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

   1 #include "ssh.h"
   2
   3 struct ssh_kex ssh_diffiehellman = {
   4     "diffie-hellman-group1-sha1"
   5 };
   6
   7 /*
   8  * The prime p used in the key exchange.
   9  */
  10 static unsigned char P[] = {
  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
  24 /*
  25  * The generator g = 2.
  26  */
  27 static unsigned char G[] = { 2 };
  28
  29 /*
  30  * Variables.
  31  */
  32 static Bignum x, e, p, q, qmask, g;
  33 static int need_to_free_pg;
  34
  35 /*
  36  * Common DH initialisation.
  37  */
  38 static void dh_init(void) {
  39     q = bignum_rshift(p, 1);
  40     qmask = bignum_bitmask(q);
  41 }
  42
  43 /*
  44  * Initialise DH for the standard group1.
  45  */
  46 void dh_setup_group1(void) {
  47     p = bignum_from_bytes(P, sizeof(P));
  48     g = bignum_from_bytes(G, sizeof(G));
  49     dh_init();
  50 }
  51
  52 /*
  53  * Clean up.
  54  */
  55 void dh_cleanup(void) {
  56     freebn(p);
  57     freebn(g);
  58     freebn(q);
  59     freebn(qmask);
  60 }
  61
  62 /*
  63  * DH stage 1: invent a number x between 1 and q, and compute e =
  64  * g^x mod p. Return e.
  65  */
  66 Bignum dh_create_e(void) {
  67     int i;
  68
  69     int nbytes;
  70     unsigned char *buf;
  71
  72     nbytes = ssh1_bignum_length(qmask);
  73     buf = smalloc(nbytes);
  74
  75     do {
  76         /*
  77          * Create a potential x, by ANDing a string of random bytes
  78          * with qmask.
  79          */
  80         if (x) freebn(x);
  81         ssh1_write_bignum(buf, qmask);
  82         for (i = 2; i < nbytes; i++)
  83             buf[i] &= random_byte();
  84         ssh1_read_bignum(buf, &x);
  85     } while (bignum_cmp(x, One) <= 0 || bignum_cmp(x, q) >= 0);
  86
  87     /*
  88      * Done. Now compute e = g^x mod p.
  89      */
  90     e = modpow(g, x, p);
  91
  92     return e;
  93 }
  94
  95 /*
  96  * DH stage 2: given a number f, compute K = f^x mod p.
  97  */
  98 Bignum dh_find_K(Bignum f) {
  99     return modpow(f, x, p);
 100 }