2 * kern_random.c -- A strong random number generator
4 * $FreeBSD: src/sys/kern/kern_random.c,v 1.36.2.4 2002/09/17 17:11:57 sam Exp $
5 * $DragonFly: src/sys/kern/Attic/kern_random.c,v 1.9 2005/06/06 15:02:28 dillon Exp $
7 * Version 0.95, last modified 18-Oct-95
9 * Copyright Theodore Ts'o, 1994, 1995. All rights reserved.
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, and the entire permission notice in its entirety,
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17 * 2. Redistributions in binary form must reproduce the above copyright
18 * notice, this list of conditions and the following disclaimer in the
19 * documentation and/or other materials provided with the distribution.
20 * 3. The name of the author may not be used to endorse or promote
21 * products derived from this software without specific prior
24 * ALTERNATIVELY, this product may be distributed under the terms of
25 * the GNU Public License, in which case the provisions of the GPL are
26 * required INSTEAD OF the above restrictions. (This clause is
27 * necessary due to a potential bad interaction between the GPL and
28 * the restrictions contained in a BSD-style copyright.)
30 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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43 #include <sys/param.h>
44 #include <sys/kernel.h>
47 #include <sys/random.h>
48 #include <sys/select.h>
49 #include <sys/systm.h>
50 #include <sys/systimer.h>
51 #include <sys/thread2.h>
54 #include <i386/isa/icu.h>
60 * The pool is stirred with a primitive polynomial of degree 128
61 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
62 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
64 #define POOLWORDS 128 /* Power of 2 - note that this is 32-bit words */
65 #define POOLBITS (POOLWORDS*32)
68 #define TAP1 99 /* The polynomial taps */
74 #define TAP1 62 /* The polynomial taps */
80 #error No primitive polynomial available for chosen POOLWORDS
83 #define WRITEBUFFER 512 /* size in bytes */
85 /* There is actually only one of these, globally. */
86 struct random_bucket {
94 /* There is one of these per entropy source */
95 struct timer_rand_state {
101 static struct random_bucket random_state;
102 static u_int32_t random_pool[POOLWORDS];
103 static struct timer_rand_state keyboard_timer_state;
104 static struct timer_rand_state extract_timer_state;
105 static struct timer_rand_state irq_timer_state[MAX_INTS];
107 static struct timer_rand_state blkdev_timer_state[MAX_BLKDEV];
109 static struct wait_queue *random_wait;
112 rand_initialize(void)
114 random_state.add_ptr = 0;
115 random_state.entropy_count = 0;
116 random_state.pool = random_pool;
118 random_state.rsel.si_flags = 0;
119 random_state.rsel.si_pid = 0;
123 * This function adds an int into the entropy "pool". It does not
124 * update the entropy estimate. The caller must do this if appropriate.
126 * The pool is stirred with a primitive polynomial of degree 128
127 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
128 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
130 * We rotate the input word by a changing number of bits, to help
131 * assure that all bits in the entropy get toggled. Otherwise, if we
132 * consistently feed the entropy pool small numbers (like ticks and
133 * scancodes, for example), the upper bits of the entropy pool don't
134 * get affected. --- TYT, 10/11/95
137 add_entropy_word(struct random_bucket *r, const u_int32_t input)
142 w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
143 i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
145 r->input_rotate = (r->input_rotate + 7) & 31;
148 * At the beginning of the pool, add an extra 7 bits
149 * rotation, so that successive passes spread the
150 * input bits across the pool evenly.
152 r->input_rotate = (r->input_rotate + 14) & 31;
154 /* XOR in the various taps */
155 w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
156 w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
157 w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
158 w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
159 w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
161 /* Rotate w left 1 bit (stolen from SHA) and store */
162 r->pool[i] = (w << 1) | (w >> 31);
166 * This function adds entropy to the entropy "pool" by using timing
167 * delays. It uses the timer_rand_state structure to make an estimate
168 * of how any bits of entropy this call has added to the pool.
170 * The number "num" is also added to the pool - it should somehow describe
171 * the type of event which just happened. This is currently 0-255 for
172 * keyboard scan codes, and 256 upwards for interrupts.
173 * On the i386, this is assumed to be at most 16 bits, and the high bits
174 * are used for a high-resolution timer.
