library/ssl_client.c

/*
 *  TLS 1.2 and 1.3 client-side functions
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of mbed TLS ( https://tls.mbed.org )
 */

#include "common.h"

#if defined(MBEDTLS_SSL_CLI_C)
#if defined(MBEDTLS_SSL_PROTO_TLS1_3) || defined(MBEDTLS_SSL_PROTO_TLS1_2)

#include <string.h>

#include "mbedtls/debug.h"
#include "mbedtls/error.h"
#include "mbedtls/platform.h"

#include "ssl_client.h"
#include "ssl_misc.h"
#include "ecdh_misc.h"
#include "ssl_tls13_keys.h"
#include "ssl_debug_helpers.h"

#if defined(MBEDTLS_SSL_ALPN)
/*
 * ssl_write_alpn_ext()
 *
 * Structure of the application_layer_protocol_negotiation extension in
 * ClientHello:
 *
 * opaque ProtocolName<1..2^8-1>;
 *
 * struct {
 *     ProtocolName protocol_name_list<2..2^16-1>
 * } ProtocolNameList;
 *
 */
static int ssl_write_alpn_ext( mbedtls_ssl_context *ssl,
                               unsigned char *buf,
                               const unsigned char *end,
                               size_t *out_len )
{
    unsigned char *p = buf;

    *out_len = 0;

    if( ssl->conf->alpn_list == NULL )
        return( 0 );

    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, adding alpn extension" ) );


    /* Check we have enough space for the extension type (2 bytes), the
     * extension length (2 bytes) and the protocol_name_list length (2 bytes).
     */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 6 );
    MBEDTLS_PUT_UINT16_BE( MBEDTLS_TLS_EXT_ALPN, p, 0 );
    /* Skip writing extension and list length for now */
    p += 6;

    /*
     * opaque ProtocolName<1..2^8-1>;
     *
     * struct {
     *     ProtocolName protocol_name_list<2..2^16-1>
     * } ProtocolNameList;
     */
    for( const char **cur = ssl->conf->alpn_list; *cur != NULL; cur++ )
    {
        /*
         * mbedtls_ssl_conf_set_alpn_protocols() checked that the length of
         * protocol names is less than 255.
         */
        size_t protocol_name_len = strlen( *cur );

        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 + protocol_name_len );
        *p++ = (unsigned char)protocol_name_len;
        memcpy( p, *cur, protocol_name_len );
        p += protocol_name_len;
    }

    *out_len = p - buf;

    /* List length = *out_len - 2 (ext_type) - 2 (ext_len) - 2 (list_len) */
    MBEDTLS_PUT_UINT16_BE( *out_len - 6, buf, 4 );

    /* Extension length = *out_len - 2 (ext_type) - 2 (ext_len) */
    MBEDTLS_PUT_UINT16_BE( *out_len - 4, buf, 2 );

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

/* Write cipher_suites
 * CipherSuite cipher_suites<2..2^16-2>;
 */
static int ssl_write_client_hello_cipher_suites(
            mbedtls_ssl_context *ssl,
            unsigned char *buf,
            unsigned char *end,
            size_t *out_len )
{
    unsigned char *p = buf;
    const int *ciphersuite_list;
    unsigned char *cipher_suites; /* Start of the cipher_suites list */
    size_t cipher_suites_len;

    *out_len = 0 ;

    /*
     * Ciphersuite list
     *
     * This is a list of the symmetric cipher options supported by
     * the client, specifically the record protection algorithm
     * ( including secret key length ) and a hash to be used with
     * HKDF, in descending order of client preference.
     */
    ciphersuite_list = ssl->conf->ciphersuite_list;

    /* Check there is space for the cipher suite list length (2 bytes). */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
    p += 2;

    /* Write cipher_suites */
    cipher_suites = p;
    for ( size_t i = 0; ciphersuite_list[i] != 0; i++ )
    {
        int cipher_suite = ciphersuite_list[i];
        const mbedtls_ssl_ciphersuite_t *ciphersuite_info;

        ciphersuite_info = mbedtls_ssl_ciphersuite_from_id( cipher_suite );
        if( ciphersuite_info == NULL )
            continue;
        if( !( MBEDTLS_SSL_MINOR_VERSION_4 >= ciphersuite_info->min_minor_ver &&
               MBEDTLS_SSL_MINOR_VERSION_4 <= ciphersuite_info->max_minor_ver ) )
            continue;

        MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, add ciphersuite: %04x, %s",
                                    (unsigned int) cipher_suite,
                                    ciphersuite_info->name ) );

        /* Check there is space for the cipher suite identifier (2 bytes). */
        MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
        MBEDTLS_PUT_UINT16_BE( cipher_suite, p, 0 );
        p += 2;
    }

