| 1 | /* |
| 2 | * Diffie-Hellman implementation for PuTTY. |
| 3 | */ |
| 4 | |
| 5 | #include "ssh.h" |
| 6 | |
| 7 | /* |
| 8 | * The primes used in the group1 and group14 key exchange. |
| 9 | */ |
| 10 | static const unsigned char P1[] = { |
| 11 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2, |
| 12 | 0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1, |
| 13 | 0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6, |
| 14 | 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD, |
| 15 | 0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D, |
| 16 | 0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45, |
| 17 | 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9, |
| 18 | 0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED, |
| 19 | 0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11, |
| 20 | 0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE6, 0x53, 0x81, |
| 21 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF |
| 22 | }; |
| 23 | static const unsigned char P14[] = { |
| 24 | 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC9, 0x0F, 0xDA, 0xA2, |
| 25 | 0x21, 0x68, 0xC2, 0x34, 0xC4, 0xC6, 0x62, 0x8B, 0x80, 0xDC, 0x1C, 0xD1, |
| 26 | 0x29, 0x02, 0x4E, 0x08, 0x8A, 0x67, 0xCC, 0x74, 0x02, 0x0B, 0xBE, 0xA6, |
| 27 | 0x3B, 0x13, 0x9B, 0x22, 0x51, 0x4A, 0x08, 0x79, 0x8E, 0x34, 0x04, 0xDD, |
| 28 | 0xEF, 0x95, 0x19, 0xB3, 0xCD, 0x3A, 0x43, 0x1B, 0x30, 0x2B, 0x0A, 0x6D, |
| 29 | 0xF2, 0x5F, 0x14, 0x37, 0x4F, 0xE1, 0x35, 0x6D, 0x6D, 0x51, 0xC2, 0x45, |
| 30 | 0xE4, 0x85, 0xB5, 0x76, 0x62, 0x5E, 0x7E, 0xC6, 0xF4, 0x4C, 0x42, 0xE9, |
| 31 | 0xA6, 0x37, 0xED, 0x6B, 0x0B, 0xFF, 0x5C, 0xB6, 0xF4, 0x06, 0xB7, 0xED, |
| 32 | 0xEE, 0x38, 0x6B, 0xFB, 0x5A, 0x89, 0x9F, 0xA5, 0xAE, 0x9F, 0x24, 0x11, |
| 33 | 0x7C, 0x4B, 0x1F, 0xE6, 0x49, 0x28, 0x66, 0x51, 0xEC, 0xE4, 0x5B, 0x3D, |
| 34 | 0xC2, 0x00, 0x7C, 0xB8, 0xA1, 0x63, 0xBF, 0x05, 0x98, 0xDA, 0x48, 0x36, |
| 35 | 0x1C, 0x55, 0xD3, 0x9A, 0x69, 0x16, 0x3F, 0xA8, 0xFD, 0x24, 0xCF, 0x5F, |
| 36 | 0x83, 0x65, 0x5D, 0x23, 0xDC, 0xA3, 0xAD, 0x96, 0x1C, 0x62, 0xF3, 0x56, |
| 37 | 0x20, 0x85, 0x52, 0xBB, 0x9E, 0xD5, 0x29, 0x07, 0x70, 0x96, 0x96, 0x6D, |
| 38 | 0x67, 0x0C, 0x35, 0x4E, 0x4A, 0xBC, 0x98, 0x04, 0xF1, 0x74, 0x6C, 0x08, |
| 39 | 0xCA, 0x18, 0x21, 0x7C, 0x32, 0x90, 0x5E, 0x46, 0x2E, 0x36, 0xCE, 0x3B, |
| 40 | 0xE3, 0x9E, 0x77, 0x2C, 0x18, 0x0E, 0x86, 0x03, 0x9B, 0x27, 0x83, 0xA2, |
| 41 | 0xEC, 0x07, 0xA2, 0x8F, 0xB5, 0xC5, 0x5D, 0xF0, 0x6F, 0x4C, 0x52, 0xC9, |
| 42 | 0xDE, 0x2B, 0xCB, 0xF6, 0x95, 0x58, 0x17, 0x18, 0x39, 0x95, 0x49, 0x7C, |
| 43 | 0xEA, 0x95, 0x6A, 0xE5, 0x15, 0xD2, 0x26, 0x18, 0x98, 0xFA, 0x05, 0x10, |
| 44 | 0x15, 0x72, 0x8E, 0x5A, 0x8A, 0xAC, 0xAA, 0x68, 0xFF, 0xFF, 0xFF, 0xFF, |
| 45 | 0xFF, 0xFF, 0xFF, 0xFF |
| 46 | }; |
| 47 | |
| 48 | /* |
