| /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
| * |
| * LibTomCrypt is a library that provides various cryptographic |
| * algorithms in a highly modular and flexible manner. |
| * |
| * The library is free for all purposes without any express |
| * guarantee it works. |
| * |
| * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.org |
| */ |
| #include "tomcrypt.h" |
| |
| /** |
| @file rsa_exptmod.c |
| RSA PKCS exptmod, Tom St Denis |
| */ |
| |
| #ifdef MRSA |
| |
| /** |
| Compute an RSA modular exponentiation |
| @param in The input data to send into RSA |
| @param inlen The length of the input (octets) |
| @param out [out] The destination |
| @param outlen [in/out] The max size and resulting size of the output |
| @param which Which exponent to use, e.g. PK_PRIVATE or PK_PUBLIC |
| @param key The RSA key to use |
| @return CRYPT_OK if successful |
| */ |
| int rsa_exptmod(const unsigned char *in, unsigned long inlen, |
| unsigned char *out, unsigned long *outlen, int which, |
| rsa_key *key) |
| { |
| mp_int tmp, tmpa, tmpb; |
| unsigned long x; |
| int err; |
| |
| LTC_ARGCHK(in != NULL); |
| LTC_ARGCHK(out != NULL); |
| LTC_ARGCHK(outlen != NULL); |
| LTC_ARGCHK(key != NULL); |
| |
| /* is the key of the right type for the operation? */ |
| if (which == PK_PRIVATE && (key->type != PK_PRIVATE)) { |
| return CRYPT_PK_NOT_PRIVATE; |
| } |
| |
| /* must be a private or public operation */ |
| if (which != PK_PRIVATE && which != PK_PUBLIC) { |
| return CRYPT_PK_INVALID_TYPE; |
| } |
| |
| /* init and copy into tmp */ |
| if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { return mpi_to_ltc_error(err); } |
| if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; } |
| |
| /* sanity check on the input */ |
| if (mp_cmp(&key->N, &tmp) == MP_LT) { |
| err = CRYPT_PK_INVALID_SIZE; |
| goto done; |
| } |
| |
| /* are we using the private exponent and is the key optimized? */ |
| if (which == PK_PRIVATE) { |
| /* tmpa = tmp^dP mod p */ |
| if ((err = mp_exptmod(&tmp, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; } |
| |
| /* tmpb = tmp^dQ mod q */ |
| if ((err = mp_exptmod(&tmp, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; } |
| |
| /* tmp = (tmpa - tmpb) * qInv (mod p) */ |
| if ((err = mp_sub(&tmpa, &tmpb, &tmp)) != MP_OKAY) { goto error; } |
| if ((err = mp_mulmod(&tmp, &key->qP, &key->p, &tmp)) != MP_OKAY) { goto error; } |
| |
| /* tmp = tmpb + q * tmp */ |
| if ((err = mp_mul(&tmp, &key->q, &tmp)) != MP_OKAY) { goto error; } |
| if ((err = mp_add(&tmp, &tmpb, &tmp)) != MP_OKAY) { goto error; } |
| } else { |
| /* exptmod it */ |
| if ((err = mp_exptmod(&tmp, &key->e, &key->N, &tmp)) != MP_OKAY) { goto error; } |
| } |
| |
| /* read it back */ |
| x = (unsigned long)mp_unsigned_bin_size(&key->N); |
| if (x > *outlen) { |
| err = CRYPT_BUFFER_OVERFLOW; |
| goto done; |
| } |
| |
| /* this should never happen ... */ |
| if (mp_unsigned_bin_size(&tmp) > mp_unsigned_bin_size(&key->N)) { |
| err = CRYPT_ERROR; |
| goto done; |
| } |
| *outlen = x; |
| |
| /* convert it */ |
| zeromem(out, x); |
| if ((err = mp_to_unsigned_bin(&tmp, out+(x-mp_unsigned_bin_size(&tmp)))) != MP_OKAY) { goto error; } |
| |
| /* clean up and return */ |
| err = CRYPT_OK; |
| goto done; |
| error: |
| err = mpi_to_ltc_error(err); |
| done: |
| mp_clear_multi(&tmp, &tmpa, &tmpb, NULL); |
| return err; |
| } |
| |
| #endif |
| |
| /* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_exptmod.c,v $ */ |
| /* $Revision: 1.4 $ */ |
| /* $Date: 2005/06/23 02:10:22 $ */ |