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1 | /* -*-c-*- |
2 | * |
3 | * $Id: bbs-rand.c,v 1.1 1999/12/10 23:14:59 mdw Exp $ |
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 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: bbs-rand.c,v $ |
33 | * Revision 1.1 1999/12/10 23:14:59 mdw |
34 | * Blum-Blum-Shub generator, and Blum-Goldwasser encryption. |
35 | * |
36 | */ |
37 | |
38 | /*----- Header files ------------------------------------------------------*/ |
39 | |
40 | #include <stdarg.h> |
41 | #include <stdlib.h> |
42 | #include <string.h> |
43 | |
44 | #include <mLib/bits.h> |
45 | #include <mLib/sub.h> |
46 | |
47 | #include "bbs.h" |
48 | #include "grand.h" |
49 | #include "mp.h" |
50 | #include "mpbarrett.h" |
51 | #include "mpint.h" |
52 | |
53 | /*----- Main code ---------------------------------------------------------*/ |
54 | |
55 | /* --- @bbs_create@ --- * |
56 | * |
57 | * Arguments: @bbs *b@ = pointer to BBS generator state to initialize |
58 | * @mp *m@ = modulus (must be a Blum integer) |
59 | * @mp *x@ = initial seed for generator |
60 | * |
61 | * Returns: --- |
62 | * |
63 | * Use: Initializes a BBS generator. The generator is stepped once |
64 | * after initialization, as for @bbs_seed@. |
65 | */ |
66 | |
67 | void bbs_create(bbs *b, mp *m, mp *x) |
68 | { |
69 | mpw kw; |
70 | mp k; |
71 | |
72 | mpbarrett_create(&b->mb, m); |
73 | kw = mp_bits(m) - 1; |
74 | mp_build(&k, &kw, &kw + 1); |
75 | b->k = mp_bits(&k) - 1; |
76 | b->x = 0; |
77 | bbs_seed(b, x); |
78 | } |
79 | |
80 | /* --- @bbs_destroy@ --- * |
81 | * |
82 | * Arguments: @bbs *b@ = pointer to BBS generator state |
83 | * |
84 | * Returns: --- |
85 | * |
86 | * Use: Destroys a generator state when it's no longer wanted. |
87 | */ |
88 | |
89 | void bbs_destroy(bbs *b) |
90 | { |
91 | mp_drop(b->x); |
92 | mpbarrett_destroy(&b->mb); |
93 | } |
94 | |
95 | /* --- @bbs_step@ --- * |
96 | * |
97 | * Arguments: @bbs *b@ = pointer to BBS generator state |
98 | * |
99 | * Returns: --- |
100 | * |
101 | * Use: Steps the generator once. This isn't too useful in client |
102 | * code. |
103 | */ |
104 | |
105 | void bbs_step(bbs *b) |
106 | { |
107 | mp *x = b->x; |
108 | x = mp_sqr(x, x); |
109 | x = mpbarrett_reduce(&b->mb, x, x); |
110 | b->x = x; |
111 | b->b = b->k; |
112 | b->r = b->x->v[0]; |
113 | } |
114 | |
115 | /* --- @bbs_set@ --- * |
116 | * |
117 | * Arguments: @bbs *b@ = pointer to BBS generator state |
118 | * @mp *x@ = new residue to set |
119 | * |
120 | * Returns: --- |
121 | * |
122 | * Use: Sets a new quadratic residue. The generator is stepped once. |
123 | */ |
124 | |
125 | void bbs_set(bbs *b, mp *x) |
126 | { |
127 | if (b->x) |
128 | mp_drop(b->x); |
129 | b->x = MP_COPY(x); |
130 | bbs_step(b); |
131 | } |
132 | |
133 | /* --- @bbs_seed@ --- * |
134 | * |
135 | * Arguments: @bbs *b@ = pointer to BBS generator state |
136 | * @mp *x@ = new seed to set |
137 | * |
138 | * Returns --- |
139 | * |
