1 /* $OpenBSD: moduli.c,v 1.16 2006/07/26 13:57:17 stevesk Exp $ */
3 * Copyright 1994 Phil Karn <karn@qualcomm.com>
4 * Copyright 1996-1998, 2003 William Allen Simpson <wsimpson@greendragon.com>
5 * Copyright 2000 Niels Provos <provos@citi.umich.edu>
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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30 * Two-step process to generate safe primes for DHGEX
32 * Sieve candidates for "safe" primes,
33 * suitable for use as Diffie-Hellman moduli;
34 * that is, where q = (p-1)/2 is also prime.
36 * First step: generate candidate primes (memory intensive)
37 * Second step: test primes' safety (processor intensive)
42 #include <sys/types.h>
44 #include <openssl/bn.h>
57 /* need line long enough for largest moduli plus headers */
58 #define QLINESIZE (100+8192)
61 * Specifies the internal structure of the prime modulus.
63 #define QTYPE_UNKNOWN (0)
64 #define QTYPE_UNSTRUCTURED (1)
65 #define QTYPE_SAFE (2)
66 #define QTYPE_SCHNORR (3)
67 #define QTYPE_SOPHIE_GERMAIN (4)
68 #define QTYPE_STRONG (5)
70 /* Tests: decimal (bit field).
71 * Specifies the methods used in checking for primality.
72 * Usually, more than one test is used.
74 #define QTEST_UNTESTED (0x00)
75 #define QTEST_COMPOSITE (0x01)
76 #define QTEST_SIEVE (0x02)
77 #define QTEST_MILLER_RABIN (0x04)
78 #define QTEST_JACOBI (0x08)
79 #define QTEST_ELLIPTIC (0x10)
83 * Specifies the number of the most significant bit (0 to M).
84 * WARNING: internally, usually 1 to N.
86 #define QSIZE_MINIMUM (511)
89 * Prime sieving defines
92 /* Constant: assuming 8 bit bytes and 32 bit words */
94 #define SHIFT_BYTE (2)
95 #define SHIFT_WORD (SHIFT_BIT+SHIFT_BYTE)
96 #define SHIFT_MEGABYTE (20)
97 #define SHIFT_MEGAWORD (SHIFT_MEGABYTE-SHIFT_BYTE)
100 * Using virtual memory can cause thrashing. This should be the largest
101 * number that is supported without a large amount of disk activity --
102 * that would increase the run time from hours to days or weeks!
104 #define LARGE_MINIMUM (8UL) /* megabytes */
107 * Do not increase this number beyond the unsigned integer bit size.
108 * Due to a multiple of 4, it must be LESS than 128 (yielding 2**30 bits).
110 #define LARGE_MAXIMUM (127UL) /* megabytes */
113 * Constant: when used with 32-bit integers, the largest sieve prime
114 * has to be less than 2**32.
116 #define SMALL_MAXIMUM (0xffffffffUL)
118 /* Constant: can sieve all primes less than 2**32, as 65537**2 > 2**32-1. */
119 #define TINY_NUMBER (1UL<<16)
121 /* Ensure enough bit space for testing 2*q. */
122 #define TEST_MAXIMUM (1UL<<16)
123 #define TEST_MINIMUM (QSIZE_MINIMUM + 1)
124 /* real TEST_MINIMUM (1UL << (SHIFT_WORD - TEST_POWER)) */
125 #define TEST_POWER (3) /* 2**n, n < SHIFT_WORD */
127 /* bit operations on 32-bit words */
128 #define BIT_CLEAR(a,n) ((a)[(n)>>SHIFT_WORD] &= ~(1L << ((n) & 31)))
129 #define BIT_SET(a,n) ((a)[(n)>>SHIFT_WORD] |= (1L << ((n) & 31)))
130 #define BIT_TEST(a,n) ((a)[(n)>>SHIFT_WORD] & (1L << ((n) & 31)))
133 * Prime testing defines
136 /* Minimum number of primality tests to perform */
137 #define TRIAL_MINIMUM (4)
140 * Sieving data (XXX - move to struct)
