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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: bbs-rand.c,v 1.5 2004/04/08 01:36:15 mdw Exp $ |
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4 | * |
5 | * Blum-Blum-Shub secure random number generator |
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 <stdarg.h> |
33 | #include <stdlib.h> |
34 | #include <string.h> |
35 | |
36 | #include <mLib/bits.h> |
37 | #include <mLib/sub.h> |
38 | |
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39 | #include "arena.h" |
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40 | #include "bbs.h" |
41 | #include "grand.h" |
42 | #include "mp.h" |
43 | #include "mpbarrett.h" |
44 | #include "mpint.h" |
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45 | #include "mprand.h" |
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46 | #include "paranoia.h" |
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47 | |
48 | /*----- Main code ---------------------------------------------------------*/ |
49 | |
50 | /* --- @bbs_create@ --- * |
51 | * |
52 | * Arguments: @bbs *b@ = pointer to BBS generator state to initialize |
53 | * @mp *m@ = modulus (must be a Blum integer) |
54 | * @mp *x@ = initial seed for generator |
55 | * |
56 | * Returns: --- |
57 | * |
58 | * Use: Initializes a BBS generator. The generator is stepped once |
59 | * after initialization, as for @bbs_seed@. |
60 | */ |
61 | |
62 | void bbs_create(bbs *b, mp *m, mp *x) |
63 | { |
64 | mpw kw; |
65 | mp k; |
66 | |
67 | mpbarrett_create(&b->mb, m); |
68 | kw = mp_bits(m) - 1; |
69 | mp_build(&k, &kw, &kw + 1); |
70 | b->k = mp_bits(&k) - 1; |
71 | b->x = 0; |
72 | bbs_seed(b, x); |
73 | } |
74 | |
75 | /* --- @bbs_destroy@ --- * |
76 | * |
77 | * Arguments: @bbs *b@ = pointer to BBS generator state |
78 | * |
79 | * Returns: --- |
80 | * |
81 | * Use: Destroys a generator state when it's no longer wanted. |
82 | */ |
83 | |
84 | void bbs_destroy(bbs *b) |
85 | { |
86 | mp_drop(b->x); |
87 | mpbarrett_destroy(&b->mb); |
88 | } |
89 | |
90 | /* --- @bbs_step@ --- * |
91 | * |
92 | * Arguments: @bbs *b@ = pointer to BBS generator state |
93 | * |
94 | * Returns: --- |
95 | * |
96 | * Use: Steps the generator once. This isn't too useful in client |
97 | * code. |
98 | */ |
99 | |
100 | void bbs_step(bbs *b) |
101 | { |
102 | mp *x = b->x; |
103 | x = mp_sqr(x, x); |
104 | x = mpbarrett_reduce(&b->mb, x, x); |
105 | b->x = x; |
106 | b->b = b->k; |
107 | b->r = b->x->v[0]; |
108 | } |
109 | |
110 | /* --- @bbs_set@ --- * |
111 | * |
112 | * Arguments: @bbs *b@ = pointer to BBS generator state |
113 | * @mp *x@ = new residue to set |
114 | * |
115 | * Returns: --- |
116 | * |
117 | * Use: Sets a new quadratic residue. The generator is stepped once. |
118 | */ |
119 | |
120 | void bbs_set(bbs *b, mp *x) |
121 | { |
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122 | mp_drop(b->x); |
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123 | b->x = MP_COPY(x); |
124 | bbs_step(b); |
125 | } |
126 | |
127 | /* --- @bbs_seed@ --- * |
128 | * |
129 | * Arguments: @bbs *b@ = pointer to BBS generator state |
130 | * @mp *x@ = new seed to set |
131 | * |
132 | * Returns --- |
133 | * |
134 | * Use: Sets a new seed. The generator is stepped until the residue |
135 | * has clearly wrapped around. |
136 | */ |
137 | |
138 | void bbs_seed(bbs *b, mp *x) |
