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comparison libtommath/bn_mp_prime_random_ex.c @ 284:eed26cff980b

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propagate from branch 'au.asn.ucc.matt.ltm.dropbear' (head 6c790cad5a7fa866ad062cb3a0c279f7ba788583) to branch 'au.asn.ucc.matt.dropbear' (head fff0894a0399405a9410ea1c6d118f342cf2aa64)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 13:23:49 +0000
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children 5ff8218bcee9
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283:bd240aa12ba7 284:eed26cff980b
1 #include <tommath.h>
2 #ifdef BN_MP_PRIME_RANDOM_EX_C
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
4 *
5 * LibTomMath is a library that provides multiple-precision
6 * integer arithmetic as well as number theoretic functionality.
7 *
8 * The library was designed directly after the MPI library by
9 * Michael Fromberger but has been written from scratch with
10 * additional optimizations in place.
11 *
12 * The library is free for all purposes without any express
13 * guarantee it works.
14 *
15 * Tom St Denis, [email protected], http://math.libtomcrypt.org
16 */
17
18 /* makes a truly random prime of a given size (bits),
19 *
20 * Flags are as follows:
21 *
22 * LTM_PRIME_BBS - make prime congruent to 3 mod 4
23 * LTM_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS)
24 * LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero
25 * LTM_PRIME_2MSB_ON - make the 2nd highest bit one
26 *
27 * You have to supply a callback which fills in a buffer with random bytes. "dat" is a parameter you can
28 * have passed to the callback (e.g. a state or something). This function doesn't use "dat" itself
29 * so it can be NULL
30 *
31 */
32
33 /* This is possibly the mother of all prime generation functions, muahahahahaha! */
34 int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat)
35 {
36 unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb;
37 int res, err, bsize, maskOR_msb_offset;
38
39 /* sanity check the input */
40 if (size <= 1 || t <= 0) {
41 return MP_VAL;
42 }
43
44 /* LTM_PRIME_SAFE implies LTM_PRIME_BBS */
45 if (flags & LTM_PRIME_SAFE) {
46 flags |= LTM_PRIME_BBS;
47 }
48
49 /* calc the byte size */
50 bsize = (size>>3) + ((size&7)?1:0);
51
52 /* we need a buffer of bsize bytes */
53 tmp = OPT_CAST(unsigned char) XMALLOC(bsize);
54 if (tmp == NULL) {
55 return MP_MEM;
56 }
57
58 /* calc the maskAND value for the MSbyte*/
59 maskAND = ((size&7) == 0) ? 0xFF : (0xFF >> (8 - (size & 7)));
60
61 /* calc the maskOR_msb */
62 maskOR_msb = 0;
63 maskOR_msb_offset = ((size & 7) == 1) ? 1 : 0;
64 if (flags & LTM_PRIME_2MSB_ON) {
65 maskOR_msb |= 1 << ((size - 2) & 7);
66 } else if (flags & LTM_PRIME_2MSB_OFF) {
67 maskAND &= ~(1 << ((size - 2) & 7));
68 }
69
70 /* get the maskOR_lsb */
71 maskOR_lsb = 1;
72 if (flags & LTM_PRIME_BBS) {
73 maskOR_lsb |= 3;
74 }
75
76 do {
77 /* read the bytes */
78 if (cb(tmp, bsize, dat) != bsize) {
79 err = MP_VAL;
80 goto error;
81 }
82
83 /* work over the MSbyte */
84 tmp[0] &= maskAND;
85 tmp[0] |= 1 << ((size - 1) & 7);
86
87 /* mix in the maskORs */
88 tmp[maskOR_msb_offset] |= maskOR_msb;
89 tmp[bsize-1] |= maskOR_lsb;
90
91 /* read it in */
92 if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY) { goto error; }
93
94 /* is it prime? */
95 if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
96 if (res == MP_NO) {
97 continue;
98 }
99
100 if (flags & LTM_PRIME_SAFE) {
101 /* see if (a-1)/2 is prime */
102 if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) { goto error; }
103 if ((err = mp_div_2(a, a)) != MP_OKAY) { goto error; }
104
105 /* is it prime? */
106 if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; }
107 }
108 } while (res == MP_NO);
109
110 if (flags & LTM_PRIME_SAFE) {
111 /* restore a to the original value */
112 if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; }
113 if ((err = mp_add_d(a, 1, a)) != MP_OKAY) { goto error; }
114 }
115
116 err = MP_OKAY;
117 error:
118 XFREE(tmp);
119 return err;
120 }
121
122
123 #endif