| 1 | #include "ssh.h" |
| 2 | |
| 3 | const struct ssh_kex ssh_diffiehellman = { |
| 4 | "diffie-hellman-group1-sha1" |
| 5 | }; |
| 6 | |
| 7 | const struct ssh_kex ssh_diffiehellman_gex = { |
| 8 | "diffie-hellman-group-exchange-sha1" |
| 9 | }; |
| 10 | |
| 11 | /* |
| 12 | * The prime p used in the key exchange. |
| 13 | */ |
| 14 | static 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 |
| 26 | }; |
| 27 | |
| 28 | /* |
| 29 | * The generator g = 2. |
| 30 | */ |
| 31 | static unsigned char G[] = { 2 }; |
| 32 | |
| 33 | /* |
| 34 | * Variables. |
| 35 | */ |
| 36 | static Bignum x, e, p, q, qmask, g; |
| 37 | static int need_to_free_pg; |
| 38 | |
| 39 | /* |
| 40 | * Common DH initialisation. |
| 41 | */ |
| 42 | static void dh_init(void) { |
| 43 | q = bignum_rshift(p, 1); |
| 44 | qmask = bignum_bitmask(q); |
| 45 | } |
| 46 | |
| 47 | /* |
| 48 | * Initialise DH for the standard group1. |
| 49 | */ |
| 50 | void 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 | /* |
| 57 | * Initialise DH for an alternative group. |
| 58 | */ |
| 59 | void dh_setup_group(Bignum pval, Bignum gval) { |
| 60 | p = copybn(pval); |
| 61 | g = copybn(gval); |
| 62 | dh_init(); |
| 63 | } |
| 64 | |
| 65 | /* |
| 66 | * Clean up. |
| 67 | */ |
| 68 | void dh_cleanup(void) { |
| 69 | freebn(p); |
| 70 | freebn(g); |
| 71 | freebn(q); |
| 72 | freebn(qmask); |
| 73 | } |
| 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 | * |
| 79 | * If `nbits' is greater than zero, it is used as an upper limit |
| 80 | * for the number of bits in x. This is safe provided that (a) you |
| 81 | * use twice as many bits in x as the number of bits you expect to |
| 82 | * use in your session key, and (b) the DH group is a safe prime |
| 83 | * (which SSH demands that it must be). |
| 84 | * |
| 85 | * P. C. van Oorschot, M. J. Wiener |
| 86 | * "On Diffie-Hellman Key Agreement with Short Exponents". |
| 87 | * Advances in Cryptology: Proceedings of Eurocrypt '96 |
| 88 | * Springer-Verlag, May 1996. |
| 89 | */ |
| 90 | Bignum dh_create_e(int nbits) { |
| 91 | int i; |
| 92 | |
| 93 | int nbytes; |
| 94 | unsigned char *buf; |
| 95 | |
| 96 | nbytes = ssh1_bignum_length(qmask); |
| 97 | buf = smalloc(nbytes); |
| 98 | |
| 99 | do { |
| 100 | /* |
| 101 | * Create a potential x, by ANDing a string of random bytes |
| 102 | * with qmask. |
| 103 | */ |
| 104 | if (x) freebn(x); |
| 105 | if (nbits == 0 || nbits > bignum_bitcount(qmask)) { |
| 106 | ssh1_write_bignum(buf, qmask); |
| 107 | for (i = 2; i < nbytes; i++) |
| 108 | buf[i] &= random_byte(); |
| 109 | ssh1_read_bignum(buf, &x); |
| 110 | } else { |
| 111 | int b, nb; |
| 112 | x = bn_power_2(nbits); |
| 113 | nb = 0; |
| 114 | for (i = 0; i < nbits; i++) { |
| 115 | if (nb == 0) { |
| 116 | nb = 8; |
| 117 | b = random_byte(); |
| 118 | } |
| 119 | bignum_set_bit(x, i, b & 1); |
| 120 | b >>= 1; |
| 121 | nb--; |
| 122 | } |
| 123 | } |
| 124 | } while (bignum_cmp(x, One) <= 0 || bignum_cmp(x, q) >= 0); |
| 125 | |
| 126 | /* |
| 127 | * Done. Now compute e = g^x mod p. |
| 128 | */ |
| 129 | e = modpow(g, x, p); |
| 130 | |
| 131 | return e; |
| 132 | } |
| 133 | |
| 134 | /* |
| 135 | * DH stage 2: given a number f, compute K = f^x mod p. |
| 136 | */ |
| 137 | Bignum dh_find_K(Bignum f) { |
| 138 | Bignum ret; |
| 139 | ret = modpow(f, x, p); |
| 140 | return ret; |
| 141 | } |