144 static u_int32_t *TinySieve, tinybits;
146 /* sieve 2**30 in 2**16 parts */
147 static u_int32_t *SmallSieve, smallbits, smallbase;
149 /* sieve relative to the initial value */
150 static u_int32_t *LargeSieve, largewords, largetries, largenumbers;
151 static u_int32_t largebits, largememory; /* megabytes */
152 static BIGNUM *largebase;
154 int gen_candidates(FILE *, u_int32_t, u_int32_t, BIGNUM *);
155 int prime_test(FILE *, FILE *, u_int32_t, u_int32_t);
158 * print moduli out in consistent form,
161 qfileout(FILE * ofile, u_int32_t otype, u_int32_t otests, u_int32_t otries,
162 u_int32_t osize, u_int32_t ogenerator, BIGNUM * omodulus)
169 gtm = gmtime(&time_now);
171 res = fprintf(ofile, "%04d%02d%02d%02d%02d%02d %u %u %u %u %x ",
172 gtm->tm_year + 1900, gtm->tm_mon + 1, gtm->tm_mday,
173 gtm->tm_hour, gtm->tm_min, gtm->tm_sec,
174 otype, otests, otries, osize, ogenerator);
179 if (BN_print_fp(ofile, omodulus) < 1)
182 res = fprintf(ofile, "\n");
185 return (res > 0 ? 0 : -1);
190 ** Sieve p's and q's with small factors
193 sieve_large(u_int32_t s)
197 debug3("sieve_large %u", s);
199 /* r = largebase mod s */
200 r = BN_mod_word(largebase, s);
202 u = 0; /* s divides into largebase exactly */
204 u = s - r; /* largebase+u is first entry divisible by s */
206 if (u < largebits * 2) {
208 * The sieve omits p's and q's divisible by 2, so ensure that
209 * largebase+u is odd. Then, step through the sieve in
213 u += s; /* Make largebase+u odd, and u even */
215 /* Mark all multiples of 2*s */
216 for (u /= 2; u < largebits; u += s)
217 BIT_SET(LargeSieve, u);
223 u = 0; /* s divides p exactly */
225 u = s - r; /* p+u is first entry divisible by s */
227 if (u < largebits * 4) {
229 * The sieve omits p's divisible by 4, so ensure that
230 * largebase+u is not. Then, step through the sieve in
234 if (SMALL_MAXIMUM - u < s)
239 /* Mark all multiples of 4*s */
240 for (u /= 4; u < largebits; u += s)
241 BIT_SET(LargeSieve, u);
246 * list candidates for Sophie-Germain primes (where q = (p-1)/2)
247 * to standard output.
248 * The list is checked against small known primes (less than 2**30).
251 gen_candidates(FILE *out, u_int32_t memory, u_int32_t power, BIGNUM *start)
254 u_int32_t j, r, s, t;
255 u_int32_t smallwords = TINY_NUMBER >> 6;
256 u_int32_t tinywords = TINY_NUMBER >> 6;
257 time_t time_start, time_stop;
261 largememory = memory;
264 (memory < LARGE_MINIMUM || memory > LARGE_MAXIMUM)) {
265 error("Invalid memory amount (min %ld, max %ld)",
266 LARGE_MINIMUM, LARGE_MAXIMUM);
271 * Set power to the length in bits of the prime to be generated.
272 * This is changed to 1 less than the desired safe prime moduli p.
274 if (power > TEST_MAXIMUM) {
275 error("Too many bits: %u > %lu", power, TEST_MAXIMUM);
277 } else if (power < TEST_MINIMUM) {
278 error("Too few bits: %u < %u", power, TEST_MINIMUM);
281 power--; /* decrement before squaring */
284 * The density of ordinary primes is on the order of 1/bits, so the
285 * density of safe primes should be about (1/bits)**2. Set test range
286 * to something well above bits**2 to be reasonably sure (but not
287 * guaranteed) of catching at least one safe prime.
