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 1.12 2006/01/26 08:19:48 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
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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>
53 #include <machine/clock.h>
56 #include <i386/icu/icu.h>
62 * The pool is stirred with a primitive polynomial of degree 128
63 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
64 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
66 #define POOLWORDS 128 /* Power of 2 - note that this is 32-bit words */
67 #define POOLBITS (POOLWORDS*32)
70 #define TAP1 99 /* The polynomial taps */
76 #define TAP1 62 /* The polynomial taps */
82 #error No primitive polynomial available for chosen POOLWORDS
85 #define WRITEBUFFER 512 /* size in bytes */
87 /* There is actually only one of these, globally. */
88 struct random_bucket {
96 /* There is one of these per entropy source */
97 struct timer_rand_state {
103 static struct random_bucket random_state;
104 static u_int32_t random_pool[POOLWORDS];
105 static struct timer_rand_state keyboard_timer_state;
106 static struct timer_rand_state extract_timer_state;
107 static struct timer_rand_state irq_timer_state[MAX_INTS];
109 static struct timer_rand_state blkdev_timer_state[MAX_BLKDEV];
111 static struct wait_queue *random_wait;
112 static thread_t rand_td;
113 static int rand_td_slot;
115 static void add_timer_randomness(struct random_bucket *r,
116 struct timer_rand_state *state, u_int num);
119 * Called from early boot
122 rand_initialize(void)
124 random_state.add_ptr = 0;
125 random_state.entropy_count = 0;
126 random_state.pool = random_pool;
128 random_state.rsel.si_flags = 0;
129 random_state.rsel.si_pid = 0;
133 * Random number generator helper thread.
135 * Note that rand_td_slot is initially 0, which means nothing will try
136 * to schedule our thread until we reset it to -1. This also prevents
137 * any attempt to schedule the thread before it has been initialized.
141 rand_thread_loop(void *dummy)
147 if ((slot = rand_td_slot) >= 0) {
148 add_timer_randomness(&random_state,
149 &irq_timer_state[slot], slot);
153 * The fewer bits we have, the shorter we sleep, up to a
154 * point. We use an interrupt to trigger the thread once
155 * we have slept the calculated amount of time.
157 count = random_state.entropy_count * hz / POOLBITS;
162 tsleep(rand_td, 0, "rwait", count);
163 lwkt_deschedule_self(rand_td);
171 rand_thread_init(void)
173 lwkt_create(rand_thread_loop, NULL, &rand_td, NULL, 0, 0, "random");
176 SYSINIT(rand, SI_SUB_HELPER_THREADS, SI_ORDER_ANY, rand_thread_init, 0);
179 * This function adds an int into the entropy "pool". It does not
180 * update the entropy estimate. The caller must do this if appropriate.
182 * The pool is stirred with a primitive polynomial of degree 128
183 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
184 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
186 * We rotate the input word by a changing number of bits, to help
187 * assure that all bits in the entropy get toggled. Otherwise, if we
188 * consistently feed the entropy pool small numbers (like ticks and
189 * scancodes, for example), the upper bits of the entropy pool don't
190 * get affected. --- TYT, 10/11/95
193 add_entropy_word(struct random_bucket *r, const u_int32_t input)
198 w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
199 i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
201 r->input_rotate = (r->input_rotate + 7) & 31;
204 * At the beginning of the pool, add an extra 7 bits
205 * rotation, so that successive passes spread the
206 * input bits across the pool evenly.
208 r->input_rotate = (r->input_rotate + 14) & 31;
210 /* XOR in the various taps */
211 w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
212 w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
213 w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
214 w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
215 w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
217 /* Rotate w left 1 bit (stolen from SHA) and store */
218 r->pool[i] = (w << 1) | (w >> 31);
222 * This function adds entropy to the entropy "pool" by using timing
223 * delays. It uses the timer_rand_state structure to make an estimate
224 * of how any bits of entropy this call has added to the pool.
226 * The number "num" is also added to the pool - it should somehow describe
227 * the type of event which just happened. This is currently 0-255 for
228 * keyboard scan codes, and 256 upwards for interrupts.
229 * On the i386, this is assumed to be at most 16 bits, and the high bits
230 * are used for a high-resolution timer.
