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*/
1 /*
2 * random.c -- A strong random number generator
3 *
4 * Version 0.92, last modified 21-Sep-95
5 *
6 * Copyright Theodore Ts'o, 1994, 1995. All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, and the entire permission notice in its entirety,
13 * including the disclaimer of warranties.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. The name of the author may not be used to endorse or promote
18 * products derived from this software without specific prior
19 * written permission.
20 *
21 * ALTERNATIVELY, this product may be distributed under the terms of
22 * the GNU Public License, in which case the provisions of the GPL are
23 * required INSTEAD OF the above restrictions. (This clause is
24 * necessary due to a potential bad interaction between the GPL and
25 * the restrictions contained in a BSD-style copyright.)
26 *
27 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
28 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
30 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
31 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
32 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
33 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
35 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
36 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
37 * OF THE POSSIBILITY OF SUCH DAMAGE.
38 */
39
40 /*
41 * (now, with legal B.S. out of the way.....)
42 *
43 * This routine gathers environmental noise from device drivers, etc.,
44 * and returns good random numbers, suitable for cryptographic use.
45 * Besides the obvious cryptographic uses, these numbers are also good
46 * for seeding TCP sequence numbers, and other places where it is
47 * desireable to have numbers which are not only random, but hard to
48 * predict by an attacker.
49 *
50 * Theory of operation
51 * ===================
52 *
53 * Computers are very predictable devices. Hence it is extremely hard
54 * to produce truely random numbers on a computer --- as opposed to
55 * pseudo-random numbers, which can easily generated by using a
56 * algorithm. Unfortunately, it is very easy for attackers to guess
57 * the sequence of pseudo-random number generators, and for some
58 * applications this is not acceptable. So instead, we must try to
59 * gather "environmental noise" from the computer's environment, which
60 * must be hard for outside attackers to observe, and use that to
61 * generate random numbers. In a Unix environment, this is best done
62 * from inside the kernel.
63 *
64 * Sources of randomness from the environment include inter-keyboard
65 * timings, inter-interrupt timings from some interrupts, and other
66 * events which are both (a) non-deterministic and (b) hard for an
67 * outside observer to measure. Randomness from these sources are
68 * added to an "entropy pool", which is periodically mixed using the
69 * MD5 compression function in CBC mode. As random bytes are mixed
70 * into the entropy pool, the routines keep an *estimate* of how many
71 * bits of randomness have been stored into the random number
72 * generator's internal state.
73 *
74 * When random bytes are desired, they are obtained by taking the MD5
75 * hash of a counter plus the contents of the "entropy pool". The
76 * reason for the MD5 hash is so that we can avoid exposing the
77 * internal state of random number generator. Although the MD5 hash
78 * does protect the pool, as each random byte which is generated from
79 * the pool reveals some information which was derived from the
80 * internal state, and thus increasing the amount of information an
81 * outside attacker has available to try to make some guesses about
82 * the random number generator's internal state. For this reason,
83 * the routine decreases its internal estimate of how many bits of
84 * "true randomness" are contained in the entropy pool as it outputs
85 * random numbers.
86 *
87 * If this estimate goes to zero, the routine can still generate random
88 * numbers; however it may now be possible for an attacker to analyze
89 * the output of the random number generator, and the MD5 algorithm,
90 * and thus have some success in guessing the output of the routine.
91 * Phil Karn (who devised this mechanism of using MD5 plus a counter
92 * to extract random numbers from an entropy pool) calls this
93 * "practical randomness", since in the worse case this is equivalent
94 * to hashing MD5 with a counter and an undisclosed secret. If MD5 is
95 * a strong cryptographic hash, this should be fairly resistant to attack.
96 *
97 * Exported interfaces ---- output
98 * ===============================
99 *
100 * There are three exported interfaces; the first is one designed to
101 * be used from within the kernel:
102 *
103 * void get_random_bytes(void *buf, int nbytes);
104 *
105 * This interface will return the requested number of random bytes,
106 * and place it in the requested buffer.
107 *
108 * The two other interfaces are two character devices /dev/random and
109 * /dev/urandom. /dev/random is suitable for use when very high
110 * quality randomness is desired (for example, for key generation.),
111 * as it will only return a maximum of the number of bits of
112 * randomness (as estimated by the random number generator) contained
113 * in the entropy pool.
114 *
115 * The /dev/urandom device does not have this limit, and will return
116 * as many bytes as are requested. As more and more random bytes are
117 * requested without giving time for the entropy pool to recharge,
118 * this will result in lower quality random numbers. For many
119 * applications, however, this is acceptable.