140 | * Use: Sets a new seed. The generator is stepped until the residue |
141 | * has clearly wrapped around. |
142 | */ |
143 | |
144 | void bbs_seed(bbs *b, mp *x) |
145 | { |
146 | mp *y; |
147 | x = MP_COPY(x); |
148 | for (;;) { |
149 | y = mp_sqr(MP_NEW, x); |
150 | y = mpbarrett_reduce(&b->mb, y, y); |
151 | if (MP_CMP(y, <, x)) |
152 | break; |
153 | mp_drop(x); |
154 | x = y; |
155 | } |
156 | mp_drop(x); |
157 | bbs_set(b, y); |
158 | mp_drop(y); |
159 | } |
160 | |
161 | /* --- @bbs_bits@ --- * |
162 | * |
163 | * Arguments: @bbs *b@ = pointer to BBS generator state |
164 | * @unsigned bits@ = number of bits wanted |
165 | * |
166 | * Returns: Bits extracted from the BBS generator. |
167 | * |
168 | * Use: Extracts a requested number of bits from the BBS generator. |
169 | */ |
170 | |
171 | uint32 bbs_bits(bbs *b, unsigned bits) |
172 | { |
173 | uint32 x = 0; |
174 | mpw m; |
175 | |
176 | /* --- Keep turning the handle until there's enough in the reservoir --- */ |
177 | |
178 | while (bits >= b->b) { |
179 | bits -= b->b; |
180 | m = (1 << b->b) - 1; |
181 | x |= (b->r & m) << bits; |
182 | bbs_step(b); |
183 | } |
184 | |
185 | /* --- Extract the last few bits needed --- */ |
186 | |
187 | if (bits) { |
188 | m = (1 << bits) - 1; |
189 | b->b -= bits; |
190 | x |= (b->r >> b->b) & m; |
191 | } |
192 | |
193 | /* --- Done --- */ |
194 | |
195 | return (x); |
196 | } |
197 | |
198 | /* --- @bbs_wrap@ --- * |
199 | * |
200 | * Arguments: @bbs *b@ = pointer to BBS generator state |
201 | * |
202 | * Returns: --- |
203 | * |
204 | * Use: Steps the generator if any of the reservoir bits are used. |
205 | * This can be used to `wrap up' after a Blum-Goldwasser |
206 | * encryption, for example, producing the final value to be sent |
207 | * along with the ciphertext. |
208 | * |
209 | * If a generator is seeded, %$b$% bits are extracted, and then |
210 | * @bbs_wrap@ is called, the generator will have been stepped |
211 | * %$\lceil b/k \rceil% times. |
212 | */ |
213 | |
214 | void bbs_wrap(bbs *b) |
215 | { |
216 | if (b->b < b->k) |
217 | bbs_step(b); |
218 | } |
219 | |
220 | /*----- Generic random number generator interface -------------------------*/ |
221 | |
222 | typedef struct gctx { |
223 | grand r; |
224 | bbs b; |
225 | } gctx; |
226 | |
227 | static void gdestroy(grand *r) |
228 | { |
229 | gctx *g = (gctx *)r; |
230 | bbs_destroy(&g->b); |
231 | DESTROY(g); |
232 | } |
233 | |
234 | static int gmisc(grand *r, unsigned op, ...) |
235 | { |
236 | gctx *g = (gctx *)r; |
237 | va_list ap; |
238 | int rc = 0; |
239 | va_start(ap, op); |
240 | |
241 | switch (op) { |
242 | case GRAND_CHECK: |
243 | switch (va_arg(ap, unsigned)) { |
244 | case GRAND_CHECK: |
245 | case GRAND_SEEDINT: |
246 | case GRAND_SEEDUINT32: |
247 | case GRAND_SEEDMP: |
248 | case BBS_SET: |
249 | rc = 1; |
250 | break; |
251 | default: |
252 | rc = 0; |
253 | break; |
254 | } |
255 | break; |
256 | case GRAND_SEEDINT: { |
257 | mp *x = mp_fromuint(MP_NEW, va_arg(ap, unsigned)); |
