TWC 2005 Frankfurt 1 INTRODUCTION TO TETRA SECURITY Brian Murgatroyd UK Police IT Organization

TWC 2005 Frankfurt2 Agenda  Threats to systems  Network Security  Overview of standard TETRA security features –Authentication –Air interface encryption –Key Management –Terminal Disabling –DMO security  End to End Encryption

TWC 2005 Frankfurt3 Security Threats  What are the main threats to your system?  Confidentiality?  Availability?  Integrity?

TWC 2005 Frankfurt4 Message and User Related Threats   Message threats – –Interception – –Eavesdropping – –Masquerading – –Manipulation of data. – –Replay  User related threats –traffic analysis –observability of user behaviour.

TWC 2005 Frankfurt5 System Related Threats

TWC 2005 Frankfurt6 Network Security IT security is vital in TETRA networks Gateways are particularly vulnerable. Operating staff need vetting

TWC 2005 Frankfurt7 TETRA Communications Security  Security is not just encryption!  Terminal Authentication  User logon/Authentication  Stolen Terminal Disabling  Key Management with minimum overhead  All the network must be secure, particularly with a managed system

TWC 2005 Frankfurt8 User authentication (aliasing)  Second layer of security  Ensures the user is associated with terminal  User logon to network aliasing server  log on with Radio User Identity and PIN  Very limited functionality allowed prior to log on  Log on/off not associated with terminal registration  Could be used as access control for applications as well as to the Radio system

TWC 2005 Frankfurt9 Authentication  Used to ensure that terminal is genuine and allowed on network.  Mutual authentication ensures that in addition to verifying the terminal, the SwMI can be trusted.  Authentication requires both SwMI and terminal have proof of secret key.  Successful authentication permits further security related functions to be downloaded.

TWC 2005 Frankfurt10 Authentication Authentication Centre (AuC) Call Controller TA11 K RS KS Generate RS KS (Session key) RS (Random seed) TA12 KS RAND1 XRES1DCK1 Generate RAND1 Compare RES1 and XRES1 TA11 TA12 K RS KS RAND1 RES1DCK1 RS, RAND1 RES1 EBTS DCK K known only to AuC and MS

TWC 2005 Frankfurt11 Encryption Process Clear data in Encrypted data out Key Stream Generator (TEA[x]) Initialization Vector (IV) ABCDEFGH y4Mv#Qt q c Traffic Key (X)CK Key Stream Segments Combining algorithm (TB5) I CN LA CC

TWC 2005 Frankfurt12 Air Interface traffic keys  Four traffic keys are used in class 3 systems:-  Derived cipher Key (DCK) –derived from authentication process used for protecting uplink, one to one calls  Common Cipher Key(CCK) –protects downlink group calls and ITSI on initial registration  Group Cipher Key(GCK) –Provides crypto separation, combined with CCK  Static Cipher Key(SCK ) –Used for protecting DMO and TMO fallback mode

TWC 2005 Frankfurt13 DMO Security Implicit Authentication Static Cipher keys No disabling

TWC 2005 Frankfurt14 TMO SCK OTAR scheme Key Management Centre SwMI

TWC 2005 Frankfurt15 Key Overlap scheme used for DMO SCKs  The scheme uses Past, Present and Future versions of an SCK.  System Rules –Terminals may only transmit on their Present version of the key. –Terminals may receive on any of the three versions of the key.  This scheme allows a one key period overlap. PastPresentFuture Receive Transmit

TWC 2005 Frankfurt16 Disabling of terminals  Vital to ensure the reduction of risk of threats to system by stolen and lost terminals  Relies on the integrity of the users to report losses quickly and accurately.  Disabling may be either temporary or permanent  Permanent disabling removes all keys including (k)  Temporary disabling removes all traffic keys but allows ambience listening

TWC 2005 Frankfurt17 End to end encryption End-to-end security between MS’s NetworkMS Air interface security between MS and network MS  Protects messages across an untrusted infrastructure  Provides enhanced confidentiality  Voice and SDS services  IP data services (soon)

TWC 2005 Frankfurt18 Key management for end to end encryption

TWC 2005 Frankfurt19 Benefits of end to end encryption in combination with Air Interface encryption  Air interface (AI) encryption alone and end to end encryption alone both have their limitations  For most users AI security measures are completely adequate  Where either the network is untrusted, or the data is extremely sensitive then end to end encryption may be used in addition  Brings the benefit of encrypting addresses and signalling as well as user data across the Air Interface and confidentiality right across the network

TWC 2005 Frankfurt20 Conclusions  Security functions built in to TETRA from the start!  User friendly and transparent key management.  Air interface encryption protects, control traffic, IDs as well as voice and user traffic.  Key management comes without user overhead because of OTAR.