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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: bbs-gen.c,v 1.6 2004/04/08 01:36:15 mdw Exp $ |
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4 | * |
5 | * Generate Blum integers |
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 | |
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30 | /*----- Header files ------------------------------------------------------*/ |
31 | |
32 | #include <stdio.h> |
33 | #include <stdlib.h> |
34 | #include <string.h> |
35 | |
36 | #include "bbs.h" |
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37 | #include "mp.h" |
38 | #include "mprand.h" |
39 | #include "pgen.h" |
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40 | #include "strongprime.h" |
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41 | |
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42 | /*----- Main code ---------------------------------------------------------*/ |
43 | |
44 | /* --- @bbs_gen@ --- * |
45 | * |
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46 | * Arguments: @bbs_priv *bp@ = pointer to parameter block |
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47 | * @unsigned nbits@ = number of bits in the modulus |
48 | * @grand *r@ = pointer to random number source |
49 | * @unsigned n@ = number of attempts to make |
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50 | * @pgen_proc *event@ = event handler function |
51 | * @void *ectx@ = argument for event handler |
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52 | * |
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53 | * Returns: If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@. |
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54 | * |
55 | * Use: Finds two prime numbers %$p'$% and %$q'$% such that both are |
56 | * congruent to %$3 \bmod 4$%, and $(p - 1)/2$% and |
57 | * %$(q - 1)/2$% have no common factors. The product %$n = pq$% |
58 | * is eminently suitable for use as a modulus in a Blum-Blum- |
59 | * Shub pseudorandom bit generator. |
60 | */ |
61 | |
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62 | int bbs_gen(bbs_priv *bp, unsigned nbits, grand *r, unsigned n, |
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63 | pgen_proc *event, void *ectx) |
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64 | { |
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65 | rabin rb; |
66 | pgen_safejumpctx j; |
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67 | pgen_gcdstepctx g; |
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68 | unsigned nb = nbits/2; |
69 | mp *x = MP_NEW; |
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70 | |
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71 | /* --- Generate @p@ --- */ |
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72 | |
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73 | again: |
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74 | if ((x = strongprime_setup("p", x, &j.jq, nb, r, n, event, ectx)) == 0) |
75 | goto fail_x; |
76 | bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_safejump, &j, |
77 | rabin_iters(nb), pgen_test, &rb); |
78 | pfilt_destroy(&j.jq); |
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79 | if (!bp->p) { |
80 | if (n) |
81 | goto fail_p; |
82 | goto again; |
83 | } |
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84 | |
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85 | /* --- Generate @q@ --- */ |
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86 | |
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87 | nb = nbits - nb; |
88 | if ((x = strongprime_setup("q", x, &g.jp, nb, r, n, event, ectx)) == 0) |
89 | goto fail_q; |
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90 | if ((x->v[0] & 3) != 3) |
91 | x = mp_add(x, x, g.jp.m); |
92 | pfilt_muladd(&g.jp, &g.jp, 2, 0); |
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93 | g.r = mp_lsr(MP_NEW, bp->p, 1); |
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94 | g.g = MP_NEW; |
95 | g.max = MP_ONE; |
96 | bp->q = pgen("q", MP_NEW, x, event, ectx, n, pgen_gcdstep, &g, |
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97 | rabin_iters(nb), pgen_test, &rb); |
98 | pfilt_destroy(&g.jp); |
99 | mp_drop(g.r); |
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100 | mp_drop(g.g); |
101 | if (!bp->q) { |
102 | if (n) |
103 | goto fail_q; |
104 | mp_drop(bp->p); |
105 | goto again; |
106 | } |
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107 | |
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108 | /* --- Compute @n@ --- */ |
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109 | |
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110 | bp->n = mp_mul(MP_NEW, bp->p, bp->q); |
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111 | mp_drop(x); |
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112 | return (PGEN_DONE); |
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113 | |
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114 | /* --- Tidy up if things went wrong --- */ |
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115 | |
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116 | fail_q: |
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117 | mp_drop(bp->p); |
118 | fail_p: |
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119 | mp_drop(x); |
120 | fail_x: |
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121 | return (PGEN_ABORT); |
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122 | } |
123 | |
124 | /*----- That's all, folks -------------------------------------------------*/ |