289 largewords = ((power * power) >> (SHIFT_WORD - TEST_POWER));
292 * Need idea of how much memory is available. We don't have to use all
295 if (largememory > LARGE_MAXIMUM) {
296 logit("Limited memory: %u MB; limit %lu MB",
297 largememory, LARGE_MAXIMUM);
298 largememory = LARGE_MAXIMUM;
301 if (largewords <= (largememory << SHIFT_MEGAWORD)) {
302 logit("Increased memory: %u MB; need %u bytes",
303 largememory, (largewords << SHIFT_BYTE));
304 largewords = (largememory << SHIFT_MEGAWORD);
305 } else if (largememory > 0) {
306 logit("Decreased memory: %u MB; want %u bytes",
307 largememory, (largewords << SHIFT_BYTE));
308 largewords = (largememory << SHIFT_MEGAWORD);
311 TinySieve = xcalloc(tinywords, sizeof(u_int32_t));
312 tinybits = tinywords << SHIFT_WORD;
314 SmallSieve = xcalloc(smallwords, sizeof(u_int32_t));
315 smallbits = smallwords << SHIFT_WORD;
318 * dynamically determine available memory
320 while ((LargeSieve = calloc(largewords, sizeof(u_int32_t))) == NULL)
321 largewords -= (1L << (SHIFT_MEGAWORD - 2)); /* 1/4 MB chunks */
323 largebits = largewords << SHIFT_WORD;
324 largenumbers = largebits * 2; /* even numbers excluded */
326 /* validation check: count the number of primes tried */
331 * Generate random starting point for subprime search, or use
332 * specified parameter.
334 largebase = BN_new();
336 BN_rand(largebase, power, 1, 1);
338 BN_copy(largebase, start);
341 BN_set_bit(largebase, 0);
345 logit("%.24s Sieve next %u plus %u-bit", ctime(&time_start),
346 largenumbers, power);
347 debug2("start point: 0x%s", BN_bn2hex(largebase));
352 for (i = 0; i < tinybits; i++) {
353 if (BIT_TEST(TinySieve, i))
354 continue; /* 2*i+3 is composite */
356 /* The next tiny prime */
359 /* Mark all multiples of t */
360 for (j = i + t; j < tinybits; j += t)
361 BIT_SET(TinySieve, j);
367 * Start the small block search at the next possible prime. To avoid
368 * fencepost errors, the last pass is skipped.
370 for (smallbase = TINY_NUMBER + 3;
371 smallbase < (SMALL_MAXIMUM - TINY_NUMBER);
372 smallbase += TINY_NUMBER) {
373 for (i = 0; i < tinybits; i++) {
374 if (BIT_TEST(TinySieve, i))
375 continue; /* 2*i+3 is composite */
377 /* The next tiny prime */
382 s = 0; /* t divides into smallbase exactly */
384 /* smallbase+s is first entry divisible by t */
389 * The sieve omits even numbers, so ensure that
390 * smallbase+s is odd. Then, step through the sieve
391 * in increments of 2*t
394 s += t; /* Make smallbase+s odd, and s even */
396 /* Mark all multiples of 2*t */
397 for (s /= 2; s < smallbits; s += t)
398 BIT_SET(SmallSieve, s);
404 for (i = 0; i < smallbits; i++) {
405 if (BIT_TEST(SmallSieve, i))
406 continue; /* 2*i+smallbase is composite */
408 /* The next small prime */
409 sieve_large((2 * i) + smallbase);
412 memset(SmallSieve, 0, smallwords << SHIFT_BYTE);
417 logit("%.24s Sieved with %u small primes in %ld seconds",
418 ctime(&time_stop), largetries, (long) (time_stop - time_start));
420 for (j = r = 0; j < largebits; j++) {
421 if (BIT_TEST(LargeSieve, j))
422 continue; /* Definitely composite, skip */
424 debug2("test q = largebase+%u", 2 * j);
425 BN_set_word(q, 2 * j);
426 BN_add(q, q, largebase);
427 if (qfileout(out, QTYPE_SOPHIE_GERMAIN, QTEST_SIEVE,
428 largetries, (power - 1) /* MSB */, (0), q) == -1) {
442 logit("%.24s Found %u candidates", ctime(&time_stop), r);
448 * perform a Miller-Rabin primality test
449 * on the list of candidates
450 * (checking both q and p)
451 * The result is a list of so-call "safe" primes