233 add_timer_randomness(struct random_bucket *r, struct timer_rand_state *state,
241 num ^= sys_cputimer->count() << 16;
243 num ^= ~(u_int)rdtsc();
244 count = r->entropy_count + 2;
245 if (count > POOLBITS)
247 r->entropy_count = count;
251 add_entropy_word(r, (u_int32_t) num);
252 add_entropy_word(r, time);
255 * Calculate number of bits of randomness we probably
256 * added. We take into account the first and second order
257 * deltas in order to make our estimate.
259 delta = time - state->last_time;
260 state->last_time = time;
262 delta2 = delta - state->last_delta;
263 state->last_delta = delta;
265 if (delta < 0) delta = -delta;
266 if (delta2 < 0) delta2 = -delta2;
267 delta = MIN(delta, delta2) >> 1;
268 for (nbits = 0; delta; nbits++)
271 /* Prevent overflow */
272 count = r->entropy_count + nbits;
273 if (count > POOLBITS)
276 r->entropy_count = count;
278 if (count >= 8 && try_mplock()) {
279 selwakeup(&random_state.rsel);
285 add_keyboard_randomness(u_char scancode)
287 add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
291 * This routine is called from an interrupt and must be very efficient.
294 add_interrupt_randomness(int intr)
296 if (rand_td_slot < 0) {
298 lwkt_schedule(rand_td);
304 add_blkdev_randomness(int major)
306 if (major >= MAX_BLKDEV)
309 add_timer_randomness(&random_state, &blkdev_timer_state[major],
315 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
318 * This function extracts randomness from the "entropy pool", and
319 * returns it in a buffer. This function computes how many remaining
320 * bits of entropy are left in the pool, but it does not restrict the
321 * number of bytes that are actually obtained.
324 extract_entropy(struct random_bucket *r, char *buf, int nbytes)
329 add_timer_randomness(r, &extract_timer_state, nbytes);
331 /* Redundant, but just in case... */
332 if (r->entropy_count > POOLBITS)
333 r->entropy_count = POOLBITS;
334 /* Why is this here? Left in from Ted Ts'o. Perhaps to limit time. */
339 if (r->entropy_count / 8 >= nbytes)
340 r->entropy_count -= nbytes*8;
342 r->entropy_count = 0;
345 /* Hash the pool to get the output */
350 for (i = 0; i < POOLWORDS; i += 16)
351 MD5Transform(tmp, (char *)(r->pool+i));
352 /* Modify pool so next hash will produce different results */
353 add_entropy_word(r, tmp[0]);
354 add_entropy_word(r, tmp[1]);
355 add_entropy_word(r, tmp[2]);
356 add_entropy_word(r, tmp[3]);
358 * Run the MD5 Transform one more time, since we want
359 * to add at least minimal obscuring of the inputs to
360 * add_entropy_word(). --- TYT
362 MD5Transform(tmp, (char *)(r->pool));
364 /* Copy data to destination buffer */
371 /* Wipe data from memory */
372 bzero(tmp, sizeof(tmp));
377 #ifdef notused /* XXX NOT the exported kernel interface */
379 * This function is the exported kernel interface. It returns some
380 * number of good random numbers, suitable for seeding TCP sequence
384 get_random_bytes(void *buf, u_int nbytes)
386 extract_entropy(&random_state, (char *) buf, nbytes);
391 read_random(void *buf, u_int nbytes)
393 if ((nbytes * 8) > random_state.entropy_count)
394 nbytes = random_state.entropy_count / 8;
396 return extract_entropy(&random_state, (char *)buf, nbytes);
400 read_random_unlimited(void *buf, u_int nbytes)
402 return extract_entropy(&random_state, (char *)buf, nbytes);
407 write_random(const char *buf, u_int nbytes)
412 for (i = nbytes, p = (u_int32_t *)buf;
413 i >= sizeof(u_int32_t);
414 i-= sizeof(u_int32_t), p++)
415 add_entropy_word(&random_state, *p);
419 add_entropy_word(&random_state, word);
426 add_true_randomness(int val)
430 add_entropy_word(&random_state, val);
431 count = random_state.entropy_count + 8 *sizeof(val);
432 if (count > POOLBITS)
434 random_state.entropy_count = count;
435 selwakeup(&random_state.rsel);
439 random_poll(dev_t dev, int events, struct thread *td)
444 if (events & (POLLIN | POLLRDNORM)) {
445 if (random_state.entropy_count >= 8)
446 revents |= events & (POLLIN | POLLRDNORM);
448 selrecord(td, &random_state.rsel);
451 if (events & (POLLOUT | POLLWRNORM))
452 revents |= events & (POLLOUT | POLLWRNORM); /* heh */