177 add_timer_randomness(struct random_bucket *r, struct timer_rand_state *state,
184 num ^= sys_cputimer->count() << 16;
185 r->entropy_count += 2;
189 add_entropy_word(r, (u_int32_t) num);
190 add_entropy_word(r, time);
193 * Calculate number of bits of randomness we probably
194 * added. We take into account the first and second order
195 * deltas in order to make our estimate.
197 delta = time - state->last_time;
198 state->last_time = time;
200 delta2 = delta - state->last_delta;
201 state->last_delta = delta;
203 if (delta < 0) delta = -delta;
204 if (delta2 < 0) delta2 = -delta2;
205 delta = MIN(delta, delta2) >> 1;
206 for (nbits = 0; delta; nbits++)
209 r->entropy_count += nbits;
211 /* Prevent overflow */
212 if (r->entropy_count > POOLBITS)
213 r->entropy_count = POOLBITS;
215 if (r->entropy_count >= 8)
216 selwakeup(&random_state.rsel);
220 add_keyboard_randomness(u_char scancode)
222 add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
226 add_interrupt_randomness(int intr)
228 add_timer_randomness(&random_state, &irq_timer_state[intr], intr);
233 add_blkdev_randomness(int major)
235 if (major >= MAX_BLKDEV)
238 add_timer_randomness(&random_state, &blkdev_timer_state[major],
244 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
247 * This function extracts randomness from the "entropy pool", and
248 * returns it in a buffer. This function computes how many remaining
249 * bits of entropy are left in the pool, but it does not restrict the
250 * number of bytes that are actually obtained.
253 extract_entropy(struct random_bucket *r, char *buf, int nbytes)
258 add_timer_randomness(r, &extract_timer_state, nbytes);
260 /* Redundant, but just in case... */
261 if (r->entropy_count > POOLBITS)
262 r->entropy_count = POOLBITS;
263 /* Why is this here? Left in from Ted Ts'o. Perhaps to limit time. */
268 if (r->entropy_count / 8 >= nbytes)
269 r->entropy_count -= nbytes*8;
271 r->entropy_count = 0;
274 /* Hash the pool to get the output */
279 for (i = 0; i < POOLWORDS; i += 16)
280 MD5Transform(tmp, (char *)(r->pool+i));
281 /* Modify pool so next hash will produce different results */
282 add_entropy_word(r, tmp[0]);
283 add_entropy_word(r, tmp[1]);
284 add_entropy_word(r, tmp[2]);
285 add_entropy_word(r, tmp[3]);
287 * Run the MD5 Transform one more time, since we want
288 * to add at least minimal obscuring of the inputs to
289 * add_entropy_word(). --- TYT
291 MD5Transform(tmp, (char *)(r->pool));
293 /* Copy data to destination buffer */
300 /* Wipe data from memory */
301 bzero(tmp, sizeof(tmp));
306 #ifdef notused /* XXX NOT the exported kernel interface */
308 * This function is the exported kernel interface. It returns some
309 * number of good random numbers, suitable for seeding TCP sequence
313 get_random_bytes(void *buf, u_int nbytes)
315 extract_entropy(&random_state, (char *) buf, nbytes);
320 read_random(void *buf, u_int nbytes)
322 if ((nbytes * 8) > random_state.entropy_count)
323 nbytes = random_state.entropy_count / 8;
325 return extract_entropy(&random_state, (char *)buf, nbytes);
329 read_random_unlimited(void *buf, u_int nbytes)
331 return extract_entropy(&random_state, (char *)buf, nbytes);
336 write_random(const char *buf, u_int nbytes)
341 for (i = nbytes, p = (u_int32_t *)buf;
342 i >= sizeof(u_int32_t);
343 i-= sizeof(u_int32_t), p++)
344 add_entropy_word(&random_state, *p);
348 add_entropy_word(&random_state, word);
355 add_true_randomness(int val)
357 add_entropy_word(&random_state, val);
358 random_state.entropy_count += 8*sizeof (val);
359 if (random_state.entropy_count > POOLBITS)
360 random_state.entropy_count = POOLBITS;
361 selwakeup(&random_state.rsel);
365 random_poll(dev_t dev, int events, struct thread *td)
370 if (events & (POLLIN | POLLRDNORM)) {
371 if (random_state.entropy_count >= 8)
372 revents |= events & (POLLIN | POLLRDNORM);
374 selrecord(td, &random_state.rsel);
377 if (events & (POLLOUT | POLLWRNORM))
378 revents |= events & (POLLOUT | POLLWRNORM); /* heh */