End-To-End Encryption; Sim Security; Figure 6: Voice And Data End To End Encryption - Motorola MTP850 S Product Information Manual

46 | Services and Features

End-to-End Encryption

The TETRA standard supports air encryption. The radio creates the PDU (Protocol Data Unit) and the PDU is
encrypted before transmission. The base station receives this PDU and must decrypt it, to know what to do with it and
where to send it. Thus, if a PDU contains voice information, the voice part of the message has been decrypted and is
now unprotected, until it is transmitted out to the caller.

Figure 6: Voice and Data End to End Encryption

Data Services
Voice Codec
End-to-End Encryption
PEI
Standard TETRA Air Interface Encryption
and Key Management
The End-to-End Encryption (E2EE) feature resolves this issue by encrypting the voice information before it is packed
into the PDU. This message is also encrypted according to the over-the-air encryption of the TETRA standard. Thus,
when the base station decrypts the PDU containing voice information, the voice part remains protected by encryption
until the called radio receives the voice and decrypts it.
The Universal Crypto Module (UCM), located in the radio, carries out voice encryption. The UCM takes the voice
stream and encrypts this stream using a set of keys. Likewise, the UCM takes encrypted voice stream and using the
same keys decrypts back into clear voice.
In the end-to-end encryption feature, the radio notifies and informs whether the call, being made or received, is voice-
encrypted. The radio also provides with means to select a different key, delete keys, request new keys and change the
encryption mode of nondefined private calls.
This feature is relevant for group calls and private calls in TMO and DMO.

SIM Security

The SIM security consists of the following security functionality groups:
• Voice E2EE and related key management.
• Network access parameters and authentication.
• Key management for AIE.
• OPTA, modification, encryption, and transfer.
• AES for E2EE of SIM Interface and SIM-Terminal Authentication.
The SIM is an integrated circuit card, which holds a file system and an application. The application performs the
following actions:
• Generation of key stream segments (KSS).
• Synchronization for E2EE.
• TETRA authentication algorithm based on K key on the SIM.
• Key management for E2EE keys.
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TETRA System
Boundary
End-to-End Key Management
Short Data Service Type 4