1 /* $OpenBSD: moduli.c,v 1.15 2006/07/22 20:48:23 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,
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22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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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>
56 /* need line long enough for largest moduli plus headers */
57 #define QLINESIZE (100+8192)
60 * Specifies the internal structure of the prime modulus.
62 #define QTYPE_UNKNOWN (0)
63 #define QTYPE_UNSTRUCTURED (1)
64 #define QTYPE_SAFE (2)
65 #define QTYPE_SCHNORR (3)
66 #define QTYPE_SOPHIE_GERMAIN (4)
67 #define QTYPE_STRONG (5)
69 /* Tests: decimal (bit field).
70 * Specifies the methods used in checking for primality.
71 * Usually, more than one test is used.
73 #define QTEST_UNTESTED (0x00)
74 #define QTEST_COMPOSITE (0x01)
75 #define QTEST_SIEVE (0x02)
76 #define QTEST_MILLER_RABIN (0x04)
77 #define QTEST_JACOBI (0x08)
78 #define QTEST_ELLIPTIC (0x10)
82 * Specifies the number of the most significant bit (0 to M).
83 * WARNING: internally, usually 1 to N.
85 #define QSIZE_MINIMUM (511)
88 * Prime sieving defines
91 /* Constant: assuming 8 bit bytes and 32 bit words */
93 #define SHIFT_BYTE (2)
94 #define SHIFT_WORD (SHIFT_BIT+SHIFT_BYTE)
95 #define SHIFT_MEGABYTE (20)
96 #define SHIFT_MEGAWORD (SHIFT_MEGABYTE-SHIFT_BYTE)
99 * Using virtual memory can cause thrashing. This should be the largest
100 * number that is supported without a large amount of disk activity --
101 * that would increase the run time from hours to days or weeks!
103 #define LARGE_MINIMUM (8UL) /* megabytes */
106 * Do not increase this number beyond the unsigned integer bit size.
107 * Due to a multiple of 4, it must be LESS than 128 (yielding 2**30 bits).
109 #define LARGE_MAXIMUM (127UL) /* megabytes */
112 * Constant: when used with 32-bit integers, the largest sieve prime
113 * has to be less than 2**32.
115 #define SMALL_MAXIMUM (0xffffffffUL)
117 /* Constant: can sieve all primes less than 2**32, as 65537**2 > 2**32-1. */
118 #define TINY_NUMBER (1UL<<16)
120 /* Ensure enough bit space for testing 2*q. */
121 #define TEST_MAXIMUM (1UL<<16)
122 #define TEST_MINIMUM (QSIZE_MINIMUM + 1)
123 /* real TEST_MINIMUM (1UL << (SHIFT_WORD - TEST_POWER)) */
124 #define TEST_POWER (3) /* 2**n, n < SHIFT_WORD */
126 /* bit operations on 32-bit words */
127 #define BIT_CLEAR(a,n) ((a)[(n)>>SHIFT_WORD] &= ~(1L << ((n) & 31)))
128 #define BIT_SET(a,n) ((a)[(n)>>SHIFT_WORD] |= (1L << ((n) & 31)))
129 #define BIT_TEST(a,n) ((a)[(n)>>SHIFT_WORD] & (1L << ((n) & 31)))
132 * Prime testing defines
135 /* Minimum number of primality tests to perform */
136 #define TRIAL_MINIMUM (4)
139 * Sieving data (XXX - move to struct)
143 static u_int32_t *TinySieve, tinybits;
145 /* sieve 2**30 in 2**16 parts */
146 static u_int32_t *SmallSieve, smallbits, smallbase;
148 /* sieve relative to the initial value */
