453 lines
14 KiB
C
453 lines
14 KiB
C
/*
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* TLS 1.3 client-side functions
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*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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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#include "common.h"
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#if defined(MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL)
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#if defined(MBEDTLS_SSL_CLI_C)
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#include <string.h>
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#include "ssl_misc.h"
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#include <mbedtls/debug.h>
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#define CLIENT_HELLO_RAND_BYTES_LEN 32
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#define CLIENT_HELLO_VERSION_LEN 2
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/* Write extensions */
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/*
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* ssl_tls13_write_supported_versions_ext():
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*
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* struct {
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* ProtocolVersion versions<2..254>;
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* } SupportedVersions;
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*/
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static int ssl_tls13_write_supported_versions_ext( mbedtls_ssl_context *ssl,
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unsigned char *buf,
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unsigned char *end,
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size_t *olen )
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{
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unsigned char *p = buf;
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*olen = 0;
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding supported version extension" ) );
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MBEDTLS_SSL_CHK_BUF_PTR( p, end, 7 );
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MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_SUPPORTED_VERSIONS, p, 0);
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/* total length */
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MBEDTLS_PUT_UINT16_BE( 3, p, 2);
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p+=4;
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/* length of next field */
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*p++ = 0x2;
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/* This implementation only supports a single TLS version, and only
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* advertises a single value.
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*/
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mbedtls_ssl_write_version( ssl->conf->max_major_ver, ssl->conf->max_minor_ver,
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ssl->conf->transport, p );
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "supported version: [%d:%d]",
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ssl->conf->max_major_ver, ssl->conf->max_minor_ver ) );
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*olen = 7;
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return( 0 );
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}
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#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
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static int ssl_tls13_write_supported_groups_ext( mbedtls_ssl_context *ssl,
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unsigned char *buf,
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unsigned char *end,
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size_t *olen )
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{
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((void) ssl);
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((void) buf);
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((void) end);
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((void) olen);
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return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
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}
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static int ssl_tls13_write_key_shares_ext( mbedtls_ssl_context *ssl,
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unsigned char *buf,
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unsigned char *end,
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size_t *olen )
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{
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((void) ssl);
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((void) buf);
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((void) end);
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((void) olen);
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return( MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE );
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}
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#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
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/* Functions for ClientHello */
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static int ssl_tls13_write_exts_client_hello( mbedtls_ssl_context *ssl,
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unsigned char *buf, size_t buflen,
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size_t *len_with_binders )
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{
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/* Extensions */
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/* extension_start
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* Used during extension writing where the
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* buffer pointer to the beginning of the
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* extension list must be kept to write
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* the total extension list size in the end.
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*/
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#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
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int ret;
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#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
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unsigned char* extension_start;
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size_t cur_ext_len; /* Size of the current extension */
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size_t total_ext_len; /* Size of list of extensions */
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/* Buffer management */
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unsigned char* start = buf;
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unsigned char* end = buf + buflen;
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/* Ciphersuite-related variables */
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const int* ciphersuites;
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const mbedtls_ssl_ciphersuite_t* ciphersuite_info;
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/* ciphersuite_start points to the start of
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the ciphersuite list, i.e. to the length field*/
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unsigned char* ciphersuite_start;
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size_t ciphersuite_count;
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/* Keeping track of the included extensions */
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ssl->handshake->extensions_present = MBEDTLS_SSL_EXT_NONE;
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/* NOTE:
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* Even for DTLS 1.3, we are writing a TLS handshake header here.
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* The actual DTLS 1.3 handshake header is inserted in
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* the record writing routine mbedtls_ssl_write_record().
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*
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* For cTLS the length, and the version field
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* are elided. The random bytes are shorter.
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*/
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if( ssl->conf->max_major_ver == 0 )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "configured max major version is invalid, "
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"consider using mbedtls_ssl_config_defaults()" ) );
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return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
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}
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ssl->major_ver = ssl->conf->min_major_ver;
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ssl->minor_ver = ssl->conf->min_minor_ver;
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/* For TLS 1.3 we use the legacy version number {0x03, 0x03}
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* instead of the true version number.
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*
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* For DTLS 1.3 we use the legacy version number
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* {254,253}.
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*
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* In cTLS the version number is elided.
