EN ISO 21177:2024

Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices (ISO 21177:2024)

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, i.e.:
—     between devices operated as bounded secured managed entities, i.e. "ITS Station Communication Units" (ITS-SCU) and "ITS station units" (ITS-SU) as 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 the authentication and secure session establishment which are required to exchange information in a trusted and secure manner.
These services are essential for many intelligent transport system (ITS) applications and services, including time-critical safety applications, automated driving, remote management of ITS stations (ISO 24102-2), and roadside/infrastructure-related services.

Intelligente Verkehrssysteme - Sicherheitsdienste für eine ITS-Station zum sicheren Aufbau von Sitzungen und zur Authentisierung zwischen vertrauenswürdigen Geräten (ISO 21177:2024)

Systèmes de transport intelligents - Services de sécurité des stations ITS pour l’établissement et l’authentification des sessions sécurisées entre dispositifs de confiance (ISO 21177:2024)

Le présent document contient les spécifications d'un ensemble de services de sécurité des stations ITS nécessaires pour garantir l'authenticité de la source et l'intégrité des informations échangées entre des entités de confiance, c'est-à-dire:
—     entre des dispositifs exploités en tant qu'entités délimitées gérées de manière sécurisée, c'est-à-dire les «unités de communication de station ITS» (ITS-SCU) et les «unités de station ITS» (ITS-SU) comme spécifié dans l'ISO 21217; et
—     entre les ITS-SU (composées d'une ou plusieurs ITS-SCU) et les entités de confiance externes telles que les réseaux de capteurs et de contrôle.
Ces services comprennent l'authentification et l'établissement de sessions sécurisées, nécessaires pour échanger des informations dans le cadre d'une relation de confiance et de manière sécurisée.
Ces services sont essentiels pour de nombreux services et applications de systèmes de transport intelligents (ITS), notamment les applications de sécurité revêtant un caractère d'urgence, la conduite automatisée, la gestion à distance des stations ITS (ISO 24102-2), et les services routiers liés aux infrastructures.

Inteligentni transportni sistemi - Storitve varovanja postaj ITS za varno vzpostavitev sej in preverjanje pristnosti med zaupanja vrednimi napravami (ISO 21177:2024)

Ta dokument vsebuje specifikacije za storitve varovanja postaj ITS, ki so potrebne za zagotovitev verodostojnosti vira in celovitosti informacij, izmenjanih med zaupanja vrednimi enotami, tj.:
–    med napravami, ki delujejo kot omejene varovane upravljane enote, tj. »komunikacijske enote postaj ITS« (ITS-SCU) in »enote postaj ITS« (ITS-SU), kot je določeno v standardu ISO 21217, ter
–    med enotami postaj ITS (sestavljenimi iz ene ali več komunikacijskih enot postaj ITS) ter zunanjimi zaupanja vrednimi enotami, kot so senzorska in nadzorna omrežja.
Te storitve vključujejo preverjanje pristnosti in varno vzpostavitev seje, ki sta potrebna za zaupno in varno izmenjavo informacij.
Te storitve so bistvene za številne aplikacije in storitve inteligentnih transportnih sistemov (ITS), vključno s časovno kritičnimi varnostnimi aplikacijami, samodejno vožnjo, daljinskim upravljanjem postaj ITS (ISO 24102-2) ter obcestnimi/infrastrukturnimi storitvami.

General Information

• Status: Published
• Publication Date: 26-Mar-2024
• ICS: 03.220.01 - Transport in general
• ICS: 35.030 - IT Security
• ICS: 35.240.60 - IT applications in transport
• Technical Committee: CEN/TC 278 - Road transport and traffic telematics
• Drafting Committee: CEN/TC 278/WG 16 - Co-operative systems
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 27-Mar-2024
• Completion Date: 27-Mar-2024
• Ref Project: SIST EN ISO 21177:2024 - Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices (ISO 21177:2024)

Relations

• Replaces: EN ISO 21177:2023 - Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices (ISO 21177:2023)
• Effective Date: 14-Jun-2023

