88 lines
2.7 KiB
C
88 lines
2.7 KiB
C
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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/* RSA Code by Tom St Denis */
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#include "mycrypt.h"
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#ifdef MRSA
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int rsa_exptmod(const unsigned char *in, unsigned long inlen,
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unsigned char *out, unsigned long *outlen, int which,
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rsa_key *key)
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{
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mp_int tmp, tmpa, tmpb;
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unsigned long x;
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int err;
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_ARGCHK(in != NULL);
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_ARGCHK(out != NULL);
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_ARGCHK(outlen != NULL);
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_ARGCHK(key != NULL);
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if (which == PK_PRIVATE && (key->type != PK_PRIVATE && key->type != PK_PRIVATE_OPTIMIZED)) {
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return CRYPT_PK_NOT_PRIVATE;
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}
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/* must be a private or public operation */
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if (which != PK_PRIVATE && which != PK_PUBLIC) {
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return CRYPT_PK_INVALID_TYPE;
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}
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/* init and copy into tmp */
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if ((err = mp_init_multi(&tmp, &tmpa, &tmpb, NULL)) != MP_OKAY) { goto error; }
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if ((err = mp_read_unsigned_bin(&tmp, (unsigned char *)in, (int)inlen)) != MP_OKAY) { goto error; }
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/* sanity check on the input */
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if (mp_cmp(&key->N, &tmp) == MP_LT) {
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err = CRYPT_PK_INVALID_SIZE;
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goto done;
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}
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/* are we using the private exponent and is the key optimized? */
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if (which == PK_PRIVATE && key->type == PK_PRIVATE_OPTIMIZED) {
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/* tmpa = tmp^dP mod p */
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if ((err = mp_exptmod(&tmp, &key->dP, &key->p, &tmpa)) != MP_OKAY) { goto error; }
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/* tmpb = tmp^dQ mod q */
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if ((err = mp_exptmod(&tmp, &key->dQ, &key->q, &tmpb)) != MP_OKAY) { goto error; }
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/* tmp = tmpa*qP + tmpb*pQ mod N */
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if ((err = mp_mul(&tmpa, &key->qP, &tmpa)) != MP_OKAY) { goto error; }
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if ((err = mp_mul(&tmpb, &key->pQ, &tmpb)) != MP_OKAY) { goto error; }
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if ((err = mp_addmod(&tmpa, &tmpb, &key->N, &tmp)) != MP_OKAY) { goto error; }
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} else {
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/* exptmod it */
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if ((err = mp_exptmod(&tmp, which==PK_PRIVATE?&key->d:&key->e, &key->N, &tmp)) != MP_OKAY) { goto error; }
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}
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/* read it back */
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x = (unsigned long)mp_unsigned_bin_size(&tmp);
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if (x > *outlen) {
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err = CRYPT_BUFFER_OVERFLOW;
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goto done;
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}
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*outlen = x;
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/* convert it */
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if ((err = mp_to_unsigned_bin(&tmp, out)) != MP_OKAY) { goto error; }
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/* clean up and return */
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err = CRYPT_OK;
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goto done;
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error:
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err = mpi_to_ltc_error(err);
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done:
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mp_clear_multi(&tmp, &tmpa, &tmpb, NULL);
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return err;
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}
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#endif
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