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 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11
12/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
13 *
14 * All curves taken from NIST recommendation paper of July 1999
15 * Available at http://csrc.nist.gov/cryptval/dss.htm
16 */
17#include "tomcrypt.h"
18
19/**
20  @file ecc_shared_secret.c
21  ECC Crypto, Tom St Denis
22*/
23
24#ifdef MECC
25
26/**
27  Create an ECC shared secret between two keys
28  @param private_key      The private ECC key
29  @param public_key       The public key
30  @param out              [out] Destination of the shared secret (Conforms to EC-DH from ANSI X9.63)
31  @param outlen           [in/out] The max size and resulting size of the shared secret
32  @return CRYPT_OK if successful
33*/
34int ecc_shared_secret(ecc_key *private_key, ecc_key *public_key,
35                      unsigned char *out, unsigned long *outlen)
36{
37   unsigned long  x;
38   ecc_point     *result;
39   void          *prime;
40   int            err;
41
42   LTC_ARGCHK(private_key != NULL);
43   LTC_ARGCHK(public_key  != NULL);
44   LTC_ARGCHK(out         != NULL);
45   LTC_ARGCHK(outlen      != NULL);
46
47   /* type valid? */
48   if (private_key->type != PK_PRIVATE) {
49      return CRYPT_PK_NOT_PRIVATE;
50   }
51
52   if (ltc_ecc_is_valid_idx(private_key->idx) == 0 || ltc_ecc_is_valid_idx(public_key->idx) == 0) {
53      return CRYPT_INVALID_ARG;
54   }
55
56   if (XSTRCMP(private_key->dp->name, public_key->dp->name) != 0) {
57      return CRYPT_PK_TYPE_MISMATCH;
58   }
59
60   /* make new point */
61   result = ltc_ecc_new_point();
62   if (result == NULL) {
63      return CRYPT_MEM;
64   }
65
66   if ((err = mp_init(&prime)) != CRYPT_OK) {
67      ltc_ecc_del_point(result);
68      return err;
69   }
70
71   if ((err = mp_read_radix(prime, (char *)private_key->dp->prime, 16)) != CRYPT_OK)                               { goto done; }
72   if ((err = ltc_mp.ecc_ptmul(private_key->k, &public_key->pubkey, result, prime, 1)) != CRYPT_OK)                { goto done; }
73
74   x = (unsigned long)mp_unsigned_bin_size(prime);
75   if (*outlen < x) {
76      *outlen = x;
77      err = CRYPT_BUFFER_OVERFLOW;
78      goto done;
79   }
80   zeromem(out, x);
81   if ((err = mp_to_unsigned_bin(result->x, out + (x - mp_unsigned_bin_size(result->x))))   != CRYPT_OK)           { goto done; }
82
83   err     = CRYPT_OK;
84   *outlen = x;
85done:
86   mp_clear(prime);
87   ltc_ecc_del_point(result);
88   return err;
89}
90
91#endif
92/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_shared_secret.c,v $ */
93/* $Revision: 1.8 $ */
94/* $Date: 2006/12/04 02:19:48 $ */
95
96