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 #ifdeflinux 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 #ifdefCONFIG_RANDOM 175
176 #defineRANDPOOL 512
177
178 structrandom_bucket{ 179 intadd_ptr;
180 intentropy_count;
181 intlength;
182 intbit_length;
183 intdelay_mix:1;
184 __u8 *pool;
185 };
186
187 structtimer_rand_state{ 188 unsignedlonglast_time;
189 intlast_delta;
190 intnbits;
191 };
192
193 staticstructrandom_bucketrandom_state;
194 static__u32rand_pool_key[16];
195 static__u8random_pool[RANDPOOL];
196 static__u32random_counter[16];
197 staticstructtimer_rand_statekeyboard_timer_state;
198 staticstructtimer_rand_stateirq_timer_state[NR_IRQS];
199
200 #ifndefMIN 201 #defineMIN(a,b) (((a) < (b)) ? (a) : (b))
202 #endif 203
204 staticvoidflush_random(structrandom_bucket *random_state)
/* */ 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 voidrand_initialize(void)
/* */ 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 #defineF1(x, y, z) (z ^ (x & (y ^ z)))
228 #defineF2(x, y, z) F1(z, x, y)
229 #defineF3(x, y, z) (x ^ y ^ z)
230 #defineF4(x, y, z) (y ^ (x | ~z))
231
232 /* This is the central step in the MD5 algorithm. */ 233 #defineMD5STEP(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 staticvoidMD5Transform(__u32buf[4],
/* */ 242 __u32constin[16])
243 { 244 __u32a, 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 #undefF1 326 #undefF2 327 #undefF3 328 #undefF4 329 #undefMD5STEP 330
331 /* 332 * The function signature should be take a struct random_bucket * as 333 * input, but this makes tqueue unhappy. 334 */ 335 staticvoidmix_bucket(void *v)
/* */ 336 { 337 structrandom_bucket *r = (structrandom_bucket *) v;
338 inti, num_passes;
339 __u32 *p;
340 __u32iv[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 staticinlinevoidadd_entropy_byte(structrandom_bucket *r,
/* */ 368 const__u8ch,
369 intdelay)
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 voidadd_entropy(structrandom_bucket *r, const__u8 *ptr,
/* */ 388 intlength, intentropy_level, intdelay)
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 staticvoidadd_timer_randomness(structrandom_bucket *r,
/* */ 404 structtimer_rand_state *state, intdelay)
405 { 406 intdelta, delta2;
407 intnbits;
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 #ifdefined (__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 unsignedlonglow, 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 voidadd_keyboard_randomness(unsignedcharscancode)
/* */ 446 { 447 structrandom_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 voidadd_interrupt_randomness(intirq)
/* */ 457 { 458 structrandom_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 staticinlineintextract_entropy(structrandom_bucket *r, char * buf,
/* */ 473 intnbytes, intto_user)
474 { 475 intlength, ret, passes, i;
476 __u32tmp[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 returnret;
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 voidget_random_bytes(void *buf, intnbytes)
/* */ 519 { 520 extract_entropy(&random_state, (char *) buf, nbytes, 0);
521 } 522
523 #ifdeflinux 524 intread_random(structinode * inode,structfile * file,char * buf,intnbytes)
/* */ 525 { 526 if ((nbytes * 8) > random_state.entropy_count)
527 nbytes = random_state.entropy_count / 8;
528
529 returnextract_entropy(&random_state, buf, nbytes, 1);
530 } 531
532 intread_random_unlimited(structinode * inode,structfile * file,
/* */ 533 char * buf,intnbytes)
534 { 535 returnextract_entropy(&random_state, buf, nbytes, 1);
536 } 537 #endif 538
539 #endif/* CONFIG_RANDOM */