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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. This is also another name 
for the keys used without OTAR.

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).

To simplify key management, a number of keys may be grouped together in a keyset. 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, and the upper four bits of this ID specify the crypto group 
(see next section).

The KEK keyset is considered always active and is 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 EFJohnson SMA keyloader or by the user if the KY CHG option switch is 
programmed. Automatic keyset changeovers are not supported by EFJohnson radios. In 
the SLN mode (see Section 11.2.2), two TEK keysets can be used if desired even if OTAR 
is not used.

A diagram of a keyset is shown in Figure 11.2. Some information may be optional as 
shown. The 5300 ES mobile does not support or use the Update Item and Time/Date 
parameters.