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