| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: ec-exp.c,v 1.1 2004/04/01 12:50:09 mdw Exp $ |
| 4 | * |
| 5 | * Point multiplication for elliptic curves |
| 6 | * |
| 7 | * (c) 2004 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Catacomb. |
| 13 | * |
| 14 | * Catacomb is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU Library General Public License as |
| 16 | * published by the Free Software Foundation; either version 2 of the |
| 17 | * License, or (at your option) any later version. |
| 18 | * |
| 19 | * Catacomb is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU Library General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Library General Public |
| 25 | * License along with Catacomb; if not, write to the Free |
| 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Revision history --------------------------------------------------* |
| 31 | * |
| 32 | * $Log: ec-exp.c,v $ |
| 33 | * Revision 1.1 2004/04/01 12:50:09 mdw |
| 34 | * Add cyclic group abstraction, with test code. Separate off exponentation |
| 35 | * functions for better static linking. Fix a buttload of bugs on the way. |
| 36 | * Generally ensure that negative exponents do inversion correctly. Add |
| 37 | * table of standard prime-field subgroups. (Binary field subgroups are |
| 38 | * currently unimplemented but easy to add if anyone ever finds a good one.) |
| 39 | * |
| 40 | */ |
| 41 | |
| 42 | /*----- Header files ------------------------------------------------------*/ |
| 43 | |
| 44 | #include "ec.h" |
| 45 | #include "ec-exp.h" |
| 46 | |
| 47 | /*----- Main code ---------------------------------------------------------*/ |
| 48 | |
| 49 | /* --- @ec_imul@, @ec_mul@ --- * |
| 50 | * |
| 51 | * Arguments: @ec_curve *c@ = pointer to an elliptic curve |
| 52 | * @ec *d@ = pointer to the destination point |
| 53 | * @const ec *p@ = pointer to the generator point |
| 54 | * @mp *n@ = integer multiplier |
| 55 | * |
| 56 | * Returns: The destination @d@. |
| 57 | * |
| 58 | * Use: Multiplies a point by a scalar, returning %$n p$%. The |
| 59 | * @imul@ variant uses internal representations for argument |
| 60 | * and result. |
| 61 | */ |
| 62 | |
| 63 | ec *ec_imul(ec_curve *c, ec *d, const ec *p, mp *n) |
| 64 | { |
| 65 | ec t = EC_INIT; |
| 66 | |
| 67 | EC_COPY(&t, p); |
| 68 | if (t.x && (n->f & MP_BURN)) |
| 69 | t.x->f |= MP_BURN; |
| 70 | MP_SHRINK(n); |
| 71 | EC_SETINF(d); |
| 72 | if (MP_LEN(n) == 0) |
| 73 | ; |
| 74 | else { |
| 75 | if (n->f & MP_NEG) |
| 76 | EC_NEG(c, &t, &t); |
| 77 | if (MP_LEN(n) < EXP_THRESH) |
| 78 | EXP_SIMPLE(*d, t, n); |
| 79 | else |
| 80 | EXP_WINDOW(*d, t, n); |
| 81 | } |
| 82 | EC_DESTROY(&t); |
| 83 | return (d); |
| 84 | } |
| 85 | |
| 86 | ec *ec_mul(ec_curve *c, ec *d, const ec *p, mp *n) |
| 87 | { |
| 88 | EC_IN(c, d, p); |
| 89 | ec_imul(c, d, d, n); |
| 90 | return (EC_OUT(c, d, d)); |
| 91 | } |
| 92 | |
| 93 | /* --- @ec_mmul@, @ec_immul@ --- * |
| 94 | * |
| 95 | * Arguments: @ec_curve *c@ = pointer to an elliptic curve |
| 96 | * @ec *d@ = pointer to the destination point |
| 97 | * @const ec_mulfactor *f@ = pointer to vector of factors |
| 98 | * @size_t n@ = number of factors |
| 99 | * |
| 100 | * Returns: The destination @d@. |
| 101 | * |
| 102 | * Use: Does simultaneous point multiplication. The @immul@ variant |
| 103 | * uses internal representations for arguments and result. |
| 104 | */ |
| 105 | |
| 106 | #undef EXP_WINSZ |
| 107 | #define EXP_WINSZ 3 |
| 108 | |
| 109 | static ec *immul(ec_curve *c, ec *d, ec_mulfactor *f, size_t n) |
| 110 | { |
| 111 | size_t i; |
| 112 | |
| 113 | for (i = 0; i < n; i++) { |
| 114 | MP_SHRINK(f[i].exp); |
| 115 | if (f[i].exp->f & MP_NEG) |
| 116 | EC_NEG(c, &f[i].base, &f[i].base); |
| 117 | if (f[i].base.x && f[i].exp->f & MP_BURN) |
| 118 | f[i].base.x->f |= MP_BURN; |
| 119 | } |
| 120 | EC_SETINF(d); |
| 121 | EXP_SIMUL(*d, f, n); |
| 122 | for (i = 0; i < n; i++) |
| 123 | EC_DESTROY(&f[i].base); |
| 124 | xfree(f); |
| 125 | return (d); |
| 126 | } |
| 127 | |
| 128 | ec *ec_immul(ec_curve *c, ec *d, const ec_mulfactor *f, size_t n) |
| 129 | { |
| 130 | ec_mulfactor *ff = xmalloc(n * sizeof(ec_mulfactor)); |
| 131 | size_t i; |
| 132 | |
| 133 | for (i = 0; i < n; i++) { |
| 134 | EC_CREATE(&ff[i].base); |
| 135 | EC_COPY(&ff[i].base, &f[i].base); |
| 136 | ff[i].exp = f[i].exp; |
| 137 | } |
| 138 | return (immul(c, d, ff, n)); |
| 139 | } |
| 140 | |
| 141 | ec *ec_mmul(ec_curve *c, ec *d, const ec_mulfactor *f, size_t n) |
| 142 | { |
| 143 | ec_mulfactor *ff = xmalloc(n * sizeof(ec_mulfactor)); |
| 144 | size_t i; |
| 145 | |
| 146 | for (i = 0; i < n; i++) { |
| 147 | EC_CREATE(&ff[i].base); |
| 148 | EC_IN(c, &ff[i].base, &f[i].base); |
| 149 | ff[i].exp = f[i].exp; |
| 150 | } |
| 151 | immul(c, d, ff, n); |
| 152 | return (EC_OUT(c, d, d)); |
| 153 | } |
| 154 | |
| 155 | /*----- That's all, folks -------------------------------------------------*/ |