ETSI TR 103 565-2 V1.1.1 (2018-05)

TETRA and Critical Communications Evolution (TCCE); Interworking between TETRA and 3GPP mission critical services Part 2: Security of interworking between TETRA and Broadband applications

DTR/TCCE-06192

General Information

• Status: Published
• Publication Date: 14-May-2018
• Technical Committee: TCCE 6 - TCCE Security
• Current Stage: 12 - Completion
• Due Date: 30-May-2018
• Completion Date: 15-May-2018

Standards Content (Sample)

ETSI TR 103 565-2 V1.1.1 (2018-05)






TECHNICAL REPORT
TETRA and Critical Communications Evolution (TCCE);
Interworking between TETRA and
3GPP mission critical services;
Part 2: Security of interworking between
TETRA and Broadband applications

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2 ETSI TR 103 565-2 V1.1.1 (2018-05)



Reference
DTR/TCCE-06192
Keywords
broadband, radio, TETRA

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3 ETSI TR 103 565-2 V1.1.1 (2018-05)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definitions and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 7
4 Interworking overview . 7
4.1 Interworking realization . 7
4.2 Use cases . 8
4.3 Security aspects of interworking . 8
5 Threats . 8
5.1 General . 8
5.2 Masquerade and impersonation . 8
5.3 Eavesdropping . 9
5.4 Traffic analysis . 9
5.5 Denial of service . 9
5.6 Manipulation/insertion . 10
5.7 Extraction of security information . 10
5.8 Replay . 10
5.9 Repudiation . 10
6 Security measures . 10
6.1 Service authorization . 10
6.2 User authentication . 11
6.3 System authentication . 11
6.3.1 Interface authentication . 11
6.3.2 System authentication by IWF . 11
6.4 Signalling protection . 11
6.5 Traffic protection . 11
6.6 Key management . 12
6.6.1 TETRA air interface security . 12
6.6.2 MC service signalling security. 12
6.6.3 Speech security . 12
6.6.3.1 Encryption translation . 12
6.6.3.2 Fully end to end . 13
6.7 Policy, auditing and reporting . 13
6.8 Solution implementation . 13
7 Threat - Security Measure Analysis . 13
7.1 Threat Summary . 13
7.2 Security Measure Summary . 14
7.3 Cross Reference Table . 16
8 Candidate solutions for standardization . 18
8.1 General . 18
8.2 Candidate measures for standardization . 18
8.2.1 M6.1 Service authorization . 18
8.2.2 M6.2 User authentication . 18
8.2.3 M6.3 Interface authentication . 18
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4 ETSI TR 103 565-2 V1.1.1 (2018-05)
8.2.4 M6.4 Signalling protection . 18
8.2.5 M6.5 Traffic confidentiality. 18
8.2.6 M6.6 Key management . 18
8.2.7 M6.7 Policy, auditing and reporting . 19
8.2.8 M6.8 Solution implementation . 19
9 Conclusions . 19
History . 20


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5 ETSI TR 103 565-2 V1.1.1 (2018-05)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Report (TR) has been produced by ETSI Technical Committee TETRA and Critical Communications
Evolution (TCCE).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
TETRA users are adopting broadband technologies based on 3GPP LTE for critical communications to add new
services and capabilities to their operations. TETRA systems are required to work alongside and together with such
broadband critical communications systems to enable the users to benefit from the strengths of both technologies.
Interworking is necessary with both the developing suite of 3GPP Mission Critical applications including MCPTT and
MCData applications, and also with more general use of broadband networks for enhanced bandwidth and higher speed
general data applications. The present document describes the security related aspects of such interworking between
technologies. It contains use cases for secure interworking, security related issues and potential security solutions.

