mdw@git.distorted.org.uk Git - secnet/blob - dh.c

   1 #include <stdio.h>
   2 #include <gmp.h>
   3
   4 #include "secnet.h"
   5 #include "util.h"
   6
   7 struct dh {
   8     closure_t cl;
   9     struct dh_if ops;
  10     struct cloc loc;
  11     MP_INT p,g; /* prime modulus and generator */
  12 };
  13
  14 static string_t dh_makepublic(void *sst, uint8_t *secret, uint32_t secretlen)
  15 {
  16     struct dh *st=sst;
  17     string_t r;
  18     MP_INT a, b; /* a is secret key, b is public key */
  19
  20     mpz_init(&a);
  21     mpz_init(&b);
  22
  23     read_mpbin(&a, secret, secretlen);
  24
  25     mpz_powm(&b, &st->g, &a, &st->p);
  26
  27     r=write_mpstring(&b);
  28
  29     mpz_clear(&a);
  30     mpz_clear(&b);
  31     return r;
  32 }
  33
  34 static dh_makeshared_fn dh_makeshared;
  35 static void dh_makeshared(void *sst, uint8_t *secret, uint32_t secretlen,
  36                           cstring_t rempublic, uint8_t *sharedsecret,
  37                           uint32_t buflen)
  38 {
  39     struct dh *st=sst;
  40     MP_INT a, b, c;
  41
  42     mpz_init(&a);
  43     mpz_init(&b);
  44     mpz_init(&c);
  45
  46     read_mpbin(&a, secret, secretlen);
  47     mpz_set_str(&b, rempublic, 16);
  48
  49     mpz_powm(&c, &b, &a, &st->p);
  50
  51     write_mpbin(&c,sharedsecret,buflen);
  52
  53     mpz_clear(&a);
  54     mpz_clear(&b);
  55     mpz_clear(&c);
  56 }
  57
  58 static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
  59                         list_t *args)
  60 {
  61     struct dh *st;
  62     string_t p,g;
  63     item_t *i;
  64
  65     st=safe_malloc(sizeof(*st),"dh_apply");
  66     st->cl.description="dh";
  67     st->cl.type=CL_DH;
  68     st->cl.apply=NULL;
  69     st->cl.interface=&st->ops;
  70     st->ops.st=st;
  71     st->ops.makepublic=dh_makepublic;
  72     st->ops.makeshared=dh_makeshared;
  73     st->loc=loc;
  74     /* We have two string arguments: the first is the modulus, and the
  75        second is the generator. Both are in hex. */
  76     i=list_elem(args,0);
  77     if (i) {
  78         if (i->type!=t_string) {
  79             cfgfatal(i->loc,"diffie-hellman","first argument must be a "
  80                      "string\n");
  81         }
  82         p=i->data.string;
  83         if (mpz_init_set_str(&st->p,p,16)!=0) {
  84             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
  85                      "string\n",p);
  86         }
  87     } else {
  88         cfgfatal(loc,"diffie-hellman","you must provide a prime modulus\n");
  89     }
  90
  91     i=list_elem(args,1);
  92     if (i) {
  93         if (i->type!=t_string) {
  94             cfgfatal(i->loc,"diffie-hellman","second argument must be a "
  95                      "string\n");
  96         }
  97         g=i->data.string;
  98         if (mpz_init_set_str(&st->g,g,16)!=0) {
  99             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
 100                      "string\n",g);
 101         }
 102     } else {
 103         cfgfatal(loc,"diffie-hellman","you must provide a generator\n");
 104     }
 105
 106     i=list_elem(args,2);
 107     if (i && i->type==t_bool && i->data.bool==False) {
 108         Message(M_INFO,"diffie-hellman (%s:%d): skipping modulus "
 109                 "primality check\n",loc.file,loc.line);
 110     } else {
 111         /* Test that the modulus is really prime */
 112         if (mpz_probab_prime_p(&st->p,5)==0) {
 113             cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
 114         }
 115     }
 116     st->ops.len=mpz_sizeinbase(&st->p,2)/8;
 117
 118     return new_closure(&st->cl);
 119 }
 120
 121 init_module dh_module;
 122 void dh_module(dict_t *dict)
 123 {
 124     add_closure(dict,"diffie-hellman",dh_apply);
 125 }