| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: dh-prime.c,v 1.1 1999/11/20 22:24:44 mdw Exp $ |
| 4 | * |
| 5 | * Generate (safe) Diffie-Hellman primes |
| 6 | * |
| 7 | * (c) 1999 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: dh-prime.c,v $ |
| 33 | * Revision 1.1 1999/11/20 22:24:44 mdw |
| 34 | * Add Diffie-Hellman support. |
| 35 | * |
| 36 | */ |
| 37 | |
| 38 | /*----- Header files ------------------------------------------------------*/ |
| 39 | |
| 40 | #include <stdio.h> |
| 41 | #include <stdlib.h> |
| 42 | #include <string.h> |
| 43 | |
| 44 | #include "dh.h" |
| 45 | #include "mp.h" |
| 46 | #include "pgen.h" |
| 47 | #include "rabin.h" |
| 48 | |
| 49 | /*----- Main code ---------------------------------------------------------*/ |
| 50 | |
| 51 | /* --- @dh_prime@ --- * |
| 52 | * |
| 53 | * Arguments: @mp *s@ = start point for search (must be odd) |
| 54 | * @size_t n@ = number of concerted attempts to make, or zero |
| 55 | * @void (*proc)(int ev, void *p)@ = event handler |
| 56 | * @void *p@ = argument for event handler |
| 57 | * |
| 58 | * Returns: A prime number %$p$% where %$p = 2q + 1$% for prime %$q$%. |
| 59 | * |
| 60 | * Use: Finds a safe prime by sequential search from a given starting |
| 61 | * point. If it fails, a null pointer is returned. |
| 62 | * |
| 63 | * The event handler is informed of the progress of the search. |
| 64 | * It may abort the search at any time by returning a nonzero |
| 65 | * value. |
| 66 | */ |
| 67 | |
| 68 | mp *dh_prime(mp *s, size_t n, |
| 69 | int (*proc)(int /*ev*/, void */*p*/), void *arg) |
| 70 | { |
| 71 | pgen pq, pp; |
| 72 | int rc_q, rc_p; |
| 73 | mpw bw; |
| 74 | mp b; |
| 75 | |
| 76 | /* --- Initialize prime generators --- */ |
| 77 | |
| 78 | rc_q = pgen_create(&pq, s); |
| 79 | rc_p = pgen_muladd(&pp, &pq, 2, 1); |
| 80 | mp_build(&b, &bw, &bw + 1); |
| 81 | |
| 82 | /* --- Now step along until something crops up --- */ |
| 83 | |
| 84 | for (;;) { |
| 85 | rabin rq, rp; |
| 86 | int i; |
| 87 | |
| 88 | /* --- Don't do expensive testing unless necessary --- */ |
| 89 | |
| 90 | if (rc_q == PGEN_PRIME && rc_p == PGEN_PRIME) |
| 91 | break; |
| 92 | if (rc_q == PGEN_COMPOSITE || rc_p == PGEN_COMPOSITE) |
| 93 | goto next; |
| 94 | |
| 95 | /* --- Initialize Rabin-Miller contexts --- */ |
| 96 | |
| 97 | if (rc_q == PGEN_MAYBE) |
| 98 | rabin_create(&rq, pq.m); |
| 99 | if (rc_p == PGEN_MAYBE) |
| 100 | rabin_create(&rp, pp.m); |
| 101 | |
| 102 | /* --- Now run tests on each in turn --- * |
| 103 | * |
| 104 | * On the sorts of modulus sizes which work well in discrete log |
| 105 | * problems, five tests should be sufficient. |
| 106 | */ |
| 107 | |
| 108 | for (i = 0; i < 5; i++) { |
| 109 | bw = ptab[i]; |
| 110 | if (rc_q == PGEN_MAYBE && |
| 111 | (rc_q = rabin_test(&rq, &b)) == PGEN_COMPOSITE) |
| 112 | break; |
| 113 | if (rc_p == PGEN_MAYBE && |
| 114 | (rc_p = rabin_test(&rp, &b)) == PGEN_COMPOSITE) |
| 115 | break; |
| 116 | if (proc && proc(DHEV_PASS, arg)) |
| 117 | break; |
| 118 | } |
| 119 | if (rc_q != PGEN_PRIME) |
| 120 | rabin_destroy(&rq); |
| 121 | if (rc_p != PGEN_PRIME) |
| 122 | rabin_destroy(&rp); |
| 123 | |
| 124 | /* --- If the tests passed, accept the numbers --- */ |
| 125 | |
| 126 | if (i >= 5) |
| 127 | break; |
| 128 | if (proc && proc(DHEV_FAIL, arg)) |
| 129 | goto fail; |
| 130 | if (n) { |
| 131 | n--; |
| 132 | if (!n) |
| 133 | goto fail; |
| 134 | } |
| 135 | |
| 136 | /* --- Step the contexts on --- */ |
| 137 | |
| 138 | next: |
| 139 | rc_q = pgen_step(&pq, 2); |
| 140 | rc_p = pgen_step(&pp, 4); |
| 141 | } |
| 142 | |
| 143 | /* --- Return a result --- */ |
| 144 | |
| 145 | { |
| 146 | mp *p = MP_COPY(pp.m); |
| 147 | pgen_destroy(&pq); |
| 148 | pgen_destroy(&pp); |
| 149 | return (p); |
| 150 | } |
| 151 | |
| 152 | /* --- Failure --- */ |
| 153 | |
| 154 | fail: |
| 155 | pgen_destroy(&pq); |
| 156 | pgen_destroy(&pp); |
| 157 | return (0); |
| 158 | } |
| 159 | |
| 160 | /*----- That's all, folks -------------------------------------------------*/ |