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 const struct ssh_kex ssh_diffiehellman_group1 = {
  50     "diffie-hellman-group1-sha1", "group1",
  51     P1, G, lenof(P1), lenof(G)
  52 };
  53
  54 const struct ssh_kex ssh_diffiehellman_group14 = {
  55     "diffie-hellman-group14-sha1", "group14",
  56     P14, G, lenof(P14), lenof(G)
  57 };
  58
  59 const struct ssh_kex ssh_diffiehellman_gex = {
  60     "diffie-hellman-group-exchange-sha1", NULL,
  61     NULL, NULL, 0, 0
  62 };
  63
  64 /*
  65  * Variables.
  66  */
  67 struct dh_ctx {
  68     Bignum x, e, p, q, qmask, g;
  69 };
  70
  71 /*
  72  * Common DH initialisation.
  73  */
  74 static void dh_init(struct dh_ctx *ctx)
  75 {
  76     ctx->q = bignum_rshift(ctx->p, 1);
  77     ctx->qmask = bignum_bitmask(ctx->q);
  78     ctx->x = ctx->e = NULL;
  79 }
  80
  81 /*
  82  * Initialise DH for a standard group.
  83  */
  84 void *dh_setup_group(const struct ssh_kex *kex)
  85 {
  86     struct dh_ctx *ctx = snew(struct dh_ctx);
  87     ctx->p = bignum_from_bytes(kex->pdata, kex->plen);
  88     ctx->g = bignum_from_bytes(kex->gdata, kex->glen);
  89     dh_init(ctx);
  90     return ctx;
  91 }
  92
  93 /*
  94  * Initialise DH for a server-supplied group.
  95  */
  96 void *dh_setup_gex(Bignum pval, Bignum gval)
  97 {
  98     struct dh_ctx *ctx = snew(struct dh_ctx);
  99     ctx->p = copybn(pval);
 100     ctx->g = copybn(gval);
 101     dh_init(ctx);
 102     return ctx;
 103 }
 104
 105 /*
 106  * Clean up and free a context.
 107  */
 108 void dh_cleanup(void *handle)
 109 {
 110     struct dh_ctx *ctx = (struct dh_ctx *)handle;
 111     freebn(ctx->x);
 112     freebn(ctx->e);
 113     freebn(ctx->p);
 114     freebn(ctx->g);
 115     freebn(ctx->q);
 116     freebn(ctx->qmask);
 117     sfree(ctx);
 118 }
 119
 120 /*
 121  * DH stage 1: invent a number x between 1 and q, and compute e =
 122  * g^x mod p. Return e.
 123  *
 124  * If `nbits' is greater than zero, it is used as an upper limit
 125  * for the number of bits in x. This is safe provided that (a) you
 126  * use twice as many bits in x as the number of bits you expect to
 127  * use in your session key, and (b) the DH group is a safe prime
 128  * (which SSH demands that it must be).
 129  *
 130  * P. C. van Oorschot, M. J. Wiener
 131  * "On Diffie-Hellman Key Agreement with Short Exponents".
 132  * Advances in Cryptology: Proceedings of Eurocrypt '96
 133  * Springer-Verlag, May 1996.
 134  */
 135 Bignum dh_create_e(void *handle, int nbits)
 136 {
 137     struct dh_ctx *ctx = (struct dh_ctx *)handle;
 138     int i;
 139
 140     int nbytes;
 141     unsigned char *buf;
 142
 143     nbytes = ssh1_bignum_length(ctx->qmask);
 144     buf = snewn(nbytes, unsigned char);
 145
 146     do {
 147         /*
 148          * Create a potential x, by ANDing a string of random bytes
 149          * with qmask.
 150          */
 151         if (ctx->x)
 152             freebn(ctx->x);
 153         if (nbits == 0 || nbits > bignum_bitcount(ctx->qmask)) {
 154             ssh1_write_bignum(buf, ctx->qmask);
 155             for (i = 2; i < nbytes; i++)
 156                 buf[i] &= random_byte();
 157             ssh1_read_bignum(buf, nbytes, &ctx->x);   /* can't fail */
 158         } else {
 159             int b, nb;
 160             ctx->x = bn_power_2(nbits);
 161             b = nb = 0;
 162             for (i = 0; i < nbits; i++) {
 163                 if (nb == 0) {
 164                     nb = 8;
 165                     b = random_byte();
 166                 }
 167                 bignum_set_bit(ctx->x, i, b & 1);
 168                 b >>= 1;
 169                 nb--;
 170             }
 171         }
 172     } while (bignum_cmp(ctx->x, One) <= 0 || bignum_cmp(ctx->x, ctx->q) >= 0);
 173
 174     sfree(buf);
 175
 176     /*
 177      * Done. Now compute e = g^x mod p.
 178      */
 179     ctx->e = modpow(ctx->g, ctx->x, ctx->p);
 180
 181     return ctx->e;
 182 }
 183
 184 /*
 185  * DH stage 2: given a number f, compute K = f^x mod p.
 186  */
 187 Bignum dh_find_K(void *handle, Bignum f)
 188 {
 189     struct dh_ctx *ctx = (struct dh_ctx *)handle;
 190     Bignum ret;
 191     ret = modpow(f, ctx->x, ctx->p);
 192     return ret;
 193 }