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2024
Nadomešča:
SIST EN ISO 21177:2023
Inteligentni transportni sistemi - Storitve varovanja postaj ITS za varno
vzpostavitev sej in preverjanje pristnosti med zaupanja vrednimi napravami (ISO
21177:2024)
Intelligent transport systems - ITS station security services for secure session
establishment and authentication between trusted devices (ISO 21177:2024)
Intelligente Verkehrssysteme - Sicherheitsdienste für eine ITS-Station zum sicheren
Aufbau von Sitzungen und zur Authentisierung zwischen vertrauenswürdigen Geräten
(ISO 21177:2024)
Systèmes de transport intelligents - Services de sécurité des stations ITS pour
l’établissement et l’authentification des sessions sécurisées entre dispositifs de
confiance (ISO 21177:2024)
Ta slovenski standard je istoveten z: EN ISO 21177:2024
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.

EN ISO 21177
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2024
EUROPÄISCHE NORM
ICS 03.220.01; 35.240.60; 35.030 Supersedes EN ISO 21177:2023
English Version
Intelligent transport systems - ITS station security services
for secure session establishment and authentication
between trusted devices (ISO 21177:2024)
Systèmes de transport intelligents - Services de Intelligente Verkehrssysteme - Sicherheitsdienste für
sécurité des stations ITS pour l'établissement et eine ITS-Station zum sicheren Aufbau von Sitzungen
l'authentification des sessions sécurisées entre und zur Authentisierung zwischen
dispositifs de confiance (ISO 21177:2024) vertrauenswürdigen Geräten (ISO 21177:2024)
This European Standard was approved by CEN on 6 March 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

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, Türkiye 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
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21177:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 21177:2024) 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.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2024, and conflicting national standards
shall be withdrawn at the latest by September 2024.
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 supersedes EN ISO 21177:2023.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 21177:2024 has been approved by CEN as EN ISO 21177:2024 without any modification.

International
Standard
ISO 21177
Second edition
Intelligent transport systems —
2024-03
ITS station security services for
secure session establishment
and authentication between
trusted devices
Systèmes de transport intelligents — Services de sécurité des
stations ITS pour l’établissement et l’authentification des sessions
sécurisées entre dispositifs de confiance
Reference number
ISO 21177:2024(en) © ISO 2024
ISO 21177:2024(en)
© ISO 2024
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.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO 21177:2024(en)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 Overview . 4
5.1 General description, relationship to transport layer security (TLS) and relationship to
application specifications .4
5.2 Goals .5
5.3 Architecture and functional entities .5
5.4 Cryptomaterial handles .10
5.5 Session IDs and state .10
5.6 Access control and authorization state .11
5.7 Application level non-repudiation .11
5.8 Service primitive conventions .11
6 Process flows and sequence diagrams .12
6.1 General . 12
6.2 Overview of process flows . 12
6.3 Sequence diagram conventions . 13
6.4 Configure .14
6.5 Start session . 15
6.6 Send data .18
6.7 Send access control PDU .21
6.8 Receive PDU . 22
6.9 Extend session .27
6.9.1 Goals .27
6.9.2 Processing . 28
6.10 Secure connection brokering . 28
6.10.1 Goals . 28
6.10.2 Prerequisites . 28
6.10.3 Overview . 29
6.10.4 Detailed specification . 30
6.11 Force end session. 38
6.12 Session terminated at session layer . 39
6.13 Deactivate . 40
6.14 Secure session example .41
7 Security subsystem: interfaces and data types .43
7.1 General .43
7.2 Access control policy and state .43
7.3 Enhanced authentication . 44
7.3.1 Definition and possible states . 44
7.3.2 States for owner role enhanced authentication .45
7.3.3 State for accessor role enhanced authentication . 46
7.3.4 Use by access control . 46
7.3.5 Methods for providing enhanced authentication .47
7.3.6 Enhanced authentication using SPAKE2 .47
7.4 Extended authentication . 48
7.5 Security Management Information Request . 48
7.5.1 Rationale . 48
7.5.2 General . 49
7.6 Data types . 50