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*/
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MBEDTLS_SSL_CHK_BUF_PTR( buf, end, CLIENT_HELLO_VERSION_LEN);
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MBEDTLS_PUT_UINT16_BE( 0x0303, buf, 0);
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buf += 2;
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buflen -= CLIENT_HELLO_VERSION_LEN;
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/* Write random bytes */
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MBEDTLS_SSL_CHK_BUF_PTR( buf, end, CLIENT_HELLO_RAND_BYTES_LEN);
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memcpy( buf, ssl->handshake->randbytes, CLIENT_HELLO_RAND_BYTES_LEN );
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MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes",
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buf, CLIENT_HELLO_RAND_BYTES_LEN );
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buf += CLIENT_HELLO_RAND_BYTES_LEN;
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buflen -= CLIENT_HELLO_RAND_BYTES_LEN;
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/* Versions of TLS before TLS 1.3 supported a
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* "session resumption" feature which has been merged with pre-shared
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* keys in this version. A client which has a
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* cached session ID set by a pre-TLS 1.3 server SHOULD set this
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* field to that value. In compatibility mode,
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* this field MUST be non-empty, so a client not offering a
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* pre-TLS 1.3 session MUST generate a new 32-byte value. This value
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* need not be random but SHOULD be unpredictable to avoid
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* implementations fixating on a specific value ( also known as
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* ossification ). Otherwise, it MUST be set as a zero-length vector
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* ( i.e., a zero-valued single byte length field ).
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*/
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if( buflen < 1 )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small to hold ClientHello" ) );
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return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
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}
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*buf++ = 0; /* session id length set to zero */
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buflen -= 1;
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/*
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* Ciphersuite list
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*
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* This is a list of the symmetric cipher options supported by
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* the client, specifically the record protection algorithm
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* ( including secret key length ) and a hash to be used with
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* HKDF, in descending order of client preference.
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*/
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ciphersuites = ssl->conf->ciphersuite_list;
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if( buflen < 2 /* for ciphersuite list length */ )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small to hold ClientHello" ) );
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return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
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}
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/* Skip writing ciphersuite length for now */
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ciphersuite_count = 0;
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ciphersuite_start = buf;
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buf += 2;
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buflen -= 2;
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for ( size_t i = 0; ciphersuites[i] != 0; i++ )
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{
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ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( ciphersuites[i] );
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if( ciphersuite_info == NULL )
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continue;
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if( ciphersuite_info->min_minor_ver != MBEDTLS_SSL_MINOR_VERSION_4 ||
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ciphersuite_info->max_minor_ver != MBEDTLS_SSL_MINOR_VERSION_4 )
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continue;
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x, %s",
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(unsigned int) ciphersuites[i],
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ciphersuite_info->name ) );
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ciphersuite_count++;
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if( buflen < 2 /* for ciphersuite list length */ )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small to hold ClientHello" ) );
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return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
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}
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MBEDTLS_PUT_UINT16_BE( ciphersuites[i], buf, 0);
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buf += 2;
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buflen -= 2;
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}
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/* write ciphersuite length now */
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MBEDTLS_PUT_UINT16_BE( ciphersuite_count*2, ciphersuite_start, 0);
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ciphersuite_start += 2;
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MBEDTLS_SSL_DEBUG_MSG( 3,
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( "client hello, got %" MBEDTLS_PRINTF_SIZET " ciphersuites",
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ciphersuite_count ) );
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/* For every TLS 1.3 ClientHello, this vector MUST contain exactly
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* one byte set to zero, which corresponds to the 'null' compression
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* method in prior versions of TLS.
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*
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* For cTLS this field is elided.
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*/
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if( buflen < 2 /* for ciphersuite list length */ )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "buffer too small to hold ClientHello" ) );
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return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );
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}
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*buf++ = 1;
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*buf++ = MBEDTLS_SSL_COMPRESS_NULL;
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buflen -= 2;
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/* First write extensions, then the total length */
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extension_start = buf;
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total_ext_len = 0;
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buf += 2;
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/* Supported Versions Extension is mandatory with TLS 1.3.
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*
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* For cTLS we only need to provide it if there is more than one version
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* and currently there is only one.
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*/
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ret = ssl_tls13_write_supported_versions_ext( ssl, buf, end, &cur_ext_len );
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if( ret != 0 )
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return( ret );
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total_ext_len += cur_ext_len;
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buf += cur_ext_len;
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#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
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/* The supported_groups and the key_share extensions are
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* REQUIRED for ECDHE ciphersuites.
