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

   1 /***************************************************************************
   2  *
   3  *              Part II Project, "A secure, private IP network"
   4  *              Stephen Early <sde1000@cam.ac.uk>
   5  *
   6  *
   7  *     $RCSfile: dh.c,v $
   8  *
   9  *  Description: Diffie-Hellman implementation
  10  *
  11  *    Copyright: (C) Stephen Early 1995
  12  *
  13  *    $Revision: 1.3 $
  14  *
  15  *        $Date: 1996/05/16 18:38:54 $
  16  *
  17  *       $State: Exp $
  18  *
  19  ***************************************************************************/
  20
  21 /*
  22  * $Log: dh.c,v $
  23  * Revision 1.3  1996/05/16 18:38:54  sde1000
  24  * Removed unused hexdigits variable.
  25  *
  26  * Revision 1.2  1996/04/14 16:33:52  sde1000
  27  * Moved mpbin/mpstring functions into util.c
  28  *
  29  * Revision 1.1  1996/04/14 16:21:47  sde1000
  30  * Initial revision
  31  *
  32  */
  33
  34 #include <stdio.h>
  35 #include <gmp.h>
  36
  37 #include "secnet.h"
  38 #include "util.h"
  39
  40 struct dh {
  41     closure_t cl;
  42     struct dh_if ops;
  43     struct cloc loc;
  44     MP_INT p,g; /* prime modulus and generator */
  45 };
  46
  47 static string_t dh_makepublic(void *sst, uint8_t *secret, uint32_t secretlen)
  48 {
  49     struct dh *st=sst;
  50     string_t r;
  51     MP_INT a, b; /* a is secret key, b is public key */
  52
  53     mpz_init(&a);
  54     mpz_init(&b);
  55
  56     read_mpbin(&a, secret, secretlen);
  57
  58     mpz_powm(&b, &st->g, &a, &st->p);
  59
  60     r=write_mpstring(&b);
  61
  62     mpz_clear(&a);
  63     mpz_clear(&b);
  64     return r;
  65 }
  66
  67 static void dh_makeshared(void *sst, uint8_t *secret, uint32_t secretlen,
  68                           string_t rempublic, uint8_t *sharedsecret,
  69                           uint32_t buflen)
  70 {
  71     struct dh *st=sst;
  72     MP_INT a, b, c;
  73
  74     mpz_init(&a);
  75     mpz_init(&b);
  76     mpz_init(&c);
  77
  78     read_mpbin(&a, secret, secretlen);
  79     mpz_set_str(&b, rempublic, 16);
  80
  81     mpz_powm(&c, &b, &a, &st->p);
  82
  83     write_mpbin(&c,sharedsecret,buflen);
  84
  85     mpz_clear(&a);
  86     mpz_clear(&b);
  87     mpz_clear(&c);
  88 }
  89
  90 static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
  91                         list_t *args)
  92 {
  93     struct dh *st;
  94     string_t p,g;
  95     item_t *i;
  96
  97     st=safe_malloc(sizeof(*st),"dh_apply");
  98     st->cl.description="dh";
  99     st->cl.type=CL_DH;
 100     st->cl.apply=NULL;
 101     st->cl.interface=&st->ops;
 102     st->ops.st=st;
 103     st->ops.makepublic=dh_makepublic;
 104     st->ops.makeshared=dh_makeshared;
 105     st->loc=loc;
 106     /* We have two string arguments: the first is the modulus, and the
 107        second is the generator. Both are in hex. */
 108     i=list_elem(args,0);
 109     if (i) {
 110         if (i->type!=t_string) {
 111             cfgfatal(i->loc,"diffie-hellman","first argument must be a "
 112                      "string\n");
 113         }
 114         p=i->data.string;
 115         if (mpz_init_set_str(&st->p,p,16)!=0) {
 116             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
 117                      "string\n",p);
 118         }
 119     } else {
 120         cfgfatal(loc,"diffie-hellman","you must provide a prime modulus\n");
 121     }
 122
 123     i=list_elem(args,1);
 124     if (i) {
 125         if (i->type!=t_string) {
 126             cfgfatal(i->loc,"diffie-hellman","second argument must be a "
 127                      "string\n");
 128         }
 129         g=i->data.string;
 130         if (mpz_init_set_str(&st->g,g,16)!=0) {
 131             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
 132                      "string\n",g);
 133         }
 134     } else {
 135         cfgfatal(loc,"diffie-hellman","you must provide a generator\n");
 136     }
 137
 138     i=list_elem(args,2);
 139     if (i && i->type==t_bool && i->data.bool==False) {
 140         Message(M_INFO,"diffie-hellman (%s:%d): skipping modulus "
 141                 "primality check\n",loc.file,loc.line);
 142     } else {
 143         /* Test that the modulus is really prime */
 144         if (mpz_probab_prime_p(&st->p,5)==0) {
 145             cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
 146         }
 147     }
 148     st->ops.len=mpz_sizeinbase(&st->p,2)/8;
 149
 150     return new_closure(&st->cl);
 151 }
 152
 153 init_module dh_module;
 154 void dh_module(dict_t *dict)
 155 {
 156     add_closure(dict,"diffie-hellman",dh_apply);
 157 }