dh.c, secnet.8: Allow `diffie-hellman' to take a dictionary of arguments.
[secnet] / dh.c
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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
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30#include <stdio.h>
31#include <gmp.h>
59230b9b 32#include <limits.h>
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33
34#include "secnet.h"
35#include "util.h"
36
37struct 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
1caa23ff 44static string_t dh_makepublic(void *sst, uint8_t *secret, int32_t secretlen)
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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
b6aae8b2 55 mpz_powm_sec(&b, &st->g, &a, &st->p);
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56
57 r=write_mpstring(&b);
58
59 mpz_clear(&a);
60 mpz_clear(&b);
61 return r;
62}
63
fe5e9cc4 64static dh_makeshared_fn dh_makeshared;
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65static bool_t dh_makeshared(void *sst, uint8_t *secret, int32_t secretlen,
66 cstring_t rempublic, uint8_t *sharedsecret,
67 int32_t buflen)
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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
b6aae8b2 79 mpz_powm_sec(&c, &b, &a, &st->p);
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80
81 write_mpbin(&c,sharedsecret,buflen);
82
83 mpz_clear(&a);
84 mpz_clear(&b);
85 mpz_clear(&c);
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86
87 return True;
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88}
89
90static 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;
8fb3bdd7 95 dict_t *dict = 0;
2fe58dfd 96 item_t *i;
8fb3bdd7 97 bool_t check = True;
2fe58dfd 98
b7886fd4 99 NEW(st);
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100 st->cl.description="dh";
101 st->cl.type=CL_DH;
102 st->cl.apply=NULL;
103 st->cl.interface=&st->ops;
104 st->ops.st=st;
105 st->ops.makepublic=dh_makepublic;
106 st->ops.makeshared=dh_makeshared;
107 st->loc=loc;
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108
109 /* We either have two string arguments and maybe a boolean, or a
110 * dictionary
111 */
2fe58dfd 112 i=list_elem(args,0);
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113 if (i && i->type==t_dict) {
114 dict=i->data.dict;
115 p=dict_read_string(dict,"p",True,"diffie-hellman",loc);
116 g=dict_read_string(dict,"g",True,"diffie-hellman",loc);
117 check=dict_read_bool(dict,"check",False,"diffie-hellman",loc,True);
2fe58dfd 118 } else {
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119 if (!i)
120 cfgfatal(loc,"diffie-hellman","you must provide a prime modulus\n");
121 else if (i->type!=t_string)
122 cfgfatal(i->loc,"diffie-hellman",
123 "first argument must be a string or a dictionary\n");
124 p=i->data.string;
125 i=list_elem(args,1);
126 if (!i)
127 cfgfatal(loc,"diffie-hellman","you must provide a generator\n");
128 else if (i->type!=t_string)
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129 cfgfatal(i->loc,"diffie-hellman","second argument must be a "
130 "string\n");
2fe58dfd 131 g=i->data.string;
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132 i=list_elem(args,2);
133 if (i) {
134 if (i->type!=t_bool)
135 cfgfatal(i->loc,"diffie-hellman",
136 "third argument must be boolean or omitted\n");
137 check=i->data.bool;
2fe58dfd 138 }
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139 }
140
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141 if (mpz_init_set_str(&st->p,p,16)!=0)
142 cfgfatal(loc,"diffie-hellman","\"%s\" is not a hex number "
143 "string\n",p);
144 if (mpz_init_set_str(&st->g,g,16)!=0)
145 cfgfatal(i->loc,"diffie-hellman","\"%s\" is not a hex number "
146 "string\n",g);
147
148 if (!check) {
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149 Message(M_INFO,"diffie-hellman (%s:%d): skipping modulus "
150 "primality check\n",loc.file,loc.line);
151 } else {
152 /* Test that the modulus is really prime */
153 if (mpz_probab_prime_p(&st->p,5)==0) {
154 cfgfatal(loc,"diffie-hellman","modulus must be a prime\n");
155 }
2fe58dfd 156 }
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157
158 size_t sz=mpz_sizeinbase(&st->p,2)/8;
159 if (sz>INT_MAX) {
160 cfgfatal(loc,"diffie-hellman","modulus far too large\n");
161 }
162 if (mpz_cmp(&st->g,&st->p) >= 0) {
163 cfgfatal(loc,"diffie-hellman","generator must be less than modulus\n");
164 }
165
5f679c36 166 st->ops.secret_len=sz;
2fe58dfd 167
5f679c36 168 st->ops.shared_len=(mpz_sizeinbase(&st->p,2)+7)/8;
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169 /* According to the docs, mpz_sizeinbase(,256) is allowed to return
170 * an answer which is 1 too large. But mpz_sizeinbase(,2) isn't. */
171
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172 return new_closure(&st->cl);
173}
174
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175void dh_module(dict_t *dict)
176{
177 add_closure(dict,"diffie-hellman",dh_apply);
178}