| 49 | * The generator g = 2 (used for both group1 and group14). |
| 50 | */ |
| 51 | static const unsigned char G[] = { 2 }; |
| 52 | |
| 53 | static const struct ssh_kex ssh_diffiehellman_group1_sha1 = { |
| 54 | "diffie-hellman-group1-sha1", "group1", |
| 55 | P1, G, lenof(P1), lenof(G), &ssh_sha1 |
| 56 | }; |
| 57 | |
| 58 | static const struct ssh_kex *const group1_list[] = { |
| 59 | &ssh_diffiehellman_group1_sha1 |
| 60 | }; |
| 61 | |
| 62 | const struct ssh_kexes ssh_diffiehellman_group1 = { |
| 63 | sizeof(group1_list) / sizeof(*group1_list), |
| 64 | group1_list |
| 65 | }; |
| 66 | |
| 67 | static const struct ssh_kex ssh_diffiehellman_group14_sha1 = { |
| 68 | "diffie-hellman-group14-sha1", "group14", |
| 69 | P14, G, lenof(P14), lenof(G), &ssh_sha1 |
| 70 | }; |
| 71 | |
| 72 | static const struct ssh_kex *const group14_list[] = { |
| 73 | &ssh_diffiehellman_group14_sha1 |
| 74 | }; |
| 75 | |
| 76 | const struct ssh_kexes ssh_diffiehellman_group14 = { |
| 77 | sizeof(group14_list) / sizeof(*group14_list), |
| 78 | group14_list |
| 79 | }; |
| 80 | |
| 81 | static const struct ssh_kex ssh_diffiehellman_gex_sha256 = { |
| 82 | "diffie-hellman-group-exchange-sha256", NULL, |
| 83 | NULL, NULL, 0, 0, &ssh_sha256 |
| 84 | }; |
| 85 | |
| 86 | static const struct ssh_kex ssh_diffiehellman_gex_sha1 = { |
| 87 | "diffie-hellman-group-exchange-sha1", NULL, |
| 88 | NULL, NULL, 0, 0, &ssh_sha1 |
| 89 | }; |
| 90 | |
| 91 | static const struct ssh_kex *const gex_list[] = { |
| 92 | &ssh_diffiehellman_gex_sha256, |
| 93 | &ssh_diffiehellman_gex_sha1 |
| 94 | }; |
| 95 | |
| 96 | const struct ssh_kexes ssh_diffiehellman_gex = { |
| 97 | sizeof(gex_list) / sizeof(*gex_list), |
| 98 | gex_list |
| 99 | }; |
| 100 | |
| 101 | /* |
| 102 | * Variables. |
| 103 | */ |
| 104 | struct dh_ctx { |
| 105 | Bignum x, e, p, q, qmask, g; |
| 106 | }; |
| 107 | |
| 108 | /* |
| 109 | * Common DH initialisation. |
| 110 | */ |
| 111 | static void dh_init(struct dh_ctx *ctx) |
| 112 | { |
| 113 | ctx->q = bignum_rshift(ctx->p, 1); |
| 114 | ctx->qmask = bignum_bitmask(ctx->q); |
| 115 | ctx->x = ctx->e = NULL; |
| 116 | } |
| 117 | |
| 118 | /* |
| 119 | * Initialise DH for a standard group. |
| 120 | */ |
| 121 | void *dh_setup_group(const struct ssh_kex *kex) |
| 122 | { |
| 123 | struct dh_ctx *ctx = snew(struct dh_ctx); |
| 124 | ctx->p = bignum_from_bytes(kex->pdata, kex->plen); |
| 125 | ctx->g = bignum_from_bytes(kex->gdata, kex->glen); |
| 126 | dh_init(ctx); |
| 127 | return ctx; |
| 128 | } |
| 129 | |
| 130 | /* |
| 131 | * Initialise DH for a server-supplied group. |
| 132 | */ |
| 133 | void *dh_setup_gex(Bignum pval, Bignum gval) |
| 134 | { |
| 135 | struct dh_ctx *ctx = snew(struct dh_ctx); |
| 136 | ctx->p = copybn(pval); |
| 137 | ctx->g = copybn(gval); |
| 138 | dh_init(ctx); |
| 139 | return ctx; |
