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 1.7 2005/04/30 23:04:21 swildner Exp $
7 * Version 0.95, last modified 18-Oct-95
9 * Copyright Theodore Ts'o, 1994, 1995. All rights reserved.
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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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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>
53 #include <i386/isa/icu.h>
59 * The pool is stirred with a primitive polynomial of degree 128
60 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
61 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
63 #define POOLWORDS 128 /* Power of 2 - note that this is 32-bit words */
64 #define POOLBITS (POOLWORDS*32)
67 #define TAP1 99 /* The polynomial taps */
73 #define TAP1 62 /* The polynomial taps */
79 #error No primitive polynomial available for chosen POOLWORDS
82 #define WRITEBUFFER 512 /* size in bytes */
84 /* There is actually only one of these, globally. */
85 struct random_bucket {
93 /* There is one of these per entropy source */
94 struct timer_rand_state {
100 static struct random_bucket random_state;
101 static u_int32_t random_pool[POOLWORDS];
102 static struct timer_rand_state keyboard_timer_state;
103 static struct timer_rand_state extract_timer_state;
104 static struct timer_rand_state irq_timer_state[MAX_INTS];
106 static struct timer_rand_state blkdev_timer_state[MAX_BLKDEV];
108 static struct wait_queue *random_wait;
111 rand_initialize(void)
113 random_state.add_ptr = 0;
114 random_state.entropy_count = 0;
115 random_state.pool = random_pool;
117 random_state.rsel.si_flags = 0;
118 random_state.rsel.si_pid = 0;
122 * This function adds an int into the entropy "pool". It does not
123 * update the entropy estimate. The caller must do this if appropriate.
125 * The pool is stirred with a primitive polynomial of degree 128
126 * over GF(2), namely x^128 + x^99 + x^59 + x^31 + x^9 + x^7 + 1.
127 * For a pool of size 64, try x^64+x^62+x^38+x^10+x^6+x+1.
129 * We rotate the input word by a changing number of bits, to help
130 * assure that all bits in the entropy get toggled. Otherwise, if we
131 * consistently feed the entropy pool small numbers (like ticks and
132 * scancodes, for example), the upper bits of the entropy pool don't
133 * get affected. --- TYT, 10/11/95
136 add_entropy_word(struct random_bucket *r, const u_int32_t input)
141 w = (input << r->input_rotate) | (input >> (32 - r->input_rotate));
142 i = r->add_ptr = (r->add_ptr - 1) & (POOLWORDS-1);
144 r->input_rotate = (r->input_rotate + 7) & 31;
147 * At the beginning of the pool, add an extra 7 bits
148 * rotation, so that successive passes spread the
149 * input bits across the pool evenly.
151 r->input_rotate = (r->input_rotate + 14) & 31;
153 /* XOR in the various taps */
154 w ^= r->pool[(i+TAP1)&(POOLWORDS-1)];
155 w ^= r->pool[(i+TAP2)&(POOLWORDS-1)];
156 w ^= r->pool[(i+TAP3)&(POOLWORDS-1)];
157 w ^= r->pool[(i+TAP4)&(POOLWORDS-1)];
158 w ^= r->pool[(i+TAP5)&(POOLWORDS-1)];
160 /* Rotate w left 1 bit (stolen from SHA) and store */
161 r->pool[i] = (w << 1) | (w >> 31);
165 * This function adds entropy to the entropy "pool" by using timing
166 * delays. It uses the timer_rand_state structure to make an estimate
167 * of how any bits of entropy this call has added to the pool.
169 * The number "num" is also added to the pool - it should somehow describe
170 * the type of event which just happened. This is currently 0-255 for
171 * keyboard scan codes, and 256 upwards for interrupts.
172 * On the i386, this is assumed to be at most 16 bits, and the high bits
173 * are used for a high-resolution timer.
176 add_timer_randomness(struct random_bucket *r, struct timer_rand_state *state,
183 num ^= cputimer_count() << 16;
184 r->entropy_count += 2;
188 add_entropy_word(r, (u_int32_t) num);
189 add_entropy_word(r, time);
192 * Calculate number of bits of randomness we probably
193 * added. We take into account the first and second order
194 * deltas in order to make our estimate.