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*/
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ret = ssl_tls13_write_supported_groups_ext( ssl, buf, end, &cur_ext_len );
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if( ret != 0 )
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return( ret );
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total_ext_len += cur_ext_len;
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buf += cur_ext_len;
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/* The supported_signature_algorithms extension is REQUIRED for
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* certificate authenticated ciphersuites. */
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ret = mbedtls_ssl_tls13_write_signature_algorithms_ext( ssl, buf,
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end, &cur_ext_len );
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if( ret != 0 )
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return( ret );
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total_ext_len += cur_ext_len;
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buf += cur_ext_len;
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/* We need to send the key shares under three conditions:
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* 1 ) A certificate-based ciphersuite is being offered. In this case
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* supported_groups and supported_signature extensions have been successfully added.
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* 2 ) A PSK-based ciphersuite with ECDHE is offered. In this case the
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* psk_key_exchange_modes has been added as the last extension.
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* 3 ) Or, in case all ciphers are supported ( which includes #1 and #2 from above )
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*/
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ret = ssl_tls13_write_key_shares_ext( ssl, buf, end, &cur_ext_len );
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if( ret != 0 )
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return( ret );
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total_ext_len += cur_ext_len;
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buf += cur_ext_len;
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#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
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/* Add more extensions here */
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MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %" MBEDTLS_PRINTF_SIZET ,
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total_ext_len ) );
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MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", extension_start, total_ext_len );
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/* Write extension length */
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MBEDTLS_PUT_UINT16_BE( total_ext_len, extension_start, 0);
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extension_start += 2;
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*len_with_binders = ( extension_start + total_ext_len ) - start;
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return( 0 );
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}
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static int ssl_tls13_finalize_client_hello( mbedtls_ssl_context* ssl )
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{
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mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );
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return( 0 );
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}
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static int ssl_tls13_prepare_client_hello( mbedtls_ssl_context *ssl )
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{
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int ret;
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if( ssl->conf->f_rng == NULL )
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{
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
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return( MBEDTLS_ERR_SSL_NO_RNG );
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}
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if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
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ssl->handshake->randbytes,
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CLIENT_HELLO_RAND_BYTES_LEN ) ) != 0 )
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{
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MBEDTLS_SSL_DEBUG_RET( 1, "ssl_generate_random", ret );
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return( ret );
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}
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return( 0 );
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}
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/*
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* ClientHello Main entry point.
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* orchestrates the other functions.
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*/
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static int ssl_tls13_write_client_hello( mbedtls_ssl_context *ssl )
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{
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int ret = 0;
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unsigned char *buf;
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size_t buf_len, msg_len;
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );
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MBEDTLS_SSL_PROC_CHK( ssl_tls13_prepare_client_hello, ( ssl ) );
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MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_start_handshake_msg,
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( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
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&buf, &buf_len ) );
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MBEDTLS_SSL_PROC_CHK( ssl_tls13_write_exts_client_hello,
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( ssl, buf, buf_len, &msg_len ) );
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mbedtls_ssl_tls13_add_hs_hdr_to_checksum( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
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msg_len );
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ssl->handshake->update_checksum( ssl, buf, 0 );
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MBEDTLS_SSL_PROC_CHK( ssl_tls13_finalize_client_hello, ( ssl ) );
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MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_tls13_finish_handshake_msg,
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( ssl, buf_len, msg_len ) );
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cleanup:
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write client hello" ) );
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return ret;
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}
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int mbedtls_ssl_tls13_handshake_client_step( mbedtls_ssl_context *ssl )
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{
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int ret = 0;
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if( ssl->state == MBEDTLS_SSL_HANDSHAKE_OVER || ssl->handshake == NULL )
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{
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "Handshake completed but ssl->handshake is NULL.\n" ) );
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return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
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}
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MBEDTLS_SSL_DEBUG_MSG( 2, ( "client state: %d", ssl->state ) );
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switch( ssl->state )
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{
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/*
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* ssl->state is initialized as HELLO_REQUEST. It is same
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* with CLIENT_HELLO status
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*/
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case MBEDTLS_SSL_HELLO_REQUEST:
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case MBEDTLS_SSL_CLIENT_HELLO:
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ret = ssl_tls13_write_client_hello( ssl );
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break;
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case MBEDTLS_SSL_SERVER_HELLO:
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// Stop here : we haven't finished whole flow
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ret = MBEDTLS_ERR_SSL_FEATURE_UNAVAILABLE;
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mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_ENCRYPTED_EXTENSIONS );
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break;
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default:
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MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid state %d", ssl->state ) );
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return( MBEDTLS_ERR_SSL_BAD_INPUT_DATA );
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}
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return( ret );
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}
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#endif /* MBEDTLS_SSL_CLI_C */
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#endif /* MBEDTLS_SSL_PROTO_TLS1_3_EXPERIMENTAL */
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