git.distorted.org.uk Git - u/mdw/putty/blob - sshdh.c

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