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6 ETSI TR 103 565-2 V1.1.1 (2018-05)
1 Scope
The present document contains use cases, threats and security solutions for interworking between TETRA and 3GPP
standardized mission critical broadband systems. The security solutions generated within the present document are
assessed for applicability to further standardization work. The security solutions also highlights areas which need to be
solved by implementation.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TR 103 565: "TETRA and Critical Communications Evolution (TCCE); Terrestrial Trunked
Radio (TETRA); Study into interworking between TETRA and 3GPP mission critical services".
[i.2] 3GPP TR 23.782: "Study on mission critical communication interworking between LTE and non-
LTE systems".
[i.3] ETSI EN 300 392-7: "Terrestrial Trunked Radio (TETRA); Voice plus Data (V+D); Part 7:
Security".
[i.4] ETSI EN 302 109: "Terrestrial Trunked Radio (TETRA); Security; Synchronization mechanism
for end-to-end encryption".
[i.5] 3GPP TS 33.180: "Security of the mission critical service".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
air interface encryption: encryption which protects a radio link only
end-to-end encryption: encryption within or at the source end system, with the corresponding decryption occurring
only within or at the destination end system
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3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
rd
3GPP 3 Generation Partnership Project
AES Advanced Encryption Standard
AI Air Interface
AIE Air Interface Encryption
BS Base Station
COTS Commercial Off The Shelf
DoS Denial of Service
E2EE End to End Encryption
eNodeB enhanced Node B
GCM Galois Counter Mode
GSSI Group Short Subscriber Identity
HTTPS Secure Hyper Text Transfer Protocol
ID IDentity
ISSI Individual Short Subscriber Identity
IWF InterWorking Function
LMR Land Mobile Radio
LTE Long Term Evolution
MC Mission Critical
MCData Mission Critical Data
MCPTT Mission Critical Push To Talk
MS Mobile Station
OTAK Over The Air Key management
OTAR Over The Air Rekeying
PIN Personal Identification Number
PLMN Public Land Mobile Network
SFPG Security and Fraud Prevention Group
SIP Session Initiation Protocol
SRTCP Secure Real Time Protocol
SRTP Secure Real-time Transport Protocol
SwMI Switching and Management Infrastructure
TCCA The Critical Communications Association
TETRA TErrestrial Trunked RAdio
TLV Type Length Value
TR Technical Report
URI Uniform Resource Identifier
XMLenc eXtensible Markup Language encryption
4 Interworking overview
4.1 Interworking realization
The interworking function is realized according to ETSI TR 103 565 [i.1] as an adaptation between a TETRA SwMI
and the 3GPP MC system LMR interworking interface, to be specified within 3GPP Release 15, and has been studied in
3GPP TR 23.782 [i.2]. This is shown in figure 4.1-1.

