ISO 21177:2023

Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices

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.

Systèmes de transport intelligents — Services de sécurité des stations ITS pour l’établissement et l’authentification des sessions sécurisées entre dispositifs de confiance

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 spécifiées dans l’ISO 21217; et — entre les ITS-SUs (composées d’une ou plusieurs ITS-SCUs) 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.

General Information

• Status: Published
• Publication Date: 06-Apr-2023
• ICS: 03.220.01 - Transport in general
• ICS: 35.030 - IT Security
• ICS: 35.240.60 - IT applications in transport
• Technical Committee: ISO/TC 204 - Intelligent transport systems
• Drafting Committee: ISO/TC 204/WG 18 - Cooperative systems
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 19-Mar-2024
• Completion Date: 13-Dec-2025

Relations

• Consolidates: ISO 26162-2:2019 - Management of terminology resources - Terminology databases - Part 2: Software
• Effective Date: 06-Jun-2022
• Revised: ISO 21177:2024 - Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices
• Effective Date: 17-Jun-2023
• Revises: ISO/TS 21177:2019 - Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices
• Effective Date: 08-May-2020

Overview

ISO 21177:2023 - Intelligent transport systems - ITS station security services for secure session establishment and authentication between trusted devices - specifies a set of security services for ITS stations to ensure authenticity and integrity of information exchanged between trusted entities. The standard covers secure session establishment and authentication between bounded secured managed entities (ITS Station Communication Units - ITS‑SCU) and ITS station units (ITS‑SU), as well as between ITS‑SUs and external trusted entities such as sensor and control networks.

Key topics and technical requirements

• Secure session establishment and authentication: Services and procedures to negotiate trusted sessions that protect source authenticity and message integrity. The standard clarifies how these services relate to Transport Layer Security (TLS) and to application-level specifications.
• Architecture and functional entities: Definitions of roles and components (ITS‑SCU, ITS‑SU), cryptomaterial handles, session identifiers and session state management.
• Access control and authorization state: Mechanisms and PDUs for access control (e.g., AccessControlPdu, AccessControlResult) and how access policy is enforced during sessions.
• Authentication enhancements: Support for enhanced and extended authentication workflows, including a referenced method using SPAKE2 for password-authenticated key exchange.
• Service primitives and interfaces: Application–security (App‑Sec) interface primitives such as App‑Sec‑Configure, App‑Sec‑StartSession, App‑Sec‑Data, App‑Sec‑EndSession and related confirm/indication primitives to integrate security services with ITS applications.
• Process flows and sequence diagrams: Detailed flows for Configure, Start session, Send/Receive data, Extend session, Secure connection brokering and session termination.
• Security management information: PDUs and messages for certificate/CRL requests and security management information exchange.

Applications and who uses this standard

ISO 21177:2023 is essential for implementers and stakeholders building secure ITS ecosystems:

• Vehicle OEMs and automotive cybersecurity teams implementing secure V2X/ITS stations
• Roadside infrastructure and traffic management operators deploying trusted roadside units
• Suppliers of ITS‑SCU and ITS‑SU hardware/software modules
• System integrators and security architects designing time‑critical safety systems and automated driving features
• Remote management and maintenance platforms for ITS stations (linked to ISO 24102‑2)

Practical applications include time‑critical safety messaging, automated driving communications, roadside/infrastructure services, and secure remote management of ITS devices.

Related standards

• ISO 21217 - ITS station and communication unit definitions (ITS‑SCU, ITS‑SU)
• ISO 24102‑2 - Remote management of ITS stations
• Transport Layer Security (TLS) - referenced for relationship to session security

