3 * $Id: rand.h,v 1.3 1999/10/15 21:04:30 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 1.3 1999/10/15 21:04:30 mdw
34 * Increase output buffer a bit for performance.
36 * Revision 1.2 1999/10/12 21:00:15 mdw
37 * Make pool and buffer sizes more sensible.
39 * Revision 1.1 1999/09/03 08:41:12 mdw
44 /*----- Notes on the random number generator ------------------------------*
46 * The algorithm is one of the author's own devising. It may therefore be
47 * worth a certain amount of skepticism. However, I've thought about this
48 * method for over a year before actually considering it worth implementing.
49 * With a little bit of luck, it should have received some peer review by the
50 * time this code is actually properly released, and it'll be worth a bit
51 * more confidence. My earlier generator was very similar in structure to
52 * the Linux /dev/random device. This generator is intended to address
53 * concerns I expressed about the Linux generator in a Usenet article to
56 * The generator is divided into two parts: an input pool and an outpu
57 * buffer. New random data is placed into the pool in the way described
58 * below, which is shamelessly stolen from the Linux /dev/random generator.
59 * The only interaction that the pool has on the output buffer is through the
60 * keyed `gating' operation, which mixes up and redistributes all of the
61 * generator's state in an irreversible manner. Random bytes, when
62 * requested, are extracted from the output buffer in a linear fashion.
64 * The input pool is best seen as being eight shift registers in parallel.
65 * Data is added to the pool one octet at a time. Each bit of a new octet is
66 * added to a different shift register, by adding it (mod 2) with other bits
67 * according to the coefficients of a primitive polynomial. Each new byte is
68 * rotated before being added into the pool, in a half-hearted attempt to
69 * protect against biases in the input data (e.g., top bits being clear on
72 * The gating operation takes a keyed hash of the entire generator state,
73 * uses it as the key for a symmetric cipher, and encrypts the state. The
74 * key is then discarded. The result is that every ouptut bit of the
75 * operation depends in a complex way on every input bit, but the operation
78 * As an added wrinkle, 160 bits of the output buffer are never actually
79 * output. They are used in the gating operation only, as an extra item that
80 * an adversary has to guess before predicting generator output.
90 /*----- Header files ------------------------------------------------------*/
94 #include "rmd160-hmac.h"
96 /*----- Magic numbers -----------------------------------------------------*/
98 #define RAND_POOLSZ 128 /* Input pool size in bytes */
99 #define RAND_BUFSZ 512 /* Output buffer size in bytes */
100 #define RAND_SECSZ 20 /* Secret octets in output buffer */
102 #define RAND_IBITS (RAND_POOLSZ * 8)
103 #define RAND_OBITS (RAND_BUFSZ * 8)
105 /*----- Data structures ---------------------------------------------------*/
107 /* --- A random number generator pool --- */
109 typedef struct rand_pool
{
110 octet pool
[RAND_POOLSZ
]; /* Actual contents of the pool */
111 unsigned i
; /* Current index into pool */
112 unsigned irot
; /* Current rotation applied */
113 unsigned ibits
; /* Number of good bits in pool */
114 octet buf
[RAND_BUFSZ
]; /* Random octet output buffer */
115 unsigned o
; /* Current index into buffer */
116 unsigned obits
; /* Number of good bits in buffer */
117 rmd160_mackey k
; /* Secret key for this pool */
118 const struct rand_source
*s
; /* System-specific noise source */
121 #define RAND_GLOBAL ((rand_pool *)0) /* The global randomness pool */
123 /* --- A noise source --- */
125 typedef struct rand_source
{
126 void (*getnoise
)(rand_pool */
*r*/
); /* Acquire more noise */
127 int (*timer
)(rand_pool */
*r*/
); /* Get noise from current time */
130 /*----- Functions provided ------------------------------------------------*/
132 /* --- @rand_init@ --- *
134 * Arguments: @rand_pool *r@ = pointer to a randomness pool
138 * Use: Initializes a randomness pool. The pool doesn't start out
139 * very random: that's your job to sort out.
