1 /*
2  * Crypto wrapper for internal crypto implementation - modexp
3  * Copyright (c) 2006-2009, Jouni Malinen <j@w1.fi>
4  *
5  * This software may be distributed under the terms of the BSD license.
6  * See README for more details.
7  */
8 
9 #include "includes.h"
10 
11 #include "common.h"
12 #include "tls/bignum.h"
13 #include "crypto.h"
14 
15 
16 int crypto_dh_init(u8 generator, const u8 *prime, size_t prime_len, u8 *privkey,
17 		   u8 *pubkey)
18 {
19 	size_t pubkey_len, pad;
20 
21 	if (os_get_random(privkey, prime_len) < 0)
22 		return -1;
23 	if (os_memcmp(privkey, prime, prime_len) > 0) {
24 		/* Make sure private value is smaller than prime */
25 		privkey[0] = 0;
26 	}
27 
28 	pubkey_len = prime_len;
29 	if (crypto_mod_exp(&generator, 1, privkey, prime_len, prime, prime_len,
30 			   pubkey, &pubkey_len) < 0)
31 		return -1;
32 	if (pubkey_len < prime_len) {
33 		pad = prime_len - pubkey_len;
34 		os_memmove(pubkey + pad, pubkey, pubkey_len);
35 		os_memset(pubkey, 0, pad);
36 	}
37 
38 	return 0;
39 }
40 
41 
42 int crypto_dh_derive_secret(u8 generator, const u8 *prime, size_t prime_len,
43 			    const u8 *order, size_t order_len,
44 			    const u8 *privkey, size_t privkey_len,
45 			    const u8 *pubkey, size_t pubkey_len,
46 			    u8 *secret, size_t *len)
47 {
48 	struct bignum *pub;
49 	int res = -1;
50 
51 	if (pubkey_len > prime_len ||
52 	    (pubkey_len == prime_len &&
53 	     os_memcmp(pubkey, prime, prime_len) >= 0))
54 		return -1;
55 
56 	pub = bignum_init();
57 	if (!pub || bignum_set_unsigned_bin(pub, pubkey, pubkey_len) < 0 ||
58 	    bignum_cmp_d(pub, 1) <= 0)
59 		goto fail;
60 
61 	if (order) {
62 		struct bignum *p, *q, *tmp;
63 		int failed;
64 
65 		/* verify: pubkey^q == 1 mod p */
66 		p = bignum_init();
67 		q = bignum_init();
68 		tmp = bignum_init();
69 		failed = !p || !q || !tmp ||
70 			bignum_set_unsigned_bin(p, prime, prime_len) < 0 ||
71 			bignum_set_unsigned_bin(q, order, order_len) < 0 ||
72 			bignum_exptmod(pub, q, p, tmp) < 0 ||
73 			bignum_cmp_d(tmp, 1) != 0;
74 		bignum_deinit(p);
75 		bignum_deinit(q);
76 		bignum_deinit(tmp);
77 		if (failed)
78 			goto fail;
79 	}
80 
81 	res = crypto_mod_exp(pubkey, pubkey_len, privkey, privkey_len,
82 			     prime, prime_len, secret, len);
83 fail:
84 	bignum_deinit(pub);
85 	return res;
86 }
87 
88 
89 int crypto_mod_exp(const u8 *base, size_t base_len,
90 		   const u8 *power, size_t power_len,
91 		   const u8 *modulus, size_t modulus_len,
92 		   u8 *result, size_t *result_len)
93 {
94 	struct bignum *bn_base, *bn_exp, *bn_modulus, *bn_result;
95 	int ret = -1;
96 
97 	bn_base = bignum_init();
98 	bn_exp = bignum_init();
99 	bn_modulus = bignum_init();
100 	bn_result = bignum_init();
101 
102 	if (bn_base == NULL || bn_exp == NULL || bn_modulus == NULL ||
103 	    bn_result == NULL)
104 		goto error;
105 
106 	if (bignum_set_unsigned_bin(bn_base, base, base_len) < 0 ||
107 	    bignum_set_unsigned_bin(bn_exp, power, power_len) < 0 ||
108 	    bignum_set_unsigned_bin(bn_modulus, modulus, modulus_len) < 0)
109 		goto error;
110 
111 	if (bignum_exptmod(bn_base, bn_exp, bn_modulus, bn_result) < 0)
112 		goto error;
113 
114 	ret = bignum_get_unsigned_bin(bn_result, result, result_len);
115 
116 error:
117 	bignum_deinit(bn_base);
118 	bignum_deinit(bn_exp);
119 	bignum_deinit(bn_modulus);
120 	bignum_deinit(bn_result);
121 	return ret;
122 }
123