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 1.11 2006/01/25 19:56:21 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,
16 * including the disclaimer of warranties.
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
31 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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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>
52 #include <machine/clock.h>
55 #include <i386/icu/icu.h>
61 * The pool is stirred with a primitive polynomial of degree 128
62 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
63 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
65 #define POOLWORDS 128 /* Power of 2 - note that this is 32-bit words */
66 #define POOLBITS (POOLWORDS*32)
69 #define TAP1 99 /* The polynomial taps */
75 #define TAP1 62 /* The polynomial taps */
81 #error No primitive polynomial available for chosen POOLWORDS
84 #define WRITEBUFFER 512 /* size in bytes */
86 /* There is actually only one of these, globally. */
87 struct random_bucket {
95 /* There is one of these per entropy source */
96 struct timer_rand_state {
102 static struct random_bucket random_state;
103 static u_int32_t random_pool[POOLWORDS];
104 static struct timer_rand_state keyboard_timer_state;
105 static struct timer_rand_state extract_timer_state;
106 static struct timer_rand_state irq_timer_state[MAX_INTS];
108 static struct timer_rand_state blkdev_timer_state[MAX_BLKDEV];
110 static struct wait_queue *random_wait;
111 static thread_t rand_td;
112 static int rand_td_slot;
114 static void add_timer_randomness(struct random_bucket *r,
115 struct timer_rand_state *state, u_int num);
118 * Called from early boot
121 rand_initialize(void)
123 random_state.add_ptr = 0;
124 random_state.entropy_count = 0;
125 random_state.pool = random_pool;
127 random_state.rsel.si_flags = 0;
128 random_state.rsel.si_pid = 0;
132 * Random number generator helper thread.
134 * Note that rand_td_slot is initially 0, which means nothing will try
135 * to schedule our thread until we reset it to -1. This also prevents
136 * any attempt to schedule the thread before it has been initialized.
140 rand_thread_loop(void *dummy)
146 if ((slot = rand_td_slot) >= 0) {
147 add_timer_randomness(&random_state,
148 &irq_timer_state[slot], slot);
152 * The fewer bits we have, the shorter we sleep, up to a
153 * point. We use an interrupt to trigger the thread once
154 * we have slept the calculated amount of time.
156 count = random_state.entropy_count * hz / POOLBITS;
161 tsleep(rand_td, 0, "rwait", count);
162 lwkt_deschedule_self(rand_td);
170 rand_thread_init(void)
172 lwkt_create(rand_thread_loop, NULL, &rand_td, NULL, 0, 0, "random");
175 SYSINIT(rand, SI_SUB_HELPER_THREADS, SI_ORDER_ANY, rand_thread_init, 0);
178 * This function adds an int into the entropy "pool". It does not
179 * update the entropy estimate. The caller must do this if appropriate.
181 * The pool is stirred with a primitive polynomial of degree 128
182 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
183 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
185 * We rotate the input word by a changing number of bits, to help
186 * assure that all bits in the entropy get toggled. Otherwise, if we
187 * consistently feed the entropy pool small numbers (like ticks and
188 * scancodes, for example), the upper bits of the entropy pool don't
189 * get affected. --- TYT, 10/11/95
192 add_entropy_word(struct random_bucket *r, const u_int32_t input)
197 w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
198 i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
200 r->input_rotate = (r->input_rotate + 7) & 31;
203 * At the beginning of the pool, add an extra 7 bits
204 * rotation, so that successive passes spread the
205 * input bits across the pool evenly.
207 r->input_rotate = (r->input_rotate + 14) & 31;
209 /* XOR in the various taps */
210 w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
211 w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
212 w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
213 w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
214 w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
216 /* Rotate w left 1 bit (stolen from SHA) and store */
217 r->pool[i] = (w << 1) | (w >> 31);
221 * This function adds entropy to the entropy "pool" by using timing
222 * delays. It uses the timer_rand_state structure to make an estimate
223 * of how any bits of entropy this call has added to the pool.
225 * The number "num" is also added to the pool - it should somehow describe
226 * the type of event which just happened. This is currently 0-255 for
227 * keyboard scan codes, and 256 upwards for interrupts.
228 * On the i386, this is assumed to be at most 16 bits, and the high bits
229 * are used for a high-resolution timer.
