1 files changed, 296 insertions, 0 deletions
diff --git a/polarssl/src/library/dhm.c b/polarssl/src/library/dhm.c
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+/*
+ *  Diffie-Hellman-Merkle key exchange
+ *
+ *  Copyright (C) 2006-2010, 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.
+ */
+/*
+ *  Reference:
+ *
+ *  http://www.cacr.math.uwaterloo.ca/hac/ (chapter 12)
+ */
+
+#include "polarssl/config.h"
+
+#if defined(POLARSSL_DHM_C)
+
+#include "polarssl/dhm.h"
+
+/*
+ * helper to validate the mpi size and import it
+ */
+static int dhm_read_bignum( mpi *X,
+                            unsigned char **p,
+                            const unsigned char *end )
+{
+    int ret, n;
+
+    if( end - *p < 2 )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    n = ( (*p)[0] << 8 ) | (*p)[1];
+    (*p) += 2;
+
+    if( (int)( end - *p ) < n )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    if( ( ret = mpi_read_binary( X, *p, n ) ) != 0 )
+        return( POLARSSL_ERR_DHM_READ_PARAMS_FAILED + ret );
+
+    (*p) += n;
+
+    return( 0 );
+}
+
+/*
+ * Verify sanity of parameter with regards to P
+ *
+ * Parameter should be: 2 <= public_param <= P - 2
+ *
+ * For more information on the attack, see:
+ *  http://www.cl.cam.ac.uk/~rja14/Papers/psandqs.pdf
+ *  http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2005-2643
+ */
+static int dhm_check_range( const mpi *param, const mpi *P )
+{
+    mpi L, U;
+    int ret = POLARSSL_ERR_DHM_BAD_INPUT_DATA;
+
+    mpi_init( &L ); mpi_init( &U );
+    mpi_lset( &L, 2 );
+    mpi_sub_int( &U, P, 2 );
+
+    if( mpi_cmp_mpi( param, &L ) >= 0 &&
+        mpi_cmp_mpi( param, &U ) <= 0 )
+    {
+        ret = 0;
+    }
+
+    mpi_free( &L ); mpi_free( &U );
+
+    return( ret );
+}
+
+/*
+ * Parse the ServerKeyExchange parameters
+ */
+int dhm_read_params( dhm_context *ctx,
+                     unsigned char **p,
+                     const unsigned char *end )
+{
+    int ret;
+
+    memset( ctx, 0, sizeof( dhm_context ) );
+
+    if( ( ret = dhm_read_bignum( &ctx->P,  p, end ) ) != 0 ||
+        ( ret = dhm_read_bignum( &ctx->G,  p, end ) ) != 0 ||
+        ( ret = dhm_read_bignum( &ctx->GY, p, end ) ) != 0 )
+        return( ret );
+
+    if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
+        return( ret );
+
+    ctx->len = mpi_size( &ctx->P );
+
+    if( end - *p < 2 )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    return( 0 );
+}
+
+/*
+ * Setup and write the ServerKeyExchange parameters
+ */
+int dhm_make_params( dhm_context *ctx, int x_size,
+                     unsigned char *output, size_t *olen,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng )
+{
+    int ret, count = 0;
+    size_t n1, n2, n3;
+    unsigned char *p;
+
+    /*
+     * Generate X as large as possible ( < P )
+     */
+    do
+    {
+        mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
+
+        while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
+            mpi_shift_r( &ctx->X, 1 );
+
+        if( count++ > 10 )
+            return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED );
+    }
+    while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
+
+    /*
+     * Calculate GX = G^X mod P
+     */
+    MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
+                          &ctx->P , &ctx->RP ) );
+
+    if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
+        return( ret );
+
+    /*
+     * export P, G, GX
+     */
+#define DHM_MPI_EXPORT(X,n)                     \
+    MPI_CHK( mpi_write_binary( X, p + 2, n ) ); \
+    *p++ = (unsigned char)( n >> 8 );           \
+    *p++ = (unsigned char)( n      ); p += n;
+
+    n1 = mpi_size( &ctx->P  );
+    n2 = mpi_size( &ctx->G  );
+    n3 = mpi_size( &ctx->GX );
+
+    p = output;
+    DHM_MPI_EXPORT( &ctx->P , n1 );
+    DHM_MPI_EXPORT( &ctx->G , n2 );
+    DHM_MPI_EXPORT( &ctx->GX, n3 );
+
+    *olen  = p - output;
+
+    ctx->len = n1;
+
+cleanup:
+
+    if( ret != 0 )
+        return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED + ret );
+
+    return( 0 );
+}
+
+/*
+ * Import the peer's public value G^Y
+ */
+int dhm_read_public( dhm_context *ctx,
+                     const unsigned char *input, size_t ilen )
+{
+    int ret;
+
+    if( ctx == NULL || ilen < 1 || ilen > ctx->len )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    if( ( ret = mpi_read_binary( &ctx->GY, input, ilen ) ) != 0 )
+        return( POLARSSL_ERR_DHM_READ_PUBLIC_FAILED + ret );
+
+    return( 0 );
+}
+
+/*
+ * Create own private value X and export G^X
+ */
+int dhm_make_public( dhm_context *ctx, int x_size,
+                     unsigned char *output, size_t olen,
+                     int (*f_rng)(void *, unsigned char *, size_t),
+                     void *p_rng )
+{
+    int ret, count = 0;
+
+    if( ctx == NULL || olen < 1 || olen > ctx->len )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    /*
+     * generate X and calculate GX = G^X mod P
+     */
+    do
+    {
+        mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
+
+        while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
+            mpi_shift_r( &ctx->X, 1 );
+
+        if( count++ > 10 )
+            return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED );
+    }
+    while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
+
+    MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
+                          &ctx->P , &ctx->RP ) );
+
+    if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
+        return( ret );
+
+    MPI_CHK( mpi_write_binary( &ctx->GX, output, olen ) );
+
+cleanup:
+
+    if( ret != 0 )
+        return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED + ret );
+
+    return( 0 );
+}
+
+/*
+ * Derive and export the shared secret (G^Y)^X mod P
+ */
+int dhm_calc_secret( dhm_context *ctx,
+                     unsigned char *output, size_t *olen )
+{
+    int ret;
+
+    if( ctx == NULL || *olen < ctx->len )
+        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
+
+    MPI_CHK( mpi_exp_mod( &ctx->K, &ctx->GY, &ctx->X,
+                          &ctx->P, &ctx->RP ) );
+
+    if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
+        return( ret );
+
+    *olen = mpi_size( &ctx->K );
+
+    MPI_CHK( mpi_write_binary( &ctx->K, output, *olen ) );
+
+cleanup:
+
+    if( ret != 0 )
+        return( POLARSSL_ERR_DHM_CALC_SECRET_FAILED + ret );
+
+    return( 0 );
+}
+
+/*
+ * Free the components of a DHM key
+ */
+void dhm_free( dhm_context *ctx )
+{
+    mpi_free( &ctx->RP ); mpi_free( &ctx->K ); mpi_free( &ctx->GY );
+    mpi_free( &ctx->GX ); mpi_free( &ctx->X ); mpi_free( &ctx->G );
+    mpi_free( &ctx->P );
+}
+
+#if defined(POLARSSL_SELF_TEST)
+
+/*
+ * Checkup routine
+ */
+int dhm_self_test( int verbose )
+{
+    return( verbose++ );
+}
+
+#endif
+
+#endif