CEN ISO/TS 21177:2019

SLOVENSKI STANDARD
01-december-2019
Inteligentni transportni sistemi - Storitve varovanja postaj ITS za varno
vzpostavitev sej in preverjanje pristnosti med zaupanja vrednimi napravami
(ISO/TS 21177:2019)
Intelligent transport systems - ITS station security services for secure session
establishment and authentication between trusted devices (ISO/TS 21177:2019)
Intelligente Verkehrssysteme - Sicherheitsdienste für eine ITS-Station zum sicheren
Aufbau und Authentizierung einer Sitzung zwischen zuverlässigen Geräten (ISO/TS
21177:2019)
Systèmes intelligents de transport - Interface véhicule sécurisée - Services de sécurité
de la station ITS pour l'établissement et l'authentification des sessions sécurisées
(ISO/TS 21177:2019)
Ta slovenski standard je istoveten z: CEN ISO/TS 21177:2019
ICS:
03.220.01 Transport na splošno Transport in general
35.030 Informacijska varnost IT Security
35.240.60 Uporabniške rešitve IT v IT applications in transport
prometu
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TS 21177
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
October 2019
TECHNISCHE SPEZIFIKATION
ICS 03.220.01; 35.030; 35.240.60
English Version
Intelligent transport systems - ITS station security services
for secure session establishment and authentication
between trusted devices (ISO/TS 21177:2019)
Systèmes intelligents de transport - Interface véhicule Intelligente Verkehrssysteme - Sicherheitsdienste für
sécurisée - Services de sécurité de la station ITS pour eine ITS-Station zum sicheren Aufbau und
l'établissement et l'authentification des sessions Authentizierung einer Sitzung zwischen zuverlässigen
sécurisées (ISO/TS 21177:2019) Geräten (ISO/TS 21177:2019)
This Technical Specification (CEN/TS) was approved by CEN on 13 August 2019 for provisional application.

The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.

CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TS 21177:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (CEN ISO/TS 21177:2019) has been prepared by Technical Committee ISO/TC 204
"Intelligent transport systems" in collaboration with Technical Committee CEN/TC 278 “Intelligent
transport systems” the secretariat of which is held by NEN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO/TS 21177:2019 has been approved by CEN as CEN ISO/TS 21177:2019 without any
modification.
TECHNICAL ISO/TS
SPECIFICATION 21177
First edition
2019-08
Intelligent transport systems —
ITS station security services for
secure session establishment and
authentication between trusted devices
Reference number
ISO/TS 21177:2019(E)
©
ISO 2019
ISO/TS 21177:2019(E)
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO/TS 21177:2019(E)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Overview . 3
5.1 Goals . 3
5.2 Architecture and functional entities . 4
5.3 Cryptomaterial handles . 7
5.4 Session IDs and state . 7
5.5 Access control and authorisation state . 8
5.6 Application level non-repudiation . 8
5.7 Service primitive conventions . 8
6 Process flows and sequence diagrams . 9
6.1 General . 9
6.2 Overview of process flows . 9
6.3 Sequence diagram conventions .10
6.4 Configure .11
6.5 Start Session .12
6.6 Send data .14
6.7 Send access control PDU .17
6.8 Receive PDU .18
6.9 Secure connection brokering .23
6.9.1 Goals .23
6.9.2 Prerequisites .24
6.9.3 Overview .24
6.9.4 Detailed specification .25
6.10 Force end session .33
6.11 Session terminated at session layer .35
6.12 Deactivate .35
6.13 Secure session example .36
7 Security Subsystem: interfaces and data types .38
7.1 General .38
7.2 Access control policy and state .39
7.3 Enhanced authentication .40
7.3.1 Definition and possible states .40
7.3.2 States for owner role enhanced authentication .40
7.3.3 State for accessor role enhanced authentication .41
7.3.4 Use by Access Control .42
7.3.5 Methods for providing enhanced authentication .42
7.3.6 Enhanced authentication using SPAKE2 .42
