5304812b2d
The issue would happen for curves whose bitlength is not a multiple of eight (the only case is NIST P-521) with hashes that are longer than the bitlength of the curve: since the wides hash is 512 bits long, this can't happen. Fixing however as a matter of principle and readability.
365 lines
9.5 KiB
C
365 lines
9.5 KiB
C
/*
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* Elliptic curve DSA
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*
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* Copyright (C) 2006-2013, Brainspark B.V.
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*
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* This file is part of PolarSSL (http://www.polarssl.org)
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* Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program 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
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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/*
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* References:
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*
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* SEC1 http://www.secg.org/index.php?action=secg,docs_secg
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*/
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#include "polarssl/config.h"
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#if defined(POLARSSL_ECDSA_C)
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#include "polarssl/ecdsa.h"
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#include "polarssl/asn1write.h"
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/*
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* Derive a suitable integer for group grp from a buffer of length len
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* SEC1 4.1.3 step 5 aka SEC1 4.1.4 step 3
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*/
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static int derive_mpi( const ecp_group *grp, mpi *x,
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const unsigned char *buf, size_t blen )
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{
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int ret;
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size_t n_size = (grp->nbits + 7) / 8;
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size_t use_size = blen > n_size ? n_size : blen;
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MPI_CHK( mpi_read_binary( x, buf, use_size ) );
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if( use_size * 8 > grp->nbits )
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MPI_CHK( mpi_shift_r( x, use_size * 8 - grp->nbits ) );
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cleanup:
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return( ret );
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}
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/*
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* Compute ECDSA signature of a hashed message (SEC1 4.1.3)
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* Obviously, compared to SEC1 4.1.3, we skip step 4 (hash message)
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*/
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int ecdsa_sign( ecp_group *grp, mpi *r, mpi *s,
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const mpi *d, const unsigned char *buf, size_t blen,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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int ret, key_tries, sign_tries;
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ecp_point R;
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mpi k, e;
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/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
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if( grp->N.p == NULL )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
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ecp_point_init( &R );
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mpi_init( &k );
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mpi_init( &e );
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sign_tries = 0;
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do
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{
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/*
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* Steps 1-3: generate a suitable ephemeral keypair
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* and set r = xR mod n
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*/
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key_tries = 0;
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do
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{
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MPI_CHK( ecp_gen_keypair( grp, &k, &R, f_rng, p_rng ) );
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MPI_CHK( mpi_mod_mpi( r, &R.X, &grp->N ) );
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if( key_tries++ > 10 )
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{
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ret = POLARSSL_ERR_ECP_RANDOM_FAILED;
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goto cleanup;
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}
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}
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while( mpi_cmp_int( r, 0 ) == 0 );
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/*
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* Step 5: derive MPI from hashed message
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*/
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MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
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/*
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* Step 6: compute s = (e + r * d) / k mod n
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*/
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MPI_CHK( mpi_mul_mpi( s, r, d ) );
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MPI_CHK( mpi_add_mpi( &e, &e, s ) );
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MPI_CHK( mpi_inv_mod( s, &k, &grp->N ) );
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MPI_CHK( mpi_mul_mpi( s, s, &e ) );
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MPI_CHK( mpi_mod_mpi( s, s, &grp->N ) );
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if( sign_tries++ > 10 )
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{
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ret = POLARSSL_ERR_ECP_RANDOM_FAILED;
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goto cleanup;
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}
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}
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while( mpi_cmp_int( s, 0 ) == 0 );
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cleanup:
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ecp_point_free( &R );
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mpi_free( &k );
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mpi_free( &e );
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return( ret );
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}
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/*
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* Verify ECDSA signature of hashed message (SEC1 4.1.4)
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* Obviously, compared to SEC1 4.1.3, we skip step 2 (hash message)
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*/
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int ecdsa_verify( ecp_group *grp,
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const unsigned char *buf, size_t blen,
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const ecp_point *Q, const mpi *r, const mpi *s)
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{
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int ret;
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mpi e, s_inv, u1, u2;
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ecp_point R, P;
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ecp_point_init( &R ); ecp_point_init( &P );
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mpi_init( &e ); mpi_init( &s_inv ); mpi_init( &u1 ); mpi_init( &u2 );
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/* Fail cleanly on curves such as Curve25519 that can't be used for ECDSA */
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if( grp->N.p == NULL )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
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/*
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* Step 1: make sure r and s are in range 1..n-1
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*/
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if( mpi_cmp_int( r, 1 ) < 0 || mpi_cmp_mpi( r, &grp->N ) >= 0 ||
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mpi_cmp_int( s, 1 ) < 0 || mpi_cmp_mpi( s, &grp->N ) >= 0 )
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{
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ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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/*
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* Additional precaution: make sure Q is valid
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*/
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MPI_CHK( ecp_check_pubkey( grp, Q ) );
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/*
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* Step 3: derive MPI from hashed message
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*/
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MPI_CHK( derive_mpi( grp, &e, buf, blen ) );
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/*
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* Step 4: u1 = e / s mod n, u2 = r / s mod n
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*/
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MPI_CHK( mpi_inv_mod( &s_inv, s, &grp->N ) );
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MPI_CHK( mpi_mul_mpi( &u1, &e, &s_inv ) );
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MPI_CHK( mpi_mod_mpi( &u1, &u1, &grp->N ) );
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MPI_CHK( mpi_mul_mpi( &u2, r, &s_inv ) );
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MPI_CHK( mpi_mod_mpi( &u2, &u2, &grp->N ) );
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/*
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* Step 5: R = u1 G + u2 Q
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*
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* Since we're not using any secret data, no need to pass a RNG to
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* ecp_mul() for countermesures.
