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/*
* 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_COOKIE_C)
#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 COOKIE_MD POLARSSL_MD_SHA224
#define COOKIE_MD_OUTLEN 32
#define COOKIE_HMAC_LEN 28
#elif defined(POLARSSL_SHA512_C)
#define COOKIE_MD POLARSSL_MD_SHA384
#define COOKIE_MD_OUTLEN 48
#define COOKIE_HMAC_LEN 28
#elif defined(POLARSSL_SHA1_C)
#define COOKIE_MD POLARSSL_MD_SHA1
#define COOKIE_MD_OUTLEN 20
#define COOKIE_HMAC_LEN 20
#else
#error "DTLS hello verify needs SHA-1 or SHA-2"
#endif
/*
* Cookies are formed of a 4-bytes timestamp (or serial number) and
* an HMAC of timestemp and client ID.
*/
#define COOKIE_LEN ( 4 + COOKIE_HMAC_LEN )
void ssl_cookie_init( ssl_cookie_ctx *ctx )
{
md_init( &ctx->hmac_ctx );
#if !defined(POLARSSL_HAVE_TIME)
ctx->serial = 0;
#endif
ctx->timeout = POLARSSL_SSL_COOKIE_TIMEOUT;
}
void ssl_cookie_set_timeout( ssl_cookie_ctx *ctx, unsigned long delay )
{
ctx->timeout = delay;
}
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[COOKIE_MD_OUTLEN];
if( ( ret = f_rng( p_rng, key, sizeof( key ) ) ) != 0 )
return( ret );
ret = md_init_ctx( &ctx->hmac_ctx, md_info_from_type( COOKIE_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 the HMAC part of a cookie
*/
static int ssl_cookie_hmac( md_context_t *hmac_ctx,
const unsigned char time[4],
unsigned char **p, unsigned char *end,
const unsigned char *cli_id, size_t cli_id_len )
{
int ret;
unsigned char hmac_out[COOKIE_MD_OUTLEN];
if( (size_t)( end - *p ) < COOKIE_HMAC_LEN )
return( POLARSSL_ERR_SSL_BUFFER_TOO_SMALL );
if( ( ret = md_hmac_reset( hmac_ctx ) ) != 0 ||
( ret = md_hmac_update( hmac_ctx, time, 4 ) ) != 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, COOKIE_HMAC_LEN );
*p += COOKIE_HMAC_LEN;
return( 0 );
}
/*
* Generate cookie for DTLS ClientHello verification
*/
int ssl_cookie_write( void *p_ctx,
unsigned char **p, unsigned char *end,
const unsigned char *cli_id, size_t cli_id_len )
{
ssl_cookie_ctx *ctx = (ssl_cookie_ctx *) p_ctx;
unsigned long t;
if( ctx == NULL || cli_id == NULL )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
if( (size_t)( end - *p ) < COOKIE_LEN )
return( POLARSSL_ERR_SSL_BUFFER_TOO_SMALL );
#if defined(POLARSSL_HAVE_TIME)
t = (unsigned long) time( NULL );
#else
t = ctx->serial++;
#endif
(*p)[0] = (unsigned char)( t >> 24 );
(*p)[1] = (unsigned char)( t >> 16 );
(*p)[2] = (unsigned char)( t >> 8 );
(*p)[3] = (unsigned char)( t );
*p += 4;
return( ssl_cookie_hmac( &ctx->hmac_ctx, *p - 4,
p, end, cli_id, cli_id_len ) );
}
/*
* Check a cookie
*/
int ssl_cookie_check( void *p_ctx,
const unsigned char *cookie, size_t cookie_len,
const unsigned char *cli_id, size_t cli_id_len )
{
unsigned char ref_hmac[COOKIE_HMAC_LEN];
unsigned char *p = ref_hmac;
ssl_cookie_ctx *ctx = (ssl_cookie_ctx *) p_ctx;
unsigned long cur_time, cookie_time;
if( ctx == NULL || cli_id == NULL )
return( POLARSSL_ERR_SSL_BAD_INPUT_DATA );
if( cookie_len != COOKIE_LEN )
return( -1 );
if( ssl_cookie_hmac( &ctx->hmac_ctx, cookie,
&p, p + sizeof( ref_hmac ),
cli_id, cli_id_len ) != 0 )
return( -1 );
if( safer_memcmp( cookie + 4, ref_hmac, sizeof( ref_hmac ) ) != 0 )
return( -1 );
#if defined(POLARSSL_HAVE_TIME)
cur_time = (unsigned long) time( NULL );
#else
cur_time = ctx->serial;
#endif
cookie_time = ( (unsigned long) cookie[0] << 24 ) |
( (unsigned long) cookie[1] << 16 ) |
( (unsigned long) cookie[2] << 8 ) |
( (unsigned long) cookie[3] );
if( ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout )
return( -1 );
return( 0 );
}
#endif /* POLARSSL_SSL_COOKIE_C */