Keywords: ISO 21177:2023, ITS station security services, secure session establishment, authentication between trusted devices, ITS‑SCU, ITS‑SU, ITS security, automated driving security, access control PDU, SPAKE2, cryptomaterial handles.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21177
First edition
2023-04
Intelligent transport systems —
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 2023
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
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Published in Switzerland
ii
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 .40
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 .44
7.3 Enhanced authentication . 45
7.3.1 Definition and possible states . 45
7.3.2 States for owner role enhanced authentication . 45
7.3.3 State for accessor role enhanced authentication . 47
7.3.4 Use by access control . 47
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 .49
7.5.1 Rationale .49
7.5.2 General .50
7.6 Data types . 51
iii
7.6.1 General . 51
7.6.2 Imports . 51
7.6.3 “Helper” data types . 51
7.6.4 Iso21177AccessControlPdu . 52
7.6.5 AccessControlResult . 52
7.6.6 ExtendedAuthPdu . 52
7.6.7 ExtendedAuthRequest .53
7.6.8 InnerExtendedAuthRequest . 53
7.6.9 AtomicExtendedAuthRequest . 53
7.6.10 ExtendedAuthResponse .54
7.6.11 ExtendedAuthResponsePayload .54
7.6.12 EnhancedAuthPdu .54
7.6.13 SpakeRequest . 55
7.6.14 SpakeResponse .55
7.6.15 SpakeRequesterResponse . 55
7.6.16 SecurityMgmtInfoPdu .55
7.6.17 SecurityMgmtInfoRequest . 55
7.6.18 EtsiCrlRequest .56
7.6.19 CertChainRequest .56
7.6.20 SecurityMgmtInfoResponse.56
7.6.21 SecurityMgmtInfoErrorResponse . 57
7.6.22 EtsiCrlResponse . 57
7.6.23 EtsiCtlResponse . . . 57
7.6.24 IeeeCrlResponse . 57
7.6.25 CertChainResponse . .58
7.6.26 SessionExtensionPdu .58
7.7 App-Sec Interface .60
7.7.1 App-Sec-Configure.request .60
7.7.2 App-Sec-Configure.confirm . 61
7.7.3 App-Sec-StartSession.indication . 61
7.7.4 App-Sec-Data.request. 61
7.7.5 App-Sec-Data.confirm . 62
7.7.6 App-Sec-Incoming.request . 62
7.7.7 App-Sec-Incoming.confirm.63
7.7.8 App-Sec-EndSession.request .64
7.7.9 App-Sec-EndSession.indication .64
7.7.10 App-Sec-Deactivate.request .65
7.7.11 App-Sec-Deactivate.confirm .65
7.7.12 App-Sec-Deactivate.indication .65
7.8 Security subsystem internal interface .66
7.8.1 General .66
7.8.2 Sec-AuthState.request .66
7.8.3 Sec-AuthState.confirm .66
8 Adaptor layer: interfaces and data types .67
8.1 General . 67
8.2 Data types .68
8.2.1 General .68
8.2.2 Iso21177AdaptorLayerPDU .68
8.2.3 Apdu . 69
8.2.4 AccessControl .69
8.2.5 TlsClientMsg1 . . .69
8.2.6 TlsServerMsg1 . 69
8.3 App-AL Interface . 69
8.3.1 App-AL-Data.request . 69
8.3.2 App-AL-Data.confirm . 70
8.3.3 App-AL-Data.indication . . . 70
8.3.4 App-AL-EnableProxy.request . 71
8.4 Sec-AL Interface .73
iv
8.4.1 Sec-AL-AccessControl.request .73
8.4.2 Sec-AL-AccessControl.confirm.73
8.4.3 Sec-AL-AccessControl.indication .73
8.4.4 Sec-AL-EndSession.request .74
8.4.5 Sec-AL-EndSession.confirm.74
9 Secure session Services .74
9.1 General .74
9.2 App-Sess interfaces .74
9.2.1 App-Sess-EnableProxy.request .74
9.3 Sec-Sess interface . 75
9.3.1 Sec-Sess-Configure.request . 75
9.3.2 Sec-Sess-Configure.confirm .77
9.3.3 Sec-Sess-Start.indication.77
9.3.4 Sec-Sess-EndSession.indication . 78
9.3.5 Sec-Sess-Deactivate.request . 78
9.3.6 Sec-Sess-Deactivate.confirm . 79
9.4 AL-Sess interface . 79
9.4.1 AL-Sess-Data.request . 79
9.4.2 AL-Sess-Data.confirm . 79
9.4.3 AL-Sess-Data.indication .80
9.4.4 AL-Sess-EndSession.request .80
9.4.5 AL-Sess-EndSession.confirm .80
9.4.6 AL-Sess-ClientHelloProxy.request .81
9.4.7 AL-Sess-ClientHelloProxy.indication .81
9.4.8 AL-Sess-ServerHelloProxy.request .82
9.4.9 AL-Sess-ServerHelloProxy.indication .82
9.5 Permitted mechanisms .83
9.5.1 TLS 1.3 .83
9.5.2 DTLS 1.3 .84
Annex A (informative) Usage scenarios .85
Annex B (normative) ASN.1 module .93
Annex C (normative) Session extension PDU functional type .94
Annex D (normative) Owner authorization .95
Bibliography .99
v
Foreword
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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
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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 first edition of ISO 21177 cancels and replaces ISO/TS 21177:2019, which has been technically
revised.
The main changes are as follows:
— change proposals presented in ISO/TR 21186-3:2021 have been incorporated, including:
— CRL request functionality added;
— session extension functionality added;
