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 (at) 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 */ 33 int 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; 66 done: 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
