1. TETRA Security meeting needs of Military
Security mechanisms in TETRA
and how to ensure that the
solution is secure…
”Jeppe” Jepsen
Motorola

2. What we want to achieve with Security
Confidentiality
No one can eavesdrop on what we are saying
Authenticity
The people we are talking to are the right people
The wrong people can’t try and join us
Integrity
The information gets there completely intact
Availability
Communications are possible where and when they are needed
Accountability (Non repudiation)
Whoever said something, can’t deny it later

3. Threats to communication and the threats to security
Message related threats
interception, eavesdropping, masquerading, replay, manipulation of data
User related threats
traffic analysis, observability of user behavior
System related threats
denial of service, jamming, unauthorized use of resources

4. Key Functions of TETRA Security
TETRA has several security features allowing most customers security needs to be met in a cost efficient way.
Authentication - ensures only valid subscriber units have access to the system and subscribers will only try and access the authorized system
Base Station
Infrastructure
Dispatcher “
????”
1. Authentication
2. Air Interface Encryption
3. End - to
End Encryption
XYZ”
Air Interface Encryption – protects all signalling, identity and traffic across the radio link
End-to-End Encryption - protects information as it passes through the system

5. Authentication
Authentication Centre
Challenge
Session keys
Calculated Response
Switch
Secret keys
Mutual Challenge MS
Calculated Response
Authentication provides proof identity of all radios attempting use of the network
Radio can authenticate the network in turn, protects against ‘fake base stations’ etc
A session key system from a central authentication centre allows highly secure key storage
Secret key need never be exposed
Authentication process derives air interface key (TETRA standard) – automatic key changing!

6. Radio Security Provisioning And Key Storage
TETRA MoU SFPG Recommendation 01 provides a standardised format for importing authentication and other air interface encryption keys
Use of Recommendation 01 files will allow multi vendor terminal supply
Separation of logical key programming step from factory can allow all keys to be loaded in country
Meets national security requirements
SCK, GCK etc…
from national security authority
Standardised format
Imports key material from any vendor
AuC
TEI
Factory
TEI
TETRA
SwMI
Key Programming K
K, TEI

7. What is Air Interface Encryption?
First level encryption used to protect information over the Air Interface
Typically software implementation
Protects almost everything – speech, data, signalling, identities…
3 different Classes
Class 1
No Encryption, can include Authentication
Class 2
Static Cipher Key Encryption, can include Authentication
Class 3
Dynamic Cipher Key Encryption
Individual Derived Cipher Key
Common Cipher Key
Group Cipher Key
Requires Authentication
Includes over the air key management protocols
Allows seamless key management

8. The purpose of Air Interface Encryption
Network fixed links are considered difficult to intercept.
Clear
Air
Interface!
The air interface was considered vulnerable.
Air Interface encryption was designed to make the air interface as secure as the fixed line connection
Air
Interface
Encryption
Fixed
Links
Operational
Information
ANIMATED SLIDE
So what is the point of Air Interface Encryption? Well the best way to describe this is to think of the following scenario. The TETRA information is available at the Air Interface and on the fixed links. (next slide).
The fixed links have an inherent security associated with them. As an attacker I have to physically get access to a network and then determine the routing etc. Therefore there is a wall of a specific height I have to climb. (next slide).
However, the Air Interface is still relatively vulnerable, the argument that it is digital and even TDMA is not valid for anything other than the extremely casual attack! (next slide)
So Air Interface Encryption was designed to increase the security of the air interface to the same level as that inherently provided by the network. There is no point in making the Air Interface more protected than the network, otherwise the attack is moved to the now relatively vulnerable network. There is some talk about extending Air Interface Encryption to some point further down the network to give more protection. This gains nothing, effectively you are building one wall behind another, both of equal height, all this does is give the attacker a firmer base to stand upon when he climbs over!

9. Important properties of Air Interface encryption
Many threats other than eavesdropping
traffic analysis, observance of user behaviour
AIE protects control channel messages and identities as well as voice and data payloads
End to end encryption - if used alone - is insufficient (it only protects the voice payload)
Continuous authentication
Encryption key generated from authentication process
Encrypted registration protects ITSIs even at switch on
Security classes can be changed in operation – essential for fallback measures if authentication cannot operate

10. End to end encryption in TETRA
ETSI Project TETRA provides standardised support for end to end Encryption
ETSI EN contains specific end to end specification
Ensures TETRA provides a standard alternative to proprietary offerings and technologies
Ensures compatibility between infrastructures and terminals
Many organisations want their own algorithm
Confidence in strength
Better control over distribution
TETRA MoU – Security and fraud Protection Group
Provides detailed recommendation on how to implement end to end encryption in TETRA
The result – Standardisation and compatibility, with choice of algorithm
A big strength of TETRA

