3 * $Id: rand.h,v 1.5 1999/12/13 15:34:15 mdw Exp $
5 * Secure random number generator
7 * (c) 1999 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.5 1999/12/13 15:34:15 mdw
36 * Revision 1.4 1999/12/10 23:29:48 mdw
37 * Change header file guard names.
39 * Revision 1.3 1999/10/15 21:04:30 mdw
40 * Increase output buffer a bit for performance.
42 * Revision 1.2 1999/10/12 21:00:15 mdw
43 * Make pool and buffer sizes more sensible.
45 * Revision 1.1 1999/09/03 08:41:12 mdw
50 /*----- Notes on the random number generator ------------------------------*
52 * The algorithm is one of the author's own devising. It may therefore be
53 * worth a certain amount of skepticism. However, I've thought about this
54 * method for over a year before actually considering it worth implementing.
55 * With a little bit of luck, it should have received some peer review by the
56 * time this code is actually properly released, and it'll be worth a bit
57 * more confidence. My earlier generator was very similar in structure to
58 * the Linux /dev/random device. This generator is intended to address
59 * concerns I expressed about the Linux generator in a Usenet article to
62 * The generator is divided into two parts: an input pool and an output
63 * buffer. New random data is placed into the pool in the way described
64 * below, which is shamelessly stolen from the Linux /dev/random generator.
65 * The only interaction that the pool has on the output buffer is through the
66 * keyed `gating' operation, which mixes up and redistributes all of the
67 * generator's state in an irreversible manner. Random bytes, when
68 * requested, are extracted from the output buffer in a linear fashion.
70 * The input pool is best seen as being eight shift registers in parallel.
71 * Data is added to the pool one octet at a time. Each bit of a new octet is
72 * added to a different shift register, by adding it (mod 2) with other bits
73 * according to the coefficients of a primitive polynomial. Each new byte is
74 * rotated before being added into the pool, in a half-hearted attempt to
75 * protect against biases in the input data (e.g., top bits being clear on
78 * The gating operation takes a keyed hash of the entire generator state,
79 * uses it as the key for a symmetric cipher, and encrypts the state. The
80 * key is then discarded. The result is that every ouptut bit of the
81 * operation depends in a complex way on every input bit, but the operation
84 * As an added wrinkle, 160 bits of the output buffer are never actually
85 * output. They are used in the gating operation only, as an extra item that
86 * an adversary has to guess before predicting generator output.
89 #ifndef CATACOMB_RAND_H
90 #define CATACOMB_RAND_H
96 /*----- Header files ------------------------------------------------------*/
100 #ifndef CATACOMB_GRAND_H
104 #ifndef CATACOMB_RMD160_HMAC_H
105 # include "rmd160-hmac.h"
108 /*----- Magic numbers -----------------------------------------------------*/
110 #define RAND_POOLSZ 128 /* Input pool size in bytes */
111 #define RAND_BUFSZ 512 /* Output buffer size in bytes */
112 #define RAND_SECSZ 20 /* Secret octets in output buffer */
114 #define RAND_IBITS (RAND_POOLSZ * 8)
115 #define RAND_OBITS (RAND_BUFSZ * 8)
117 /*----- Data structures ---------------------------------------------------*/
119 /* --- A random number generator pool --- */
121 typedef struct rand_pool
{
122 octet pool
[RAND_POOLSZ
]; /* Actual contents of the pool */
123 unsigned i
; /* Current index into pool */
124 unsigned irot
; /* Current rotation applied */
125 unsigned ibits
; /* Number of good bits in pool */
126 octet buf
[RAND_BUFSZ
]; /* Random octet output buffer */
127 unsigned o
; /* Current index into buffer */
128 unsigned obits
; /* Number of good bits in buffer */
129 rmd160_mackey k
; /* Secret key for this pool */
130 const struct rand_source
*s
; /* System-specific noise source */
133 #define RAND_GLOBAL ((rand_pool *)0) /* The global randomness pool */
135 /* --- A noise source --- */
137 typedef struct rand_source
{
138 void (*getnoise
)(rand_pool */
*r*/
); /* Acquire more noise */
139 int (*timer
)(rand_pool */
*r*/
); /* Get noise from current time */
142 /*----- Functions provided ------------------------------------------------*/
144 /* --- @rand_init@ --- *
146 * Arguments: @rand_pool *r@ = pointer to a randomness pool
150 * Use: Initializes a randomness pool. The pool doesn't start out
151 * very random: that's your job to sort out.