120 *
121 * Exported interfaces ---- input
122 * ==============================
123 *
124 * The two current exported interfaces for gathering environmental
125 * noise from the devices are:
126 *
127 * void add_keyboard_randomness(unsigned char scancode);
128 * void add_interrupt_randomness(int irq);
129 *
130 * The first function uses the inter-keypress timing, as well as the
131 * scancode as random inputs into the "entropy pool".
132 *
133 * The second function uses the inter-interrupt timing as random
134 * inputs to the entropy pool. Note that not all interrupts are good
135 * sources of randomness! For example, the timer interrupts is not a
136 * good choice, because the periodicity of the interrupts is to
137 * regular, and hence predictable to an attacker. Disk interrupts are
138 * a better measure, since the timing of the disk interrupts are more
139 * unpredictable. The routines try to estimate how many bits of
140 * randomness a particular interrupt channel offers, by keeping track
141 * of the first and second order deltas in the interrupt timings.
142 *
143 * Acknowledgements:
144 * =================
145 *
146 * Ideas for constructing this random number generator were derived
147 * from the Pretty Good Privacy's random number generator, and from
148 * private discussions with Phil Karn. This design has been further
149 * modified by myself, so any flaws are solely my responsibility, and
150 * should not be attributed to the authors of PGP or to Phil.
151 *
152 * The code for MD5 transform was taken from Colin Plumb's
153 * implementation, which has been placed in the public domain. The
154 * MD5 cryptographic checksum was devised by Ronald Rivest, and is
155 * documented in RFC 1321, "The MD5 Message Digest Algorithm".
156 *
157 * Further background information on this topic may be obtained from
158 * RFC 1750, "Randomness Recommendations for Security", by Donald
159 * Eastlake, Steve Crocker, and Jeff Schiller.
160 */
161
162 #ifdef linux
163 #include <linux/sched.h>
164 #include <linux/kernel.h>
165 #include <linux/major.h>
166 #include <linux/string.h>
167 #include <linux/random.h>
168
169 #include <asm/segment.h>
170 #include <asm/irq.h>
171 #include <asm/io.h>
172 #endif
173
174 #ifdef CONFIG_RANDOM
175
176 #define RANDPOOL 512
177
178 struct random_bucket {
179 int add_ptr;
180 int entropy_count;
181 int length;
182 int bit_length;
183 int delay_mix:1;
184 __u8 *pool;
185 };
186
187 struct timer_rand_state {
188 unsigned long last_time;
189 int last_delta;
190 int nbits;
191 };
192
193 static struct random_bucket random_state;
194 static __u32 rand_pool_key[16];
195 static __u8 random_pool[RANDPOOL];
196 static __u32 random_counter[16];
197 static struct timer_rand_state keyboard_timer_state;
198 static struct timer_rand_state irq_timer_state[NR_IRQS];
199
200 #ifndef MIN
201 #define MIN(a,b) (((a) < (b)) ? (a) : (b))
202 #endif
203
204 static void flush_random(struct random_bucket *random_state)
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*/
205 {
206 random_state->add_ptr = 0;
207 random_state->bit_length = random_state->length * 8;
208 random_state->entropy_count = 0;
209 random_state->delay_mix = 0;
210 }
211
212 void rand_initialize(void)
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*/
213 {
214 random_state.length = RANDPOOL;
215 random_state.pool = random_pool;
216 flush_random(&random_state);
217 }
218
219 /*
220 * MD5 transform algorithm, taken from code written by Colin Plumb,
221 * and put into the public domain
222 */
223
224 /* The four core functions - F1 is optimized somewhat */
225
226 /* #define F1(x, y, z) (x & y | ~x & z) */
227 #define F1(x, y, z) (z ^ (x & (y ^ z)))
228 #define F2(x, y, z) F1(z, x, y)
229 #define F3(x, y, z) (x ^ y ^ z)
230 #define F4(x, y, z) (y ^ (x | ~z))
231
232 /* This is the central step in the MD5 algorithm. */
233 #define MD5STEP(f, w, x, y, z, data, s) \
234 ( w += f(x, y, z) + data, w = w<<s | w>>(32-s), w += x )
235
236 /*
237 * The core of the MD5 algorithm, this alters an existing MD5 hash to
238 * reflect the addition of 16 longwords of new data. MD5Update blocks
239 * the data and converts bytes into longwords for this routine.