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*/
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MPI_CHK( ecp_mul( grp, &R, &u1, &grp->G, NULL, NULL ) );
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MPI_CHK( ecp_mul( grp, &P, &u2, Q, NULL, NULL ) );
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MPI_CHK( ecp_add( grp, &R, &R, &P ) );
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if( ecp_is_zero( &R ) )
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{
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ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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/*
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* Step 6: convert xR to an integer (no-op)
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* Step 7: reduce xR mod n (gives v)
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*/
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MPI_CHK( mpi_mod_mpi( &R.X, &R.X, &grp->N ) );
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/*
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* Step 8: check if v (that is, R.X) is equal to r
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*/
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if( mpi_cmp_mpi( &R.X, r ) != 0 )
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{
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ret = POLARSSL_ERR_ECP_VERIFY_FAILED;
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goto cleanup;
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}
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cleanup:
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ecp_point_free( &R ); ecp_point_free( &P );
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mpi_free( &e ); mpi_free( &s_inv ); mpi_free( &u1 ); mpi_free( &u2 );
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return( ret );
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}
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/*
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* RFC 4492 page 20:
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*
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* Ecdsa-Sig-Value ::= SEQUENCE {
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* r INTEGER,
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* s INTEGER
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* }
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*
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* Size is at most
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* 1 (tag) + 1 (len) + 1 (initial 0) + ECP_MAX_BYTES for each of r and s,
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* twice that + 1 (tag) + 2 (len) for the sequence
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* (assuming ECP_MAX_BYTES is less than 126 for r and s,
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* and less than 124 (total len <= 255) for the sequence)
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*/
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#if POLARSSL_ECP_MAX_BYTES > 124
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#error "POLARSSL_ECP_MAX_BYTES bigger than expected, please fix MAX_SIG_LEN"
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#endif
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#define MAX_SIG_LEN ( 3 + 2 * ( 2 + POLARSSL_ECP_MAX_BYTES ) )
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/*
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* Compute and write signature
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*/
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int ecdsa_write_signature( ecdsa_context *ctx,
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const unsigned char *hash, size_t hlen,
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unsigned char *sig, size_t *slen,
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int (*f_rng)(void *, unsigned char *, size_t),
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void *p_rng )
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{
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int ret;
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unsigned char buf[MAX_SIG_LEN];
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unsigned char *p = buf + sizeof( buf );
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size_t len = 0;
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if( ( ret = ecdsa_sign( &ctx->grp, &ctx->r, &ctx->s, &ctx->d,
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hash, hlen, f_rng, p_rng ) ) != 0 )
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{
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return( ret );
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}
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ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->s ) );
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ASN1_CHK_ADD( len, asn1_write_mpi( &p, buf, &ctx->r ) );
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ASN1_CHK_ADD( len, asn1_write_len( &p, buf, len ) );
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ASN1_CHK_ADD( len, asn1_write_tag( &p, buf,
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ASN1_CONSTRUCTED | ASN1_SEQUENCE ) );
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memcpy( sig, p, len );
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*slen = len;
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return( 0 );
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}
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/*
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* Read and check signature
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*/
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int ecdsa_read_signature( ecdsa_context *ctx,
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const unsigned char *hash, size_t hlen,
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const unsigned char *sig, size_t slen )
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{
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int ret;
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unsigned char *p = (unsigned char *) sig;
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const unsigned char *end = sig + slen;
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size_t len;
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if( ( ret = asn1_get_tag( &p, end, &len,
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ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
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{
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
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}
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if( p + len != end )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA +
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POLARSSL_ERR_ASN1_LENGTH_MISMATCH );
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if( ( ret = asn1_get_mpi( &p, end, &ctx->r ) ) != 0 ||
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( ret = asn1_get_mpi( &p, end, &ctx->s ) ) != 0 )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA + ret );
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if( p != end )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA +
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POLARSSL_ERR_ASN1_LENGTH_MISMATCH );
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return( ecdsa_verify( &ctx->grp, hash, hlen, &ctx->Q, &ctx->r, &ctx->s ) );
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}
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/*
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* Generate key pair
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*/
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int ecdsa_genkey( ecdsa_context *ctx, ecp_group_id gid,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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return( ecp_use_known_dp( &ctx->grp, gid ) ||
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ecp_gen_keypair( &ctx->grp, &ctx->d, &ctx->Q, f_rng, p_rng ) );
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}
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/*
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* Set context from an ecp_keypair
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*/
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int ecdsa_from_keypair( ecdsa_context *ctx, const ecp_keypair *key )
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{
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int ret;
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if( ( ret = ecp_group_copy( &ctx->grp, &key->grp ) ) != 0 ||
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( ret = mpi_copy( &ctx->d, &key->d ) ) != 0 ||
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( ret = ecp_copy( &ctx->Q, &key->Q ) ) != 0 )
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{
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ecdsa_free( ctx );
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}
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return( ret );
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}
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/*
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* Initialize context
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*/
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void ecdsa_init( ecdsa_context *ctx )
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{
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ecp_group_init( &ctx->grp );
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mpi_init( &ctx->d );
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ecp_point_init( &ctx->Q );
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mpi_init( &ctx->r );
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mpi_init( &ctx->s );
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}
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/*
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* Free context
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*/
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void ecdsa_free( ecdsa_context *ctx )
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{
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ecp_group_free( &ctx->grp );
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mpi_free( &ctx->d );
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ecp_point_free( &ctx->Q );
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mpi_free( &ctx->r );
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mpi_free( &ctx->s );
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}
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#if defined(POLARSSL_SELF_TEST)
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/*
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* Checkup routine
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*/
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int ecdsa_self_test( int verbose )
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{
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return( verbose++ );
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}
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#endif
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#endif /* defined(POLARSSL_ECDSA_C) */
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