139 | { |
140 | mp *y; |
141 | x = MP_COPY(x); |
142 | for (;;) { |
143 | y = mp_sqr(MP_NEW, x); |
144 | y = mpbarrett_reduce(&b->mb, y, y); |
145 | if (MP_CMP(y, <, x)) |
146 | break; |
147 | mp_drop(x); |
148 | x = y; |
149 | } |
150 | mp_drop(x); |
151 | bbs_set(b, y); |
152 | mp_drop(y); |
153 | } |
154 | |
155 | /* --- @bbs_bits@ --- * |
156 | * |
157 | * Arguments: @bbs *b@ = pointer to BBS generator state |
158 | * @unsigned bits@ = number of bits wanted |
159 | * |
160 | * Returns: Bits extracted from the BBS generator. |
161 | * |
162 | * Use: Extracts a requested number of bits from the BBS generator. |
163 | */ |
164 | |
165 | uint32 bbs_bits(bbs *b, unsigned bits) |
166 | { |
167 | uint32 x = 0; |
168 | mpw m; |
169 | |
170 | /* --- Keep turning the handle until there's enough in the reservoir --- */ |
171 | |
172 | while (bits >= b->b) { |
173 | bits -= b->b; |
174 | m = (1 << b->b) - 1; |
175 | x |= (b->r & m) << bits; |
176 | bbs_step(b); |
177 | } |
178 | |
179 | /* --- Extract the last few bits needed --- */ |
180 | |
181 | if (bits) { |
182 | m = (1 << bits) - 1; |
183 | b->b -= bits; |
184 | x |= (b->r >> b->b) & m; |
185 | } |
186 | |
187 | /* --- Done --- */ |
188 | |
189 | return (x); |
190 | } |
191 | |
192 | /* --- @bbs_wrap@ --- * |
193 | * |
194 | * Arguments: @bbs *b@ = pointer to BBS generator state |
195 | * |
196 | * Returns: --- |
197 | * |
198 | * Use: Steps the generator if any of the reservoir bits are used. |
199 | * This can be used to `wrap up' after a Blum-Goldwasser |
200 | * encryption, for example, producing the final value to be sent |
201 | * along with the ciphertext. |
202 | * |
203 | * If a generator is seeded, %$b$% bits are extracted, and then |
204 | * @bbs_wrap@ is called, the generator will have been stepped |
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205 | * %$\lceil b/k \rceil$% times. |
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206 | */ |
207 | |
208 | void bbs_wrap(bbs *b) |
209 | { |
210 | if (b->b < b->k) |
211 | bbs_step(b); |
212 | } |
213 | |
214 | /*----- Generic random number generator interface -------------------------*/ |
215 | |
216 | typedef struct gctx { |
217 | grand r; |
218 | bbs b; |
219 | } gctx; |
220 | |
221 | static void gdestroy(grand *r) |
222 | { |
223 | gctx *g = (gctx *)r; |
224 | bbs_destroy(&g->b); |
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225 | BURN(*g); |
226 | S_DESTROY(g); |
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227 | } |
228 | |
229 | static int gmisc(grand *r, unsigned op, ...) |
230 | { |
231 | gctx *g = (gctx *)r; |
232 | va_list ap; |
233 | int rc = 0; |
234 | va_start(ap, op); |
235 | |
236 | switch (op) { |
237 | case GRAND_CHECK: |
238 | switch (va_arg(ap, unsigned)) { |
239 | case GRAND_CHECK: |
240 | case GRAND_SEEDINT: |
241 | case GRAND_SEEDUINT32: |
242 | case GRAND_SEEDMP: |
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243 | case GRAND_SEEDRAND: |
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244 | case BBS_SET: |
245 | rc = 1; |
246 | break; |
247 | default: |
248 | rc = 0; |
249 | break; |
250 | } |
251 | break; |
252 | case GRAND_SEEDINT: { |
253 | mp *x = mp_fromuint(MP_NEW, va_arg(ap, unsigned)); |
254 | bbs_seed(&g->b, x); |
255 | mp_drop(x); |
256 | } break; |
257 | case GRAND_SEEDUINT32: { |
258 | mp *x = mp_fromuint32(MP_NEW, va_arg(ap, uint32)); |
