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comparison tim_exptmod.c @ 15:6362d3854bb4 libtomcrypt-orig

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0.96 release of LibTomCrypt
author Matt Johnston <matt@ucc.asn.au>
date Tue, 15 Jun 2004 14:07:21 +0000
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children 5d99163f7e32
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3:7faae8f46238 15:6362d3854bb4
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, [email protected], http://libtomcrypt.org
10 */
11
12 /* RSA Code by Tom St Denis */
13 #include "mycrypt.h"
14
15 #ifdef RSA_TIMING
16
17 /* decrypts c into m */
18 int tim_exptmod(prng_state *prng, int prng_idx,
19 mp_int *c, mp_int *e, mp_int *d, mp_int *n, mp_int *m)
20 {
21 int err;
22 mp_int r, tmp, tmp2;
23 unsigned char *rtmp;
24 unsigned long rlen;
25
26 _ARGCHK(c != NULL);
27 _ARGCHK(e != NULL);
28 _ARGCHK(d != NULL);
29 _ARGCHK(n != NULL);
30 _ARGCHK(m != NULL);
31
32 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
33 return err;
34 }
35
36 /* pick random r */
37 rtmp = XMALLOC(MAX_RSA_SIZE/8);
38 if (rtmp == NULL) {
39 return CRYPT_MEM;
40 }
41
42
43 rlen = mp_unsigned_bin_size(n);
44 if (prng_descriptor[prng_idx].read(rtmp, rlen, prng) != rlen) {
45 XFREE(rtmp);
46 return CRYPT_ERROR_READPRNG;
47 }
48
49 if ((err = mp_init_multi(&r, &tmp, &tmp2, NULL)) != MP_OKAY) {
50 XFREE(rtmp);
51 return mpi_to_ltc_error(err);
52 }
53
54 /* read in r */
55 if ((err = mp_read_unsigned_bin(&r, rtmp, rlen)) != MP_OKAY) { goto __ERR; }
56
57 /* compute tmp = r^e */
58 if ((err = mp_exptmod(&r, e, n, &tmp)) != MP_OKAY) { goto __ERR; }
59
60 /* multiply C into the mix */
61 if ((err = mp_mulmod(c, &tmp, n, &tmp)) != MP_OKAY) { goto __ERR; }
62
63 /* raise to d */
64 if ((err = mp_exptmod(&tmp, d, n, &tmp)) != MP_OKAY) { goto __ERR; }
65
66 /* invert r and multiply */
67 if ((err = mp_invmod(&r, n, &tmp2)) != MP_OKAY) { goto __ERR; }
68
69 /* multiply and we are totally set */
70 if ((err = mp_mulmod(&tmp, &tmp2, n, m)) != MP_OKAY) { goto __ERR; }
71
72 __ERR: mp_clear_multi(&r, &tmp, &tmp2, NULL);
73 XFREE(rtmp);
74 return mpi_to_ltc_error(err);
75 }
76
77 #endif