| 140 | } |
| 141 | |
| 142 | /* |
| 143 | * Clean up and free a context. |
| 144 | */ |
| 145 | void dh_cleanup(void *handle) |
| 146 | { |
| 147 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
| 148 | freebn(ctx->x); |
| 149 | freebn(ctx->e); |
| 150 | freebn(ctx->p); |
| 151 | freebn(ctx->g); |
| 152 | freebn(ctx->q); |
| 153 | freebn(ctx->qmask); |
| 154 | sfree(ctx); |
| 155 | } |
| 156 | |
| 157 | /* |
| 158 | * DH stage 1: invent a number x between 1 and q, and compute e = |
| 159 | * g^x mod p. Return e. |
| 160 | * |
| 161 | * If `nbits' is greater than zero, it is used as an upper limit |
| 162 | * for the number of bits in x. This is safe provided that (a) you |
| 163 | * use twice as many bits in x as the number of bits you expect to |
| 164 | * use in your session key, and (b) the DH group is a safe prime |
| 165 | * (which SSH demands that it must be). |
| 166 | * |
| 167 | * P. C. van Oorschot, M. J. Wiener |
| 168 | * "On Diffie-Hellman Key Agreement with Short Exponents". |
| 169 | * Advances in Cryptology: Proceedings of Eurocrypt '96 |
| 170 | * Springer-Verlag, May 1996. |
| 171 | */ |
| 172 | Bignum dh_create_e(void *handle, int nbits) |
| 173 | { |
| 174 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
| 175 | int i; |
| 176 | |
| 177 | int nbytes; |
| 178 | unsigned char *buf; |
| 179 | |
| 180 | nbytes = ssh1_bignum_length(ctx->qmask); |
| 181 | buf = snewn(nbytes, unsigned char); |
| 182 | |
| 183 | do { |
| 184 | /* |
| 185 | * Create a potential x, by ANDing a string of random bytes |
| 186 | * with qmask. |
| 187 | */ |
| 188 | if (ctx->x) |
| 189 | freebn(ctx->x); |
| 190 | if (nbits == 0 || nbits > bignum_bitcount(ctx->qmask)) { |
| 191 | ssh1_write_bignum(buf, ctx->qmask); |
| 192 | for (i = 2; i < nbytes; i++) |
| 193 | buf[i] &= random_byte(); |
| 194 | ssh1_read_bignum(buf, nbytes, &ctx->x); /* can't fail */ |
| 195 | } else { |
| 196 | int b, nb; |
| 197 | ctx->x = bn_power_2(nbits); |
| 198 | b = nb = 0; |
| 199 | for (i = 0; i < nbits; i++) { |
| 200 | if (nb == 0) { |
| 201 | nb = 8; |
| 202 | b = random_byte(); |
| 203 | } |
| 204 | bignum_set_bit(ctx->x, i, b & 1); |
| 205 | b >>= 1; |
| 206 | nb--; |
| 207 | } |
| 208 | } |
| 209 | } while (bignum_cmp(ctx->x, One) <= 0 || bignum_cmp(ctx->x, ctx->q) >= 0); |
| 210 | |
| 211 | sfree(buf); |
| 212 | |
| 213 | /* |
| 214 | * Done. Now compute e = g^x mod p. |
| 215 | */ |
| 216 | ctx->e = modpow(ctx->g, ctx->x, ctx->p); |
| 217 | |
| 218 | return ctx->e; |
| 219 | } |
| 220 | |
| 221 | /* |
| 222 | * DH stage 2: given a number f, compute K = f^x mod p. |
| 223 | */ |
| 224 | Bignum dh_find_K(void *handle, Bignum f) |
| 225 | { |
| 226 | struct dh_ctx *ctx = (struct dh_ctx *)handle; |
| 227 | Bignum ret; |
| 228 | ret = modpow(f, ctx->x, ctx->p); |
| 229 | return ret; |
| 230 | } |