7.4 Extended authentication .43
7.5 Data types .44
7.5.1 General.44
7.5.2 Imports .44
7.5.3 Iso21177AccessControlPdu .44
7.5.4 AccessControlResult .44
7.5.5 ExtendedAuthPdu .44
7.5.6 ExtendedAuthRequest .45
7.5.7 InnerExtendedAuthRequest .45
7.5.8 AtomicExtendedAuthRequest .46
ISO/TS 21177:2019(E)
7.5.9 ExtendedAuthResponse .46
7.5.10 ExtendedAuthResponsePayload .46
7.5.11 EnhancedAuthPdu .47
7.5.12 SpakeRequest.47
7.5.13 SpakeResponse .47
7.5.14 SpakeRequesterResponse .48
7.6 App-Sec Interface .48
7.6.1 App-Sec-Configure.request .48
7.6.2 App-Sec-Configure.confirm.49
7.6.3 App-Sec-StartSession.indication .49
7.6.4 App-Sec-Data.request .50
7.6.5 App-Sec-Data.confirm . .50
7.6.6 App-Sec-Incoming.request .51
7.6.7 App-Sec-Incoming.confirm .51
7.6.8 App-Sec-EndSession.request .52
7.6.9 App-Sec-EndSession.confirm .52
7.6.10 App-Sec-EndSession.indication.52
7.6.11 App-Sec-Deactivate.request .53
7.6.12 App-Sec-Deactivate.confirm .53
7.6.13 App-Sec-Deactivate.indication .53
7.7 Security Subsystem internal interface .54
7.7.1 General.54
7.7.2 Sec-AuthState.request .54
7.7.3 Sec-AuthState.confirm . .55
8 Adaptor Layer: Interfaces and data types .55
8.1 General .55
8.2 Data types .56
8.2.1 General.56
8.2.2 Iso21177AdaptorLayerPDU .56
8.2.3 Apdu . .57
8.2.4 Access Control .57
8.2.5 TlsClientMsg1 .57
8.2.6 TlsServerMsg1 .57
8.3 App-AL Interface .57
8.3.1 App-AL-Data.request .57
8.3.2 App-AL-Data.confirm .58
8.3.3 App-AL-Data.indication .58
8.3.4 App-AL-EnableProxy.request .59
8.4 Sec-AL Interface .61
8.4.1 Sec-AL-AccessControl.request.61
8.4.2 Sec-AL-AccessControl.confirm .61
8.4.3 Sec-AL-AccessControl.indication .61
8.4.4 Sec-AL-EndSession.request .62
8.4.5 Sec-AL-EndSession.confirm.62
9 Secure Session services .62
9.1 General .62
9.2 App-Sess interfaces .62
9.2.1 App-Sess-EnableProxy.request .62
9.3 Sec-Sess interface .63
9.3.1 Sec-Sess-Configure.request .63
9.3.2 Sec-Sess-Configure.confirm .65
9.3.3 Sec-Sess-Start.indication .65
9.3.4 Sec-Sess-EndSession.indication .66
9.3.5 Sec-Sess-Deactivate.request .66
9.3.6 Sec-Sess-Deactivate.confirm .67
9.4 AL-Sess interface .67
9.4.1 AL-Sess-Data.request .67
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ISO/TS 21177:2019(E)
9.4.2 AL-Sess-Data.confirm.67
9.4.3 AL-Sess-Data.indication .68
9.4.4 AL-Sess-EndSession.request .68
9.4.5 AL-Sess-EndSession.confirm .68
9.4.6 AL-Sess-ClientHelloProxy.request .69
9.4.7 AL-Sess-ClientHelloProxy.indication .69
9.4.8 AL-Sess-ServerHelloProxy.request .70
9.4.9 AL-Sess-ServerHelloProxy.indication .70
9.4.10 AL-Sess-EndSession.request .71
9.4.11 AL-Sess-EndSession.confirm .72
9.5 Permitted mechanisms .72
9.5.1 TLS 1.3 .72
9.5.2 DTLS 1.3.73
Annex A (informative) Usage scenarios .74
Annex B (normative) ASN.1 module .81
Bibliography .82
ISO/TS 21177:2019(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 204, Intelligent transport systems.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
vi © ISO 2019 – All rights reserved

ISO/TS 21177:2019(E)
Introduction
This document is about ITS station security services required to ensure the authenticity of the source
and confidentiality and integrity of application activities taking place between trusted devices.
The trust relation between two devices is illustrated in Figure 1. Two devices cooperate in a trusted
way, i.e. exchange information with optional explicit bi-directional protection.
Figure 1 — Interconnection of trusted devices
According to ISO 21217, an ITS station unit (ITS-SU), i.e. the physical implementation of the ITS station
(ITS-S) functionality, is a trusted device, and an ITS-SU may be composed of ITS station communication
units (ITS-SCU) that are interconnected via an ITS station-internal network. Thus an ITS-SCU is the
smallest physical entity of an ITS-SU that is referred to as a trusted device.
[15]
NOTE 1 ISO 21217 fully covers the functionality of EN 302 665 , which is a predecessor of ISO 21217.
