d03ab969 |
1 | /* -*-c-*- |
2 | * |
3 | * $Id: rand.h,v 1.1 1999/09/03 08:41:12 mdw Exp $ |
4 | * |
5 | * 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: rand.h,v $ |
33 | * Revision 1.1 1999/09/03 08:41:12 mdw |
34 | * Initial import. |
35 | * |
36 | */ |
37 | |
38 | /*----- Notes on the random number generator ------------------------------* |
39 | * |
40 | * The algorithm is one of the author's own devising. It may therefore be |
41 | * worth a certain amount of skepticism. However, I've thought about this |
42 | * method for over a year before actually considering it worth implementing. |
43 | * With a little bit of luck, it should have received some peer review by the |
44 | * time this code is actually properly released, and it'll be worth a bit |
45 | * more confidence. My earlier generator was very similar in structure to |
46 | * the Linux /dev/random device. This generator is intended to address |
47 | * concerns I expressed about the Linux generator in a Usenet article to |
48 | * sci.crypt. |
49 | * |
50 | * The generator is divided into two parts: an input pool and an outpu |
51 | * buffer. New random data is placed into the pool in the way described |
52 | * below, which is shamelessly stolen from the Linux /dev/random generator. |
53 | * The only interaction that the pool has on the output buffer is through the |
54 | * keyed `gating' operation, which mixes up and redistributes all of the |
55 | * generator's state in an irreversible manner. Random bytes, when |
56 | * requested, are extracted from the output buffer in a linear fashion. |
57 | * |
58 | * The input pool is best seen as being eight shift registers in parallel. |
59 | * Data is added to the pool one octet at a time. Each bit of a new octet is |
60 | * added to a different shift register, by adding it (mod 2) with other bits |
61 | * according to the coefficients of a primitive polynomial. Each new byte is |
62 | * rotated before being added into the pool, in a half-hearted attempt to |
63 | * protect against biases in the input data (e.g., top bits being clear on |
64 | * ASCII text). |
65 | * |
66 | * The gating operation takes a keyed hash of the entire generator state, |
67 | * uses it as the key for a symmetric cipher, and encrypts the state. The |
68 | * key is then discarded. The result is that every ouptut bit of the |
69 | * operation depends in a complex way on every input bit, but the operation |
70 | * cannot be reversed. |
71 | * |
72 | * As an added wrinkle, 160 bits of the output buffer are never actually |
73 | * output. They are used in the gating operation only, as an extra item that |
74 | * an adversary has to guess before predicting generator output. |
75 | */ |
76 | |
77 | #ifndef RAND_H |
78 | #define RAND_H |
79 | |
80 | #ifdef __cplusplus |
81 | extern "C" { |
82 | #endif |
83 | |
84 | /*----- Header files ------------------------------------------------------*/ |
85 | |
86 | #include <stddef.h> |
87 | |
88 | #include "rmd160-hmac.h" |
89 | |
90 | /*----- Magic numbers -----------------------------------------------------*/ |
91 | |
92 | #define RAND_POOLSZ 1279 /* Input pool size in bytes */ |
93 | #define RAND_BUFSZ 1024 /* Output buffer size in bytes */ |
94 | #define RAND_SECSZ 20 /* Secret octets in output buffer */ |
95 | |
96 | #define RAND_IBITS (RAND_POOLSZ * 8) |
97 | #define RAND_OBITS (RAND_BUFSZ * 8) |
98 | |
99 | /*----- Data structures ---------------------------------------------------*/ |
100 | |
101 | /* --- A random number generator pool --- */ |
102 | |
103 | typedef struct rand_pool { |
104 | octet pool[RAND_POOLSZ]; /* Actual contents of the pool */ |
105 | unsigned i; /* Current index into pool */ |
106 | unsigned irot; /* Current rotation applied */ |
107 | unsigned ibits; /* Number of good bits in pool */ |
108 | octet buf[RAND_BUFSZ]; /* Random octet output buffer */ |
109 | unsigned o; /* Current index into buffer */ |
110 | unsigned obits; /* Number of good bits in buffer */ |
111 | rmd160_mackey k; /* Secret key for this pool */ |
112 | const struct rand_source *s; /* System-specific noise source */ |
113 | } rand_pool; |
114 | |
115 | #define RAND_GLOBAL ((rand_pool *)0) /* The global randomness pool */ |
116 | |
117 | /* --- A noise source --- */ |
118 | |
119 | typedef struct rand_source { |
120 | void (*getnoise)(rand_pool */*r*/); /* Acquire more noise */ |
121 | int (*timer)(rand_pool */*r*/); /* Get noise from current time */ |
122 | } rand_source; |
123 | |
124 | /*----- Functions provided ------------------------------------------------*/ |
125 | |
126 | /* --- @rand_init@ --- * |
127 | * |
128 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
129 | * |
130 | * Returns: --- |
131 | * |
132 | * Use: Initializes a randomness pool. The pool doesn't start out |
133 | * very random: that's your job to sort out. |
134 | */ |
135 | |
136 | extern void rand_init(rand_pool */*r*/); |
137 | |