240 */
241 static void MD5Transform(__u32 buf[4],
/* */
242 __u32 const in[16])
243 {
244 __u32 a, b, c, d;
245
246 a = buf[0];
247 b = buf[1];
248 c = buf[2];
249 d = buf[3];
250
251 MD5STEP(F1, a, b, c, d, in[ 0]+0xd76aa478, 7);
252 MD5STEP(F1, d, a, b, c, in[ 1]+0xe8c7b756, 12);
253 MD5STEP(F1, c, d, a, b, in[ 2]+0x242070db, 17);
254 MD5STEP(F1, b, c, d, a, in[ 3]+0xc1bdceee, 22);
255 MD5STEP(F1, a, b, c, d, in[ 4]+0xf57c0faf, 7);
256 MD5STEP(F1, d, a, b, c, in[ 5]+0x4787c62a, 12);
257 MD5STEP(F1, c, d, a, b, in[ 6]+0xa8304613, 17);
258 MD5STEP(F1, b, c, d, a, in[ 7]+0xfd469501, 22);
259 MD5STEP(F1, a, b, c, d, in[ 8]+0x698098d8, 7);
260 MD5STEP(F1, d, a, b, c, in[ 9]+0x8b44f7af, 12);
261 MD5STEP(F1, c, d, a, b, in[10]+0xffff5bb1, 17);
262 MD5STEP(F1, b, c, d, a, in[11]+0x895cd7be, 22);
263 MD5STEP(F1, a, b, c, d, in[12]+0x6b901122, 7);
264 MD5STEP(F1, d, a, b, c, in[13]+0xfd987193, 12);
265 MD5STEP(F1, c, d, a, b, in[14]+0xa679438e, 17);
266 MD5STEP(F1, b, c, d, a, in[15]+0x49b40821, 22);
267
268 MD5STEP(F2, a, b, c, d, in[ 1]+0xf61e2562, 5);
269 MD5STEP(F2, d, a, b, c, in[ 6]+0xc040b340, 9);
270 MD5STEP(F2, c, d, a, b, in[11]+0x265e5a51, 14);
271 MD5STEP(F2, b, c, d, a, in[ 0]+0xe9b6c7aa, 20);
272 MD5STEP(F2, a, b, c, d, in[ 5]+0xd62f105d, 5);
273 MD5STEP(F2, d, a, b, c, in[10]+0x02441453, 9);
274 MD5STEP(F2, c, d, a, b, in[15]+0xd8a1e681, 14);
275 MD5STEP(F2, b, c, d, a, in[ 4]+0xe7d3fbc8, 20);
276 MD5STEP(F2, a, b, c, d, in[ 9]+0x21e1cde6, 5);
277 MD5STEP(F2, d, a, b, c, in[14]+0xc33707d6, 9);
278 MD5STEP(F2, c, d, a, b, in[ 3]+0xf4d50d87, 14);
279 MD5STEP(F2, b, c, d, a, in[ 8]+0x455a14ed, 20);
280 MD5STEP(F2, a, b, c, d, in[13]+0xa9e3e905, 5);
281 MD5STEP(F2, d, a, b, c, in[ 2]+0xfcefa3f8, 9);
282 MD5STEP(F2, c, d, a, b, in[ 7]+0x676f02d9, 14);
283 MD5STEP(F2, b, c, d, a, in[12]+0x8d2a4c8a, 20);
284
285 MD5STEP(F3, a, b, c, d, in[ 5]+0xfffa3942, 4);
286 MD5STEP(F3, d, a, b, c, in[ 8]+0x8771f681, 11);
287 MD5STEP(F3, c, d, a, b, in[11]+0x6d9d6122, 16);
288 MD5STEP(F3, b, c, d, a, in[14]+0xfde5380c, 23);
289 MD5STEP(F3, a, b, c, d, in[ 1]+0xa4beea44, 4);
290 MD5STEP(F3, d, a, b, c, in[ 4]+0x4bdecfa9, 11);
291 MD5STEP(F3, c, d, a, b, in[ 7]+0xf6bb4b60, 16);
292 MD5STEP(F3, b, c, d, a, in[10]+0xbebfbc70, 23);
293 MD5STEP(F3, a, b, c, d, in[13]+0x289b7ec6, 4);
294 MD5STEP(F3, d, a, b, c, in[ 0]+0xeaa127fa, 11);
295 MD5STEP(F3, c, d, a, b, in[ 3]+0xd4ef3085, 16);
296 MD5STEP(F3, b, c, d, a, in[ 6]+0x04881d05, 23);
297 MD5STEP(F3, a, b, c, d, in[ 9]+0xd9d4d039, 4);
298 MD5STEP(F3, d, a, b, c, in[12]+0xe6db99e5, 11);
299 MD5STEP(F3, c, d, a, b, in[15]+0x1fa27cf8, 16);
300 MD5STEP(F3, b, c, d, a, in[ 2]+0xc4ac5665, 23);
301
302 MD5STEP(F4, a, b, c, d, in[ 0]+0xf4292244, 6);
303 MD5STEP(F4, d, a, b, c, in[ 7]+0x432aff97, 10);
304 MD5STEP(F4, c, d, a, b, in[14]+0xab9423a7, 15);
305 MD5STEP(F4, b, c, d, a, in[ 5]+0xfc93a039, 21);
306 MD5STEP(F4, a, b, c, d, in[12]+0x655b59c3, 6);
307 MD5STEP(F4, d, a, b, c, in[ 3]+0x8f0ccc92, 10);
