Motorola MOTOTRBO SYSTEM PLANNER Specifications download pdf (Page 77)

68 System Feature Overview

November, 2008

A customer may need to change one or more keys (in the case of Enhanced Privacy) with a set of

new keys into a set of radios. Some of the reasons for changing keys are:

• Compromise of keys

• Security policy of the customer requires periodic update of keys

• Loss of a radio resulting in a concern that this may lead to compromise of keys or

eavesdropping.

The easiest way to implement a key switchover is to gather all radios and re-program them at one

go. But it may not always be possible to gather all the radios without seriously affecting day-to-day

operations.

An alternate method is to create two zones where one zone is set to unprotected while the other is

set to “protected”. The key can be changed on the protected zone and the users shall use the

unprotected zone until all radios have been updated. Once all radios have been updated, the

dispatcher informs the fielded radios to switch zones. This allows users to communicate in clear

until the all radios are provisioned, and then all the users switch keys at the same time.

A similar zone strategy can be used to perform periodic key set changeovers. For example, when

one zone has January’s keys and another duplicate zone has February’s keys. On the first of

February, the users switch to the February zone. Throughout February, the January zone is

updated with March’s keys and renamed to “March Keys”. On the first of March, the users switch,

and so cycle starts again. This makes sure that only two months of keys are compromised if a

radio is stolen or lost.

2.7.9 Multiple Keys in a Basic Privacy System

Although a radio can only use one key in a Basic privacy system at a time, a Basic privacy system

may utilize multiple keys to sub-divide a group into a set of groups. Note that this is not a

recommended configuration, and some considerations need to taken into account, if the decision

is made to utilize multiple keys in a system.

It is not recommended that Groups be sub-divided into smaller groups with the use of keys. This

results in one sub-group of users hearing unintelligible audio (or digital warbles) when the other

sub-group communicates. It is recommended that the users should be divided into Groups, and

provisioned so that a user can not transmit nor receive on the other’s Group. If users with different

keys are allowed to communicate with Basic privacy enabled, for example via a protected private

call, a key mismatch will occur and unintelligible audio will be heard. Although these users with

different keys will never be able to communicate privately, they will be able to communicate when

privacy is disabled.

For example, two different Groups are isolated by provisioning different privacy keys. When a user

in each Group needs to communicate to each other via a private call, they must do it with privacy

disabled. If a radio user needs to communicate with both Groups via an All Call, the radio user

must transmit in clear mode so that both Groups can monitor. If users respond with privacy-

enabled, the user who initiated the All Call only monitors the responses protected with a matching

key.

If the system is utilizing data applications and must communicate through a control station to the

application server, all radios on a slot must have the same key or they will not all be able to

properly communicate with the control station. For similar reasons, it is not recommended to have

radios without privacy capability, i.e. older software versions, in the same Group as radios with

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Motorola MOTOTRBO SYSTEM PLANNER Specifications Page 77

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