259 | bbs_seed(&g->b, x); |
260 | mp_drop(x); |
261 | } break; |
262 | case GRAND_SEEDMP: |
263 | bbs_seed(&g->b, va_arg(ap, mp *)); |
264 | break; |
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265 | case GRAND_SEEDRAND: { |
266 | grand *rr = va_arg(ap, grand *); |
267 | mp *m = mprand(MP_NEW, mp_bits(g->b.mb.m) - 1, rr, 0); |
268 | bbs_seed(&g->b, m); |
269 | mp_drop(m); |
270 | } break; |
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271 | case BBS_SET: |
272 | bbs_set(&g->b, va_arg(ap, mp *)); |
273 | break; |
274 | default: |
275 | GRAND_BADOP; |
276 | break; |
277 | } |
278 | |
279 | va_end(ap); |
280 | return (rc); |
281 | } |
282 | |
283 | static octet gbyte(grand *r) |
284 | { |
285 | gctx *g = (gctx *)r; |
286 | return (bbs_bits(&g->b, 8)); |
287 | } |
288 | |
289 | static uint32 gword(grand *r) |
290 | { |
291 | gctx *g = (gctx *)r; |
292 | return (bbs_bits(&g->b, 32)); |
293 | } |
294 | |
295 | static const grand_ops gops = { |
296 | "bbs", |
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297 | GRAND_CRYPTO, 0, |
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298 | gmisc, gdestroy, |
299 | gword, gbyte, gword, grand_range, grand_fill |
300 | }; |
301 | |
302 | /* --- @bbs_rand@ --- * |
303 | * |
304 | * Arguments: @mp *m@ = modulus |
305 | * @mp *x@ = initial seed |
306 | * |
307 | * Returns: Pointer to a generic generator. |
308 | * |
309 | * Use: Constructs a generic generator interface over a |
310 | * Blum-Blum-Shub generator. |
311 | */ |
312 | |
313 | grand *bbs_rand(mp *m, mp *x) |
314 | { |
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315 | gctx *g = S_CREATE(gctx); |
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316 | g->r.ops = &gops; |
317 | bbs_create(&g->b, m, x); |
318 | return (&g->r); |
319 | } |
320 | |
321 | /*----- Test rig ----------------------------------------------------------*/ |
322 | |
323 | #ifdef TEST_RIG |
324 | |
325 | static int verify(dstr *v) |
326 | { |
327 | mp *n = *(mp **)v[0].buf; |
328 | mp *x = *(mp **)v[1].buf; |
329 | grand *b = bbs_rand(n, x); |
330 | dstr d = DSTR_INIT; |
331 | int ok = 1; |
332 | |
333 | dstr_ensure(&d, v[2].len); |
334 | b->ops->fill(b, d.buf, v[2].len); |
335 | d.len = v[2].len; |
336 | if (memcmp(d.buf, v[2].buf, v[2].len) != 0) { |
337 | fputs("\n*** bbs failure\n", stderr); |
338 | fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr); |
339 | fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr); |
340 | fputs("expected = ", stderr); type_hex.dump(&v[2], stderr); |
341 | fputc('\n', stderr); |
342 | fputs(" found = ", stderr); type_hex.dump(&d, stderr); |
343 | fputc('\n', stderr); |
344 | fprintf(stderr, "k = %u\n", ((gctx *)b)->b.k); |
345 | ok = 0; |
346 | } |
347 | b->ops->destroy(b); |
348 | mp_drop(x); |
349 | mp_drop(n); |
350 | dstr_destroy(&d); |
351 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
352 | return (ok); |
353 | } |
354 | |
355 | static test_chunk tests[] = { |
356 | { "bbs", verify, { &type_mp, &type_mp, &type_hex, 0 } }, |
357 | { 0, 0, { 0 } } |
358 | }; |
359 | |
360 | int main(int argc, char *argv[]) |
361 | { |
362 | sub_init(); |
363 | test_run(argc, argv, tests, SRCDIR "/tests/bbs"); |
364 | return (0); |
365 | } |
366 | |
367 | #endif |
368 | |
369 | /*----- That's all, folks -------------------------------------------------*/ |