+++ /dev/null
-/* -*-c-*-
- *
- * Key length conversions
- *
- * (c) 2007 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 <math.h>
-
-#include "keysz.h"
-
-/*----- Main code ---------------------------------------------------------*/
-
-/* --- Primitive conversions --- */
-
-static double fromnfs(double nbits)
-{
- /* --- Magic taken from P1363 --- */
-#define LOG2 0.6931471805599453094172321214581765680755
-#define MAGIC 8.567936 /* = 17.135872 / 2 */
- double z = log(nbits * LOG2)/LOG2;
- return 4.0/3.0 * pow(3 * nbits * z*z, 1.0/3.0) - MAGIC;
-}
-
-static double tonfs(double nbits)
-{
- double hi, lo, mid, val;
-
- /* --- Find upper and lower bounds --- */
-
- for (hi = nbits; fromnfs(hi) < nbits; hi *= 2);
- for (lo = nbits; fromnfs(lo) > nbits; lo /= 2);
-
- /* --- Bisect the interval until we get an answer --- */
-
-#define THRESH 0.01
- for (;;) {
- mid = (hi + lo)/2;
- val = fromnfs(mid);
- if (fabs(val - nbits) < THRESH)
- return (mid);
- else if (val < nbits)
- lo = mid;
- else
- hi = mid;
- }
-}
-
-static double torho(double nbits) { return 2*nbits; }
-static double fromrho(double nbits) { return nbits/2; }
-
-/* --- @keysz_fromdl@, @_fromschnorr@, @_fromif@, @_fromec@ --- *
- *
- * Arguments: @double nbits@ = key size
- *
- * Returns: Equivalent symmetric key size.
- *
- * Use: Converts key lengths of various kinds of reference problems
- * to (roughly) equivalent symmetric key sizes.
- *
- * * Given the bit length of %$p$%, @keysz_fromdl@ returns a
- * key size representing the difficulty of computing
- * discrete logarithms in %$\gf{p}$%, for %$p$% prime or a
- * small power of a prime.
- *
- * * Given the bit length of %$r$%, @keysz_fromschnorr@
- * returns a key size representing the difficulty of
- * computing discrete logarithms in a subgroup of %$\gf{q}$%
- * of order %$r$%.
- *
- * * Given the bit length of %$n$%, @keysz_fromif@ returns a
- * key size representing the difficulty of factoring a
- * `hard' number %$n = p q$%, where %$p$% and %$q$% are
- * primes of (near enough) the same length.
- *
- * * Given the bit length of %$r$%, @keysz_fromec@ returns a
- * key size representing the difficulty of computing
- * discrete logarithms in a subgroup of order-%$r$% of an
- * elliptic curve over a finite field.
- *
- * These functions take and return @double@ rather than an
- * integer type in order to preserve precision between
- * conversions.
- */
-
-#define CONVERSIONS(_) \
- _(dl, nfs) \
- _(schnorr, rho) \
- _(if, nfs) \
- _(ec, rho)
-
-#define DEFINE_FROM(what, how) \
- double keysz_from##what(double nbits) { return from##how(nbits); }
-
-CONVERSIONS(DEFINE_FROM)
-
-/* --- @keysz_todl@, @_toschnorr@, @_toif@, @_toec@ --- *
- *
- * Arguments: @unsigned long nbits@ = symmetric key size
- *
- * Returns: Equivalent key size.
- *
- * Use: Converts symmetric key sizes to (roughly) equivalent key
- * sizes for various kinds of reference problems. These are the
- * approximate inverses of the functions above.
- */
-
-#define DEFINE_TO(what, how) \
- double keysz_to##what(double nbits) { return to##how(nbits); }
-
-CONVERSIONS(DEFINE_TO)
-
-/*----- Interactive mode for testing --------------------------------------*/
-
-#ifdef TEST_RIG
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
-static const struct entry {
- const char *name;
- double (*func)(double);
-} tab[] = {
-#define ENTRY_FROM(what, how) { "from" #what, keysz_from##what },
-#define ENTRY_TO(what, how) { "to" #what, keysz_to##what },
- CONVERSIONS(ENTRY_FROM)
- CONVERSIONS(ENTRY_TO)
- { 0 }
-};
-
-int main(int argc, char *argv[])
-{
- const struct entry *e;
- double d;
-
- if (!argv[1]) {
- fprintf(stderr, "conversions:");
- for (e = tab; e->name; e++) fprintf(stderr, " %s", e->name);
- putc('\n', stderr);
- return (1);
- }
- for (e = tab; e->name && strcmp(e->name, argv[1]); e++);
- if (!e) {
- fprintf(stderr, "unknown conversion `%s'\n", argv[1]);
- return (1);
- }
- for (argv += 2; *argv; argv++) {
- d = strtod(*argv, 0);
- printf("%s(%g) = %g\n", e->name, d, e->func(d));
- }
- return (0);
-}
-
-#endif
-
-/*----- That's all, folks -------------------------------------------------*/
projects / u / mdw / catacomb / blobdiff