iii
ISO 21177:2024(en)
7.6.1 General . 50
7.6.2 Imports . 50
7.6.3 “Helper” data types . 50
7.6.4 Iso21177AccessControlPdu .51
7.6.5 AccessControlResult .51
7.6.6 ExtendedAuthPdu .51
7.6.7 ExtendedAuthRequest .52
7.6.8 InnerExtendedAuthRequest .52
7.6.9 AtomicExtendedAuthRequest . 53
7.6.10 ExtendedAuthResponse . 53
7.6.11 ExtendedAuthResponsePayload . 53
7.6.12 EnhancedAuthPdu . 53
7.6.13 SpakeRequest . 54
7.6.14 SpakeResponse . 54
7.6.15 SpakeRequesterResponse . 54
7.6.16 SecurityMgmtInfoPdu . 54
7.6.17 SecurityMgmtInfoRequest . 55
7.6.18 EtsiCrlRequest . 55
7.6.19 CertChainRequest . 55
7.6.20 SecurityMgmtInfoResponse. 56
7.6.21 SecurityMgmtInfoErrorResponse . 56
7.6.22 EtsiCrlResponse . 56
7.6.23 EtsiCtlResponse . . . 56
7.6.24 IeeeCrlResponse .57
7.6.25 CertChainResponse . .57
7.6.26 SessionExtensionPdu .57
7.7 App-Sec Interface .59
7.7.1 App-Sec-Configure.request .59
7.7.2 App-Sec-Configure.confirm . 60
7.7.3 App-Sec-StartSession.indication . 60
7.7.4 App-Sec-Data.request. 60
7.7.5 App-Sec-Data.confirm .61
7.7.6 App-Sec-Incoming.request .61
7.7.7 App-Sec-Incoming.confirm.62
7.7.8 App-Sec-EndSession.request . 63
7.7.9 App-Sec-EndSession.indication . 63
7.7.10 App-Sec-Deactivate.request . 63
7.7.11 App-Sec-Deactivate.confirm . 64
7.7.12 App-Sec-Deactivate.indication . 64
7.8 Security subsystem internal interface . 64
7.8.1 General . 64
7.8.2 Sec-AuthState.request . 65
7.8.3 Sec-AuthState.confirm . 65
8 Adaptor layer: interfaces and data types .66
8.1 General . 66
8.2 Data types .67
8.2.1 General .67
8.2.2 Iso21177AdaptorLayerPDU .67
8.2.3 Apdu . 68
8.2.4 AccessControl . 68
8.2.5 TlsClientMsg1 . . . 68
8.2.6 TlsServerMsg1 . 68
8.3 App-AL Interface . 68
8.3.1 App-AL-Data.request . 68
8.3.2 App-AL-Data.confirm . 69
8.3.3 App-AL-Data.indication . . . 69
8.3.4 App-AL-EnableProxy.request .70
8.4 Sec-AL Interface .71

iv
ISO 21177:2024(en)
8.4.1 Sec-AL-AccessControl.request .71
8.4.2 Sec-AL-AccessControl.confirm. 72
8.4.3 Sec-AL-AccessControl.indication . 72
8.4.4 Sec-AL-EndSession.request . 73
8.4.5 Sec-AL-EndSession.confirm. 73
9 Secure session Services .73
9.1 General . 73
9.2 App-Sess interfaces . 73
9.2.1 App-Sess-EnableProxy.request . 73
9.3 Sec-Sess interface .74
9.3.1 Sec-Sess-Configure.request .74
9.3.2 Sec-Sess-Configure.confirm .76
9.3.3 Sec-Sess-Start.indication.76
9.3.4 Sec-Sess-EndSession.indication . 77
9.3.5 Sec-Sess-Deactivate.request . 77
9.3.6 Sec-Sess-Deactivate.confirm . 78
9.4 AL-Sess interface . 78
9.4.1 AL-Sess-Data.request . 78
9.4.2 AL-Sess-Data.confirm . 78
9.4.3 AL-Sess-Data.indication . 78
9.4.4 AL-Sess-EndSession.request . 79
9.4.5 AL-Sess-EndSession.confirm . 79
9.4.6 AL-Sess-ClientHelloProxy.request . 79
9.4.7 AL-Sess-ClientHelloProxy.indication . 80
9.4.8 AL-Sess-ServerHelloProxy.request . 81
9.4.9 AL-Sess-ServerHelloProxy.indication . 81
9.5 Permitted mechanisms . 82
9.5.1 TLS 1.3 . 82
9.5.2 DTLS 1.3 . 83
Annex A (informative) Usage scenarios .84
Annex B (normative) ASN.1 module .92
Annex C (normative) Session extension PDU functional type .93
Annex D (normative) Owner authorization .94
Bibliography .98