149 static u_int32_t *LargeSieve, largewords, largetries, largenumbers;
150 static u_int32_t largebits, largememory; /* megabytes */
151 static BIGNUM *largebase;
153 int gen_candidates(FILE *, u_int32_t, u_int32_t, BIGNUM *);
154 int prime_test(FILE *, FILE *, u_int32_t, u_int32_t);
157 * print moduli out in consistent form,
160 qfileout(FILE * ofile, u_int32_t otype, u_int32_t otests, u_int32_t otries,
161 u_int32_t osize, u_int32_t ogenerator, BIGNUM * omodulus)
168 gtm = gmtime(&time_now);
170 res = fprintf(ofile, "%04d%02d%02d%02d%02d%02d %u %u %u %u %x ",
171 gtm->tm_year + 1900, gtm->tm_mon + 1, gtm->tm_mday,
172 gtm->tm_hour, gtm->tm_min, gtm->tm_sec,
173 otype, otests, otries, osize, ogenerator);
178 if (BN_print_fp(ofile, omodulus) < 1)
181 res = fprintf(ofile, "\n");
184 return (res > 0 ? 0 : -1);
189 ** Sieve p's and q's with small factors
192 sieve_large(u_int32_t s)
196 debug3("sieve_large %u", s);
198 /* r = largebase mod s */
199 r = BN_mod_word(largebase, s);
201 u = 0; /* s divides into largebase exactly */
203 u = s - r; /* largebase+u is first entry divisible by s */
205 if (u < largebits * 2) {
207 * The sieve omits p's and q's divisible by 2, so ensure that
208 * largebase+u is odd. Then, step through the sieve in
212 u += s; /* Make largebase+u odd, and u even */
214 /* Mark all multiples of 2*s */
215 for (u /= 2; u < largebits; u += s)
216 BIT_SET(LargeSieve, u);
222 u = 0; /* s divides p exactly */
224 u = s - r; /* p+u is first entry divisible by s */
226 if (u < largebits * 4) {
228 * The sieve omits p's divisible by 4, so ensure that
229 * largebase+u is not. Then, step through the sieve in
233 if (SMALL_MAXIMUM - u < s)
238 /* Mark all multiples of 4*s */
239 for (u /= 4; u < largebits; u += s)
240 BIT_SET(LargeSieve, u);
245 * list candidates for Sophie-Germain primes (where q = (p-1)/2)
246 * to standard output.
247 * The list is checked against small known primes (less than 2**30).
250 gen_candidates(FILE *out, u_int32_t memory, u_int32_t power, BIGNUM *start)
253 u_int32_t j, r, s, t;
254 u_int32_t smallwords = TINY_NUMBER >> 6;
255 u_int32_t tinywords = TINY_NUMBER >> 6;
256 time_t time_start, time_stop;
260 largememory = memory;
263 (memory < LARGE_MINIMUM || memory > LARGE_MAXIMUM)) {
264 error("Invalid memory amount (min %ld, max %ld)",
265 LARGE_MINIMUM, LARGE_MAXIMUM);
270 * Set power to the length in bits of the prime to be generated.
271 * This is changed to 1 less than the desired safe prime moduli p.
273 if (power > TEST_MAXIMUM) {
274 error("Too many bits: %u > %lu", power, TEST_MAXIMUM);
276 } else if (power < TEST_MINIMUM) {
277 error("Too few bits: %u < %u", power, TEST_MINIMUM);
280 power--; /* decrement before squaring */
283 * The density of ordinary primes is on the order of 1/bits, so the
284 * density of safe primes should be about (1/bits)**2. Set test range
285 * to something well above bits**2 to be reasonably sure (but not
286 * guaranteed) of catching at least one safe prime.
