302 lines
7 KiB
C
302 lines
7 KiB
C
/*
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* Diffie-Hellman-Merkle key exchange
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*
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* Copyright (C) 2006-2010, 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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* Reference:
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*
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* http://www.cacr.math.uwaterloo.ca/hac/ (chapter 12)
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*/
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#include "polarssl/config.h"
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#if defined(POLARSSL_DHM_C)
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#include "polarssl/dhm.h"
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#include <string.h>
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/*
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* helper to validate the mpi size and import it
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*/
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static int dhm_read_bignum( mpi *X,
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unsigned char **p,
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const unsigned char *end )
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{
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int ret, n;
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if( end - *p < 2 )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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n = ( (*p)[0] << 8 ) | (*p)[1];
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(*p) += 2;
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if( (int)( end - *p ) < n )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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if( ( ret = mpi_read_binary( X, *p, n ) ) != 0 )
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return( POLARSSL_ERR_DHM_READ_PARAMS_FAILED | ret );
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(*p) += n;
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return( 0 );
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}
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/*
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* Verify sanity of public value with regards to P
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*/
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static int dhm_verifypub( const mpi *P, const mpi *pub_value )
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{
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mpi X;
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mpi_init( &X, NULL );
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mpi_lset( &X, 1 );
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/* Check G^Y or G^X is valid */
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if( mpi_cmp_mpi( pub_value, &X ) <= 0 )
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{
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mpi_free( &X, NULL );
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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}
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/* Reset: x = P - 1 */
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mpi_sub_int( &X, P, 1 );
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if( mpi_cmp_mpi( pub_value, &X ) >= 0 )
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{
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mpi_free( &X, NULL );
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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}
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mpi_free( &X, NULL );
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return( 0 );
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}
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/*
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* Parse the ServerKeyExchange parameters
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*/
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int dhm_read_params( dhm_context *ctx,
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unsigned char **p,
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const unsigned char *end )
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{
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int ret, n;
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memset( ctx, 0, sizeof( dhm_context ) );
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if( ( ret = dhm_read_bignum( &ctx->P, p, end ) ) != 0 ||
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( ret = dhm_read_bignum( &ctx->G, p, end ) ) != 0 ||
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( ret = dhm_read_bignum( &ctx->GY, p, end ) ) != 0 )
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return( ret );
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ctx->len = mpi_size( &ctx->P );
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if( end - *p < 2 )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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n = ( (*p)[0] << 8 ) | (*p)[1];
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(*p) += 2;
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if( end != *p + n )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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if( ( ret = dhm_verifypub( &ctx->P, &ctx->GY ) ) != 0 )
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return( ret );
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return( 0 );
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}
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/*
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* Setup and write the ServerKeyExchange parameters
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*/
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int dhm_make_params( dhm_context *ctx, int x_size,
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unsigned char *output, int *olen,
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int (*f_rng)(void *), void *p_rng )
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{
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int i, ret, n, n1, n2, n3;
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unsigned char *p;
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/*
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* Generate X as large as possible ( < P )
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*/
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n = x_size / sizeof( t_int ) + 1;
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MPI_CHK( mpi_grow( &ctx->X, n ) );
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MPI_CHK( mpi_lset( &ctx->X, 0 ) );
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p = (unsigned char *) ctx->X.p;
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for( i = 0; i < x_size; i++ )
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*p++ = (unsigned char) f_rng( p_rng );
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while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
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mpi_shift_r( &ctx->X, 1 );
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/*
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* Calculate GX = G^X mod P
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*/
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MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
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&ctx->P , &ctx->RP ) );
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if( ( ret = dhm_verifypub( &ctx->P, &ctx->GX ) ) != 0 )
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return( ret );
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/*
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* export P, G, GX
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*/
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#define DHM_MPI_EXPORT(X,n) \
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MPI_CHK( mpi_write_binary( X, p + 2, n ) ); \
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*p++ = (unsigned char)( n >> 8 ); \
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*p++ = (unsigned char)( n ); p += n;
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n1 = mpi_size( &ctx->P );
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n2 = mpi_size( &ctx->G );
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n3 = mpi_size( &ctx->GX );
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p = output;
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DHM_MPI_EXPORT( &ctx->P , n1 );
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DHM_MPI_EXPORT( &ctx->G , n2 );
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DHM_MPI_EXPORT( &ctx->GX, n3 );
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*olen = p - output;
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ctx->len = n1;
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cleanup:
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if( ret != 0 )
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return( ret | POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED );
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return( 0 );
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}
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/*
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* Import the peer's public value G^Y
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*/
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int dhm_read_public( dhm_context *ctx,
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const unsigned char *input, int ilen )
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{
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int ret;
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if( ctx == NULL || ilen < 1 || ilen > ctx->len )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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if( ( ret = mpi_read_binary( &ctx->GY, input, ilen ) ) != 0 )
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return( POLARSSL_ERR_DHM_READ_PUBLIC_FAILED | ret );
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return( 0 );
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}
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/*
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* Create own private value X and export G^X
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*/
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int dhm_make_public( dhm_context *ctx, int x_size,
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unsigned char *output, int olen,
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int (*f_rng)(void *), void *p_rng )
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{
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int ret, i, n;
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unsigned char *p;
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if( ctx == NULL || olen < 1 || olen > ctx->len )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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/*
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* generate X and calculate GX = G^X mod P
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*/
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n = x_size / sizeof( t_int ) + 1;
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MPI_CHK( mpi_grow( &ctx->X, n ) );
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MPI_CHK( mpi_lset( &ctx->X, 0 ) );
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p = (unsigned char *) ctx->X.p;
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for( i = 0; i < x_size; i++ )
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*p++ = (unsigned char) f_rng( p_rng );
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while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
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mpi_shift_r( &ctx->X, 1 );
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MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
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&ctx->P , &ctx->RP ) );
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if( dhm_verifypub( &ctx->P, &ctx->GX ) != 0 )
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return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED );
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MPI_CHK( mpi_write_binary( &ctx->GX, output, olen ) );
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cleanup:
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if( ret != 0 )
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return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED | ret );
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return( 0 );
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}
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/*
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* Derive and export the shared secret (G^Y)^X mod P
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*/
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int dhm_calc_secret( dhm_context *ctx,
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unsigned char *output, int *olen )
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{
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int ret;
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if( ctx == NULL || *olen < ctx->len )
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return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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MPI_CHK( mpi_exp_mod( &ctx->K, &ctx->GY, &ctx->X,
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&ctx->P, &ctx->RP ) );
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if( ( ret = dhm_verifypub( &ctx->P, &ctx->GY ) ) != 0 )
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return( ret );
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*olen = mpi_size( &ctx->K );
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MPI_CHK( mpi_write_binary( &ctx->K, output, *olen ) );
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cleanup:
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if( ret != 0 )
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return( POLARSSL_ERR_DHM_CALC_SECRET_FAILED | ret );
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return( 0 );
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}
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/*
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* Free the components of a DHM key
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*/
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void dhm_free( dhm_context *ctx )
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{
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mpi_free( &ctx->RP, &ctx->K, &ctx->GY,
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&ctx->GX, &ctx->X, &ctx->G,
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&ctx->P, NULL );
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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 dhm_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
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