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79 lines
1.9 KiB
C
79 lines
1.9 KiB
C
/* rsa-blind.c
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RSA blinding. Used for resistance to timing-attacks.
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Copyright (C) 2001, 2012 Niels Möller, Nikos Mavrogiannopoulos
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This file is part of GNU Nettle.
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GNU Nettle is free software: you can redistribute it and/or
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modify it under the terms of either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free
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Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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or both in parallel, as here.
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GNU Nettle is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received copies of the GNU General Public License and
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the GNU Lesser General Public License along with this program. If
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not, see http://www.gnu.org/licenses/.
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*/
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#if HAVE_CONFIG_H
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# include "config.h"
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#endif
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#include "rsa.h"
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#include "rsa-internal.h"
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#include "bignum.h"
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/* Blinds the c, by computing c *= r^e (mod n), for a random r. Also
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returns the inverse (ri), for use by rsa_unblind. */
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void
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_rsa_blind (const struct rsa_public_key *pub,
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void *random_ctx, nettle_random_func *random,
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mpz_t c, mpz_t ri)
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{
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mpz_t r;
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mpz_init(r);
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/* c = c*(r^e)
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* ri = r^(-1)
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*/
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do
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{
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nettle_mpz_random(r, random_ctx, random, pub->n);
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/* invert r */
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}
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while (!mpz_invert (ri, r, pub->n));
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/* c = c*(r^e) mod n */
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mpz_powm_sec(r, r, pub->e, pub->n);
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mpz_mul(c, c, r);
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mpz_fdiv_r(c, c, pub->n);
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mpz_clear(r);
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}
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/* c *= ri mod n */
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void
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_rsa_unblind (const struct rsa_public_key *pub, mpz_t c, const mpz_t ri)
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{
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mpz_mul(c, c, ri);
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mpz_fdiv_r(c, c, pub->n);
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}
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