— editorial improvements to improve readability and clarity have been made, including:
— revision of Figure 7, renumbered to Figure 8;
— insertion of new Figure 7.
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
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 ITSstations.
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
vii
networks (IRN), some of which require secure local access to time-critical information; see Figure 2
and Figure 3.
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
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
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 priorities;
— protection of private data, e.g. in compliance with the European "General Data Protection Regulation"
[18]
(GDPR);
— local access to certified real-time data for sustainability applications, e.g. dynamic emission zones
(controlled zones as currently standardized by CEN/TC 278), intersection priorities based on
emissions, and 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 this number will grow (see the US
[19]
National ITS Reference Architecture, for example). It is critical that ultimately all ITS-SUs in a given
area be 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 to be 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 need to 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.
The subject of this document thus is three-fold.
1) Specification of 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 prioritization and restricted access.
2) Specification of ITS station security services for enabling trust between ITS-S application processes
running on the same ITS-SU.
3) Extension of these ITS security services for enabling trust between an ITS-SCU and devices being
part of a sensor and control network.
Such security services include, for example, the basic security features of:
a) authentication and authorization;
x
b) confidentiality and privacy;
c) data integrity;
d) non-repudiation.
Tasks related to communications are:
e) establishing secure sessions for bi-directional communications, e.g. based on service advertisement
as specified in ISO 22418;
f) authenticating a sender of broadcast messages, e.g. CAM, DENM, BSM, SPaT, MAP, FSAM, WSA, etc.;
g) encrypting messages.
NOTE 3 Tasks f) and g) above related to communications are already specified in other standards, see
IEEE 1609.2 and several related standards from ETSI, for example.
The International Organization for Standardization (ISO) draws attention to the fact that it is claimed
that compliance with this document may involve the use of a patent.
ISO takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured ISO that he/she is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In
this respect, the statement of the holder of this patent right is registered with ISO. Information may be
obtained from the patent database available at www.iso.org/patents.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those in the patent database. ISO shall not be held responsible for identifying
any or all such patent rights.
xi
INTERNATIONAL STANDARD ISO 21177:2023(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, 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.
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.
ETSI TS 102 941, Intelligent Transport Systems (ITS); Security; Trust and privacy management
ETSI TS 103 097, Intelligent Transport Systems (ITS); Security; Security header and certificate formats
IEEE 1609.2including Amendment 1, IEEE Standard for Wireless Access in Vehicular Environments—
Security Services for Applications and Management Messages
IEEE 1003.1:2017, IEEE Standard for Information Technology--Portable Operating System Interface
(POSIX(R)) Base Specifications, Issue 7
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
access control PDU
protocol data unit (PDU) generated by the security subsystem for purposes of establishing the
authorization 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
3.3
application
functional entity, i.e. an ITS-S application process
Note 1 to entry: The natural language term "application" is used in this document as a synonym to the term
"ITS-S application process" specified in ISO 21217.
3.4
cryptomaterial
cryptographic keys and associated material
Note 1 to entry: Cryptomaterial refers to either a secret key for a symmetric algorithm, or a private key for an
asymmetric algorithm and the associated public key or certificate.
3.5
cryptomaterial handle
reference to cryptomaterial allowing that cryptomaterial to b
...