308 MD5STEP(F4, c, d, a, b, in[10]+0xffeff47d, 15);
309 MD5STEP(F4, b, c, d, a, in[ 1]+0x85845dd1, 21);
310 MD5STEP(F4, a, b, c, d, in[ 8]+0x6fa87e4f, 6);
311 MD5STEP(F4, d, a, b, c, in[15]+0xfe2ce6e0, 10);
312 MD5STEP(F4, c, d, a, b, in[ 6]+0xa3014314, 15);
313 MD5STEP(F4, b, c, d, a, in[13]+0x4e0811a1, 21);
314 MD5STEP(F4, a, b, c, d, in[ 4]+0xf7537e82, 6);
315 MD5STEP(F4, d, a, b, c, in[11]+0xbd3af235, 10);
316 MD5STEP(F4, c, d, a, b, in[ 2]+0x2ad7d2bb, 15);
317 MD5STEP(F4, b, c, d, a, in[ 9]+0xeb86d391, 21);
318
319 buf[0] += a;
320 buf[1] += b;
321 buf[2] += c;
322 buf[3] += d;
323 }
324
325 #undef F1
326 #undef F2
327 #undef F3
328 #undef F4
329 #undef MD5STEP
330
331 /*
332 * The function signature should be take a struct random_bucket * as
333 * input, but this makes tqueue unhappy.
334 */
335 static void mix_bucket(void *v)
/* */
336 {
337 struct random_bucket *r = (struct random_bucket *) v;
338 int i, num_passes;
339 __u32 *p;
340 __u32 iv[4];
341
342 r->delay_mix = 0;
343
344 /* Start IV from last block of the random pool */
345 memcpy(iv, r->pool + r->length - sizeof(iv), sizeof(iv));
346
347 num_passes = r->length / 16;
348 for (i = 0, p = (__u32 *) r->pool; i < num_passes; i++) {
349 MD5Transform(iv, rand_pool_key);
350 iv[0] = (*p++ ^= iv[0]);
351 iv[1] = (*p++ ^= iv[1]);
352 iv[2] = (*p++ ^= iv[2]);
353 iv[3] = (*p++ ^= iv[3]);
354 }
355 memcpy(rand_pool_key, r->pool, sizeof(rand_pool_key));
356
357 /* Wipe iv from memory */
358 memset(iv, 0, sizeof(iv));
359
360 r->add_ptr = 0;
361 }
362
363 /*
364 * This function adds a byte into the entropy "pool". It does not
365 * update the entropy estimate. The caller must do this if appropriate.
366 */
367 static inline void add_entropy_byte(struct random_bucket *r,
/* */
368 const __u8 ch,
369 int delay)
370 {
371 if (!delay && r->delay_mix)
372 mix_bucket(r);
373 r->pool[r->add_ptr++] ^= ch;
374 if (r->add_ptr >= r->length) {
375 if (delay) {
376 r->delay_mix = 1;
377 r->add_ptr = 0;
378 } else
379 mix_bucket(r);
380 }
381 }
382
383 /*
384 * This function adds some number of bytes into the entropy pool and
385 * updates the entropy count as appropriate.
386 */
387 void add_entropy(struct random_bucket *r, const __u8 *ptr,
/* */
388 int length, int entropy_level, int delay)
389 {
390 while (length-- > 0)
391 add_entropy_byte(r, *ptr++, delay);
392
393 r->entropy_count += entropy_level;
394 if (r->entropy_count > r->length*8)
395 r->entropy_count = r->length * 8;
396 }
397
398 /*
399 * This function adds entropy to the entropy "pool" by using timing
400 * delays. It uses the timer_rand_state structure to make an estimate
401 * of how many bits of entropy this call has added to the pool.
402 */
403 static void add_timer_randomness(struct random_bucket *r,
/* */
404 struct timer_rand_state *state, int delay)
405 {
406 int delta, delta2;
407 int nbits;
408
409 /*
410 * Calculate number of bits of randomness we probably
411 * added. We take into account the first and second order
412 * delta's in order to make our estimate.