NOTE 2 An ITS-SU can be composed of ITS-SCUs from different vendors where each ITS-SCU is linked to a
[5]
different ITS-SCU configuration and management centre specified in ISO 24102-2 and ISO 17419. Station-
[7]
internal management communications between ITS-SCUs of the same ITS-SU is specified in ISO 24102-4 .
European C-ITS regulation refers to the "ITS-SCU configuration and management centre" as "C-ITS station
operator" meaning the entity responsible for the operation of a C-ITS station. The C-ITS station operator can be
responsible for the operation of one single C-ITS station (fixed or mobile), or a C-ITS infrastructure composed of a
number of fixed C-ITS stations, or a number of mobile ITS-Stations.
Four implementation contexts of communication nodes in ITS communications networks are identified
in the ITS station and communication architecture ISO 21217, each comprised of ITS-station units (ITS-
SU) taking on a particular role; personal, vehicular, roadside, or central. These ITS-SUs are ITS-secured
communication nodes as required in ISO 21217 that participate in a wide variety of ITS services related
to, e.g. sustainability, road safety and transportation efficiency.
Over the last decade, ITS services have arisen that require secure access to data from Sensor and Control
Networks (SCN), e.g. from In-Vehicle Networks (IVN) and from Infrastructure/Roadside Networks
(IRN), some of which require secure local access to time-critical information; see Figures 2 and 3.
ISO/TS 21177:2019(E)
Figure 2 — Example of a roadside ITS-SU connected with proprietary IRN
Figure 3 — Example of a vehicle ITS-SU connected with proprietary IRN
Trust in the ITS domain primarily is between ITS Station Communication Units (ITS-SCUs) introduced
in ISO 21217; see Figure 4.
viii © ISO 2019 – All rights reserved

ISO/TS 21177:2019(E)
Figure 4 — Interconnection of ITS-SCUs in an ITS-SU
ITS-SCUs are interconnected via an ITS station-internal network. Applying basic security means
specified in this document, the ITS-SCUs trust each other. Additionally, protocol data units exchanged
between ITS-SCUs may be further protected by additional means, e.g. applying encryption. Major
application domains of secure communications between ITS-SCUs of the same ITS-SU are local station
[4]
management specified in ISO 24102-1 using station-internal management communications specified
[7]
in ISO 24102-4 .
Trust in the ITS domain further is between ITS-SUs introduced in ISO 21217; see Figure 5.
Figure 5 — Interconnection of ITS-SUs
Applying basic security means specified in this document, the ITS-SUs can establish secure application
sessions. Establishment of sessions either needs a-priori knowledge about a session partner or can
[3]
be achieved by means of service announcement specified in ISO 22418 . Further on, broadcast of
messages is secured by means of authenticating the sender of such a message, applicable for the service
[1] [3]
advertisement message (SAM) specified in ISO/TS 16460 and used in ISO 22418 . Additionally, other
security means may be applied, e.g. encryption of messages.
A further trust relation in the ITS domain is between an ITS-SU consisting of one or several ITS-SCUs
and a sensor and control network (SCN). Trust is achieved by applying security means in an interface as
illustrated in Figure 6 with details specified in this document.
ISO/TS 21177:2019(E)
Figure 6 — Interface between ITS-SU and sensor and control network
The interface presented in Figure 6 may be a stand-alone device, or may be integrated in the ITS-SU,
or may be part of the SCN. Examples of SCNs are "In-Vehicle Networks" (IVN) and "Infrastructure/
Roadside Networks" (IRN).
Related use cases of these ITS services have largely been derived from regulatory requirements and ITS
operational needs, and they include:
— secure real-time access to time-critical vehicle-related data for safety of life and property
applications, e.g. collision avoidance, emergency electronic brake light and event determination;
— secure local access to detailed real-time data for efficiency applications (traffic management), e.g.
intersection interaction, congestion avoidance, dynamic priorities;
— protection of private data, e.g. in compliance with the European "General Data Protection Regulation"
[16]
(GDPR) ;
— local access to certified real-time data for sustainability applications, e.g. dynamic emission zones
(controlled zones as currently standardized in CEN TC 278 within the Project Team PT 1705 funded
by the European Commission), intersection priorities based on emissions, interactive optimum
vehicle settings to minimize fuel consumption.
There are many use cases of ITS services currently identified where real-time exchange of time-critical
information between ITS-SUs in close proximity is essential, and the number will grow, see e.g. the US
[17]
National ITS Reference Architecture . It is critical that ultimately all ITS-SUs in a given area are able
to be engaged in these distributed services. This, in turn, requires vehicle ITS-SUs to have real-time
access to vehicle data, and roadside ITS-SUs to have real-time access to infrastructure data. All ITS-SUs
need being capable of secure software updates.
