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
13 Katja PKCS-style exptmod, Tom St Denis
19 Compute an RSA modular exponentiation
20 @param in The input data to send into RSA
21 @param inlen The length of the input (octets)
22 @param out [out] The destination
23 @param outlen [in/out] The max size and resulting size of the output
24 @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC
25 @param key The RSA key to use
26 @return CRYPT_OK if successful
28 int katja_exptmod(const unsigned char *in, unsigned long inlen,
29 unsigned char *out, unsigned long *outlen, int which,
32 void *tmp, *tmpa, *tmpb;
36 LTC_ARGCHK(in != NULL);
37 LTC_ARGCHK(out != NULL);
38 LTC_ARGCHK(outlen != NULL);
39 LTC_ARGCHK(key != NULL);
41 /* is the key of the right type for the operation? */
42 if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) {
43 return CRYPT_PK_NOT_PRIVATE;
46 /* must be a private or public operation */
47 if (which != PK_PRIVATE && which != PK_PUBLIC) {
48 return CRYPT_PK_INVALID_TYPE;
51 /* init and copy into tmp */
52 if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != CRYPT_OK) { return err; }
53 if ((err = mp_read_unsigned_bin(tmp, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto error; }
55 /* sanity check on the input */
56 if (mp_cmp(key->N, tmp) == LTC_MP_LT) {
57 err = CRYPT_PK_INVALID_SIZE;
61 /* are we using the private exponent and is the key optimized? */
62 if (which == PK_PRIVATE) {
63 /* tmpa = tmp^dP mod p */
64 if ((err = mp_exptmod(tmp, key->dP, key->p, tmpa)) != CRYPT_OK) { goto error; }
66 /* tmpb = tmp^dQ mod q */
67 if ((err = mp_exptmod(tmp, key->dQ, key->q, tmpb)) != CRYPT_OK) { goto error; }
69 /* tmp = (tmpa - tmpb) * qInv (mod p) */
70 if ((err = mp_sub(tmpa, tmpb, tmp)) != CRYPT_OK) { goto error; }
71 if ((err = mp_mulmod(tmp, key->qP, key->p, tmp)) != CRYPT_OK) { goto error; }
73 /* tmp = tmpb + q * tmp */
74 if ((err = mp_mul(tmp, key->q, tmp)) != CRYPT_OK) { goto error; }
75 if ((err = mp_add(tmp, tmpb, tmp)) != CRYPT_OK) { goto error; }
78 if ((err = mp_exptmod(tmp, key->N, key->N, tmp)) != CRYPT_OK) { goto error; }
82 x = (unsigned long)mp_unsigned_bin_size(key->N);
85 err = CRYPT_BUFFER_OVERFLOW;
89 /* this should never happen ... */
90 if (mp_unsigned_bin_size(tmp) > mp_unsigned_bin_size(key->N)) {
98 if ((err = mp_to_unsigned_bin(tmp, out+(x-mp_unsigned_bin_size(tmp)))) != CRYPT_OK) { goto error; }
100 /* clean up and return */
105 mp_clear_multi(tmp, tmpa, tmpb, NULL);
111 /* ref: $Format:%D$ */
112 /* git commit: $Format:%H$ */
113 /* commit time: $Format:%ai$ */