diff options
Diffstat (limited to 'libtomcrypt/src/pk/ecc/ltc_ecc_map.c')
| -rw-r--r-- | libtomcrypt/src/pk/ecc/ltc_ecc_map.c | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/libtomcrypt/src/pk/ecc/ltc_ecc_map.c b/libtomcrypt/src/pk/ecc/ltc_ecc_map.c new file mode 100644 index 0000000..eec28b3 --- /dev/null +++ b/libtomcrypt/src/pk/ecc/ltc_ecc_map.c @@ -0,0 +1,76 @@ +/* LibTomCrypt, modular cryptographic library -- Tom St Denis + * + * LibTomCrypt is a library that provides various cryptographic + * algorithms in a highly modular and flexible manner. + * + * The library is free for all purposes without any express + * guarantee it works. + * + * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com + */ + +/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b + * + * All curves taken from NIST recommendation paper of July 1999 + * Available at http://csrc.nist.gov/cryptval/dss.htm + */ +#include "tomcrypt.h" + +/** + @file ltc_ecc_map.c + ECC Crypto, Tom St Denis +*/ + +#ifdef MECC + +/** + Map a projective jacbobian point back to affine space + @param P [in/out] The point to map + @param modulus The modulus of the field the ECC curve is in + @param mp The "b" value from montgomery_setup() + @return CRYPT_OK on success +*/ +int ltc_ecc_map(ecc_point *P, void *modulus, void *mp) +{ + void *t1, *t2; + int err; + + LTC_ARGCHK(P != NULL); + LTC_ARGCHK(modulus != NULL); + LTC_ARGCHK(mp != NULL); + + if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) { + return CRYPT_MEM; + } + + /* first map z back to normal */ + if ((err = mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK) { goto done; } + + /* get 1/z */ + if ((err = mp_invmod(P->z, modulus, t1)) != CRYPT_OK) { goto done; } + + /* get 1/z^2 and 1/z^3 */ + if ((err = mp_sqr(t1, t2)) != CRYPT_OK) { goto done; } + if ((err = mp_mod(t2, modulus, t2)) != CRYPT_OK) { goto done; } + if ((err = mp_mul(t1, t2, t1)) != CRYPT_OK) { goto done; } + if ((err = mp_mod(t1, modulus, t1)) != CRYPT_OK) { goto done; } + + /* multiply against x/y */ + if ((err = mp_mul(P->x, t2, P->x)) != CRYPT_OK) { goto done; } + if ((err = mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK) { goto done; } + if ((err = mp_mul(P->y, t1, P->y)) != CRYPT_OK) { goto done; } + if ((err = mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK) { goto done; } + if ((err = mp_set(P->z, 1)) != CRYPT_OK) { goto done; } + + err = CRYPT_OK; +done: + mp_clear_multi(t1, t2, NULL); + return err; +} + +#endif + +/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_map.c,v $ */ +/* $Revision: 1.5 $ */ +/* $Date: 2006/12/04 02:50:11 $ */ + |