11. End To End Encryption ‘Standardisation’
TETRA MoU SFPG Recommendation 02
Framework for end to end encryption
Recommended synchronisation method for speech calls
Protocol for Over The Air Keying
Sample implementations including algorithm mode and key encryption for IDEA, but AES128 is now preferred
DOES NOT specify implementation – can be implemented with module, software, SIM card etc..
DOES NOT provide module interface specification

12. Related Recommendations
TETRA MoU SFPG Recommendation 01
Key transfer specification
Currently being updated to include end to end encryption key import formats
TETRA MoU SFPG Recommendation 07
Short data service encryption
Currently being updated to reflect larger algorithm block sizes, e.g. 128 bits for AES
TETRA MoU SFPG Recommendation 08
Framework for dividing encryption functionality between a SIM (smartcard) and a radio
No defined bit level interface (export control issue)
TETRA MoU SFPG Recommendation 11
IP Packet data encryption
Work in process
Will provide a suitable means for high security packet data encryption, with commonality with voice encryption

13. Implementing TETRA security
TETRA security measures are by no means the complete picture
How well they are implemented – and how the implementation is evaluated is critical
The rest of the network – what else connects to TETRA – is equally important
The operational process and procedures equally provide countermeasures to the threats
Link
Other
Network
Other
Network
TETRA
Network
Other
Network
Landline

14. Implementation considerations – Air Interface Encryption
AIE should provide security equivalent to the fixed network
There are several issues of trust here
Do I trust that the AIE has been implemented properly?
Does AIE always operate (during registration, in fallback modes etc)?
Do I trust the way that the network (or radio) stores keys?
Do I trust the fixed network itself or can someone break in?
A strong AIE implementation and an evaluated network can provide essential protection of information
An untested implementation and network may need reinforcing, for example with end to end encryption

15. Useful Recommendations
TETRA MoU SFPG Recommendation 03 – TETRA threat analysis
Gives an idea of possible threats and countermeasures against a radio system
TETRA MoU SFPG Recommendation 04 – Implementing TETRA security features
Provides guidance on how to design and configure a TETRA system
Both documents are restricted access requiring Non Disclosure Agreement with SFPG

16. Assuring your security solution
There are two important steps in assuring the security of the solution: Evaluation and Accreditation
Evaluation of solutions should be by a trusted independent body
Technical analysis of design and implementation
Accreditation is the continual assessment of risks
Assessment of threats vs solutions
Procedural and technical solutions
Should be undertaken by end user representative

17. Maximising cost effectiveness
Evaluation can be extremely expensive – how to get best value for money?
Establish the requirements in advance
as far as they are known – security is always a changing requirement!
Look for suppliers with track record and reputation
Look for validations of an equivalent solution elsewhere
Consider expert help on processes and procedures

18. Summary: The essentials of a secure system
A strong standard
A good implementation
Experienced supplier
Trusted evaluation
Continual assessment of threats and solutions
Standard
EVALUATED

20. Military Operational Requirements (MOR)
NATO C3 Board has approved the MOR from a policy point of view
MOR has to be implemented in
MOR covers the use of Mobile Communications for Support Elements of NATO Activities
The MOR addresses the use of Mobile Communications, within a non-hostile environment, allowing interoperability with systems of other NATO Forces, PfP nations and civil organisations, ensuring an appropriate level of security

21. NC3A SET - 2 SHF SATCOM Terminal
13 meter antenna located
in the dunes near Nc3A-NL
connected to the SATIN lab
typical of a large NATO SGT

22. Example 4: SET 12 (System parameters)
Diameter size of the dish 1.2 m
Transmit Gain: 37 dBi
G/T 13 dB/K
Maximal EIRP 55 dBW
Power: 100 W
antenna tracking (open loop)
controlled via a laptop (rs 232)
transportable ,
6 transit cases, total weight < 350 kg
fast setup and teardown by 2 persons
Datarate depends on link budget and allocated resource
128 kbps duplex between Set 2 and Set 12 in Denmark on NATO IV

23. TETRA Extension Demonstration
NATO IV (channel 4)
RS 449
64/128 kbps
Copenhagen : SET 12
NC3A-NL
TETRA BS
modem
modem
RS 449 interface
(satcom boundary)
TETRA Switch

24. What security level do you want?
TETRA Class 1
TETRA Class 2
TETRA Class 3
TETRA w/ E2E algoritm on Smart Card
TETRA w/ E2E SW algorithm in radio
TETRA w/ E2E hardware solution using AES128
TETRA w/ E2E hardware solution using own algorithm
TETRA your Service

25. www.motorola.com/tetra Jeppe.Jepsen@Motorola.com
Thank You 18