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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: dsarand.c,v 1.4 2004/04/08 01:36:15 mdw Exp $ |
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4 | * |
5 | * Random number generator for DSA |
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 <string.h> |
34 | |
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35 | #include <mLib/alloc.h> |
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36 | #include <mLib/bits.h> |
37 | #include <mLib/sub.h> |
38 | |
39 | #include "dsarand.h" |
40 | #include "grand.h" |
41 | #include "sha.h" |
42 | |
43 | /*----- Main code ---------------------------------------------------------*/ |
44 | |
45 | /* --- @STEP@ --- * |
46 | * |
47 | * Arguments: @dsarand *d@ = pointer to context |
48 | * |
49 | * Use: Increments the buffer by one, interpreting it as a big-endian |
50 | * integer. Carries outside the integer are discarded. |
51 | */ |
52 | |
53 | #define STEP(d) do { \ |
54 | dsarand *_d = (d); \ |
55 | octet *_p = _d->p; \ |
56 | octet *_q = _p + _d->sz; \ |
57 | unsigned _c = 1; \ |
58 | while (_c && _q > _p) { \ |
59 | _c += *--_q; \ |
60 | *_q = U8(_c); \ |
61 | _c >>= 8; \ |
62 | } \ |
63 | } while (0) |
64 | |
65 | /* --- @dsarand_init@ --- * |
66 | * |
67 | * Arguments: @dsarand *d@ = pointer to context |
68 | * @const void *p@ = pointer to seed buffer |
69 | * @size_t sz@ = size of the buffer |
70 | * |
71 | * Returns: --- |
72 | * |
73 | * Use: Initializes a DSA random number generator. |
74 | */ |
75 | |
76 | void dsarand_init(dsarand *d, const void *p, size_t sz) |
77 | { |
78 | d->p = xmalloc(sz); |
79 | d->sz = sz; |
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80 | d->passes = 1; |
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81 | if (p) |
82 | memcpy(d->p, p, sz); |
83 | } |
84 | |
85 | /* --- @dsarand_reseed@ --- * |
86 | * |
87 | * Arguments: @dsarand *d@ = pointer to context |
88 | * @const void *p@ = pointer to seed buffer |
89 | * @size_t sz@ = size of the buffer |
90 | * |
91 | * Returns: --- |
92 | * |
93 | * Use: Initializes a DSA random number generator. |
94 | */ |
95 | |
96 | void dsarand_reseed(dsarand *d, const void *p, size_t sz) |
97 | { |
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98 | xfree(d->p); |
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99 | d->p = xmalloc(sz); |
100 | d->sz = sz; |
101 | d->passes = 1; |
102 | if (p) |
103 | memcpy(d->p, p, sz); |
104 | } |
105 | |
106 | /* --- @dsarand_destroy@ --- * |
107 | * |
108 | * Arguments: @dsarand *d@ = pointer to context |
109 | * |
110 | * Returns: --- |
111 | * |
112 | * Use: Disposes of a DSA random number generation context. |
113 | */ |
114 | |
115 | void dsarand_destroy(dsarand *d) |
116 | { |
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117 | xfree(d->p); |
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118 | } |
119 | |
120 | /* --- @dsarand_fill@ --- * |
121 | * |
122 | * Arguments: @dsarand *d@ = pointer to context |
123 | * @void *p@ = pointer to output buffer |
124 | * @size_t sz@ = size of output buffer |
125 | * |
126 | * Returns: --- |
127 | * |
128 | * Use: Fills an output buffer with pseudorandom data. |
129 | * |
130 | * Let %$p$% be the numerical value of the input buffer, and let |
131 | * %$b$% be the number of bytes required. Let |
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132 | * %$z = \lceil b / 20 \rceil$% be the number of SHA outputs |
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133 | * required. Then the output of pass %$n$% is |
134 | * |
135 | * %$P_n = \sum_{0 \le i < z} 2^{160i} SHA(p + nz + i)$% |
136 | * %${} \bmod 2^{8b}$% |
137 | * |
138 | * and the actual result in the output buffer is the XOR of all |
139 | * of the output passes. |
140 | * |
141 | * The DSA procedure for choosing @q@ involves two passes with |
142 | * %$z = 1$%; the procedure for choosing @p@ involves one pass |
143 | * with larger %$z$%. This generalization of the DSA generation |
144 | * procedure is my own invention but it seems relatively sound. |
145 | */ |
146 | |
147 | void dsarand_fill(dsarand *d, void *p, size_t sz) |
148 | { |
149 | octet *q = p; |
150 | unsigned n = d->passes; |
151 | |
152 | /* --- Write out the first pass --- * |
153 | * |
154 | * This can write directly to the output buffer, so it's done differently |
155 | * from the latter passes. |
156 | */ |
157 | |
158 | { |
159 | size_t o = sz; |
160 | |
161 | while (o) { |
162 | sha_ctx h; |
163 | |
164 | /* --- Hash the input buffer --- */ |
