);
+ MP_DROP(e);
+ return (d);
+}
+
+/*----- Test rig ----------------------------------------------------------*/
+
+#ifdef TEST_RIG
+
+static int texp(dstr *v)
+{
+ mp *m = *(mp **)v[0].buf;
+ mp *a = *(mp **)v[1].buf;
+ mp *b = *(mp **)v[2].buf;
+ mp *r = *(mp **)v[3].buf;
+ mp *mr;
+ int ok = 1;
+
+ mpmont mm;
+ mpmont_create(&mm, m);
+
+ mr = mpmont_exp(&mm, MP_NEW, a, b);
+
+ if (!MP_EQ(mr, r)) {
+ fputs("\n*** montgomery modexp failed", stderr);
+ fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
+ fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
+ fputs("\n e = ", stderr); mp_writefile(b, stderr, 10);
+ fputs("\n r = ", stderr); mp_writefile(r, stderr, 10);
+ fputs("\nmr = ", stderr); mp_writefile(mr, stderr, 10);
+ fputc('\n', stderr);
+ ok = 0;
+ }
+
+ MP_DROP(m);
+ MP_DROP(a);
+ MP_DROP(b);
+ MP_DROP(r);
+ MP_DROP(mr);
+ mpmont_destroy(&mm);
+ assert(mparena_count(MPARENA_GLOBAL) == 0);
+ return ok;
+}
+
+
+static test_chunk tests[] = {
+ { "exp", texp, { &type_mp, &type_mp, &type_mp, &type_mp, 0 } },
+ { 0, 0, { 0 } },
+};
+
+int main(int argc, char *argv[])
+{
+ sub_init();
+ test_run(argc, argv, tests, SRCDIR "/tests/mpmont");
+ return (0);
+}
+
+#endif
+
+/*----- That's all, folks -------------------------------------------------*/