1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
6 * The library is free for all purposes without any express
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
15 RSA PKCS exptmod, Tom St Denis
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
30 int rsa_exptmod(const unsigned char *in, unsigned long inlen,
31 unsigned char *out, unsigned long *outlen, int which,
34 void *tmp, *tmpa, *tmpb;
38 LTC_ARGCHK(in != NULL);
39 LTC_ARGCHK(out != NULL);
40 LTC_ARGCHK(outlen != NULL);
41 LTC_ARGCHK(key != NULL);
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;
48 /* must be a private or public operation */
49 if (which != PK_PRIVATE && which != PK_PUBLIC) {
50 return CRYPT_PK_INVALID_TYPE;
53 /* init and copy into tmp */
54 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK) { return err; }
55 if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto error; }
57 /* sanity check on the input */
58 if (mp_cmp(key->N, tmp) == LTC_MP_LT) {
59 err = CRYPT_PK_INVALID_SIZE;
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)) != CRYPT_OK) { goto error; }
68 /* tmpb = tmp^dQ mod q */
69 if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK) { goto error; }
71 /* tmp = (tmpa - tmpb) * qInv (mod p) */
72 if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK) { goto error; }
73 if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK) { goto error; }
75 /* tmp = tmpb + q * tmp */
76 if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK) { goto error; }
77 if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK) { goto error; }
80 if ((err = mp_exptmod(tmp, key->e, key->N, tmp)) != CRYPT_OK) { goto error; }
84 x = (unsigned long)mp_unsigned_bin_size(key->N);
87 err = CRYPT_BUFFER_OVERFLOW;
91 /* this should never happen ... */
92 if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) {
100 if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK) { goto error; }
102 /* clean up and return */
105 mp_clear_multi(tmp, tmpa, tmpb, NULL);
111 /* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_exptmod.c,v $ */
112 /* $Revision: 1.16 $ */
113 /* $Date: 2006/12/04 03:09:28 $ */