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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: pgen-safe.c,v 1.4 2000/07/03 18:09:27 mdw Exp $ |
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4 | * |
5 | * Safe prime generation |
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: pgen-safe.c,v $ |
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33 | * Revision 1.4 2000/07/03 18:09:27 mdw |
34 | * Bug fix to the GCD check. With any luck, this is the last of these to |
35 | * need nailing to the wall. |
36 | * |
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37 | * Revision 1.3 2000/06/17 11:52:36 mdw |
38 | * Signal a pgen abort if the jump and base share a common factor. |
39 | * |
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40 | * Revision 1.2 2000/02/12 18:21:03 mdw |
41 | * Overhaul of key management (again). |
42 | * |
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43 | * Revision 1.1 1999/12/22 16:01:34 mdw |
44 | * Find `safe' primes (i.e., %$p = 2q + 1$%). |
45 | * |
46 | */ |
47 | |
48 | /*----- Header files ------------------------------------------------------*/ |
49 | |
50 | #include "mp.h" |
51 | #include "mprand.h" |
52 | #include "pgen.h" |
53 | |
54 | /*----- Main code ---------------------------------------------------------*/ |
55 | |
56 | /* --- @pgen_safestep@ --- * |
57 | * |
58 | * Steps two numbers, %$q$% and %$p = 2q + 1$%, such that neither has any |
59 | * small factors. %$p$% is put in the event block. |
60 | */ |
61 | |
62 | int pgen_safestep(int rq, pgen_event *ev, void *p) |
63 | { |
64 | pgen_safestepctx *c = p; |
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65 | int rc = PGEN_ABORT, qrc = 0; |
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66 | |
67 | switch (rq) { |
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68 | |
69 | /* --- Set up the contexts --- */ |
70 | |
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71 | case PGEN_BEGIN: { |
72 | mp *p = mp_split(MP_COPY(ev->m)); |
73 | mp *q; |
74 | p->v[0] |= 3; |
75 | q = mp_lsr(MP_NEW, p, 1); |
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76 | rc = pfilt_create(&c->p, p); |
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77 | qrc = pfilt_create(&c->q, q); |
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78 | mp_drop(p); mp_drop(q); |
79 | } break; |
80 | |
81 | /* --- Step along --- */ |
82 | |
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83 | case PGEN_TRY: |
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84 | mp_drop(ev->m); |
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85 | rc = pfilt_step(&c->p, 4); |
86 | qrc = pfilt_step(&c->q, 2); |
87 | break; |
88 | |
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89 | break; |
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90 | |
91 | /* --- Tidy the toys away --- */ |
92 | |
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93 | case PGEN_DONE: |
94 | pfilt_destroy(&c->q); |
95 | pfilt_destroy(&c->p); |
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96 | return (PGEN_DONE); |
97 | } |
98 | |
99 | /* --- Continue stepping if necessary --- */ |
100 | |
101 | while (rc == PGEN_FAIL || qrc == PGEN_FAIL) { |
102 | rc = pfilt_step(&c->p, 4); |
103 | qrc = pfilt_step(&c->q, 2); |
104 | } |
105 | |
106 | ev->m = MP_COPY(c->p.m); |
107 | if (qrc == PGEN_TRY) |
108 | rc = PGEN_TRY; |
109 | return (rc); |
110 | } |
111 | |
112 | /* --- @pgen_safejump@ --- * |
113 | * |
114 | * Jumps two numbers, %$q$% and %$p = 2q + 1$% such that neither has any |
115 | * small factors. |
116 | */ |
117 | |
118 | int pgen_safejump(int rq, pgen_event *ev, void *p) |
119 | { |
120 | pgen_safejumpctx *j = p; |
121 | int rc = PGEN_ABORT, qrc = 0; |
122 | |
123 | switch (rq) { |
124 | |
125 | /* --- Set up the jump contexts --- * |
126 | * |
127 | * The jump in @j.q@ is congruent to 2 (mod 4); see @strongprime_setup@. |
128 | * If @p@ is initially 1 (mod 4) then add @j.q@. Then double @j.q@ to |
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129 | * ensure that the step is 0 (mod 4). Ensure that @jq@ and @q@ don't |
130 | * have any common factors. |
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131 | */ |
132 | |
133 | case PGEN_BEGIN: { |
134 | mp *p = ev->m; |
135 | mp *q; |
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136 | mp *g = MP_NEW; |
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137 | if ((p->v[0] & 3) != 3) |
138 | p = mp_add(p, p, j->jq.m); |
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139 | q = mp_lsr(MP_NEW, p, 1); |
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140 | mp_gcd(&g, 0, 0, p, j->jq.m); |
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141 | if (MP_CMP(g, >, MP_ONE)) { |
142 | ev->m = p; |
143 | mp_drop(q); |
144 | mp_drop(g); |
145 | return (PGEN_ABORT); |
146 | } |
147 | mp_drop(g); |
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148 | rc = pfilt_create(&j->p, p); |
149 | pfilt_muladd(&j->jp, &j->jq, 2, 0); |
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150 | qrc = pfilt_create(&j->q, q); |
151 | mp_drop(p); |
152 | mp_drop(q); |
153 | } break; |
154 | |
155 | /* --- Step on one place --- */ |
156 | |
157 | case PGEN_TRY: |
158 | mp_drop(ev->m); |
159 | rc = pfilt_jump(&j->p, &j->jp); |
160 | qrc = pfilt_jump(&j->q, &j->jq); |
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161 | break; |
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162 | |
163 | /* --- Tidy everything up --- */ |
164 | |
165 | case PGEN_DONE: |
166 | pfilt_destroy(&j->jp); |
167 | pfilt_destroy(&j->p); |
168 | pfilt_destroy(&j->q); |
169 | return (PGEN_DONE); |
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170 | } |
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171 | |
172 | /* --- Step on while @p@ or @q@ have small factors --- */ |
173 | |
174 | while (rc == PGEN_FAIL || qrc == PGEN_FAIL) { |
175 | rc = pfilt_jump(&j->p, &j->jp); |
176 | qrc = pfilt_jump(&j->q, &j->jq); |
177 | } |
178 | ev->m = MP_COPY(j->p.m); |
179 | if (qrc == PGEN_TRY) |
180 | rc = PGEN_TRY; |
181 | return (rc); |
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182 | } |
183 | |
184 | /* --- @pgen_safetest@ --- * |
185 | * |
186 | * Applies Rabin-Miller tests to %$p$% and %$q$%. |
187 | */ |
188 | |
189 | int pgen_safetest(int rq, pgen_event *ev, void *p) |
190 | { |
191 | pgen_safetestctx *c = p; |
192 | int rc = PGEN_ABORT; |
193 | |
194 | switch (rq) { |
195 | case PGEN_BEGIN: |
196 | rabin_create(&c->q, c->c.q.m); |
197 | rabin_create(&c->p, c->c.p.m); |
198 | rc = PGEN_TRY; |
199 | break; |
200 | case PGEN_TRY: { |
201 | mp *m = mprand_range(MP_NEW, c->c.q.m, ev->r, 0); |
202 | rc = rabin_test(&c->p, m); |
203 | if (rc == PGEN_PASS) |
204 | rc = rabin_test(&c->q, m); |
205 | mp_drop(m); |
206 | } break; |
207 | case PGEN_DONE: |
208 | rabin_destroy(&c->q); |
209 | rabin_destroy(&c->p); |
210 | break; |
211 | } |
212 | return (rc); |
213 | } |
214 | |
215 | /*----- That's all, folks -------------------------------------------------*/ |