According to ISO 21217, an ITS-SCU of an ITS-SU can communicate with devices that, in a strict sense,
are not compliant with the architecture specified in ISO 21217. However, in order to have trusted
communications, a certain minimum level of security measures must be shared between an ITS-SCU
and such an external device. Examples of such external devices are a node in the Internet, or a node in a
sensor and control network. In this document, the assumption is made that ITS-S application processes
operating on ITS-SUs are issued with certificates by a Certificate Authority (CA), and that the CA is a
trusted third party in the sense that before issuing the certificate to the ITS-S application process, it
ensures that the ITS-SU on which the ITS-S application process is resident meets the minimum security
requirements for that application. This allows peer ITS-S application processes which observe that
an ITS-S application process possesses a valid certificate to have a level of assurance that the ITS-S
application process is in fact secure and trustworthy.
x © ISO 2019 – All rights reserved

ISO/TS 21177:2019(E)
The subject of this document thus is three-fold:
1) Specify ITS station security services for enabling trust between ITS-S application processes
running on different ITS-SCUs of the same ITS-SU, i.e. establishing a trusted processing platform,
considering also trust inside an ITS-SCU:
— protection of applications from the actions of other applications;
— protection of shared information;
— protection of shared processing resources such as communications software and hardware,
which includes methods of prioritisation and restricted access.
2) Specify ITS station security services for enabling trust between ITS-S application processes
running on the same ITS-SU.
3) Extend these ITS security services for enabling trust between an ITS-SCU and devices being part of
a sensor and control network.
NOTE 3 It is intended to extend the subject of this document in future editions.
Such security services include e.g. the basic security features of:
a) authentication and authorisation;
b) confidentiality and privacy;
c) data integrity;
d) non-repudiation.
Tasks related to communications are:
a) establishing secure sessions for bi-directional communications, e.g. based on service advertisement
[3]
specified in ISO 22418 ;
b) authenticating a sender of broadcast messages, e.g. CAM, DENM, BSM, SPaT, MAP, FSAM, WSA;
c) encrypting messages.
NOTE 4 Tasks b) and c) above related to communications are already specified in other standards, see e.g.
IEEE Std. 1609.2™ and several related standards from ETSI TC ITS.
TECHNICAL SPECIFICATION ISO/TS 21177:2019(E)
Intelligent transport systems — ITS station security
services for secure session establishment and
authentication between trusted devices
1 Scope
This document contains specifications for a set of ITS station security services required to ensure the
authenticity of the source and integrity of information exchanged between trusted entities:
— devices operated as bounded secured managed entities, i.e. "ITS Station Communication Units"
(ITS-SCU) and "ITS station units" (ITS-SU) specified in ISO 21217, and
— between ITS-SUs (composed of one or several ITS-SCUs) and external trusted entities such as sensor
and control networks.
These services include authentication and secure session establishment which are required to exchange
information in a trusted and secure manner.
These services are essential for many ITS applications and services including time-critical safety
[5]
applications, automated driving, remote management of ITS stations (ISO 24102-2 ), and roadside/
infrastructure related services.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 17419, Intelligent transport systems — Cooperative systems — Globally unique identification
IEEE Std 1609.2™, IEEE Standard for Wireless Access in Vehicular Environments — Security Services for
Applications and Management Messages
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
Access Control PDU
PDU generated by the Security Subsystem for purposes of establishing the authorisation status of a
peer ITS-S application process
3.2
Access Control Policy
data source governing what access to resources is permissible by peer Applications
ISO/TS 21177:2019(E)
3.3
application
functional entity, i.e. an ITS-S application process
3.4
security subsystem
functional entity providing security functionality for use by an ITS-S application process
3.5
Security Adaptor Layer
functional entity providing multiplexing and demultiplexing functionality for data and session control
commands
3.6
Secure Session
functional entity providing confidentiality, integrity, authentication, guaranteed in-order delivery, and
replay protection on the datagrams that are passed over it
3.7
resources
functional entity constituting endpoints of ITS-S application process activity
3.8
Cryptomaterial Handle
reference to Cryptomaterial allowing that Cryptomaterial to be used in cryptographic operations, i.e.
sign, verify, encrypt, decrypt
3.9
Cryptomaterial
cryptographic keys and associated material, either a secret key for a symmetric algorithm, or a private
key for an asymmetric algorithm, and the associated public key or certificate
3.10
Secure Session Service
functional entity responsible for establishing secure communications sessions with its peer instances
4 Symbols and abbreviated terms
ACK acknowledge
ALPDU adaptor layer PDU
...