Network Working Group M. Msahli, Ed.
Internet-Draft Telecom ParisTech
Intended status: Experimental N. Cam-Winget, Ed.
Expires: February 16, 2020 Cisco
August 15, 2019

TLS Authentication using IEEE 1609.2 certificate


This document specifies the use of the IEEE/ETSI certificate type to authenticate TLS entities. The goal is to enable the use of end-entity certificate specified by the IEEE and the European Telecommunications Standards Institute (ETSI). This specification defines an experimental change of TLS to support IEEE/ETSI certificate type.

Status of This Memo

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Table of Contents

1. Introduction

The TLS protocol [RFC8446] [RFC5246] uses X.509 certificates and Raw Public Key in order to authenticate servers and clients. This document describes an experimental extension following the [RFC7250] to support use of the certificate format specified by the IEEE in [IEEE1609.2] and profiled by the European Telecommunications Standards Institute (ETSI) in [TS103097]. These standards specify secure communications in vehicular environments. The certificate types are optimized for bandwidth and processing time to support delay-sensitive applications, and also to provide both authentication and authorization information to enable fast access control decisions in ad hoc networks such as are found in Intelligent Transportation Systems (ITS). The standards specify different types of certificate to support a full Public Key Infrastructure (PKI) specification; the certificates to be used in this context are end-entity certificates, i.e. certificates that have the 1609.2 appPermissions field present.

1.1. Experiment Overview

This document describes an experimental extension of TLS security model. We are using a form of certificate that has not traditionally been used in the Internet. Systems using this Experimental approach are segregated from system using standard TLS by the use of a new Certificate Type value, reserved through IANA. The implementation of TLS is not involved in the Experiment and it will not be able to interact with an Experimental implementation. In fact, an implementation of TLS can recognize that the Certificate Type value used in this document is unknown. This extension has been encouraged by stakeholders in the Cooperative ITS community including ISO internationally, and SAE in the US and ETSI in EU , in order to support the deployment of a number of use cases in cooperative ITS and it is anticipated that its use will be widespread.

2. Requirements Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174]when, and only when, they appear in all capitals, as shown here.

3. Extension Overview

  /* Managed by IANA */
   enum {
   } CertificateType;
   struct {
       select (certificate_type) {
           /* certificate type defined in this document.*/
            case 1609Dot2:
            opaque cert_data<1..2^24-1>;
            /* RawPublicKey defined in RFC 7250*/
           case RawPublicKey:
           opaque ASN.1_subjectPublicKeyInfo<1..2^24-1>;
           /* X.509 certificate defined in RFC 5246*/
           case X.509:
           opaque cert_data<1..2^24-1>;
          Extension extensions<0..2^16-1>;
      } CertificateEntry;

For TLS 1.2[RFC5246], the "extension_data" field SHALL follow the [RFC7250]. In case of TLS 1.3, the "extension_data" field SHALL contain a list of supported certificate types proposed by the client as provided in the figure below:

In case where the TLS server accepts the described extension, it selects one of the certificate types. Note that a server MAY authenticate the client using other authentication methods.

4. TLS Client and Server Handshake

  Client                                           Server

Key  ^ ClientHello
Exch | + server_certificate_type*
     | + client_certificate_type*
     | + key_share*
     v + signature_algorithms*       -------->
                                                  ServerHello  ^ Key
                                                 + key_share*  v Exch
                                        {EncryptedExtensions}  ^ Server
                                   {+ server_certificate_type*}| Params
                                   {+ client_certificate_type*}|
                                        {CertificateRequest*}  v
                                               {Certificate*}  ^
                                         {CertificateVerify*}  | Auth
                                                   {Finished}  v
                               <-------   [Application Data*]
     ^ {Certificate*}
Auth | {CertificateVerify*}
     v {Finished}              -------->
       [Application Data]      <------->   [Application Data]		
              +  Indicates noteworthy extensions sent in the
                 previously noted message.

              *  Indicates optional or situation-dependent
                 messages/extensions that are not always sent.

              {} Indicates messages protected using keys
                 derived from a [sender]_handshake_traffic_secret.

              [] Indicates messages protected using keys
                 derived from [sender]_application_traffic_secret_N.


Figure 1: Message Flow with certificate type extension for Full TLS 1.3 Handshake

The "client_certificate_type" and "server_certificate_type" extensions MUST be sent in handshake phase as illustrated in figure 1 below.

In case of TLS 1.3 and in order to negotiate the support of IEEE 1609.2 or ETSI TS 103097 certificate-based authentication, the clients and the servers MAY include the extension of type "client_certificate_type" and "server_certificate_type" in the extended Client Hello and "EncryptedExtensions". In case of TLS 1.2, used extensions are in Client Hello and Server Hello.

4.1. Client Hello

In order to indicate the support of IEEE 1609.2 or ETSI TS 103097 certificates, client MUST include an extension of type "client_certificate_type" or "server_certificate_type" in the extended Client Hello message as described in Section 4.1.2 of TLS 1.3 [RFC8446].