165 | |
166 | sha_init(&h); |
167 | sha_hash(&h, d->p, d->sz); |
168 | |
169 | /* --- If enough space, extract the hash output directly --- */ |
170 | |
171 | if (o >= SHA_HASHSZ) { |
172 | o -= SHA_HASHSZ; |
173 | sha_done(&h, q + o); |
174 | } |
175 | |
176 | /* --- Otherwise take the hash result out of line and copy it --- */ |
177 | |
178 | else { |
179 | octet hash[SHA_HASHSZ]; |
180 | sha_done(&h, hash); |
181 | memcpy(q, hash + (SHA_HASHSZ - o), o); |
182 | o = 0; |
183 | } |
184 | |
185 | /* --- Step the input buffer --- */ |
186 | |
187 | STEP(d); |
188 | } |
189 | |
190 | /* --- Another pass has been done --- */ |
191 | |
192 | n--; |
193 | } |
194 | |
195 | /* --- Write out subsequent passes --- * |
196 | * |
197 | * The hash output has to be done offline, so this is slightly easier. |
198 | */ |
199 | |
200 | while (n) { |
201 | size_t o = sz; |
202 | |
203 | while (o) { |
204 | sha_ctx h; |
205 | octet hash[SHA_HASHSZ]; |
206 | size_t n; |
207 | octet *pp, *qq; |
208 | |
209 | /* --- Hash the input buffer --- */ |
210 | |
211 | sha_init(&h); |
212 | sha_hash(&h, d->p, d->sz); |
213 | sha_done(&h, hash); |
214 | |
215 | /* --- Work out how much output is wanted --- */ |
216 | |
217 | n = SHA_HASHSZ; |
218 | if (n > o) |
219 | n = o; |
220 | o -= n; |
221 | |
222 | /* --- XOR the data out --- */ |
223 | |
224 | for (pp = hash + (SHA_HASHSZ - n), qq = q + o; |
225 | pp < hash + SHA_HASHSZ; pp++, qq++) |
226 | *qq ^= *pp; |
227 | |
228 | /* --- Step the input buffer --- */ |
229 | |
230 | STEP(d); |
231 | } |
232 | |
233 | /* --- Another pass is done --- */ |
234 | |
235 | n--; |
236 | } |
237 | } |
238 | |
239 | /*----- Generic pseudorandom-number generator interface -------------------*/ |
240 | |
241 | static const grand_ops gops; |
242 | |
243 | typedef struct gctx { |
244 | grand r; |
245 | dsarand d; |
246 | } gctx; |
247 | |
248 | static void gdestroy(grand *r) |
249 | { |
250 | gctx *g = (gctx *)r; |
251 | dsarand_destroy(&g->d); |
252 | DESTROY(g); |
253 | } |
254 | |
255 | static int gmisc(grand *r, unsigned op, ...) |
256 | { |
257 | gctx *g = (gctx *)r; |
258 | va_list ap; |
259 | int rc = 0; |
260 | va_start(ap, op); |
261 | |
262 | switch (op) { |
263 | case GRAND_CHECK: |
264 | switch (va_arg(ap, unsigned)) { |
265 | case GRAND_CHECK: |
266 | case GRAND_SEEDBLOCK: |
267 | case GRAND_SEEDRAND: |
268 | case DSARAND_PASSES: |
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269 | case DSARAND_SEEDSZ: |
270 | case DSARAND_GETSEED: |
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271 | rc = 1; |
272 | break; |
273 | default: |
274 | rc = 0; |
275 | break; |
276 | } |
277 | break; |
278 | case GRAND_SEEDBLOCK: { |
279 | const void *p = va_arg(ap, const void *); |
280 | size_t sz = va_arg(ap, size_t); |
281 | dsarand_reseed(&g->d, p, sz); |
282 | } break; |
283 | case GRAND_SEEDRAND: { |
284 | grand *rr = va_arg(ap, grand *); |
285 | rr->ops->fill(rr, g->d.p, g->d.sz); |
286 | } break; |
287 | case DSARAND_PASSES: |
288 | g->d.passes = va_arg(ap, unsigned); |
289 | break; |
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290 | case DSARAND_SEEDSZ: |
291 | rc = g->d.sz; |
292 | break; |
293 | case DSARAND_GETSEED: |
294 | memcpy(va_arg(ap, void *), g->d.p, g->d.sz); |
295 | break; |
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296 | default: |
297 | GRAND_BADOP; |
298 | break; |
299 | } |
300 | |
301 | va_end(ap); |
302 | return (rc); |
303 | } |
304 | |
305 | static void gfill(grand *r, void *p, size_t sz) |
306 | { |
307 | gctx *g = (gctx *)r; |
308 | dsarand_fill(&g->d, p, sz); |
309 | } |
310 | |
311 | static const grand_ops gops = { |
312 | "dsarand", |
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313 | 0, 0, |
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314 | gmisc, gdestroy, |
315 | grand_word, grand_byte, grand_word, grand_range, gfill |
316 | }; |
317 | |
318 | /* --- @dsarand_create@ --- * |
319 | * |
320 | * Arguments: @const void *p@ = pointer to seed buffer |
321 | * @size_t sz@ = size of seed buffer |
322 | * |
323 | * Returns: Pointer to a generic generator. |
324 | * |
325 | * Use: Constructs a generic generator interface over a Catacomb |
326 | * entropy pool generator. |
327 | */ |
328 | |
329 | grand *dsarand_create(const void *p, size_t sz) |
330 | { |
331 | gctx *g = CREATE(gctx); |
332 | g->r.ops = &gops; |
333 | dsarand_init(&g->d, p, sz); |
334 | return (&g->r); |
335 | } |
336 | |
337 | /*----- That's all, folks -------------------------------------------------*/ |