library/ssl_cookie.c

/*
 *  DTLS cookie callbacks implementation
 *
 *  Copyright (C) 2014, 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.
 */
/*
 * These session callbacks use a simple chained list
 * to store and retrieve the session information.
 */

#if !defined(POLARSSL_CONFIG_FILE)
#include "polarssl/config.h"
#else
#include POLARSSL_CONFIG_FILE
#endif

#if defined(POLARSSL_SSL_DTLS_HELLO_VERIFY)

#include "polarssl/ssl_cookie.h"

#if defined(POLARSSL_PLATFORM_C)
#include "polarssl/platform.h"
#else
#define polarssl_malloc     malloc
#define polarssl_free       free
#endif

/* Implementation that should never be optimized out by the compiler */
static void polarssl_zeroize( void *v, size_t n ) {
    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
}

/*
 * If DTLS is in use, then at least one of SHA-1, SHA-256, SHA-512 is
 * available. Try SHA-256 first, 512 wastes resources since we need to stay
 * with max 32 bytes of cookie for DTLS 1.0
 */
#if defined(POLARSSL_SHA256_C)
#define HVR_MD      POLARSSL_MD_SHA256
#define HVR_MD_LEN  32
#define HVR_MD_USE  32
#elif defined(POLARSSL_SHA512_C)
#define HVR_MD      POLARSSL_MD_SHA384
#define HVR_MD_LEN  48
#define HVR_MD_USE  32
#elif defined(POLARSSL_SHA1_C)
#define HVR_MD      POLARSSL_MD_SHA1
#define HVR_MD_LEN  20
#define HVR_MD_USE  20
#else
#error "DTLS hello verify needs SHA-1 or SHA-2"
#endif

void ssl_cookie_init( ssl_cookie_ctx *ctx )
{
    md_init( &ctx->hmac_ctx );
}

void ssl_cookie_free( ssl_cookie_ctx *ctx )
{
    md_free( &ctx->hmac_ctx );
}

int ssl_cookie_setup( ssl_cookie_ctx *ctx,
                      int (*f_rng)(void *, unsigned char *, size_t),
                      void *p_rng )
{
    int ret;
    unsigned char key[HVR_MD_LEN];

    if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
        return( ret );

    ret = md_init_ctx( &ctx->hmac_ctx, md_info_from_type( HVR_MD ) );
    if( ret != 0 )
        return( ret );

    ret = md_hmac_starts( &ctx->hmac_ctx, key, sizeof( key ) );
    if( ret != 0 )
        return( ret );

    polarssl_zeroize( key, sizeof( key ) );

    return( 0 );
}

/*
 * Generate cookie for DTLS ClientHello verification
 */
int ssl_cookie_write( void *ctx,
                      unsigned char **p, unsigned char *end,
                      const unsigned char *cli_id, size_t cli_id_len )
{
    int ret;
    unsigned char hmac_out[HVR_MD_LEN];
    md_context_t *hmac_ctx = (md_context_t *) ctx;

    if( (size_t)( end - *p ) < HVR_MD_USE )
        return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );

    if( ( ret = md_hmac_reset(  hmac_ctx ) ) != 0 ||
        ( ret = md_hmac_update( hmac_ctx, cli_id, cli_id_len ) ) != 0 ||
        ( ret = md_hmac_finish( hmac_ctx, hmac_out ) ) != 0 )
    {
        return( POLARSSL_ERR_SSL_INTERNAL_ERROR );
    }

    memcpy( *p, hmac_out, HVR_MD_USE );
    *p += HVR_MD_USE;

    return( 0 );
}

/*
 * Check a cookie
 */
int ssl_cookie_check( void *ctx,
                      const unsigned char *cookie, size_t cookie_len,
                      const unsigned char *cli_id, size_t cli_id_len )
{
    unsigned char ref_cookie[HVR_MD_USE];
    unsigned char *p = ref_cookie;
    md_context_t *hmac_ctx = (md_context_t *) ctx;

    if( cookie_len != HVR_MD_USE )
        return( -1 );

    if( ssl_cookie_write( hmac_ctx,
                          &p, p + sizeof( ref_cookie ),
                          cli_id, cli_id_len ) != 0 )
        return( -1 );

    if( safer_memcmp( cookie, ref_cookie, sizeof( ref_cookie ) ) != 0 )
        return( -1 );

    return( 0 );
}
#endif /* POLARSSL_SSL_COOKIE_C */