Tiny bug in bn_power_2() - didn't work with powers that were a
[u/mdw/putty] / sshdh.c
CommitLineData
e5574168 1#include "ssh.h"
2
65a22376 3const struct ssh_kex ssh_diffiehellman = {
e5574168 4 "diffie-hellman-group1-sha1"
5};
6
65a22376 7const struct ssh_kex ssh_diffiehellman_gex = {
a92dd380 8 "diffie-hellman-group-exchange-sha1"
9};
10
e5574168 11/*
12 * The prime p used in the key exchange.
13 */
3709bfe9 14static unsigned char P[] = {
15 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2,
16 0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1,
17 0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6,
18 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD,
19 0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D,
20 0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45,
21 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9,
22 0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED,
23 0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11,
24 0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE6, 0x53, 0x81,
25 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
e5574168 26};
27
28/*
3709bfe9 29 * The generator g = 2.
e5574168 30 */
3709bfe9 31static unsigned char G[] = { 2 };
e5574168 32
33/*
3709bfe9 34 * Variables.
e5574168 35 */
3709bfe9 36static Bignum x, e, p, q, qmask, g;
37static int need_to_free_pg;
e5574168 38
39/*
3709bfe9 40 * Common DH initialisation.
e5574168 41 */
3709bfe9 42static void dh_init(void) {
43 q = bignum_rshift(p, 1);
44 qmask = bignum_bitmask(q);
45}
e5574168 46
47/*
3709bfe9 48 * Initialise DH for the standard group1.
e5574168 49 */
3709bfe9 50void dh_setup_group1(void) {
51 p = bignum_from_bytes(P, sizeof(P));
52 g = bignum_from_bytes(G, sizeof(G));
53 dh_init();
54}
55
56/*
a92dd380 57 * Initialise DH for an alternative group.
58 */
59void dh_setup_group(Bignum pval, Bignum gval) {
60 p = copybn(pval);
61 g = copybn(gval);
62 dh_init();
63}
64
65/*
3709bfe9 66 * Clean up.
67 */
68void dh_cleanup(void) {
69 freebn(p);
70 freebn(g);
71 freebn(q);
72 freebn(qmask);
73}
e5574168 74
75/*
76 * DH stage 1: invent a number x between 1 and q, and compute e =
77 * g^x mod p. Return e.
78 */
79Bignum dh_create_e(void) {
80 int i;
81
3709bfe9 82 int nbytes;
83 unsigned char *buf;
84
85 nbytes = ssh1_bignum_length(qmask);
86 buf = smalloc(nbytes);
e5574168 87
a71540b9 88 do {
89 /*
90 * Create a potential x, by ANDing a string of random bytes
3709bfe9 91 * with qmask.
a71540b9 92 */
3709bfe9 93 if (x) freebn(x);
94 ssh1_write_bignum(buf, qmask);
95 for (i = 2; i < nbytes; i++)
96 buf[i] &= random_byte();
97 ssh1_read_bignum(buf, &x);
98 } while (bignum_cmp(x, One) <= 0 || bignum_cmp(x, q) >= 0);
e5574168 99
100 /*
101 * Done. Now compute e = g^x mod p.
102 */
3709bfe9 103 e = modpow(g, x, p);
e5574168 104
105 return e;
106}
107
108/*
109 * DH stage 2: given a number f, compute K = f^x mod p.
110 */
111Bignum dh_find_K(Bignum f) {
3709bfe9 112 return modpow(f, x, p);
e5574168 113}