3 * $Id: rand.h,v 1.4 1999/12/10 23:29:48 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 1.4 1999/12/10 23:29:48 mdw
34 * Change header file guard names.
36 * Revision 1.3 1999/10/15 21:04:30 mdw
37 * Increase output buffer a bit for performance.
39 * Revision 1.2 1999/10/12 21:00:15 mdw
40 * Make pool and buffer sizes more sensible.
42 * Revision 1.1 1999/09/03 08:41:12 mdw
47 /*----- Notes on the random number generator ------------------------------*
49 * The algorithm is one of the author's own devising. It may therefore be
50 * worth a certain amount of skepticism. However, I've thought about this
51 * method for over a year before actually considering it worth implementing.
52 * With a little bit of luck, it should have received some peer review by the
53 * time this code is actually properly released, and it'll be worth a bit
54 * more confidence. My earlier generator was very similar in structure to
55 * the Linux /dev/random device. This generator is intended to address
56 * concerns I expressed about the Linux generator in a Usenet article to
59 * The generator is divided into two parts: an input pool and an output
60 * buffer. New random data is placed into the pool in the way described
61 * below, which is shamelessly stolen from the Linux /dev/random generator.
62 * The only interaction that the pool has on the output buffer is through the
63 * keyed `gating' operation, which mixes up and redistributes all of the
64 * generator's state in an irreversible manner. Random bytes, when
65 * requested, are extracted from the output buffer in a linear fashion.
67 * The input pool is best seen as being eight shift registers in parallel.
68 * Data is added to the pool one octet at a time. Each bit of a new octet is
69 * added to a different shift register, by adding it (mod 2) with other bits
70 * according to the coefficients of a primitive polynomial. Each new byte is
71 * rotated before being added into the pool, in a half-hearted attempt to
72 * protect against biases in the input data (e.g., top bits being clear on
75 * The gating operation takes a keyed hash of the entire generator state,
76 * uses it as the key for a symmetric cipher, and encrypts the state. The
77 * key is then discarded. The result is that every ouptut bit of the
78 * operation depends in a complex way on every input bit, but the operation
81 * As an added wrinkle, 160 bits of the output buffer are never actually
82 * output. They are used in the gating operation only, as an extra item that
83 * an adversary has to guess before predicting generator output.
86 #ifndef CATACOMB_RAND_H
87 #define CATACOMB_RAND_H
93 /*----- Header files ------------------------------------------------------*/
97 #ifndef CATACOMB_GRAND_H
101 #ifndef CATACOMB_RMD160_HMAC_H
102 # include "rmd160-hmac.h"
105 /*----- Magic numbers -----------------------------------------------------*/
107 #define RAND_POOLSZ 128 /* Input pool size in bytes */
108 #define RAND_BUFSZ 512 /* Output buffer size in bytes */
109 #define RAND_SECSZ 20 /* Secret octets in output buffer */
111 #define RAND_IBITS (RAND_POOLSZ * 8)
112 #define RAND_OBITS (RAND_BUFSZ * 8)
114 /*----- Data structures ---------------------------------------------------*/
116 /* --- A random number generator pool --- */
118 typedef struct rand_pool
{
119 octet pool
[RAND_POOLSZ
]; /* Actual contents of the pool */
120 unsigned i
; /* Current index into pool */
121 unsigned irot
; /* Current rotation applied */
122 unsigned ibits
; /* Number of good bits in pool */
123 octet buf
[RAND_BUFSZ
]; /* Random octet output buffer */
124 unsigned o
; /* Current index into buffer */
125 unsigned obits
; /* Number of good bits in buffer */
126 rmd160_mackey k
; /* Secret key for this pool */
127 const struct rand_source
*s
; /* System-specific noise source */
130 #define RAND_GLOBAL ((rand_pool *)0) /* The global randomness pool */
132 /* --- A noise source --- */
134 typedef struct rand_source
{
135 void (*getnoise
)(rand_pool */
*r*/
); /* Acquire more noise */
136 int (*timer
)(rand_pool */
*r*/
); /* Get noise from current time */
139 /*----- Functions provided ------------------------------------------------*/
141 /* --- @rand_init@ --- *
143 * Arguments: @rand_pool *r@ = pointer to a randomness pool
147 * Use: Initializes a randomness pool. The pool doesn't start out
148 * very random: that's your job to sort out.
151 extern void rand_init(rand_pool */
*r*/
);
153 /* --- @rand_noisesrc@ --- *
155 * Arguments: @rand_pool *r@ = pointer to a randomness pool
156 * @const rand_source *s@ = pointer to source definition
160 * Use: Sets a noise source for a randomness pool. When the pool's
161 * estimate of good random bits falls to zero, the @getnoise@
162 * function is called, passing the pool handle as an argument.
