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

   1 /*
   2  * dh.c
   3  */
   4 /*
   5  * This file is Free Software.  It was originally written for secnet.
   6  *
   7  * Copyright 1995-2003 Stephen Early
   8  * Copyright 2002-2014 Ian Jackson
   9  *
  10  * You may redistribute secnet as a whole and/or modify it under the
  11  * terms of the GNU General Public License as published by the Free
  12  * Software Foundation; either version 3, or (at your option) any
  13  * later version.
  14  *
  15  * You may redistribute this file and/or modify it under the terms of
  16  * the GNU General Public License as published by the Free Software
  17  * Foundation; either version 2, or (at your option) any later
  18  * version.
  19  *
  20  * This software is distributed in the hope that it will be useful,
  21  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  22  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  23  * GNU General Public License for more details.
  24  *
  25  * You should have received a copy of the GNU General Public License
  26  * along with this software; if not, see
  27  * https://www.gnu.org/licenses/gpl.html.
  28  */
  29
  30 #include <stdio.h>
  31 #include <gmp.h>
  32 #include <limits.h>
  33
  34 #include "secnet.h"
  35 #include "util.h"
  36
  37 struct dh {
  38     closure_t cl;
  39     struct dh_if ops;
  40     struct cloc loc;
  41     MP_INT p,g; /* prime modulus and generator */
  42 };
  43
  44 static string_t dh_makepublic(void *sst, uint8_t *secret, int32_t secretlen)
  45 {
  46     struct dh *st=sst;
  47     string_t r;
  48     MP_INT a, b; /* a is secret key, b is public key */
  49
  50     mpz_init(&a);
  51     mpz_init(&b);
  52
  53     read_mpbin(&a, secret, secretlen);
  54
  55     mpz_powm(&b, &st->g, &a, &st->p);
  56
  57     r=write_mpstring(&b);
  58
  59     mpz_clear(&a);
  60     mpz_clear(&b);
  61     return r;
  62 }
  63
  64 static dh_makeshared_fn dh_makeshared;
  65 static void dh_makeshared(void *sst, uint8_t *secret, int32_t secretlen,
  66                           cstring_t rempublic, uint8_t *sharedsecret,
  67                           int32_t buflen)
  68 {
  69     struct dh *st=sst;
  70     MP_INT a, b, c;
  71
  72     mpz_init(&a);
  73     mpz_init(&b);
  74     mpz_init(&c);
  75
  76     read_mpbin(&a, secret, secretlen);
  77     mpz_set_str(&b, rempublic, 16);
  78
  79     mpz_powm(&c, &b, &a, &st->p);
  80
  81     write_mpbin(&c,sharedsecret,buflen);
  82
  83     mpz_clear(&a);
  84     mpz_clear(&b);
  85     mpz_clear(&c);
  86 }
  87
  88 static list_t *dh_apply(closure_t *self, struct cloc loc, dict_t *context,
  89                         list_t *args)
  90 {
  91     struct dh *st;
  92     string_t p,g;
  93     item_t *i;
  94
  95     NEW(st);
  96     st->cl.description="dh";
  97     st->cl.type=CL_DH;
  98     st->cl.apply=NULL;
  99     st->cl.interface=&st->ops;
 100     st->ops.st=st;
 101     st->ops.makepublic=dh_makepublic;
 102     st->ops.makeshared=dh_makeshared;
 103     st->loc=loc;
 104     /* We have two string arguments: the first is the modulus, and the
 105        second is the generator. Both are in hex. */
 106     i=list_elem(args,0);
 107     if (i) {
 108         if (i->type!=t_string) {
 109             cfgfatal(i->loc,"diffie-hellman","first argument must be a "
 110                      "string\n");
 111         }
 112         p=i->data.string;
 113         if (mpz_init_set_str(&st->p,p,16)!=0) {
 114             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
 115                      "string\n",p);
 116         }
 117     } else {
 118         cfgfatal(loc,"diffie-hellman","you must provide a prime modulus\n");
 119     }
 120
 121     i=list_elem(args,1);
 122     if (i) {
 123         if (i->type!=t_string) {
 124             cfgfatal(i->loc,"diffie-hellman","second argument must be a "
 125                      "string\n");
 126         }
 127         g=i->data.string;
 128         if (mpz_init_set_str(&st->g,g,16)!=0) {
 129             cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
 130                      "string\n",g);
 131         }
 132     } else {
 133         cfgfatal(loc,"diffie-hellman","you must provide a generator\n");
 134     }
 135
 136     i=list_elem(args,2);
 137     if (i && i->type==t_bool && i->data.bool==False) {
 138         Message(M_INFO,"diffie-hellman (%s:%d): skipping modulus "
 139                 "primality check\n",loc.file,loc.line);
 140     } else {
 141         /* Test that the modulus is really prime */
 142         if (mpz_probab_prime_p(&st->p,5)==0) {
 143             cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
 144         }
 145     }
 146
 147     size_t sz=mpz_sizeinbase(&st->p,2)/8;
 148     if (sz>INT_MAX) {
 149         cfgfatal(loc,"diffie-hellman","modulus far too large\n");
 150     }
 151     if (mpz_cmp(&st->g,&st->p) >= 0) {
 152         cfgfatal(loc,"diffie-hellman","generator must be less than modulus\n");
 153     }
 154
 155     st->ops.len=sz;
 156
 157     st->ops.ceil_len=(mpz_sizeinbase(&st->p,2)+7)/8;
 158     /* According to the docs, mpz_sizeinbase(,256) is allowed to return
 159      * an answer which is 1 too large.  But mpz_sizeinbase(,2) isn't. */
 160
 161     return new_closure(&st->cl);
 162 }
 163
 164 void dh_module(dict_t *dict)
 165 {
 166     add_closure(dict,"diffie-hellman",dh_apply);
 167 }