The extension 'client_certificate_type' sent in the Client Hello MAY carry a list of supported certificate types, sorted by client preference. It is a list in the case where the client supports multiple certificate types.

In both TLS 1.2 and 1.3, the rules if client Certificate and CertificateVerify messages appear is as follows:

All implementations SHOULD be prepared to handle extraneous certificates and arbitrary orderings from any TLS version, with the exception of the end-entity certificate which MUST be first.

4.2. Server Hello

When the server receives the Client Hello containing the client_certificate_type extension and/or the server_certificate_type extension, the following options are possible:

It is worth to mention that the TLS client or server public keys are obtained from an online repository.

5. Certificate Verification

Verification of an IEEE 1609.2/ ETSI TS 103097 certificates or certificate chain is described in section 5.1 of [IEEE1609.2]. In the case of TLS 1.3 and when the certificate_type is 1609Dot2, the CertificateVerify contents and processing are different than for the CertificateVerify message specified for other values of certificate_type in [RFC8446]. In this case, the CertificateVerify message contains a Canonical Octet Encoding Rules (COER)[ITU-TX.696] -encoded IEEE1609Dot2Data of type signed as specified in [IEEE1609.2], [IEEE1609.2b], where:

All other fields in the headerInfo are omitted.

The certificate appPermissions field shall be present and shall permit (as defined in 1609.2) signing of PDUs with the PSID indicated in the HeaderInfo of the SignedData. If the application specification for that PSID requires Service Specific Permissions (SSP) for signing a pduFunctionalType of tlsHandsahke, this SSP shall also be present.

The message input to the signature calculation is the usual message input for TLS 1.3, as specified in [RFC8446] section 4.4.3, consisting of pad, context string, separator and content, where content is Transcript- Hash(Handshake Context, Certificate).

The signature and verification are carried out as specified in [IEEE1609.2].

6. Examples

Some of exchanged messages examples are illustrated in Figures 2 and 3.

6.1. TLS Server and TLS Client use the 1609Dot2 Certificate

   Client                                           Server

server_certificate_type=1609Dot2,   -------->     ServerHello,
  {Certificate}           <-------          [Application Data]
  {Finished}              --------> 
  [Application Data]      <------->         [Application Data]		

Figure 2: TLS Client and TLS Server use the IEEE 1609.2 certificate

This section shows an example where the TLS client as well as the TLS server use the IEEE 1609.2 certificate. In consequence, both the server and the client populate the client_certificate_type and server_certificate_type with extension IEEE 1609.2 certificates as mentioned in figure 2.

6.2. TLS Client uses the IEEE 1609.2 certificate and TLS Server uses the X.509 certificate

Client                                           Server
X509,RawPublicKey),         ----------->         ServerHello,
                            <---------     [Application Data]
{Finished}                  --------->
[Application Data]          <-------->     [Application Data]		

Figure 3: TLS Client uses the IEEE 1609.2 certificate and TLS Server uses the X.509 certificate

This example shows the TLS authentication, where the TLS Client populates the server_certificate_type extension with the X.509 certificate and Raw Public Key type as presented in figure 3. the client indicates its ability to receive and to validate an X.509 certificate from the server. The server chooses the X.509 certificate to make its authentication with the Client.

7. Security Considerations

This section provides an overview of the basic security considerations which need to be taken into account before implementing the necessary security mechanisms. The security considerations described throughout [RFC8446] regarding the supported groups and signature algorithms apply here as well.

TLS extensions to be considered are:

This specification does not address the security of online repository.

8. Privacy Considerations

For privacy considerations in a vehicular environment the use of IEEE 1609.2/ETSI TS 103097 certificate is recommended for many reasons:

9. IANA Considerations

IANA is requested to update the registry to reference the RFC: to point to this document.

10. Acknowledgements

The authors wish to thank Eric Rescola , Russ Housley and Ilari Liusvaara for their feedback and suggestions on improving this document. Thanks are due to Sean Turner for his valuable and detailed comments. Special thanks to Panos Kampanakis, Jasja Tijink and Maik Seewald for their guidance and support of the draft.

11. Normative References

[IEEE1609.2] "IEEE Standard for Wireless Access in Vehicular Environments - Security Services for Applications and Management Messages", 2016.
[IEEE1609.2b] "IEEE Standard for Wireless Access in Vehicular Environments--Security Services for Applications and Management Messages - Amendment 2--PDU Functional Types and Encryption Key Management", 2019.
[ITU-TX.696] , INTERNATIONAL., "Procedures for the operation of object identifier registration authorities: General procedures and top arcs of the international object identifier tree", July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", August 2008.
[RFC7250] Wouters, P., Tschofenig, H., Weiler, S. and T. Kivinen, "Using Raw Public Keys in Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)", June 2014.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", May 2017.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", August 2018.
[TS103097] "ETSI TS 103 097 : Intelligent Transport Systems (ITS); Security; Security header and certificate formats"

Appendix A. Contributors

Authors' Addresses

Mounira Msahli (editor) Telecom ParisTech France EMail:
Nancy Cam-Winget (editor) Cisco USA EMail: