EF JOHNSON 5100 ES II, Руководство по эксплуатации, Страница: 129 / 144

December 2006 5100 ES Model II/III Portable Radio Operating Manual 10-7
Secure Communication (Encryption)
The actual OTAR rekeying functions are performed by a Key Management Facility
(KMF) that sends Key Management Messages (KMM) to the radios. These messages are
themselves encrypted using an encryption key. Radios must be OTAR-compatible and
programmed for OTAR for this type of rekeying to occur.
OTAR is available only on P25 conventional and trunked channels, and only to program
DES-OFB and AES keys. It is not used on SMARTNET/SmartZone channels.
10.4.1 Encryption Key Types
There are two types of keys used with OTAR:
TEK (Traffic Encryption Key) - The key used to encrypt voice and data traffic. All
radios using encryption must have at least one of these keys.
KEK (Key Encryption Key) - The key used to encrypt keys contained in OTAR Key
Management Messages (KMMs). All radios which use OTAR must contain at least one
of these keys. The KEK used to decrypt/encrypt keys in an OTAR message is defined
by the algorithm and key IDs transmitted in the decryption instructions field. A KEK
may be unique to a particular radio (UKEK) or common to a group of radios (CKEK).
10.4.2 Keysets
A keyset is simply a set of one or more keys of the same type (either TEK or KEK).
Keysets are identified by Keyset IDs.
The KEK keyset is considered always active and has ID 255. Two TEK keysets are
normally used, and one is always active and the other inactive. This allows the inactive
keyset to be replaced without interrupting operation. One is Keyset ID 1 and the other
Keyset ID 2. With EFJohnson radios, each keyset can contain up to 128 keys, but less than
16 are normally used for optimum keying efficiency and because only up to 16 can be
selected by the radio.
The active keyset is usually selected by the Key Management Facility. It can also be
selected by the keyloader function of the EFJohnson SMA (Subscriber Management
Assistant) or by the user if the Change Keyset option switch or menu parameter is
programmed. Automatic keyset changeovers are not supported by EFJohnson radios. In
the SLN mode (see Section 10.2.2), two TEK keysets can be used if desired even if OTAR
is not used.