196 delta = time - state->last_time;
197 state->last_time = time;
199 delta2 = delta - state->last_delta;
200 state->last_delta = delta;
202 if (delta < 0) delta = -delta;
203 if (delta2 < 0) delta2 = -delta2;
204 delta = MIN(delta, delta2) >> 1;
205 for (nbits = 0; delta; nbits++)
208 r->entropy_count += nbits;
210 /* Prevent overflow */
211 if (r->entropy_count > POOLBITS)
212 r->entropy_count = POOLBITS;
214 if (r->entropy_count >= 8)
215 selwakeup(&random_state.rsel);
219 add_keyboard_randomness(u_char scancode)
221 add_timer_randomness(&random_state, &keyboard_timer_state, scancode);
225 add_interrupt_randomness(int intr)
227 add_timer_randomness(&random_state, &irq_timer_state[intr], intr);
232 add_blkdev_randomness(int major)
234 if (major >= MAX_BLKDEV)
237 add_timer_randomness(&random_state, &blkdev_timer_state[major],
243 #error extract_entropy() assumes that POOLWORDS is a multiple of 16 words.
246 * This function extracts randomness from the "entropy pool", and
247 * returns it in a buffer. This function computes how many remaining
248 * bits of entropy are left in the pool, but it does not restrict the
249 * number of bytes that are actually obtained.
252 extract_entropy(struct random_bucket *r, char *buf, int nbytes)
257 add_timer_randomness(r, &extract_timer_state, nbytes);
259 /* Redundant, but just in case... */
260 if (r->entropy_count > POOLBITS)
261 r->entropy_count = POOLBITS;
262 /* Why is this here? Left in from Ted Ts'o. Perhaps to limit time. */
267 if (r->entropy_count / 8 >= nbytes)
268 r->entropy_count -= nbytes*8;
270 r->entropy_count = 0;
273 /* Hash the pool to get the output */
278 for (i = 0; i < POOLWORDS; i += 16)
279 MD5Transform(tmp, (char *)(r->pool+i));
280 /* Modify pool so next hash will produce different results */
281 add_entropy_word(r, tmp[0]);
282 add_entropy_word(r, tmp[1]);
283 add_entropy_word(r, tmp[2]);
284 add_entropy_word(r, tmp[3]);
286 * Run the MD5 Transform one more time, since we want
287 * to add at least minimal obscuring of the inputs to
288 * add_entropy_word(). --- TYT
290 MD5Transform(tmp, (char *)(r->pool));
292 /* Copy data to destination buffer */
299 /* Wipe data from memory */
300 bzero(tmp, sizeof(tmp));
305 #ifdef notused /* XXX NOT the exported kernel interface */
307 * This function is the exported kernel interface. It returns some
308 * number of good random numbers, suitable for seeding TCP sequence
312 get_random_bytes(void *buf, u_int nbytes)
314 extract_entropy(&random_state, (char *) buf, nbytes);
319 read_random(void *buf, u_int nbytes)
321 if ((nbytes * 8) > random_state.entropy_count)
322 nbytes = random_state.entropy_count / 8;
324 return extract_entropy(&random_state, (char *)buf, nbytes);
328 read_random_unlimited(void *buf, u_int nbytes)
330 return extract_entropy(&random_state, (char *)buf, nbytes);
335 write_random(const char *buf, u_int nbytes)
340 for (i = nbytes, p = (u_int32_t *)buf;
341 i >= sizeof(u_int32_t);
342 i-= sizeof(u_int32_t), p++)
343 add_entropy_word(&random_state, *p);
347 add_entropy_word(&random_state, word);
354 add_true_randomness(int val)
356 add_entropy_word(&random_state, val);
357 random_state.entropy_count += 8*sizeof (val);
358 if (random_state.entropy_count > POOLBITS)
359 random_state.entropy_count = POOLBITS;
360 selwakeup(&random_state.rsel);
364 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 */