annotate tim_exptmod.c @ 143:5d99163f7e32 libtomcrypt-orig

import of libtomcrypt 0.99
author Matt Johnston <matt@ucc.asn.au>
date Sun, 19 Dec 2004 11:34:45 +0000
parents 6362d3854bb4
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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 rlen = mp_unsigned_bin_size(n);
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38 rtmp = XMALLOC(rlen);
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39 if (rtmp == NULL) {
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40 return CRYPT_MEM;
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41 }
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42
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43 /* read in random value "r" */
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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