Security Services 2-35
September 2008
Chapter 2 - MTM800 Product Information Manual 6866537D87-F
• ITSI: Individual TETRA Subscriber Identity
• K: Authentication key – unique for each terminal unit
• GTSI: Group TETRA Subscriber Identity
Benefits:
❏ Major enhancement of overall system security & integrity
❏ Prevents eavesdropping / ensures airtime is not stolen
❏ Allows user safety in the knowledge that only authorized users are using the network
❏ Prove that an MS is not a Different Terminal, not a “Clone” or not a “Hacker”
11.3 Air Interface Encryption (AIE)
The terminals support TETRA Air Interface Encryption AIE using the standard TETRA Public
Encryption algorithms - TEA1, TEA2 and TEA3 in AsiaPac.
The Focus of Cryptography in TETRA is the Encryption Key:
TETRA AIE provides 12,000,000,000,000,000,000,000,000 key combinations
Benefits:
❏ Which will take a long time and cost a lot of money to attack, even with tomorrows computer
power!
TETRA has 3 Classes of Encryption:
• Class 1 - Clear (None)
• Class 2 - Static Key Encryption
• Class 3 - Derived Key Encryption (sometimes called Dynamic key), Common Cipher Key and
Group Cipher Key
In Direct Mode only the Static Cipher Key (SCK) type is defined.
11.3.1 Clear Terminals (Class 1)
A terminal can be configured as a “clear” terminal, in which case it will identify itself in registration as
a “Security Class 1” terminal and not support encryption. A Security Class 1 terminal will not contain
any encryption algorithms in its software.
11.3.2 Static Cipher Key SCK (Class 2)
The terminals support static air interface encryption and authorized terminals share up to 32 static
cipher keys (SCK) with the system.
The terminal determines which static cipher key to use based on the SCK Number (SCKN) and the
SCK version number (SCK_VN) broadcast by the system on the control channel.
Terminals can be either ‘Clear’ or ‘Encrypted’ and a Clear terminal will identify itself to the system
during registry as a Class 1 terminal. An encrypted terminal identifies itself as a Class 2 terminal
during registry.
In Direct Mode the SCK can be chosen by the system manager and may be distributed from the
TMO SwMI using the OTAR mechanism or it can be entered manually.
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