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