413 */
414 delta = jiffies - state->last_time;
415 delta2 = delta - state->last_delta;
416 state->last_time = jiffies;
417 state->last_delta = delta;
418 if (delta < 0) delta = -delta;
419 if (delta2 < 0) delta2 = -delta2;
420 delta = MIN(delta, delta2) >> 1;
421 for (nbits = 0; delta; nbits++)
422 delta >>= 1;
423
424 add_entropy(r, (__u8 *) &jiffies, sizeof(jiffies),
425 nbits, delay);
426
427 #if defined (__i386__)
428 /*
429 * On a Pentium, read the cycle counter. We assume that
430 * this gives us 8 bits of randomness. XXX This needs
431 * investigation.
432 */
433 if (x86_capability & 16) {
434 unsigned long low, high;
435 __asm__(".byte 0x0f,0x31"
436 :"=a" (low), "=d" (high));
437 add_entropy_byte(r, low, 1);
438 r->entropy_count += 8;
439 if (r->entropy_count > r->bit_length)
440 r->entropy_count = r->bit_length;
441 }
442 #endif
443 }
444
445 void add_keyboard_randomness(unsigned char scancode)
/* */
446 {
447 struct random_bucket *r = &random_state;
448
449 add_timer_randomness(r, &keyboard_timer_state, 0);
450 add_entropy_byte(r, scancode, 0);
451 r->entropy_count += 6;
452 if (r->entropy_count > r->bit_length)
453 r->entropy_count = r->bit_length;
454 }
455
456 void add_interrupt_randomness(int irq)
/* */
457 {
458 struct random_bucket *r = &random_state;
459
460 if (irq >= NR_IRQS)
461 return;
462
463 add_timer_randomness(r, &irq_timer_state[irq], 1);
464 }
465
466 /*
467 * This function extracts randomness from the "entropy pool", and
468 * returns it in a buffer. This function computes how many remaining
469 * bits of entropy are left in the pool, but it does not restrict the
470 * number of bytes that are actually obtained.
471 */
472 static inline int extract_entropy(struct random_bucket *r, char * buf,
/* */
473 int nbytes, int to_user)
474 {
475 int length, ret, passes, i;
476 __u32 tmp[4];
477 u8 *cp;
478
479 add_entropy(r, (u8 *) &jiffies, sizeof(jiffies), 0, 0);
480
481 if (r->entropy_count > r->bit_length)
482 r->entropy_count = r->bit_length;
483 if (nbytes > 32768)
484 nbytes = 32768;
485 ret = nbytes;
486 r->entropy_count -= ret * 8;
487 if (r->entropy_count < 0)
488 r->entropy_count = 0;
489 passes = r->length / 64;
490 while (nbytes) {
491 length = MIN(nbytes, 16);
492 for (i=0; i < 16; i++) {
493 if (++random_counter[i] != 0)
494 break;
495 }
496 tmp[0] = 0x67452301;
497 tmp[1] = 0xefcdab89;
498 tmp[2] = 0x98badcfe;
499 tmp[3] = 0x10325476;
500 MD5Transform(tmp, random_counter);
501 for (i = 0, cp = r->pool; i < passes; i++, cp+=64)
502 MD5Transform(tmp, (__u32 *) cp);
503 if (to_user)
504 memcpy_tofs(buf, tmp, length);
505 else
506 memcpy(buf, tmp, length);
507 nbytes -= length;
508 buf += length;
509 }
510 return ret;
511 }
512
513 /*
514 * This function is the exported kernel interface. It returns some
515 * number of good random numbers, suitable for seeding TCP sequence
516 * numbers, etc.
517 */
518 void get_random_bytes(void *buf, int nbytes)
/* */
519 {
520 extract_entropy(&random_state, (char *) buf, nbytes, 0);
521 }
522
523 #ifdef linux
524 int read_random(struct inode * inode,struct file * file,char * buf,int nbytes)
/* */
525 {
526 if ((nbytes * 8) > random_state.entropy_count)
527 nbytes = random_state.entropy_count / 8;
528
529 return extract_entropy(&random_state, buf, nbytes, 1);
530 }
531
532 int read_random_unlimited(struct inode * inode,struct file * file,
/* ![[last]](../icons/n_last.png)
*/
533 char * buf,int nbytes)
534 {
535 return extract_entropy(&random_state, buf, nbytes, 1);
536 }
537 #endif
538
539 #endif /* CONFIG_RANDOM */
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*/