/*
* 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"
#include "polarssl/asn1write.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 )
{
ret = POLARSSL_ERR_ECP_GENERIC;
goto cleanup;
}
}
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 )
{
ret = POLARSSL_ERR_ECP_GENERIC;
goto cleanup;
}
}
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 )
{
ret = POLARSSL_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
/*
* 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 ) )
{
ret = POLARSSL_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
/*
* Step 6: check that xR == r
*/
if( mpi_cmp_mpi( &R.X, r ) != 0 )
{
ret = POLARSSL_ERR_ECP_BAD_INPUT_DATA;
goto cleanup;
}
cleanup:
ecp_point_free( &R ); ecp_point_free( &P );
mpi_free( &e ); mpi_free( &s_inv ); mpi_free( &u1 ); mpi_free( &u2 );
return( ret );
}
/*
* RFC 4492 page 20:
*
* Ecdsa-Sig-Value ::= SEQUENCE {
* r INTEGER,
* s INTEGER
* }
*
* Size is at most
* 1 (tag) + 1 (len) + 1 (initial 0) + ECP_MAX_BYTES for each of r and s,
* twice that + 1 (tag) + 2 (len) for the sequence
* (assuming ECP_MAX_BYTES is less than 126 for r and s,
* and less than 124 (total len <= 255) for the sequence)
*/
#if POLARSSL_ECP_MAX_BYTES > 124
#error "POLARSSL_ECP_MAX_BYTES bigger than expected, please fix MAX_SIG_LEN"
#endif
#define MAX_SIG_LEN ( 3 + 2 * ( 2 + POLARSSL_ECP_MAX_BYTES ) )
/*
* Compute and write signature
*/
int ecdsa_write_signature( ecdsa_context *ctx,
const unsigned char *hash, size_t hlen,
unsigned char *sig, size_t *slen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
unsigned char buf[MAX_SIG_LEN];
unsigned char *p = buf + MAX_SIG_LEN - 1;
size_t len = 0;
if( ( ret = ecdsa_sign( &ctx->grp, &ctx->r, &ctx->s, &ctx->d,
hash, hlen, f_rng, p_rng ) ) != 0 )
{
return( ret );
}
ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->s ) );
ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->r ) );
ASN1_CHK_ADD( len, asn1_write_len( &p, buf, len ) );
ASN1_CHK_ADD( len, asn1_write_tag( &p, buf,
ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
memcpy( sig, p, len );
*slen = len;
return( 0 );
}
/*
* Read and check signature
*/
int ecdsa_read_signature( ecdsa_context *ctx,
const unsigned char *hash, size_t hlen,
const unsigned char *sig, size_t slen )
{
int ret;
unsigned char *p = (unsigned char *) sig;
const unsigned char *end = sig + slen;
size_t len;
if( ( ret = asn1_get_tag( &p, end, &len,
ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
{
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
}
if( p + len != end )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA +
POLARSSL_ERR_ASN1_LENGTH_MISMATCH );
if( ( ret = asn1_get_mpi( &p, end, &ctx->r ) ) != 0 ||
( ret = asn1_get_mpi( &p, end, &ctx->s ) ) != 0 )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
if( p != end )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA +
POLARSSL_ERR_ASN1_LENGTH_MISMATCH );
return( ecdsa_verify( &ctx->grp, hash, hlen, &ctx->Q, &ctx->r, &ctx->s ) );
}
/*
* Generate key pair
*/
int ecdsa_genkey( ecdsa_context *ctx, ecp_group_id gid,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
return( ecp_use_known_dp( &ctx->grp, gid ) ||
ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
}
/*
* Initialize context
*/
void ecdsa_init( ecdsa_context *ctx )
{
ecp_group_init( &ctx->grp );
mpi_init( &ctx->d );
ecp_point_init( &ctx->Q );
mpi_init( &ctx->r );
mpi_init( &ctx->s );
}
/*
* Free context
*/
void ecdsa_free( ecdsa_context *ctx )
{
ecp_group_free( &ctx->grp );
mpi_free( &ctx->d );
ecp_point_free( &ctx->Q );
mpi_free( &ctx->r );
mpi_free( &ctx->s );
}
#if defined(POLARSSL_SELF_TEST)
/*
* Checkup routine
*/
int ecdsa_self_test( int verbose )
{
return( verbose++ );
}
#endif
#endif /* defined(POLARSSL_ECDSA_C) */