    /* Write the cipher_suites length in number of bytes */
    cipher_suites_len = p - cipher_suites;
    MBEDTLS_PUT_UINT16_BE( cipher_suites_len, buf, 0 );
    MBEDTLS_SSL_DEBUG_MSG( 3,
                           ( "client hello, got %" MBEDTLS_PRINTF_SIZET " cipher suites",
                             cipher_suites_len/2 ) );

    /* Output the total length of cipher_suites field. */
    *out_len = p - buf;

    return( 0 );
}

/*
 * Structure of the TLS 1.3 ClientHello message:
 *
 *    struct {
 *        ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
 *        Random random;
 *        opaque legacy_session_id<0..32>;
 *        CipherSuite cipher_suites<2..2^16-2>;
 *        opaque legacy_compression_methods<1..2^8-1>;
 *        Extension extensions<8..2^16-1>;
 *    } ClientHello;
 *
 * Structure of the (D)TLS 1.2 ClientHello message:
 *
 * struct {
 *     ProtocolVersion client_version;
 *     Random random;
 *     SessionID session_id;
 *     opaque cookie<0..2^8-1>; // DTLS 1.2 ONLY
 *     CipherSuite cipher_suites<2..2^16-2>;
 *     CompressionMethod compression_methods<1..2^8-1>;
 *     select (extensions_present) {
 *         case false:
 *             struct {};
 *         case true:
 *             Extension extensions<0..2^16-1>;
 *     };
 * } ClientHello;
 */
static int ssl_write_client_hello_body( mbedtls_ssl_context *ssl,
                                        unsigned char *buf,
                                        unsigned char *end,
                                        size_t *out_len )
{

    int ret;
    unsigned char *p_extensions_len; /* Pointer to extensions length */
    size_t output_len;               /* Length of buffer used by function */
    size_t extensions_len;           /* Length of the list of extensions*/

    /* Buffer management */
    unsigned char *p = buf;

    *out_len = 0;

    /* No validation needed here. It has been done by ssl_conf_check() */
    ssl->major_ver = ssl->conf->min_major_ver;
    ssl->minor_ver = ssl->conf->min_minor_ver;

    /*
     * Write legacy_version
     *    ProtocolVersion legacy_version = 0x0303;    // TLS v1.2
     *
     *  For TLS 1.3 we use the legacy version number {0x03, 0x03}
     *  instead of the true version number.
     */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
    MBEDTLS_PUT_UINT16_BE( 0x0303, p, 0 );
    p += 2;

    /* Write the random bytes ( random ).*/
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
    memcpy( p, ssl->handshake->randbytes, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello, random bytes",
                           p, MBEDTLS_CLIENT_HELLO_RANDOM_LEN );
    p += MBEDTLS_CLIENT_HELLO_RANDOM_LEN;

    /*
     * Write legacy_session_id
     *
     * Versions of TLS before TLS 1.3 supported a "session resumption" feature
     * which has been merged with pre-shared keys in this version. A client
     * which has a cached session ID set by a pre-TLS 1.3 server SHOULD set
     * this field to that value. In compatibility mode, this field MUST be
     * non-empty, so a client not offering a pre-TLS 1.3 session MUST generate
     * a new 32-byte value. This value need not be random but SHOULD be
     * unpredictable to avoid implementations fixating on a specific value
     * ( also known as ossification ). Otherwise, it MUST be set as a zero-length
     * vector ( i.e., a zero-valued single byte length field ).
     */
#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, ssl->session_negotiate->id_len + 1 );
    *p++ = (unsigned char)ssl->session_negotiate->id_len;
    memcpy( p, ssl->session_negotiate->id, ssl->session_negotiate->id_len );
    p += ssl->session_negotiate->id_len;

    MBEDTLS_SSL_DEBUG_BUF( 3, "session id", ssl->session_negotiate->id,
                              ssl->session_negotiate->id_len );
#else
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 1 );
    *p++ = 0; /* session id length set to zero */
#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */

    /* Write cipher_suites */
    ret = ssl_write_client_hello_cipher_suites( ssl, p, end, &output_len );
    if( ret != 0 )
        return( ret );
    p += output_len;

    /* Write legacy_compression_methods
     *
     * For every TLS 1.3 ClientHello, this vector MUST contain exactly
     * one byte set to zero, which corresponds to the 'null' compression
     * method in prior versions of TLS.
     */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
    *p++ = 1;
    *p++ = MBEDTLS_SSL_COMPRESS_NULL;

    /* Write extensions */

#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
    /* Keeping track of the included extensions */
    ssl->handshake->extensions_present = MBEDTLS_SSL_EXT_NONE;
#endif