288 largewords = ((power * power) >> (SHIFT_WORD - TEST_POWER));
291 * Need idea of how much memory is available. We don't have to use all
294 if (largememory > LARGE_MAXIMUM) {
295 logit("Limited memory: %u MB; limit %lu MB",
296 largememory, LARGE_MAXIMUM);
297 largememory = LARGE_MAXIMUM;
300 if (largewords <= (largememory << SHIFT_MEGAWORD)) {
301 logit("Increased memory: %u MB; need %u bytes",
302 largememory, (largewords << SHIFT_BYTE));
303 largewords = (largememory << SHIFT_MEGAWORD);
304 } else if (largememory > 0) {
305 logit("Decreased memory: %u MB; want %u bytes",
306 largememory, (largewords << SHIFT_BYTE));
307 largewords = (largememory << SHIFT_MEGAWORD);
310 TinySieve = xcalloc(tinywords, sizeof(u_int32_t));
311 tinybits = tinywords << SHIFT_WORD;
313 SmallSieve = xcalloc(smallwords, sizeof(u_int32_t));
314 smallbits = smallwords << SHIFT_WORD;
317 * dynamically determine available memory
319 while ((LargeSieve = calloc(largewords, sizeof(u_int32_t))) == NULL)
320 largewords -= (1L << (SHIFT_MEGAWORD - 2)); /* 1/4 MB chunks */
322 largebits = largewords << SHIFT_WORD;
323 largenumbers = largebits * 2; /* even numbers excluded */
325 /* validation check: count the number of primes tried */
330 * Generate random starting point for subprime search, or use
331 * specified parameter.
333 largebase = BN_new();
335 BN_rand(largebase, power, 1, 1);
337 BN_copy(largebase, start);
340 BN_set_bit(largebase, 0);
344 logit("%.24s Sieve next %u plus %u-bit", ctime(&time_start),
345 largenumbers, power);
346 debug2("start point: 0x%s", BN_bn2hex(largebase));
351 for (i = 0; i < tinybits; i++) {
352 if (BIT_TEST(TinySieve, i))
353 continue; /* 2*i+3 is composite */
355 /* The next tiny prime */
358 /* Mark all multiples of t */
359 for (j = i + t; j < tinybits; j += t)
360 BIT_SET(TinySieve, j);
366 * Start the small block search at the next possible prime. To avoid
367 * fencepost errors, the last pass is skipped.
369 for (smallbase = TINY_NUMBER + 3;
370 smallbase < (SMALL_MAXIMUM - TINY_NUMBER);
371 smallbase += TINY_NUMBER) {
372 for (i = 0; i < tinybits; i++) {
373 if (BIT_TEST(TinySieve, i))
374 continue; /* 2*i+3 is composite */
376 /* The next tiny prime */
381 s = 0; /* t divides into smallbase exactly */
383 /* smallbase+s is first entry divisible by t */
388 * The sieve omits even numbers, so ensure that
389 * smallbase+s is odd. Then, step through the sieve
390 * in increments of 2*t
393 s += t; /* Make smallbase+s odd, and s even */
395 /* Mark all multiples of 2*t */
396 for (s /= 2; s < smallbits; s += t)
397 BIT_SET(SmallSieve, s);
403 for (i = 0; i < smallbits; i++) {
404 if (BIT_TEST(SmallSieve, i))
405 continue; /* 2*i+smallbase is composite */
407 /* The next small prime */
408 sieve_large((2 * i) + smallbase);
411 memset(SmallSieve, 0, smallwords << SHIFT_BYTE);
416 logit("%.24s Sieved with %u small primes in %ld seconds",
417 ctime(&time_stop), largetries, (long) (time_stop - time_start));
419 for (j = r = 0; j < largebits; j++) {
420 if (BIT_TEST(LargeSieve, j))
421 continue; /* Definitely composite, skip */
423 debug2("test q = largebase+%u", 2 * j);
424 BN_set_word(q, 2 * j);
425 BN_add(q, q, largebase);
426 if (qfileout(out, QTYPE_SOPHIE_GERMAIN, QTEST_SIEVE,
427 largetries, (power - 1) /* MSB */, (0), q) == -1) {
441 logit("%.24s Found %u candidates", ctime(&time_stop), r);
447 * perform a Miller-Rabin primality test
448 * on the list of candidates
449 * (checking both q and p)
450 * The result is a list of so-call "safe" primes