232 add_timer_randomness(struct random_bucket *r, struct timer_rand_state *state,
240 num ^= sys_cputimer->count() << 16;
242 num ^= ~(u_int)rdtsc();
243 count = r->entropy_count + 2;
244 if (count > POOLBITS)
246 r->entropy_count = count;
250 add_entropy_word(r, (u_int32_t) num);
251 add_entropy_word(r, time);
254 * Calculate number of bits of randomness we probably
255 * added. We take into account the first and second order
256 * deltas in order to make our estimate.
258 delta = time - state->last_time;
259 state->last_time = time;
261 delta2 = delta - state->last_delta;
262 state->last_delta = delta;
264 if (delta < 0) delta = -delta;
265 if (delta2 < 0) delta2 = -delta2;
266 delta = MIN(delta, delta2) >> 1;
267 for (nbits = 0; delta; nbits++)
270 /* Prevent overflow */
271 count = r->entropy_count + nbits;
272 if (count > POOLBITS)
275 r->entropy_count = count;
277 if (count >= 8 && try_mplock()) {
278 selwakeup(&random_state.rsel);
284 add_keyboard_randomness(u_char scancode)
286 add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
290 * This routine is called from an interrupt and must be very efficient.
293 add_interrupt_randomness(int intr)
295 if (rand_td_slot < 0) {
297 lwkt_schedule(rand_td);
303 add_blkdev_randomness(int major)
305 if (major >= MAX_BLKDEV)
308 add_timer_randomness(&random_state, &blkdev_timer_state[major],
314 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
317 * This function extracts randomness from the "entropy pool", and
318 * returns it in a buffer. This function computes how many remaining
319 * bits of entropy are left in the pool, but it does not restrict the
320 * number of bytes that are actually obtained.
323 extract_entropy(struct random_bucket *r, char *buf, int nbytes)
328 add_timer_randomness(r, &extract_timer_state, nbytes);
330 /* Redundant, but just in case... */
331 if (r->entropy_count > POOLBITS)
332 r->entropy_count = POOLBITS;
333 /* Why is this here? Left in from Ted Ts'o. Perhaps to limit time. */
338 if (r->entropy_count / 8 >= nbytes)
339 r->entropy_count -= nbytes*8;
341 r->entropy_count = 0;
344 /* Hash the pool to get the output */
349 for (i = 0; i < POOLWORDS; i += 16)
350 MD5Transform(tmp, (char *)(r->pool+i));
351 /* Modify pool so next hash will produce different results */
352 add_entropy_word(r, tmp[0]);
353 add_entropy_word(r, tmp[1]);
354 add_entropy_word(r, tmp[2]);
355 add_entropy_word(r, tmp[3]);
357 * Run the MD5 Transform one more time, since we want
358 * to add at least minimal obscuring of the inputs to
359 * add_entropy_word(). --- TYT
361 MD5Transform(tmp, (char *)(r->pool));
363 /* Copy data to destination buffer */
370 /* Wipe data from memory */
371 bzero(tmp, sizeof(tmp));
376 #ifdef notused /* XXX NOT the exported kernel interface */
378 * This function is the exported kernel interface. It returns some
379 * number of good random numbers, suitable for seeding TCP sequence
383 get_random_bytes(void *buf, u_int nbytes)
385 extract_entropy(&random_state, (char *) buf, nbytes);
390 read_random(void *buf, u_int nbytes)
392 if ((nbytes * 8) > random_state.entropy_count)
393 nbytes = random_state.entropy_count / 8;
395 return extract_entropy(&random_state, (char *)buf, nbytes);
399 read_random_unlimited(void *buf, u_int nbytes)
401 return extract_entropy(&random_state, (char *)buf, nbytes);
406 write_random(const char *buf, u_int nbytes)
411 for (i = nbytes, p = (u_int32_t *)buf;
412 i >= sizeof(u_int32_t);
413 i-= sizeof(u_int32_t), p++)
414 add_entropy_word(&random_state, *p);
418 add_entropy_word(&random_state, word);
425 add_true_randomness(int val)
429 add_entropy_word(&random_state, val);
430 count = random_state.entropy_count + 8 *sizeof(val);
431 if (count > POOLBITS)
433 random_state.entropy_count = count;
434 selwakeup(&random_state.rsel);
438 random_poll(dev_t dev, int events, struct thread *td)
443 if (events & (POLLIN | POLLRDNORM)) {
444 if (random_state.entropy_count >= 8)
445 revents |= events & (POLLIN | POLLRDNORM);
447 selrecord(td, &random_state.rsel);
450 if (events & (POLLOUT | POLLWRNORM))
451 revents |= events & (POLLOUT | POLLWRNORM); /* heh */