154 extern void rand_init(rand_pool */
*r*/
);
156 /* --- @rand_noisesrc@ --- *
158 * Arguments: @rand_pool *r@ = pointer to a randomness pool
159 * @const rand_source *s@ = pointer to source definition
163 * Use: Sets a noise source for a randomness pool. When the pool's
164 * estimate of good random bits falls to zero, the @getnoise@
165 * function is called, passing the pool handle as an argument.
166 * It is expected to increase the number of good bits by at
167 * least one, because it'll be called over and over again until
168 * there are enough bits to satisfy the caller. The @timer@
169 * function is called frequently throughout the generator's
173 extern void rand_noisesrc(rand_pool */
*r*/
, const rand_source */
*s*/
);
175 /* --- @rand_key@ --- *
177 * Arguments: @rand_pool *r@ = pointer to a randomness pool
178 * @const void *k@ = pointer to key data
179 * @size_t sz@ = size of key data
183 * Use: Sets the secret key for a randomness pool. The key is used
184 * when mixing in new random bits.
187 extern void rand_key(rand_pool */
*r*/
, const void */
*k*/
, size_t /*sz*/);
189 /* --- @rand_add@ --- *
191 * Arguments: @rand_pool *r@ = pointer to a randomness pool
192 * @const void *p@ = pointer a buffer of data to add
193 * @size_t sz@ = size of the data buffer
194 * @unsigned goodbits@ = number of good bits estimated in buffer
198 * Use: Mixes the data in the buffer with the contents of the
199 * pool. The estimate of the number of good bits is added to
200 * the pool's own count. The mixing operation is not
201 * cryptographically strong. However, data in the input pool
202 * isn't output directly, only through the one-way gating
203 * operation, so that shouldn't matter.
206 extern void rand_add(rand_pool */
*r*/
,
207 const void */
*p*/
, size_t /*sz*/,
208 unsigned /*goodbits*/);
210 /* --- @rand_goodbits@ --- *
212 * Arguments: @rand_pool *r@ = pointer to a randomness pool
214 * Returns: Estimate of the number of good bits remaining in the pool.
217 extern unsigned rand_goodbits(rand_pool */
*r*/
);
219 /* --- @rand_gate@ --- *
221 * Arguments: @rand_pool *r@ = pointer to a randomness pool
225 * Use: Mixes up the entire state of the generator in a nonreversible
229 extern void rand_gate(rand_pool */
*r*/
);
231 /* --- @rand_stretch@ --- *
233 * Arguments: @rand_pool *r@ = pointer to a randomness pool
237 * Use: Stretches the contents of the output buffer by transforming
238 * it in a nonreversible way. This doesn't add any entropy
239 * worth speaking about, but it works well enough when the
240 * caller doesn't care about that sort of thing.
243 extern void rand_stretch(rand_pool */
*r*/
);
245 /* --- @rand_get@ --- *
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
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 without also having knowledge of the secret key.
257 * The good bits counter is decremented, although no special
258 * action is taken if it reaches zero.
261 extern void rand_get(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
263 /* --- @rand_getgood@ --- *
265 * Arguments: @rand_pool *r@ = pointer to a randomness pool
266 * @void *p@ = pointer to output buffer
267 * @size_t sz@ = size of output buffer
271 * Use: Gets random data from the pool. The pool's contents can't be
272 * determined from the output of this function; nor can the
273 * output data be determined from a knowledge of the data input
274 * to the pool wihtout also having knowledge of the secret key.
275 * If a noise source is attached to the pool in question, it is
276 * called to replenish the supply of good bits in the pool;
277 * otherwise this call is equivalent to @rand_get@.
280 extern void rand_getgood(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
282 /*----- Generic random number generator interface -------------------------*/
284 /* --- Miscellaneous operations --- */
287 RAND_GATE
= GRAND_SPECIFIC
, /* No args */
288 RAND_STRETCH
, /* No args */
289 RAND_KEY
, /* @const void *k, size_t sz@ */
290 RAND_NOISESRC
/* @const rand_source *s@ */
293 /* --- Default random number generator --- */
295 extern grand rand_global
;
297 /* --- @rand_create@ --- *
301 * Returns: Pointer to a generic generator.
303 * Use: Constructs a generic generator interface over a Catacomb
304 * entropy pool generator.
307 extern grand
*rand_create(void);
309 /*----- That's all, folks -------------------------------------------------*/