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_projective_dbl_point.c 21 ECC Crypto, Tom St Denis 22 */ 23 24 #if defined(MECC) && (!defined(MECC_ACCEL) || defined(LTM_DESC)) 25 26 /** 27 Double an ECC point 28 @param P The point to double 29 @param R [out] The destination of the double 30 @param modulus The modulus of the field the ECC curve is in 31 @param mp The "b" value from montgomery_setup() 32 @return CRYPT_OK on success 33 */ 34 int ltc_ecc_projective_dbl_point(ecc_point *P, ecc_point *R, void *modulus, void *mp) 35 { 36 void *t1, *t2; 37 int err; 38 39 LTC_ARGCHK(P != NULL); 40 LTC_ARGCHK(R != NULL); 41 LTC_ARGCHK(modulus != NULL); 42 LTC_ARGCHK(mp != NULL); 43 44 if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) { 45 return err; 46 } 47 48 if (P != R) { 49 if ((err = mp_copy(P->x, R->x)) != CRYPT_OK) { goto done; } 50 if ((err = mp_copy(P->y, R->y)) != CRYPT_OK) { goto done; } 51 if ((err = mp_copy(P->z, R->z)) != CRYPT_OK) { goto done; } 52 } 53 54 /* t1 = Z * Z */ 55 if ((err = mp_sqr(R->z, t1)) != CRYPT_OK) { goto done; } 56 if ((err = mp_montgomery_reduce(t1, modulus, mp)) != CRYPT_OK) { goto done; } 57 /* Z = Y * Z */ 58 if ((err = mp_mul(R->z, R->y, R->z)) != CRYPT_OK) { goto done; } 59 if ((err = mp_montgomery_reduce(R->z, modulus, mp)) != CRYPT_OK) { goto done; } 60 /* Z = 2Z */ 61 if ((err = mp_add(R->z, R->z, R->z)) != CRYPT_OK) { goto done; } 62 if (mp_cmp(R->z, modulus) != LTC_MP_LT) { 63 if ((err = mp_sub(R->z, modulus, R->z)) != CRYPT_OK) { goto done; } 64 } 65 66 /* T2 = X - T1 */ 67 if ((err = mp_sub(R->x, t1, t2)) != CRYPT_OK) { goto done; } 68 if (mp_cmp_d(t2, 0) == LTC_MP_LT) { 69 if ((err = mp_add(t2, modulus, t2)) != CRYPT_OK) { goto done; } 70 } 71 /* T1 = X + T1 */ 72 if ((err = mp_add(t1, R->x, t1)) != CRYPT_OK) { goto done; } 73 if (mp_cmp(t1, modulus) != LTC_MP_LT) { 74 if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK) { goto done; } 75 } 76 /* T2 = T1 * T2 */ 77 if ((err = mp_mul(t1, t2, t2)) != CRYPT_OK) { goto done; } 78 if ((err = mp_montgomery_reduce(t2, modulus, mp)) != CRYPT_OK) { goto done; } 79 /* T1 = 2T2 */ 80 if ((err = mp_add(t2, t2, t1)) != CRYPT_OK) { goto done; } 81 if (mp_cmp(t1, modulus) != LTC_MP_LT) { 82 if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK) { goto done; } 83 } 84 /* T1 = T1 + T2 */ 85 if ((err = mp_add(t1, t2, t1)) != CRYPT_OK) { goto done; } 86 if (mp_cmp(t1, modulus) != LTC_MP_LT) { 87 if ((err = mp_sub(t1, modulus, t1)) != CRYPT_OK) { goto done; } 88 } 89 90 /* Y = 2Y */ 91 if ((err = mp_add(R->y, R->y, R->y)) != CRYPT_OK) { goto done; } 92 if (mp_cmp(R->y, modulus) != LTC_MP_LT) { 93 if ((err = mp_sub(R->y, modulus, R->y)) != CRYPT_OK) { goto done; } 94 } 95 /* Y = Y * Y */ 96 if ((err = mp_sqr(R->y, R->y)) != CRYPT_OK) { goto done; } 97 if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK) { goto done; } 98 /* T2 = Y * Y */ 99 if ((err = mp_sqr(R->y, t2)) != CRYPT_OK) { goto done; } 100 if ((err = mp_montgomery_reduce(t2, modulus, mp)) != CRYPT_OK) { goto done; } 101 /* T2 = T2/2 */ 102 if (mp_isodd(t2)) { 103 if ((err = mp_add(t2, modulus, t2)) != CRYPT_OK) { goto done; } 104 } 105 if ((err = mp_div_2(t2, t2)) != CRYPT_OK) { goto done; } 106 /* Y = Y * X */ 107 if ((err = mp_mul(R->y, R->x, R->y)) != CRYPT_OK) { goto done; } 108 if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK) { goto done; } 109 110 /* X = T1 * T1 */ 111 if ((err = mp_sqr(t1, R->x)) != CRYPT_OK) { goto done; } 112 if ((err = mp_montgomery_reduce(R->x, modulus, mp)) != CRYPT_OK) { goto done; } 113 /* X = X - Y */ 114 if ((err = mp_sub(R->x, R->y, R->x)) != CRYPT_OK) { goto done; } 115 if (mp_cmp_d(R->x, 0) == LTC_MP_LT) { 116 if ((err = mp_add(R->x, modulus, R->x)) != CRYPT_OK) { goto done; } 117 } 118 /* X = X - Y */ 119 if ((err = mp_sub(R->x, R->y, R->x)) != CRYPT_OK) { goto done; } 120 if (mp_cmp_d(R->x, 0) == LTC_MP_LT) { 121 if ((err = mp_add(R->x, modulus, R->x)) != CRYPT_OK) { goto done; } 122 } 123 124 /* Y = Y - X */ 125 if ((err = mp_sub(R->y, R->x, R->y)) != CRYPT_OK) { goto done; } 126 if (mp_cmp_d(R->y, 0) == LTC_MP_LT) { 127 if ((err = mp_add(R->y, modulus, R->y)) != CRYPT_OK) { goto done; } 128 } 129 /* Y = Y * T1 */ 130 if ((err = mp_mul(R->y, t1, R->y)) != CRYPT_OK) { goto done; } 131 if ((err = mp_montgomery_reduce(R->y, modulus, mp)) != CRYPT_OK) { goto done; } 132 /* Y = Y - T2 */ 133 if ((err = mp_sub(R->y, t2, R->y)) != CRYPT_OK) { goto done; } 134 if (mp_cmp_d(R->y, 0) == LTC_MP_LT) { 135 if ((err = mp_add(R->y, modulus, R->y)) != CRYPT_OK) { goto done; } 136 } 137 138 err = CRYPT_OK; 139 done: 140 mp_clear_multi(t1, t2, NULL); 141 return err; 142 } 143 #endif 144 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_projective_dbl_point.c,v $ */ 145 /* $Revision: 1.8 $ */ 146 /* $Date: 2006/12/04 05:07:59 $ */ 147 148
