mbedtls/library/ecdsa.c
2013-01-26 19:11:28 +01:00

191 lines
4.9 KiB
C

/*
* Elliptic curve DSA
*
* Copyright (C) 2006-2013, Brainspark B.V.
*
* This file is part of PolarSSL (http://www.polarssl.org)
* Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
*
* All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/*
* References:
*
* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
*/
#include "polarssl/config.h"
#if defined(POLARSSL_ECDSA_C)
#include "polarssl/ecdsa.h"
/*
* Derive a suitable integer for group grp from a buffer of length len
* SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
*/
static int derive_mpi( const ecp_group *grp, mpi *x,
const unsigned char *buf, size_t blen )
{
size_t n_size = (grp->nbits + 7) / 8;
return( mpi_read_binary( x, buf, blen > n_size ? n_size : blen ) );
}
/*
* Compute ECDSA signature of a hashed message (SEC1 4.1.3)
* Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
*/
int ecdsa_sign( const ecp_group *grp, mpi *r, mpi *s,
const mpi *d, const unsigned char *buf, size_t blen,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret, key_tries, sign_tries;
ecp_point R;
mpi k, e;
ecp_point_init( &R );
mpi_init( &k );
mpi_init( &e );
sign_tries = 0;
do
{
/*
* Steps 1-3: generate a suitable ephemeral keypair
*/
key_tries = 0;
do
{
MPI_CHK( ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
MPI_CHK( mpi_copy( r, &R.X ) );
if( key_tries++ > 10 )
return( POLARSSL_ERR_ECP_GENERIC );
}
while( mpi_cmp_int( r, 0 ) == 0 );
/*
* Step 5: derive MPI from hashed message
*/
MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
/*
* Step 6: compute s = (e + r * d) / k mod n
*/
MPI_CHK( mpi_mul_mpi( s, r, d ) );
MPI_CHK( mpi_add_mpi( &e, &e, s ) );
MPI_CHK( mpi_inv_mod( s, &k, &grp->N ) );
MPI_CHK( mpi_mul_mpi( s, s, &e ) );
MPI_CHK( mpi_mod_mpi( s, s, &grp->N ) );
if( sign_tries++ > 10 )
return( POLARSSL_ERR_ECP_GENERIC );
}
while( mpi_cmp_int( s, 0 ) == 0 );
cleanup:
ecp_point_free( &R );
mpi_free( &k );
mpi_free( &e );
return( ret );
}
/*
* Verify ECDSA signature of hashed message (SEC1 4.1.4)
* Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
*/
int ecdsa_verify( const ecp_group *grp,
const unsigned char *buf, size_t blen,
const ecp_point *Q, const mpi *r, const mpi *s)
{
int ret;
mpi e, s_inv, u1, u2;
ecp_point R, P;
ecp_point_init( &R ); ecp_point_init( &P );
mpi_init( &e ); mpi_init( &s_inv ); mpi_init( &u1 ); mpi_init( &u2 );
/*
* Step 1: make sure r and s are in range 1..n-1
*/
if( mpi_cmp_int( r, 1 ) < 0 || mpi_cmp_mpi( r, &grp->N ) >= 0 ||
mpi_cmp_int( s, 1 ) < 0 || mpi_cmp_mpi( s, &grp->N ) >= 0 )
{
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
}
/*
* Additional precaution: make sure Q is valid
*/
MPI_CHK( ecp_check_pubkey( grp, Q ) );
/*
* Step 3: derive MPI from hashed message
*/
MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
/*
* Step 4: u1 = e / s mod n, u2 = r / s mod n
*/
MPI_CHK( mpi_inv_mod( &s_inv, s, &grp->N ) );
MPI_CHK( mpi_mul_mpi( &u1, &e, &s_inv ) );
MPI_CHK( mpi_mod_mpi( &u1, &u1, &grp->N ) );
MPI_CHK( mpi_mul_mpi( &u2, r, &s_inv ) );
MPI_CHK( mpi_mod_mpi( &u2, &u2, &grp->N ) );
/*
* Step 5: R = u1 G + u2 Q
*/
MPI_CHK( ecp_mul( grp, &R, &u1, &grp->G ) );
MPI_CHK( ecp_mul( grp, &P, &u2, Q ) );
MPI_CHK( ecp_add( grp, &R, &R, &P ) );
if( ecp_is_zero( &R ) )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
/*
* Step 6: check that xR == r
*/
if( mpi_cmp_mpi( &R.X, r ) != 0 )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
cleanup:
ecp_point_free( &R ); ecp_point_free( &P );
mpi_free( &e ); mpi_free( &s_inv ); mpi_free( &u1 ); mpi_free( &u2 );
return( ret );
}
#if defined(POLARSSL_SELF_TEST)
/*
* Checkup routine
*/
int ecdsa_self_test( int verbose )
{
return( verbose++ );
}
#endif
#endif /* defined(POLARSSL_ECDSA_C) */