258 | bbs_seed(&g->b, x); |
259 | mp_drop(x); |
260 | } break; |
261 | case GRAND_SEEDUINT32: { |
262 | mp *x = mp_fromuint32(MP_NEW, va_arg(ap, uint32)); |
263 | bbs_seed(&g->b, x); |
264 | mp_drop(x); |
265 | } break; |
266 | case GRAND_SEEDMP: |
267 | bbs_seed(&g->b, va_arg(ap, mp *)); |
268 | break; |
269 | case BBS_SET: |
270 | bbs_set(&g->b, va_arg(ap, mp *)); |
271 | break; |
272 | default: |
273 | GRAND_BADOP; |
274 | break; |
275 | } |
276 | |
277 | va_end(ap); |
278 | return (rc); |
279 | } |
280 | |
281 | static octet gbyte(grand *r) |
282 | { |
283 | gctx *g = (gctx *)r; |
284 | return (bbs_bits(&g->b, 8)); |
285 | } |
286 | |
287 | static uint32 gword(grand *r) |
288 | { |
289 | gctx *g = (gctx *)r; |
290 | return (bbs_bits(&g->b, 32)); |
291 | } |
292 | |
293 | static const grand_ops gops = { |
294 | "bbs", |
295 | 0, |
296 | gmisc, gdestroy, |
297 | gword, gbyte, gword, grand_range, grand_fill |
298 | }; |
299 | |
300 | /* --- @bbs_rand@ --- * |
301 | * |
302 | * Arguments: @mp *m@ = modulus |
303 | * @mp *x@ = initial seed |
304 | * |
305 | * Returns: Pointer to a generic generator. |
306 | * |
307 | * Use: Constructs a generic generator interface over a |
308 | * Blum-Blum-Shub generator. |
309 | */ |
310 | |
311 | grand *bbs_rand(mp *m, mp *x) |
312 | { |
313 | gctx *g = CREATE(gctx); |
314 | g->r.ops = &gops; |
315 | bbs_create(&g->b, m, x); |
316 | return (&g->r); |
317 | } |
318 | |
319 | /*----- Test rig ----------------------------------------------------------*/ |
320 | |
321 | #ifdef TEST_RIG |
322 | |
323 | static int verify(dstr *v) |
324 | { |
325 | mp *n = *(mp **)v[0].buf; |
326 | mp *x = *(mp **)v[1].buf; |
327 | grand *b = bbs_rand(n, x); |
328 | dstr d = DSTR_INIT; |
329 | int ok = 1; |
330 | |
331 | dstr_ensure(&d, v[2].len); |
332 | b->ops->fill(b, d.buf, v[2].len); |
333 | d.len = v[2].len; |
334 | if (memcmp(d.buf, v[2].buf, v[2].len) != 0) { |
335 | fputs("\n*** bbs failure\n", stderr); |
336 | fputs("n = ", stderr); mp_writefile(n, stderr, 10); fputc('\n', stderr); |
337 | fputs("x = ", stderr); mp_writefile(x, stderr, 10); fputc('\n', stderr); |
338 | fputs("expected = ", stderr); type_hex.dump(&v[2], stderr); |
339 | fputc('\n', stderr); |
340 | fputs(" found = ", stderr); type_hex.dump(&d, stderr); |
341 | fputc('\n', stderr); |
342 | fprintf(stderr, "k = %u\n", ((gctx *)b)->b.k); |
343 | ok = 0; |
344 | } |
345 | b->ops->destroy(b); |
346 | mp_drop(x); |
347 | mp_drop(n); |
348 | dstr_destroy(&d); |
349 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
350 | return (ok); |
351 | } |
352 | |
353 | static test_chunk tests[] = { |
354 | { "bbs", verify, { &type_mp, &type_mp, &type_hex, 0 } }, |
355 | { 0, 0, { 0 } } |
356 | }; |
357 | |
358 | int main(int argc, char *argv[]) |
359 | { |
360 | sub_init(); |
361 | test_run(argc, argv, tests, SRCDIR "/tests/bbs"); |
362 | return (0); |
363 | } |
364 | |
365 | #endif |
366 | |
367 | /*----- That's all, folks -------------------------------------------------*/ |