| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Generate KCDSA prime groups |
| 4 | * |
| 5 | * (c) 2006 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of Catacomb. |
| 11 | * |
| 12 | * Catacomb is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU Library General Public License as |
| 14 | * published by the Free Software Foundation; either version 2 of the |
| 15 | * License, or (at your option) any later version. |
| 16 | * |
| 17 | * Catacomb is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU Library General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU Library General Public |
| 23 | * License along with Catacomb; if not, write to the Free |
| 24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 25 | * MA 02111-1307, USA. |
| 26 | */ |
| 27 | |
| 28 | /*----- Header files ------------------------------------------------------*/ |
| 29 | |
| 30 | #include <mLib/macros.h> |
| 31 | |
| 32 | #include "dh.h" |
| 33 | #include "mprand.h" |
| 34 | #include "pgen.h" |
| 35 | #include "prim.h" |
| 36 | |
| 37 | /*----- Main code ---------------------------------------------------------*/ |
| 38 | |
| 39 | /* --- @dh_kcdsagen@ --- * |
| 40 | * |
| 41 | * Arguments: @dh_param *dp@ = pointer to output parameter block |
| 42 | * @unsigned ql@ = size of small factor of %$(p - 1)/2$% |
| 43 | * @unsigned pl@ = size of %$p$% in bits |
| 44 | * @unsigned flags@ = other generation flags |
| 45 | * @unsigned steps@ = number of steps to go |
| 46 | * @grand *r@ = random number source |
| 47 | * @pgen_proc *ev@ = event handler function |
| 48 | * @void *ec@ = context for the event handler |
| 49 | * |
| 50 | * Returns: @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it failed. |
| 51 | * |
| 52 | * Use: Generates a KCDSA prime group. That is, it chooses a prime |
| 53 | * %$p$%, such that $%p = 2 q v + 1$%, for primes %$q$% and |
| 54 | * %$v$%. The actual group of interest is the subgroup of order |
| 55 | * %$q$%. |
| 56 | */ |
| 57 | |
| 58 | int dh_kcdsagen(dh_param *dp, unsigned ql, unsigned pl, |
| 59 | unsigned flags, unsigned steps, grand *r, |
| 60 | pgen_proc *ev, void *ec) |
| 61 | { |
| 62 | pgen_filterctx pf; |
| 63 | pgen_simulprime sp[2]; |
| 64 | pgen_simulctx ss; |
| 65 | prim_ctx pc; |
| 66 | rabin rb; |
| 67 | int rc = PGEN_ABORT; |
| 68 | int i; |
| 69 | mp *x; |
| 70 | |
| 71 | /* --- First trick: find %$q$% --- */ |
| 72 | |
| 73 | pf.step = 2; |
| 74 | x = mprand(MP_NEW, pl - ql, r, 1); |
| 75 | x = pgen("v", x, x, ev, ec, |
| 76 | steps, pgen_filter, &pf, |
| 77 | rabin_iters(pl - ql), pgen_test, &rb); |
| 78 | if (!x) |
| 79 | goto fail_0; |
| 80 | |
| 81 | /* --- Second trick: find %$p$% and %$v$% --- */ |
| 82 | |
| 83 | x = mp_lsl(x, x, 1); |
| 84 | sp[0].add = MP_ZERO; sp[0].mul = MP_ONE; sp[0].f = 0; |
| 85 | sp[1].add = MP_ONE; sp[1].mul = x; sp[1].f = PGENF_KEEP; |
| 86 | ss.step = MP_TWO; ss.v = sp; ss.n = N(sp); |
| 87 | x = mprand(MP_NEW, ql, r, 1); |
| 88 | dp->q = pgen("p", MP_NEW, x, ev, ec, |
| 89 | steps, pgen_simulstep, &ss, |
| 90 | rabin_iters(ql), pgen_simultest, &ss); |
| 91 | mp_drop(sp[1].mul); |
| 92 | if (!dp->q) |
| 93 | goto fail_1; |
| 94 | dp->p = sp[1].u.x; |
| 95 | |
| 96 | /* --- Third trick: find a generator --- */ |
| 97 | |
| 98 | mpmont_create(&pc.mm, dp->p); |
| 99 | mp_div(&x, 0, dp->p, dp->q); |
| 100 | i = 0; |
| 101 | pc.exp = x; |
| 102 | pc.n = 0; |
| 103 | dp->g = pgen("g", MP_NEW, MP_NEW, ev, ec, |
| 104 | 0, prim_step, &i, 1, prim_test, &pc); |
| 105 | mpmont_destroy(&pc.mm); |
| 106 | if (!dp->g) |
| 107 | goto fail_2; |
| 108 | |
| 109 | rc = PGEN_DONE; |
| 110 | goto done; |
| 111 | |
| 112 | /* --- Tidying up and going home --- */ |
| 113 | |
| 114 | fail_2: |
| 115 | mp_drop(dp->p); |
| 116 | fail_1: |
| 117 | fail_0: |
| 118 | done: |
| 119 | mp_drop(x); |
| 120 | return (rc); |
| 121 | } |
| 122 | |
| 123 | /*----- That's all, folks -------------------------------------------------*/ |