v
ISO 21177:2024(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 278,
Intelligent transport systems, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 21177:2023), of which it constitutes a minor
revision. The changes are as follows:
— cross-references to RFC 8942 have been updated to RFC 8902 throughout the document;
— information concerning patent(s) required for the implementation of this document has been moved
from the Introduction to the Foreword.
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 21177:2024(en)
Introduction
This document specifies ITS station security services that provide authenticity of the source and
confidentiality and integrity of application activities taking place between trusted devices. The two devices
taking part in a data exchange establish a cryptographically secure session. As part of establishing this
session, each device [or, more precisely, each end entity (EE) which is an application on the device] is sent
one or more digital certificates that are cryptographically bound to the other EE and contain statements,
made by a trusted third party, about the EE’s capabilities, properties and permissions. This allows each EE
to have assurance about the properties of the other EE in the session, and this in turn allows each EE to
make trust and access control decisions about data that the other EE can access, commands that the other
EE can execute, states that the other EE can change, and other types of access that the other EE can request.
In other words, the two EEs establish a trust relationship where each EE is trusted by the other EE to carry
out specific actions, without requiring one EE to allow the other EE to have arbitrary access.
The mechanisms specified in this document allow each EE to establish trusted facts about the other EE.
For these mechanisms to be used, the EE specification needs to include an access control policy, indicating
which properties are required to be known to be true about the other EE for that other EE to be allowed to
carry out particular actions. In other words, this document provides a means to obtain security-relevant
information, but the use of that security-relevant information is to be specified in the specification of the EE.
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-SCUs) 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.
[16]
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 different
ITS-SCU configuration and management centre specified in ISO 24102-2 and ISO 17419. Station-internal management
communications between ITS-SCUs of the same ITS-SU are specified in ISO 24102-4. The 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 of ISO 21217, each comprised of ITS-SUs 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, for example,
sustainability, road safety and transportation efficiency. See also Figure 2, Figure 3, Figure 4 and Figure 5.
Over the last decade, ITS services have arisen that require secure access to data from sensor and control
networks (SCN), for example, from in-vehicle networks (IVN) and from infrastructure/roadside networks
(IRN), some of which require secure local access to time-critical information; see Figure 2 and Figure 3.

vii
ISO 21177:2024(en)
Key
VMS variable message sign
Figure 2 — Example of a roadside ITS-SU connected with proprietary IRN
Key
ECU electronic control unit
Figure 3 — Example of a vehicle ITS-SU connected with proprietary IVN

viii
ISO 21177:2024(en)
Key
N&T Networking & Transport
Figure 4 — Interconnection of ITS-SCUs in an ITS-SU
Key
N&T Networking & Transport
Figure 5 — Interconnection of ITS-SUs
By applying basic security means specified in this document, the ITS-SUs can establish secure application
sessions. Establishment of sessions either requires prior knowledge about a session partner or can be
achieved by means of a service announcement as specified in ISO 22418. Further on, the broadcasting of
messages is secured by means of authenticating the sender of such a message, applicable for the service
advertisement message (SAM) specified in ISO 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.
Key
N&T Networking & Transport
Figure 6 — Interface between ITS-SU and sensor and control network

ix
ISO 21177:2024(en)
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 and dynamic pr
...