142 extern void rand_init(rand_pool */
*r*/
);
144 /* --- @rand_noisesrc@ --- *
146 * Arguments: @rand_pool *r@ = pointer to a randomness pool
147 * @const rand_source *s@ = pointer to source definition
151 * Use: Sets a noise source for a randomness pool. When the pool's
152 * estimate of good random bits falls to zero, the @getnoise@
153 * function is called, passing the pool handle as an argument.
154 * It is expected to increase the number of good bits by at
155 * least one, because it'll be called over and over again until
156 * there are enough bits to satisfy the caller. The @timer@
157 * function is called frequently throughout the generator's
161 extern void rand_noisesrc(rand_pool */
*r*/
, const rand_source */
*s*/
);
163 /* --- @rand_key@ --- *
165 * Arguments: @rand_pool *r@ = pointer to a randomness pool
166 * @const void *k@ = pointer to key data
167 * @size_t sz@ = size of key data
171 * Use: Sets the secret key for a randomness pool. The key is used
172 * when mixing in new random bits.
175 extern void rand_key(rand_pool */
*r*/
, const void */
*k*/
, size_t /*sz*/);
177 /* --- @rand_add@ --- *
179 * Arguments: @rand_pool *r@ = pointer to a randomness pool
180 * @const void *p@ = pointer a buffer of data to add
181 * @size_t sz@ = size of the data buffer
182 * @unsigned goodbits@ = number of good bits estimated in buffer
186 * Use: Mixes the data in the buffer with the contents of the
187 * pool. The estimate of the number of good bits is added to
188 * the pool's own count. The mixing operation is not
189 * cryptographically strong. However, data in the input pool
190 * isn't output directly, only through the one-way gating
191 * operation, so that shouldn't matter.
194 extern void rand_add(rand_pool */
*r*/
,
195 const void */
*p*/
, size_t /*sz*/,
196 unsigned /*goodbits*/);
198 /* --- @rand_goodbits@ --- *
200 * Arguments: @rand_pool *r@ = pointer to a randomness pool
202 * Returns: Estimate of the number of good bits remaining in the pool.
205 extern unsigned rand_goodbits(rand_pool */
*r*/
);
207 /* --- @rand_gate@ --- *
209 * Arguments: @rand_pool *r@ = pointer to a randomness pool
213 * Use: Mixes up the entire state of the generator in a nonreversible
217 extern void rand_gate(rand_pool */
*r*/
);
219 /* --- @rand_stretch@ --- *
221 * Arguments: @rand_pool *r@ = pointer to a randomness pool
225 * Use: Stretches the contents of the output buffer by transforming
226 * it in a nonreversible way. This doesn't add any entropy
227 * worth speaking about, but it works well enough when the
228 * caller doesn't care about that sort of thing.
231 extern void rand_stretch(rand_pool */
*r*/
);
233 /* --- @rand_get@ --- *
235 * Arguments: @rand_pool *r@ = pointer to a randomness pool
236 * @void *p@ = pointer to output buffer
237 * @size_t sz@ = size of output buffer
241 * Use: Gets random data from the pool. The pool's contents can't be
242 * determined from the output of this function; nor can the
243 * output data be determined from a knowledge of the data input
244 * to the pool wihtout also having knowledge of the secret key.
245 * The good bits counter is decremented, although no special
246 * action is taken if it reaches zero.
249 extern void rand_get(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
251 /* --- @rand_getgood@ --- *
253 * Arguments: @rand_pool *r@ = pointer to a randomness pool
254 * @void *p@ = pointer to output buffer
255 * @size_t sz@ = size of output buffer
259 * Use: Gets random data from the pool. The pool's contents can't be
260 * determined from the output of this function; nor can the
261 * output data be determined from a knowledge of the data input
262 * to the pool wihtout also having knowledge of the secret key.
263 * If a noise source is attached to the pool in question, it is
264 * called to replenish the supply of good bits in the pool;
265 * otherwise this call is equivalent to @rand_get@.
268 extern void rand_getgood(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
270 /*----- That's all, folks -------------------------------------------------*/