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mbedtls/library/ssl_ticket.c
Manuel Pégourié-Gonnard d59675d92c Move to callback for session tickets
2015-05-20 11:14:57 +02:00

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/*
* TLS server tickets callbacks implementation
*
* Copyright (C) 2015, ARM Limited, All Rights Reserved
*
* This file is part of mbed TLS (https://tls.mbed.org)
*
* 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.
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_SSL_TICKET_C)
#include "mbedtls/ssl_ticket.h"
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#define mbedtls_malloc malloc
#define mbedtls_free free
#endif
#include <string.h>
/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize( void *v, size_t n ) {
volatile unsigned char *p = v; while( n-- ) *p++ = 0;
}
/*
* Initialze context
*/
void mbedtls_ssl_ticket_init( mbedtls_ssl_ticket_context *ctx )
{
memset( ctx, 0, sizeof( mbedtls_ssl_ticket_context ) );
}
/*
* Setup context for actual use
*/
int mbedtls_ssl_ticket_setup( mbedtls_ssl_ticket_context *ctx,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng,
uint32_t lifetime )
{
int ret;
unsigned char buf[16];
ctx->f_rng = f_rng;
ctx->p_rng = p_rng;
ctx->ticket_lifetime = lifetime;
mbedtls_aes_init( &ctx->enc );
mbedtls_aes_init( &ctx->dec );
if( ( ret = f_rng( p_rng, ctx->key_name, 16 ) != 0 ) ||
( ret = f_rng( p_rng, ctx->mac_key, 16 ) != 0 ) ||
( ret = f_rng( p_rng, buf, 16 ) != 0 ) )
{
return( ret );
}
if( ( ret = mbedtls_aes_setkey_enc( &ctx->enc, buf, 128 ) ) != 0 ||
( ret = mbedtls_aes_setkey_dec( &ctx->dec, buf, 128 ) ) != 0 )
{
mbedtls_ssl_ticket_free( ctx );
return( ret );
}
mbedtls_zeroize( buf, sizeof( buf ) );
return( 0 );
}
/*
* Serialize a session in the following format:
* 0 . n-1 session structure, n = sizeof(mbedtls_ssl_session)
* n . n+2 peer_cert length = m (0 if no certificate)
* n+3 . n+2+m peer cert ASN.1
*
* Assumes ticket is NULL (always true on server side).
*/
static int ssl_save_session( const mbedtls_ssl_session *session,
unsigned char *buf, size_t buf_len,
size_t *olen )
{
unsigned char *p = buf;
size_t left = buf_len;
#if defined(MBEDTLS_X509_CRT_PARSE_C)
size_t cert_len;
#endif /* MBEDTLS_X509_CRT_PARSE_C */
if( left < sizeof( mbedtls_ssl_session ) )
return( -1 );
memcpy( p, session, sizeof( mbedtls_ssl_session ) );
p += sizeof( mbedtls_ssl_session );
left -= sizeof( mbedtls_ssl_session );
#if defined(MBEDTLS_X509_CRT_PARSE_C)
if( session->peer_cert == NULL )
cert_len = 0;
else
cert_len = session->peer_cert->raw.len;
if( left < 3 + cert_len )
return( -1 );
*p++ = (unsigned char)( cert_len >> 16 & 0xFF );
*p++ = (unsigned char)( cert_len >> 8 & 0xFF );
*p++ = (unsigned char)( cert_len & 0xFF );
if( session->peer_cert != NULL )
memcpy( p, session->peer_cert->raw.p, cert_len );
p += cert_len;
#endif /* MBEDTLS_X509_CRT_PARSE_C */
*olen = p - buf;
return( 0 );
}
/*
* Unserialise session, see ssl_save_session()
*/
static int ssl_load_session( mbedtls_ssl_session *session,
const unsigned char *buf, size_t len )
{
const unsigned char *p = buf;
const unsigned char * const end = buf + len;
#if defined(MBEDTLS_X509_CRT_PARSE_C)
size_t cert_len;
#endif /* MBEDTLS_X509_CRT_PARSE_C */
if( p + sizeof( mbedtls_ssl_session ) > end )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
memcpy( session, p, sizeof( mbedtls_ssl_session ) );
p += sizeof( mbedtls_ssl_session );
#if defined(MBEDTLS_X509_CRT_PARSE_C)
if( p + 3 > end )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
cert_len = ( p[0] << 16 ) | ( p[1] << 8 ) | p[2];
p += 3;
if( cert_len == 0 )
{
session->peer_cert = NULL;
}
else
{
int ret;
if( p + cert_len > end )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
session->peer_cert = mbedtls_malloc( sizeof( mbedtls_x509_crt ) );
if( session->peer_cert == NULL )
return( MBEDTLS_ERR_SSL_MALLOC_FAILED );
mbedtls_x509_crt_init( session->peer_cert );
if( ( ret = mbedtls_x509_crt_parse_der( session->peer_cert,
p, cert_len ) ) != 0 )
{
mbedtls_x509_crt_free( session->peer_cert );
mbedtls_free( session->peer_cert );
session->peer_cert = NULL;
return( ret );
}
p += cert_len;
}
#endif /* MBEDTLS_X509_CRT_PARSE_C */
if( p != end )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
return( 0 );
}
/*
* Create session ticket, secured as recommended in RFC 5077 section 4:
*
* struct {
* opaque key_name[16];
* opaque iv[16];
* opaque encrypted_state<0..2^16-1>;
* opaque mac[32];
* } ticket;
*
* (the internal state structure differs, however).
