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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.org |
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10 */ |
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11 |
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12 /* RSA Code by Tom St Denis */ |
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13 #include "mycrypt.h" |
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14 |
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15 #ifdef RSA_TIMING |
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16 |
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17 /* decrypts c into m */ |
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18 int tim_exptmod(prng_state *prng, int prng_idx, |
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19 mp_int *c, mp_int *e, mp_int *d, mp_int *n, mp_int *m) |
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20 { |
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21 int err; |
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22 mp_int r, tmp, tmp2; |
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23 unsigned char *rtmp; |
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24 unsigned long rlen; |
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25 |
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26 _ARGCHK(c != NULL); |
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27 _ARGCHK(e != NULL); |
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28 _ARGCHK(d != NULL); |
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29 _ARGCHK(n != NULL); |
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30 _ARGCHK(m != NULL); |
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31 |
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32 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) { |
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33 return err; |
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34 } |
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35 |
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36 /* pick random r */ |
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37 rtmp = XMALLOC(MAX_RSA_SIZE/8); |
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38 if (rtmp == NULL) { |
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39 return CRYPT_MEM; |
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40 } |
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41 |
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42 |
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43 rlen = mp_unsigned_bin_size(n); |
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44 if (prng_descriptor[prng_idx].read(rtmp, rlen, prng) != rlen) { |
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45 XFREE(rtmp); |
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46 return CRYPT_ERROR_READPRNG; |
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47 } |
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48 |
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49 if ((err = mp_init_multi(&r, &tmp, &tmp2, NULL)) != MP_OKAY) { |
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50 XFREE(rtmp); |
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51 return mpi_to_ltc_error(err); |
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52 } |
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53 |
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54 /* read in r */ |
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55 if ((err = mp_read_unsigned_bin(&r, rtmp, rlen)) != MP_OKAY) { goto __ERR; } |
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56 |
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57 /* compute tmp = r^e */ |
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58 if ((err = mp_exptmod(&r, e, n, &tmp)) != MP_OKAY) { goto __ERR; } |
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59 |
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60 /* multiply C into the mix */ |
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61 if ((err = mp_mulmod(c, &tmp, n, &tmp)) != MP_OKAY) { goto __ERR; } |
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62 |
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63 /* raise to d */ |
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64 if ((err = mp_exptmod(&tmp, d, n, &tmp)) != MP_OKAY) { goto __ERR; } |
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65 |
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66 /* invert r and multiply */ |
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67 if ((err = mp_invmod(&r, n, &tmp2)) != MP_OKAY) { goto __ERR; } |
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68 |
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69 /* multiply and we are totally set */ |
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70 if ((err = mp_mulmod(&tmp, &tmp2, n, m)) != MP_OKAY) { goto __ERR; } |
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71 |
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72 __ERR: mp_clear_multi(&r, &tmp, &tmp2, NULL); |
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73 XFREE(rtmp); |
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74 return mpi_to_ltc_error(err); |
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75 } |
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76 |
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77 #endif |
