| 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_sec(&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_sec(&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 | } |