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