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

   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     KEXTYPE_DH, 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     KEXTYPE_DH, 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     KEXTYPE_DH, 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     KEXTYPE_DH, 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 }