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comparison libtomcrypt/src/pk/dh/dh_shared_secret.c @ 1471:6dba84798cd5

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Update to libtomcrypt 1.18.1, merged with Dropbear changes
author Matt Johnston <matt@ucc.asn.au>
date Fri, 09 Feb 2018 21:44:05 +0800
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1470:8bba51a55704 1471:6dba84798cd5
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 */
9
10 #include "tomcrypt.h"
11
12 #ifdef LTC_MDH
13
14 /**
15 Create a DH shared secret.
16 @param private_key The private DH key in the pair
17 @param public_key The public DH key in the pair
18 @param out [out] The destination of the shared data
19 @param outlen [in/out] The max size and resulting size of the shared data.
20 @return CRYPT_OK if successful
21 */
22 int dh_shared_secret(dh_key *private_key, dh_key *public_key,
23 unsigned char *out, unsigned long *outlen)
24 {
25 void *tmp;
26 unsigned long x;
27 int err;
28
29 LTC_ARGCHK(private_key != NULL);
30 LTC_ARGCHK(public_key != NULL);
31 LTC_ARGCHK(out != NULL);
32 LTC_ARGCHK(outlen != NULL);
33
34 /* types valid? */
35 if (private_key->type != PK_PRIVATE) {
36 return CRYPT_PK_NOT_PRIVATE;
37 }
38
39 /* same DH group? */
40 if (mp_cmp(private_key->prime, public_key->prime) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
41 if (mp_cmp(private_key->base, public_key->base) != LTC_MP_EQ) { return CRYPT_PK_TYPE_MISMATCH; }
42
43 /* init big numbers */
44 if ((err = mp_init(&tmp)) != CRYPT_OK) {
45 return err;
46 }
47
48 /* check public key */
49 if ((err = dh_check_pubkey(public_key)) != CRYPT_OK) {
50 goto error;
51 }
52
53 /* compute tmp = y^x mod p */
54 if ((err = mp_exptmod(public_key->y, private_key->x, private_key->prime, tmp)) != CRYPT_OK) {
55 goto error;
56 }
57
58 /* enough space for output? */
59 x = (unsigned long)mp_unsigned_bin_size(tmp);
60 if (*outlen < x) {
61 *outlen = x;
62 err = CRYPT_BUFFER_OVERFLOW;
63 goto error;
64 }
65 if ((err = mp_to_unsigned_bin(tmp, out)) != CRYPT_OK) {
66 goto error;
67 }
68 *outlen = x;
69 err = CRYPT_OK;
70
71 error:
72 mp_clear(tmp);
73 return err;
74 }
75
76 #endif /* LTC_MDH */
77
78 /* ref: $Format:%D$ */
79 /* git commit: $Format:%H$ */
80 /* commit time: $Format:%ai$ */