Figure 4.1-1: Concept of the interworking function
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8 ETSI TR 103 565-2 V1.1.1 (2018-05)
The interworking function provides a single logical interface between each pair of one MC service and one TETRA
SwMI. Any realization of multiple interfaces between a pair of systems e.g. for resilience is outside the scope of the
present document.
Note that the interworking function in ETSI TR 103 565 [i.1] specifies behaviour, and is not necessarily intended to be
a specification for a physical interface device. Thus either or both of the interfaces to an interworking function may not
be exposed and may be internal to the implementation of a solution. This should be taken into account when assessing
the security issues.
4.2 Use cases
The use cases for interworking between TETRA and 3GPP MCPTT and associated MCData services are as follow:
• Short term usage, where a user community is in transition from use of TETRA to use of MCPTT and MCData,
and requires communications between users during this activity. 'Short term' may still require interworking for
several years, especially where nationwide systems are deployed.
• Long term, where users use both TETRA and LTE for communications for the foreseeable future, without time
limit. Use of one or the other technology may be dependent on user role, on user location or communications
type (e.g. use of TETRA for voice, LTE for high speed data aspects).
There may be no difference in the solutions for security between a 'short term' and a 'long term' use of interworking;
however a user organization may be prepared to accept some increased level of risk for a shorter term and take an
increased level of risk into account as part of a cost-benefit decision when deciding which measures to implement.
Either use case may require security to be maintained fully end to end.
4.3 Security aspects of interworking
Each system will be responsible for managing its own security aspects, such as authorization, authentication of user or
device and protection of signalling and traffic information. End to end encrypted material should be able to pass
between users on both systems.
There are two goals associated with security:
• The solution should not affect security for any users of either system that are not involved in interworking with
the other system.
• The solution should maintain as high a level of security as possible for users that are involved in interworking
communications with users in the other system.
5 Threats
5.1 General
This clause details some of the threats to interworking between TETRA and MC systems.
5.2 Masquerade and impersonation
The following threats are possible relating to masquerade and impersonation:
• Systems: one system may be impersonated at the interworking function to the other system.
• Interworking function: a fake interworking function impersonates an interworking function and associated
system.
• Clients: a client on one system may enable impersonation of another client of the same system to gain access
to inter-system communications.
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• Users: a user on one system may impersonate another of the same system to gain access to inter-system
communications.
5.3 Eavesdropping
Eavesdropping could apply to speech or data traffic, as well as to control functions.
Eavesdropping may take place on an exposed interface in one system between clients and servers (or between clients
and peripheral devices) which compromises communications on the other system during interworking communications,
this could include an air interface.
Eavesdropping may take place on external links to the interworking function, or in a device introduced into a link as a
'man in the middle' device with the intention of eavesdropping on that link.
Eavesdropping may take place on links to the interworking function that are internal to one system.
Eavesdropping may take place within the interworking function, for example if the interworking function needs to
decrypt information received from one system prior to re-encrypting it for transmission into the other system.
NOTE: The interworking function may be internal to one system, or even to both systems if a single physical
infrastructure provides both TETRA and MC services.
Ambience listening invoked across the interworking function (if supported) provides an additional possibility for
eavesdropping on a user, without the user being aware.
5.4 Traffic analysis
Access to one system discovers information concerning traffic on the other system.
Access to the interworking function or to links either side of the interworking function allows traffic analysis to be
carried out with respect to users or groups on either system.
• Direct access to call flow information through access to the interworking function.
• Access to address books or group linking tables allows information discovered on one system to be aligned
with information on the other system.
• Information concerning group member affiliation.
• Access to accounting and management tools on one system or on the interworking function provides
information about call statistics applying to interworking calls.
Eavesdropping on links to the interworking function provides direct access to traffic flow information.
5.5 Denial of service
Generate excessive traffic on a group on one system to deny service to the interconnected (linked) group on the other
system.
Placing a call with high priority on one system may affect the available resources on the interconnected system.
Upset operation of the interworking function; e.g. erase an address book, interrupt a link, physical attack.
Interrupt key management services.
A successful attack on the interworking function resulting in its unavailability will cause loss of inter system
communications.
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5.6 Manipulation/insertion
Modification of frame formats to confuse encrypted speech with synchronization stolen frames or signalling frames.
May also be a denial of service attack by modifying control information.
Insertion or modification of signalling information.
Modification of mapping of groups between systems.
Attack on configuration management interfaces to modify addresses, mapping and other configuration data.
Modification of traffic passed between systems.
Insertion of acknowledgements (positive or negative) to falsify delivery responses.
Adding unauthorised users to a group, or unauthorised linking of groups on one system may misdirect traffic to users
who are unknown to the interconnected system.
It may not be apparent to a user that the group in which he is communicating is interconnected to a group on the other
system.
5.7 Extraction of security information
Extraction of encryption keys or other security parameters that are stored in the interworking function or other network
elements for the purpose of enabling secure interworking; security parameters can then be used to mount an attack at the
interface or within one of the interconnected systems.
Extraction of encryption keys or other security parameters from terminals, especially from Commercial Off The Shelf
(COTS) terminals and applications.
5.8 Replay
Replay of signalling or traffic information at the interworking interface.
Replay on one system may not be obvious from the perspective of the interconnected system.
5.9 Repudiation
It may be difficult to prove the origin of communications from the interconnected system.
6 Security measures
6.1 Service authorization
Users will be expected to be authorized to interwork across the interworking function with users in the other type of
system. Groups are expected to also be authorized for interworking communications.
If group call affiliations are managed locally, then each system can be responsible for authorizing its users to join
groups which are connected to groups in the other system, without involvement of the interworking function.
If identity translation is needed by an address book in order to interwork with individual services, then being present in
this address book can provide additional authorization for interworking, in addition to any authorization within the local
system. If the MC system uses different addresses for different services (e.g. MCPTT-ID, MCData ID) then the
presence of a service specific address will also provide some degree of service level authorization.
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6.2 User authentication
Each system carries out its own authentication locally. The TETRA system authenticates the MSs, the MC system
authenticates the user. PIN entry can provide some additional level of user authentication to the device. Each system
will have to trust that the connected system has correctly authenticated any user or the device as appropriate that makes
a call request that is carried by the interworking function.
6.3 System authentication
6.3.1 Interface authentication
The authenticity of the interworking function will have to be verified by each system independently.
Users making calls across the interworking function will have to trust that their local system has verified the
authenticity of that interface.
6.3.2 System authentication by IWF
The IWF will need to verify that the connected system(s) is valid and authentic, by explicit or implicit means.
6.4 Signalling protection
Each system may require signalling, including addressing of users and groups, to be kept confidential from
unauthorised parties. These include eavesdroppers at the air interface. In the case of an MC system, confidentiality will
generally also be required from the PLMN operator providing the underlying LTE service.
Each system has separate mechanisms to protect signalling from eavesdropping, and also to protect integrity of
signalling. TETRA uses air interface encryption; MCPTT and MCData use a mixture of encryption of information
within SIP bodies (XMLenc) and HTTPS for its signalling plane protection, and SRTCP for floor control. The
connection between SIP core and SIP client in the device may also be encrypted, but this mechanism may not be in the
trust domain of the MC service.
As these mechanisms are different, any interface carrying signalling between either system and the interworking
function (as shown on figure 4.1-1) cannot be encrypted. Therefore, where any interconnecting network between a
system and the interworking function is not trusted, additional measures should be taken to secure links between the
relevant inter-system interface(s) and the interworking function. The interworking function itself will need to be
protected by appropriate measures (e.g. physical, procedural) to prevent it from becoming a point of attack.
Both systems should implement their signalling protection mechanisms, to prevent one system operating without
signalling confidentiality from providing a point of atta
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