163 * It is expected to increase the number of good bits by at
164 * least one, because it'll be called over and over again until
165 * there are enough bits to satisfy the caller. The @timer@
166 * function is called frequently throughout the generator's
170 extern void rand_noisesrc(rand_pool */
*r*/
, const rand_source */
*s*/
);
172 /* --- @rand_key@ --- *
174 * Arguments: @rand_pool *r@ = pointer to a randomness pool
175 * @const void *k@ = pointer to key data
176 * @size_t sz@ = size of key data
180 * Use: Sets the secret key for a randomness pool. The key is used
181 * when mixing in new random bits.
184 extern void rand_key(rand_pool */
*r*/
, const void */
*k*/
, size_t /*sz*/);
186 /* --- @rand_add@ --- *
188 * Arguments: @rand_pool *r@ = pointer to a randomness pool
189 * @const void *p@ = pointer a buffer of data to add
190 * @size_t sz@ = size of the data buffer
191 * @unsigned goodbits@ = number of good bits estimated in buffer
195 * Use: Mixes the data in the buffer with the contents of the
196 * pool. The estimate of the number of good bits is added to
197 * the pool's own count. The mixing operation is not
198 * cryptographically strong. However, data in the input pool
199 * isn't output directly, only through the one-way gating
200 * operation, so that shouldn't matter.
203 extern void rand_add(rand_pool */
*r*/
,
204 const void */
*p*/
, size_t /*sz*/,
205 unsigned /*goodbits*/);
207 /* --- @rand_goodbits@ --- *
209 * Arguments: @rand_pool *r@ = pointer to a randomness pool
211 * Returns: Estimate of the number of good bits remaining in the pool.
214 extern unsigned rand_goodbits(rand_pool */
*r*/
);
216 /* --- @rand_gate@ --- *
218 * Arguments: @rand_pool *r@ = pointer to a randomness pool
222 * Use: Mixes up the entire state of the generator in a nonreversible
226 extern void rand_gate(rand_pool */
*r*/
);
228 /* --- @rand_stretch@ --- *
230 * Arguments: @rand_pool *r@ = pointer to a randomness pool
234 * Use: Stretches the contents of the output buffer by transforming
235 * it in a nonreversible way. This doesn't add any entropy
236 * worth speaking about, but it works well enough when the
237 * caller doesn't care about that sort of thing.
240 extern void rand_stretch(rand_pool */
*r*/
);
242 /* --- @rand_get@ --- *
244 * Arguments: @rand_pool *r@ = pointer to a randomness pool
245 * @void *p@ = pointer to output buffer
246 * @size_t sz@ = size of output buffer
250 * Use: Gets random data from the pool. The pool's contents can't be
251 * determined from the output of this function; nor can the
252 * output data be determined from a knowledge of the data input
253 * to the pool wihtout also having knowledge of the secret key.
254 * The good bits counter is decremented, although no special
255 * action is taken if it reaches zero.
258 extern void rand_get(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
260 /* --- @rand_getgood@ --- *
262 * Arguments: @rand_pool *r@ = pointer to a randomness pool
263 * @void *p@ = pointer to output buffer
264 * @size_t sz@ = size of output buffer
268 * Use: Gets random data from the pool. The pool's contents can't be
269 * determined from the output of this function; nor can the
270 * output data be determined from a knowledge of the data input
271 * to the pool wihtout also having knowledge of the secret key.
272 * If a noise source is attached to the pool in question, it is
273 * called to replenish the supply of good bits in the pool;
274 * otherwise this call is equivalent to @rand_get@.
277 extern void rand_getgood(rand_pool */
*r*/
, void */
*p*/
, size_t /*sz*/);
279 /*----- Generic random number generator interface -------------------------*/
281 /* --- Miscellaneous operations --- */
284 RAND_GATE
= GRAND_SPECIFIC
, /* No args */
285 RAND_STRETCH
, /* No args */
286 RAND_KEY
, /* @const void *k, size_t sz@ */
287 RAND_NOISESRC
/* @const rand_source *s@ */
290 /* --- Default random number generator --- */
292 extern grand rand_global
;
294 /* --- @rand_create@ --- *
298 * Returns: Pointer to a generic generator.
300 * Use: Constructs a generic generator interface over a Catacomb
301 * entropy pool generator.
304 extern grand
*rand_create(void);
306 /*----- That's all, folks -------------------------------------------------*/