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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
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2 * |
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3 * LibTomCrypt is a library that provides various cryptographic |
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4 * algorithms in a highly modular and flexible manner. |
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5 * |
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6 * The library is free for all purposes without any express |
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7 * guarantee it works. |
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8 * |
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9 * Tom St Denis, [email protected], http://libtomcrypt.com |
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10 */ |
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11 |
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12 /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b |
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13 * |
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14 * All curves taken from NIST recommendation paper of July 1999 |
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15 * Available at http://csrc.nist.gov/cryptval/dss.htm |
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16 */ |
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17 #include "tomcrypt.h" |
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18 |
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19 /** |
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20 @file ltc_ecc_map.c |
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21 ECC Crypto, Tom St Denis |
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22 */ |
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23 |
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24 #ifdef MECC |
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25 |
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26 /** |
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27 Map a projective jacbobian point back to affine space |
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28 @param P [in/out] The point to map |
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29 @param modulus The modulus of the field the ECC curve is in |
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30 @param mp The "b" value from montgomery_setup() |
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31 @return CRYPT_OK on success |
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32 */ |
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33 int ltc_ecc_map(ecc_point *P, void *modulus, void *mp) |
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34 { |
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35 void *t1, *t2; |
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36 int err; |
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37 |
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38 LTC_ARGCHK(P != NULL); |
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39 LTC_ARGCHK(modulus != NULL); |
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40 LTC_ARGCHK(mp != NULL); |
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41 |
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42 if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) { |
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43 return CRYPT_MEM; |
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44 } |
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45 |
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46 /* first map z back to normal */ |
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47 if ((err = mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK) { goto done; } |
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48 |
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49 /* get 1/z */ |
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50 if ((err = mp_invmod(P->z, modulus, t1)) != CRYPT_OK) { goto done; } |
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51 |
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52 /* get 1/z^2 and 1/z^3 */ |
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53 if ((err = mp_sqr(t1, t2)) != CRYPT_OK) { goto done; } |
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54 if ((err = mp_mod(t2, modulus, t2)) != CRYPT_OK) { goto done; } |
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55 if ((err = mp_mul(t1, t2, t1)) != CRYPT_OK) { goto done; } |
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56 if ((err = mp_mod(t1, modulus, t1)) != CRYPT_OK) { goto done; } |
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57 |
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58 /* multiply against x/y */ |
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59 if ((err = mp_mul(P->x, t2, P->x)) != CRYPT_OK) { goto done; } |
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60 if ((err = mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK) { goto done; } |
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61 if ((err = mp_mul(P->y, t1, P->y)) != CRYPT_OK) { goto done; } |
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62 if ((err = mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK) { goto done; } |
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63 if ((err = mp_set(P->z, 1)) != CRYPT_OK) { goto done; } |
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64 |
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65 err = CRYPT_OK; |
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66 done: |
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67 mp_clear_multi(t1, t2, NULL); |
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68 return err; |
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69 } |
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70 |
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71 #endif |
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72 |
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73 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_map.c,v $ */ |
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74 /* $Revision: 1.5 $ */ |
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75 /* $Date: 2006/12/04 02:50:11 $ */ |
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76 |
