E.F. Johnson Company 5100 ES, Руководство по эксплуатации

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ES Series Models II/III Portable Radio Operating Manual 11-3
Secure Communication (Encryption)
11.2 Encryption Keys
An encryption key is a cryptographic variable that is required by the encryption algorithm
to encrypt and decrypt voice or data. To maintain system security, these keys must be
protected from disclosure and also periodically replaced or updated.
With the AES and DES encryption used by EFJohnson Technologies radios (see Section
11.1), the same encryption key is used by both the encrypting (sending) and decrypting
(receiving) radio. AES encryption keys are generated from a string of 64 hexadecimal
characters, and DES keys are generated from a string of 16 hexadecimal characters.
Another four hexadecimal characters are used to specify the key ID. Multiple keys can be
loaded into a radio using OTAR or manual loading.
When an encrypted message is transmitted, the encryption Algorithm ID (ALID) and key
ID (KID) are usually included in the message. This tells the receiving radio which key and
algorithm must be used to decrypt the message.
If an attempt is made to transmit a secure message without loading the corresponding key,
“Keyfail” is displayed. The message must then be transmitted in the clear mode (this is
possible only if the channel is strapped to “switchable”) or the key must be loaded.
11.2.1 Key and Algorithm IDs
Each encryption key is programmed with a Key ID (also called Logical ID). This ID plus
the algorithm ID (ALGID) is transmitted in the message on digital channels. The radio
receiving the message must have a key with the same IDs in order to decrypt it.