*/
int mbedtls_ssl_ticket_write( void *p_ticket,
const mbedtls_ssl_session *session,
unsigned char *start,
const unsigned char *end,
size_t *tlen,
uint32_t *ticket_lifetime )
{
int ret;
mbedtls_ssl_ticket_context *ctx = p_ticket;
unsigned char *p = start;
unsigned char *state;
unsigned char iv[16];
size_t clear_len, enc_len, pad_len, i;
*tlen = 0;
if( ctx == NULL )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
*ticket_lifetime = ctx->ticket_lifetime;
/* We need at least 16 bytes for key_name, 16 for IV, 2 for len
* 16 for padding, 32 for MAC, in addition to session itself,
* that will be checked when writing it. */
if( end - start < 16 + 16 + 2 + 16 + 32 )
return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
/* Write key name */
memcpy( p, ctx->key_name, 16 );
p += 16;
/* Generate and write IV (with a copy for aes_crypt) */
if( ( ret = ctx->f_rng( ctx->p_rng, p, 16 ) ) != 0 )
return( ret );
memcpy( iv, p, 16 );
p += 16;
/* Dump session state */
state = p + 2;
if( ssl_save_session( session, state, end - state, &clear_len ) != 0 )
return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
/* Apply PKCS padding */
pad_len = 16 - clear_len % 16;
enc_len = clear_len + pad_len;
for( i = clear_len; i < enc_len; i++ )
state[i] = (unsigned char) pad_len;
/* Encrypt */
if( ( ret = mbedtls_aes_crypt_cbc( &ctx->enc, MBEDTLS_AES_ENCRYPT,
enc_len, iv, state, state ) ) != 0 )
{
return( ret );
}
/* Write length */
*p++ = (unsigned char)( ( enc_len >> 8 ) & 0xFF );
*p++ = (unsigned char)( ( enc_len ) & 0xFF );
p = state + enc_len;
/* Compute and write MAC( key_name + iv + enc_state_len + enc_state ) */
if( ( ret = mbedtls_md_hmac( mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ),
ctx->mac_key, 16,
start, p - start, p ) ) != 0 )
{
return( ret );
}
p += 32;
*tlen = p - start;
return( 0 );
}
/*
* Load session ticket (see mbedtls_ssl_ticket_write for structure)
*/
int mbedtls_ssl_ticket_parse( void *p_ticket,
mbedtls_ssl_session *session,
unsigned char *buf,
size_t len )
{
int ret;
mbedtls_ssl_ticket_context *ctx = p_ticket;
unsigned char *key_name = buf;
unsigned char *iv = buf + 16;
unsigned char *enc_len_p = iv + 16;
unsigned char *ticket = enc_len_p + 2;
unsigned char *mac;
unsigned char computed_mac[32];
size_t enc_len, clear_len, i;
unsigned char pad_len, diff;
if( len < 34 || ctx == NULL )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
enc_len = ( enc_len_p[0] << 8 ) | enc_len_p[1];
mac = ticket + enc_len;
if( len != enc_len + 66 )
return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
/* Check name, in constant time though it's not a big secret */
diff = 0;
for( i = 0; i < 16; i++ )
diff |= key_name[i] ^ ctx->key_name[i];
/* don't return yet, check the MAC anyway */
/* Check mac, with constant-time buffer comparison */
if( ( ret = mbedtls_md_hmac( mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ),
ctx->mac_key, 16,
buf, len - 32, computed_mac ) ) != 0 )
{
return( ret );
}
for( i = 0; i < 32; i++ )
diff |= mac[i] ^ computed_mac[i];
/* Now return if ticket is not authentic, since we want to avoid
* decrypting arbitrary attacker-chosen data */
if( diff != 0 )
return( MBEDTLS_ERR_SSL_INVALID_MAC );
/* Decrypt */
if( ( ret = mbedtls_aes_crypt_cbc( &ctx->dec, MBEDTLS_AES_DECRYPT,
enc_len, iv, ticket, ticket ) ) != 0 )
{
return( ret );
}
/* Check PKCS padding */
pad_len = ticket[enc_len - 1];
ret = 0;
for( i = 2; i < pad_len; i++ )
if( ticket[enc_len - i] != pad_len )
ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
if( ret != 0 )
return( ret );
clear_len = enc_len - pad_len;
/* Actually load session */
if( ( ret = ssl_load_session( session, ticket, clear_len ) ) != 0 )
return( ret );
#if defined(MBEDTLS_HAVE_TIME)
/* Check if still valid */
if( ( time( NULL) - session->start ) > ctx->ticket_lifetime )
return( MBEDTLS_ERR_SSL_SESSION_TICKET_EXPIRED );
#endif
return( 0 );
}
/*
* Free context
*/
void mbedtls_ssl_ticket_free( mbedtls_ssl_ticket_context *ctx )
{
mbedtls_aes_free( &ctx->enc );
mbedtls_aes_free( &ctx->dec );
mbedtls_zeroize( ctx, sizeof( mbedtls_ssl_ticket_context ) );
}
#endif /* MBEDTLS_SSL_TICKET_C */
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