453 prime_test(FILE *in, FILE *out, u_int32_t trials, u_int32_t generator_wanted)
458 u_int32_t count_in = 0, count_out = 0, count_possible = 0;
459 u_int32_t generator_known, in_tests, in_tries, in_type, in_size;
460 time_t time_start, time_stop;
463 if (trials < TRIAL_MINIMUM) {
464 error("Minimum primality trials is %d", TRIAL_MINIMUM);
474 debug2("%.24s Final %u Miller-Rabin trials (%x generator)",
475 ctime(&time_start), trials, generator_wanted);
478 lp = xmalloc(QLINESIZE + 1);
479 while (fgets(lp, QLINESIZE, in) != NULL) {
483 if (ll < 14 || *lp == '!' || *lp == '#') {
484 debug2("%10u: comment or short line", count_in);
488 /* XXX - fragile parser */
490 cp = &lp[14]; /* (skip) */
493 in_type = strtoul(cp, &cp, 10);
496 in_tests = strtoul(cp, &cp, 10);
498 if (in_tests & QTEST_COMPOSITE) {
499 debug2("%10u: known composite", count_in);
504 in_tries = strtoul(cp, &cp, 10);
506 /* size (most significant bit) */
507 in_size = strtoul(cp, &cp, 10);
509 /* generator (hex) */
510 generator_known = strtoul(cp, &cp, 16);
512 /* Skip white space */
513 cp += strspn(cp, " ");
517 case QTYPE_SOPHIE_GERMAIN:
518 debug2("%10u: (%u) Sophie-Germain", count_in, in_type);
527 case QTYPE_UNSTRUCTURED:
532 debug2("%10u: (%u)", count_in, in_type);
539 debug2("Unknown prime type");
544 * due to earlier inconsistencies in interpretation, check
545 * the proposed bit size.
547 if ((u_int32_t)BN_num_bits(p) != (in_size + 1)) {
548 debug2("%10u: bit size %u mismatch", count_in, in_size);
551 if (in_size < QSIZE_MINIMUM) {
552 debug2("%10u: bit size %u too short", count_in, in_size);
556 if (in_tests & QTEST_MILLER_RABIN)
562 * guess unknown generator
564 if (generator_known == 0) {
565 if (BN_mod_word(p, 24) == 11)
567 else if (BN_mod_word(p, 12) == 5)
570 u_int32_t r = BN_mod_word(p, 10);
572 if (r == 3 || r == 7)
577 * skip tests when desired generator doesn't match
579 if (generator_wanted > 0 &&
580 generator_wanted != generator_known) {
581 debug2("%10u: generator %d != %d",
582 count_in, generator_known, generator_wanted);
587 * Primes with no known generator are useless for DH, so
590 if (generator_known == 0) {
591 debug2("%10u: no known generator", count_in);
598 * The (1/4)^N performance bound on Miller-Rabin is
599 * extremely pessimistic, so don't spend a lot of time
600 * really verifying that q is prime until after we know
601 * that p is also prime. A single pass will weed out the
602 * vast majority of composite q's.
604 if (BN_is_prime(q, 1, NULL, ctx, NULL) <= 0) {
605 debug("%10u: q failed first possible prime test",
611 * q is possibly prime, so go ahead and really make sure
612 * that p is prime. If it is, then we can go back and do
613 * the same for q. If p is composite, chances are that
614 * will show up on the first Rabin-Miller iteration so it
615 * doesn't hurt to specify a high iteration count.
617 if (!BN_is_prime(p, trials, NULL, ctx, NULL)) {
618 debug("%10u: p is not prime", count_in);
621 debug("%10u: p is almost certainly prime", count_in);
623 /* recheck q more rigorously */
624 if (!BN_is_prime(q, trials - 1, NULL, ctx, NULL)) {
625 debug("%10u: q is not prime", count_in);
628 debug("%10u: q is almost certainly prime", count_in);
630 if (qfileout(out, QTYPE_SAFE, (in_tests | QTEST_MILLER_RABIN),
631 in_tries, in_size, generator_known, p)) {
645 logit("%.24s Found %u safe primes of %u candidates in %ld seconds",
646 ctime(&time_stop), count_out, count_possible,
647 (long) (time_stop - time_start));