454 prime_test(FILE *in, FILE *out, u_int32_t trials, u_int32_t generator_wanted)
459 u_int32_t count_in = 0, count_out = 0, count_possible = 0;
460 u_int32_t generator_known, in_tests, in_tries, in_type, in_size;
461 time_t time_start, time_stop;
464 if (trials < TRIAL_MINIMUM) {
465 error("Minimum primality trials is %d", TRIAL_MINIMUM);
475 debug2("%.24s Final %u Miller-Rabin trials (%x generator)",
476 ctime(&time_start), trials, generator_wanted);
479 lp = xmalloc(QLINESIZE + 1);
480 while (fgets(lp, QLINESIZE, in) != NULL) {
484 if (ll < 14 || *lp == '!' || *lp == '#') {
485 debug2("%10u: comment or short line", count_in);
489 /* XXX - fragile parser */
491 cp = &lp[14]; /* (skip) */
494 in_type = strtoul(cp, &cp, 10);
497 in_tests = strtoul(cp, &cp, 10);
499 if (in_tests & QTEST_COMPOSITE) {
500 debug2("%10u: known composite", count_in);
505 in_tries = strtoul(cp, &cp, 10);
507 /* size (most significant bit) */
508 in_size = strtoul(cp, &cp, 10);
510 /* generator (hex) */
511 generator_known = strtoul(cp, &cp, 16);
513 /* Skip white space */
514 cp += strspn(cp, " ");
518 case QTYPE_SOPHIE_GERMAIN:
519 debug2("%10u: (%u) Sophie-Germain", count_in, in_type);
528 case QTYPE_UNSTRUCTURED:
533 debug2("%10u: (%u)", count_in, in_type);
540 debug2("Unknown prime type");
545 * due to earlier inconsistencies in interpretation, check
546 * the proposed bit size.
548 if ((u_int32_t)BN_num_bits(p) != (in_size + 1)) {
549 debug2("%10u: bit size %u mismatch", count_in, in_size);
552 if (in_size < QSIZE_MINIMUM) {
553 debug2("%10u: bit size %u too short", count_in, in_size);
557 if (in_tests & QTEST_MILLER_RABIN)
563 * guess unknown generator
565 if (generator_known == 0) {
566 if (BN_mod_word(p, 24) == 11)
568 else if (BN_mod_word(p, 12) == 5)
571 u_int32_t r = BN_mod_word(p, 10);
573 if (r == 3 || r == 7)
578 * skip tests when desired generator doesn't match
580 if (generator_wanted > 0 &&
581 generator_wanted != generator_known) {
582 debug2("%10u: generator %d != %d",
583 count_in, generator_known, generator_wanted);
588 * Primes with no known generator are useless for DH, so
591 if (generator_known == 0) {
592 debug2("%10u: no known generator", count_in);
599 * The (1/4)^N performance bound on Miller-Rabin is
600 * extremely pessimistic, so don't spend a lot of time
601 * really verifying that q is prime until after we know
602 * that p is also prime. A single pass will weed out the
603 * vast majority of composite q's.
605 if (BN_is_prime(q, 1, NULL, ctx, NULL) <= 0) {
606 debug("%10u: q failed first possible prime test",
612 * q is possibly prime, so go ahead and really make sure
613 * that p is prime. If it is, then we can go back and do
614 * the same for q. If p is composite, chances are that
615 * will show up on the first Rabin-Miller iteration so it
616 * doesn't hurt to specify a high iteration count.
618 if (!BN_is_prime(p, trials, NULL, ctx, NULL)) {
619 debug("%10u: p is not prime", count_in);
622 debug("%10u: p is almost certainly prime", count_in);
624 /* recheck q more rigorously */
625 if (!BN_is_prime(q, trials - 1, NULL, ctx, NULL)) {
626 debug("%10u: q is not prime", count_in);
629 debug("%10u: q is almost certainly prime", count_in);
631 if (qfileout(out, QTYPE_SAFE, (in_tests | QTEST_MILLER_RABIN),
632 in_tries, in_size, generator_known, p)) {
646 logit("%.24s Found %u safe primes of %u candidates in %ld seconds",
647 ctime(&time_stop), count_out, count_possible,
648 (long) (time_stop - time_start));