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comparison src/pk/rsa/rsa_exptmod.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +0000
parents 1c15b283127b
children 39d5d58461d6
comparison
equal deleted inserted replaced
164:cd1143579f00 192:9cc34777b479
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 #include "tomcrypt.h"
12
13 /**
14 @file rsa_exptmod.c
15 RSA PKCS exptmod, Tom St Denis
16 */
17
18 #ifdef MRSA
19
20 /**
21 Compute an RSA modular exponentiation
22 @param in The input data to send into RSA
23 @param inlen The length of the input (octets)
24 @param out [out] The destination
25 @param outlen [in/out] The max size and resulting size of the output
26 @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
27 @param key The RSA key to use
28 @return CRYPT_OK if successful
29 */
30 int rsa_exptmod(const unsigned char *in, unsigned long inlen,
31 unsigned char *out, unsigned long *outlen, int which,
32 rsa_key *key)
33 {
34 mp_int tmp, tmpa, tmpb;
35 unsigned long x;
36 int err;
37
38 LTC_ARGCHK(in != NULL);
39 LTC_ARGCHK(out != NULL);
40 LTC_ARGCHK(outlen != NULL);
41 LTC_ARGCHK(key != NULL);
42
43 /* is the key of the right type for the operation? */
44 if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
45 return CRYPT_PK_NOT_PRIVATE;
46 }
47
48 /* must be a private or public operation */
49 if (which != PK_PRIVATE && which != PK_PUBLIC) {
50 return CRYPT_PK_INVALID_TYPE;
51 }
52
53 /* init and copy into tmp */
54 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); }
55 if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; }
56
57 /* sanity check on the input */
58 if (mp_cmp(&key->N, &tmp) == MP_LT) {
59 err = CRYPT_PK_INVALID_SIZE;
60 goto done;
61 }
62
63 /* are we using the private exponent and is the key optimized? */
64 if (which == PK_PRIVATE) {
65 /* tmpa = tmp^dP mod p */
66 if ((err = mp_exptmod(&tmp, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; }
67
68 /* tmpb = tmp^dQ mod q */
69 if ((err = mp_exptmod(&tmp, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; }
70
71 /* tmp = (tmpa - tmpb) * qInv (mod p) */
72 if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; }
73 if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; }
74
75 /* tmp = tmpb + q * tmp */
76 if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; }
77 if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; }
78 } else {
79 /* exptmod it */
80 if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }
81 }
82
83 /* read it back */
84 x = (unsigned long)mp_unsigned_bin_size(&key->N);
85 if (x > *outlen) {
86 err = CRYPT_BUFFER_OVERFLOW;
87 goto done;
88 }
89 *outlen = x;
90
91 /* convert it */
92 zeromem(out, x);
93 if ((err = mp_to_unsigned_bin(&tmp, out+(x-mp_unsigned_bin_size(&tmp)))) != MP_OKAY) { goto error; }
94
95 /* clean up and return */
96 err = CRYPT_OK;
97 goto done;
98 error:
99 err = mpi_to_ltc_error(err);
100 done:
101 mp_clear_multi(&tmp, &tmpa, &tmpb, NULL);
102 return err;
103 }
104
105 #endif