    /* First write extensions, then the total length */
    MBEDTLS_SSL_CHK_BUF_PTR( p, end, 2 );
    p_extensions_len = p;
    p += 2;

#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
    ret = mbedtls_ssl_tls13_write_client_hello_exts( ssl, p, end, &output_len );
    if( ret != 0 )
        return( ret );
    p += output_len;
#endif

#if defined(MBEDTLS_SSL_ALPN)
    ret = ssl_write_alpn_ext( ssl, p, end, &output_len );
    if( ret != 0 )
        return( ret );
    p += output_len;
#endif /* MBEDTLS_SSL_ALPN */

#if defined(MBEDTLS_SSL_PROTO_TLS1_3)
#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
    if( mbedtls_ssl_conf_tls13_some_ephemeral_enabled( ssl ) )
    {
        ret = mbedtls_ssl_write_supported_groups_ext( ssl, p, end, &output_len );
        if( ret != 0 )
            return( ret );
        p += output_len;
    }

    if( mbedtls_ssl_conf_tls13_ephemeral_enabled( ssl ) )
    {
        ret = mbedtls_ssl_write_sig_alg_ext( ssl, p, end, &output_len );
        if( ret != 0 )
            return( ret );
        p += output_len;
    }
#endif /* MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
#endif /* MBEDTLS_SSL_PROTO_TLS1_3 */

#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
    /* Write server name extension */
    ret = mbedtls_ssl_write_hostname_ext( ssl, p, end, &output_len );
    if( ret != 0 )
        return( ret );
    p += output_len;
#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */

    /* Add more extensions here */

    /* Write the length of the list of extensions. */
    extensions_len = p - p_extensions_len - 2;
    MBEDTLS_PUT_UINT16_BE( extensions_len, p_extensions_len, 0 );
    MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, total extension length: %" MBEDTLS_PRINTF_SIZET ,
                                extensions_len ) );
    MBEDTLS_SSL_DEBUG_BUF( 3, "client hello extensions", p_extensions_len, extensions_len );

    *out_len = p - buf;
    return( 0 );
}

static int ssl_prepare_client_hello( mbedtls_ssl_context *ssl )
{
    int ret;

    if( ssl->conf->f_rng == NULL )
    {
        MBEDTLS_SSL_DEBUG_MSG( 1, ( "no RNG provided" ) );
        return( MBEDTLS_ERR_SSL_NO_RNG );
    }

    if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
                                  ssl->handshake->randbytes,
                                  MBEDTLS_CLIENT_HELLO_RANDOM_LEN ) ) != 0 )
    {
        MBEDTLS_SSL_DEBUG_RET( 1, "f_rng", ret );
        return( ret );
    }

#if defined(MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE)
    /*
     * Create a session identifier for the purpose of middlebox compatibility
     * only if one has not been created already.
     */
    if( ssl->session_negotiate->id_len == 0 )
    {
        /* Creating a session id with 32 byte length */
        if( ( ret = ssl->conf->f_rng( ssl->conf->p_rng,
                                      ssl->session_negotiate->id, 32 ) ) != 0 )
        {
            MBEDTLS_SSL_DEBUG_RET( 1, "creating session id failed", ret );
            return( ret );
        }
        ssl->session_negotiate->id_len = 32;
    }
#endif /* MBEDTLS_SSL_TLS1_3_COMPATIBILITY_MODE */

    return( 0 );
}

/*
 * Write ClientHello handshake message.
 * Handler for MBEDTLS_SSL_CLIENT_HELLO
 */
int mbedtls_ssl_write_client_hello( mbedtls_ssl_context *ssl )
{
    int ret = 0;
    unsigned char *buf;
    size_t buf_len, msg_len;

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> write client hello" ) );

    MBEDTLS_SSL_PROC_CHK( ssl_prepare_client_hello( ssl ) );

    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_start_handshake_msg(
                                ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
                                &buf, &buf_len ) );

    MBEDTLS_SSL_PROC_CHK( ssl_write_client_hello_body( ssl, buf,
                                                       buf + buf_len,
                                                       &msg_len ) );

    mbedtls_ssl_add_hs_msg_to_checksum( ssl, MBEDTLS_SSL_HS_CLIENT_HELLO,
                                        buf, msg_len );

    MBEDTLS_SSL_PROC_CHK( mbedtls_ssl_finish_handshake_msg( ssl,
                                                            buf_len,
                                                            msg_len ) );

    mbedtls_ssl_handshake_set_state( ssl, MBEDTLS_SSL_SERVER_HELLO );

cleanup:

    MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= write client hello" ) );
    return ret;
}

#endif /* MBEDTLS_SSL_PROTO_TLS1_3 || MBEDTLS_SSL_PROTO_TLS1_2 */
#endif /* MBEDTLS_SSL_CLI_C */