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Nettle
nettle
Commits
baea8c8e
Commit
baea8c8e
authored
Oct 30, 2001
by
Niels Möller
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New file with general rsa functions.
Rev: src/nettle/rsa.c:1.1
parent
365388ba
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baea8c8e
/* rsa.c
*
* The RSA publickey algorithm.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2001 Niels Mller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
#if HAVE_CONFIG_H
#include "config.h"
#endif
#if HAVE_LIBGMP
#include "rsa.h"
#include "bignum.h"
/* FIXME: Perhaps we should split this into several functions, so that
* one can link in the signature functions without also getting the
* verify functions. */
int
rsa_init_public_key
(
struct
rsa_public_key
*
key
)
{
unsigned
size
=
(
mpz_sizeinbase
(
key
->
n
,
2
)
+
7
)
/
8
;
/* For PKCS#1 to make sense, the size of the modulo, in octets, must
* be at least 11 + the length of the DER-encoded Digest Info.
*
* And a DigestInfo is 34 octets for md5, and 35 octets for sha1.
* 46 octets is 368 bits. */
if
(
size
<
46
)
{
/* Make sure the signing and verification functions doesn't
* try to use this key. */
key
->
size
=
0
;
return
0
;
}
else
{
key
->
size
=
size
;
return
1
;
}
}
int
rsa_init_private_key
(
struct
rsa_private_key
*
key
)
{
return
rsa_init_public_key
(
&
key
->
pub
);
}
#ifndef RSA_CRT
#define RSA_CRT 1
#endif
/* Internal function for computing an rsa root.
*
* NOTE: We don't really need n not e, so we could delete the public
* key info from struct rsa_private_key. We do need the size,
* though. */
void
rsa_compute_root
(
struct
rsa_private_key
*
key
,
mpz_t
x
,
mpz_t
m
)
{
#if RSA_CRT
{
mpz_t
xp
;
/* modulo p */
mpz_t
xq
;
/* modulo q */
mpz_init
(
xp
);
mpz_init
(
xq
);
/* Compute xq = m^d % q = (m%q)^b % q */
mpz_fdiv_r
(
xq
,
m
,
key
->
q
);
mpz_powm
(
xq
,
xq
,
key
->
b
,
key
->
q
);
/* Compute xp = m^d % p = (m%p)^a % p */
mpz_fdiv_r
(
xp
,
m
,
key
->
p
);
mpz_powm
(
xp
,
xp
,
key
->
a
,
key
->
p
);
/* Set xp' = (xp - xq) c % p. */
mpz_sub
(
xp
,
xp
,
xq
);
mpz_mul
(
xp
,
xp
,
key
->
c
);
mpz_fdiv_r
(
xp
,
xp
,
key
->
p
);
/* Finally, compute x = xq + q xp'
*
* To prove that this works, note that
*
* xp = x + i p,
* xq = x + j q,
* c q = 1 + k p
*
* for some integers i, j and k. Now, for some integer l,
*
* xp' = (xp - xq) c + l p
* = (x + i p - (x + j q)) c + l p
* = (i p - j q) c + l p
* = (i c + l) p - j (c q)
* = (i c + l) p - j (1 + kp)
* = (i c + l - j k) p - j
*
* which shows that xp' = -j (mod p). We get
*
* xq + q xp' = x + j q + (i c + l - j k) p q - j q
* = x + (i c + l - j k) p q
*
* so that
*
* xq + q xp' = x (mod pq)
*
* We also get 0 <= xq + q xp' < p q, because
*
* 0 <= xq < q and 0 <= xp' < p.
*/
mpz_mul
(
x
,
key
->
q
,
xp
);
mpz_add
(
x
,
x
,
xq
);
mpz_clear
(
xp
);
mpz_clear
(
xq
);
}
#else
/* !RSA_CRT */
mpz_powm
(
x
,
m
,
key
->
d
,
key
->
pub
->
n
);
#endif
/* !RSA_CRT */
}
#endif
/* HAVE_LIBGMP */
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