3 * $Id: rand.h,v 1.1 1999/09/03 08:41:12 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 1.1 1999/09/03 08:41:12 mdw
38 /*----- Notes on the random number generator ------------------------------*
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
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.
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
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
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.
84 /*----- Header files ------------------------------------------------------*/
88 #include "rmd160-hmac.h"
90 /*----- Magic numbers -----------------------------------------------------*/
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 */
96 #define RAND_IBITS (RAND_POOLSZ * 8)
97 #define RAND_OBITS (RAND_BUFSZ * 8)
99 /*----- Data structures ---------------------------------------------------*/
101 /* --- A random number generator pool --- */
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 */
115 #define RAND_GLOBAL ((rand_pool *)0) /* The global randomness pool */
117 /* --- A noise source --- */
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 */
124 /*----- Functions provided ------------------------------------------------*/
126 /* --- @rand_init@ --- *
128 * Arguments: @rand_pool *r@ = pointer to a randomness pool
132 * Use: Initializes a randomness pool. The pool doesn't start out
133 * very random: that's your job to sort out.
136 extern void rand_init(rand_pool */
*r*/
);
138 /* --- @rand_noisesrc@ --- *
140 * Arguments: @rand_pool *r@ = pointer to a randomness pool
141 * @const rand_source *s@ = pointer to source definition
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
155 extern void rand_noisesrc(rand_pool */
*r*/
, const rand_source */
*s*/
);
157 /* --- @rand_key@ --- *
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
165 * Use: Sets the secret key for a randomness pool. The key is used
166 * when mixing in new random bits.
169 extern void rand_key(rand_pool */
*r*/
, const void */
*k*/
, size_t /*sz*/);
171 /* --- @rand_add@ --- *
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
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.
188 extern void rand_add(rand_pool */
*r*/
,
189 const void */
*p*/
, size_t /*sz*/,
190 unsigned /*goodbits*/);
192 /* --- @rand_goodbits@ --- *
194 * Arguments: @rand_pool *r@ = pointer to a randomness pool
196 * Returns: Estimate of the number of good bits remaining in the pool.
199 extern unsigned rand_goodbits(rand_pool */
*r*/
);
201 /* --- @rand_gate@ --- *
203 * Arguments: @rand_pool *r@ = pointer to a randomness pool
207 * Use: Mixes up the entire state of the generator in a nonreversible
211 extern void rand_gate(rand_pool */
*r*/
);
213 /* --- @rand_stretch@ --- *
215 * Arguments: @rand_pool *r@ = pointer to a randomness pool
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.
225 extern void rand_stretch(rand_pool */
*r*/
);
227 /* --- @rand_get@ --- *
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
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.
243 extern void rand_get(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
245 /* --- @rand_getgood@ --- *
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 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@.
262 extern void rand_getgood(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
264 /*----- That's all, folks -------------------------------------------------*/