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 ltc_ecc_map.c
21  ECC Crypto, Tom St Denis
22*/
23
24#ifdef MECC
25
26/**
27  Map a projective jacbobian point back to affine space
28  @param P        [in/out] The point to map
29  @param modulus  The modulus of the field the ECC curve is in
30  @param mp       The "b" value from montgomery_setup()
31  @return CRYPT_OK on success
32*/
33int ltc_ecc_map(ecc_point *P, void *modulus, void *mp)
34{
35   void *t1, *t2;
36   int   err;
37
38   LTC_ARGCHK(P       != NULL);
39   LTC_ARGCHK(modulus != NULL);
40   LTC_ARGCHK(mp      != NULL);
41
42   if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) {
43      return CRYPT_MEM;
44   }
45
46   /* first map z back to normal */
47   if ((err = mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK)           { goto done; }
48
49   /* get 1/z */
50   if ((err = mp_invmod(P->z, modulus, t1)) != CRYPT_OK)                      { goto done; }
51
52   /* get 1/z^2 and 1/z^3 */
53   if ((err = mp_sqr(t1, t2)) != CRYPT_OK)                                    { goto done; }
54   if ((err = mp_mod(t2, modulus, t2)) != CRYPT_OK)                           { goto done; }
55   if ((err = mp_mul(t1, t2, t1)) != CRYPT_OK)                                { goto done; }
56   if ((err = mp_mod(t1, modulus, t1)) != CRYPT_OK)                           { goto done; }
57
58   /* multiply against x/y */
59   if ((err = mp_mul(P->x, t2, P->x)) != CRYPT_OK)                            { goto done; }
60   if ((err = mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK)           { goto done; }
61   if ((err = mp_mul(P->y, t1, P->y)) != CRYPT_OK)                            { goto done; }
62   if ((err = mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK)           { goto done; }
63   if ((err = mp_set(P->z, 1)) != CRYPT_OK)                                   { goto done; }
64
65   err = CRYPT_OK;
66done:
67   mp_clear_multi(t1, t2, NULL);
68   return err;
69}
70
71#endif
72
73/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_map.c,v $ */
74/* $Revision: 1.5 $ */
75/* $Date: 2006/12/04 02:50:11 $ */
76
77