138 | /* --- @rand_noisesrc@ --- * |
139 | * |
140 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
141 | * @const rand_source *s@ = pointer to source definition |
142 | * |
143 | * Returns: --- |
144 | * |
145 | * Use: Sets a noise source for a randomness pool. When the pool's |
146 | * estimate of good random bits falls to zero, the @getnoise@ |
147 | * function is called, passing the pool handle as an argument. |
148 | * It is expected to increase the number of good bits by at |
149 | * least one, because it'll be called over and over again until |
150 | * there are enough bits to satisfy the caller. The @timer@ |
151 | * function is called frequently throughout the generator's |
152 | * operation. |
153 | */ |
154 | |
155 | extern void rand_noisesrc(rand_pool */*r*/, const rand_source */*s*/); |
156 | |
157 | /* --- @rand_key@ --- * |
158 | * |
159 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
160 | * @const void *k@ = pointer to key data |
161 | * @size_t sz@ = size of key data |
162 | * |
163 | * Returns: --- |
164 | * |
165 | * Use: Sets the secret key for a randomness pool. The key is used |
166 | * when mixing in new random bits. |
167 | */ |
168 | |
169 | extern void rand_key(rand_pool */*r*/, const void */*k*/, size_t /*sz*/); |
170 | |
171 | /* --- @rand_add@ --- * |
172 | * |
173 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
174 | * @const void *p@ = pointer a buffer of data to add |
175 | * @size_t sz@ = size of the data buffer |
176 | * @unsigned goodbits@ = number of good bits estimated in buffer |
177 | * |
178 | * Returns: --- |
179 | * |
180 | * Use: Mixes the data in the buffer with the contents of the |
181 | * pool. The estimate of the number of good bits is added to |
182 | * the pool's own count. The mixing operation is not |
183 | * cryptographically strong. However, data in the input pool |
184 | * isn't output directly, only through the one-way gating |
185 | * operation, so that shouldn't matter. |
186 | */ |
187 | |
188 | extern void rand_add(rand_pool */*r*/, |
189 | const void */*p*/, size_t /*sz*/, |
190 | unsigned /*goodbits*/); |
191 | |
192 | /* --- @rand_goodbits@ --- * |
193 | * |
194 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
195 | * |
196 | * Returns: Estimate of the number of good bits remaining in the pool. |
197 | */ |
198 | |
199 | extern unsigned rand_goodbits(rand_pool */*r*/); |
200 | |
201 | /* --- @rand_gate@ --- * |
202 | * |
203 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
204 | * |
205 | * Returns: --- |
206 | * |
207 | * Use: Mixes up the entire state of the generator in a nonreversible |
208 | * way. |
209 | */ |
210 | |
211 | extern void rand_gate(rand_pool */*r*/); |
212 | |
213 | /* --- @rand_stretch@ --- * |
214 | * |
215 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
216 | * |
217 | * Returns: --- |
218 | * |
219 | * Use: Stretches the contents of the output buffer by transforming |
220 | * it in a nonreversible way. This doesn't add any entropy |
221 | * worth speaking about, but it works well enough when the |
222 | * caller doesn't care about that sort of thing. |
223 | */ |
224 | |
225 | extern void rand_stretch(rand_pool */*r*/); |
226 | |
227 | /* --- @rand_get@ --- * |
228 | * |
229 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
230 | * @void *p@ = pointer to output buffer |
231 | * @size_t sz@ = size of output buffer |
232 | * |
233 | * Returns: --- |
234 | * |
235 | * Use: Gets random data from the pool. The pool's contents can't be |
236 | * determined from the output of this function; nor can the |
237 | * output data be determined from a knowledge of the data input |
238 | * to the pool wihtout also having knowledge of the secret key. |
239 | * The good bits counter is decremented, although no special |
240 | * action is taken if it reaches zero. |
241 | */ |
242 | |
243 | extern void rand_get(rand_pool */*r*/, void */*p*/, size_t /*sz*/); |
244 | |
245 | /* --- @rand_getgood@ --- * |
246 | * |
247 | * Arguments: @rand_pool *r@ = pointer to a randomness pool |
248 | * @void *p@ = pointer to output buffer |
249 | * @size_t sz@ = size of output buffer |
250 | * |
251 | * Returns: --- |
252 | * |
253 | * Use: Gets random data from the pool. The pool's contents can't be |
254 | * determined from the output of this function; nor can the |
255 | * output data be determined from a knowledge of the data input |
256 | * to the pool wihtout also having knowledge of the secret key. |
257 | * If a noise source is attached to the pool in question, it is |
258 | * called to replenish the supply of good bits in the pool; |
259 | * otherwise this call is equivalent to @rand_get@. |
260 | */ |
261 | |
262 | extern void rand_getgood(rand_pool */*r*/, void */*p*/, size_t /*sz*/); |
263 | |
264 | /*----- That's all, folks -------------------------------------------------*/ |
265 | |
266 | #ifdef __cplusplus |
267 | } |
268 | #endif |
269 | |
270 | #endif |