Functional Descriptions ......
To prevent unauthorised or ‘accidental’ over-air operations, items (b), (c) and (d), described
Security
Checks
on the previous page are carried out using a secure authentication protocol based upon the
synchronization of two pseudo-random number generators, one in the base, one in the
CM1481 unit. Figure 10 shows an operational security transaction.
BASE transmits
Over-Air Request
1
BASE transmits
SEED for Security Check
2
Generates KEY
BASE uses SEED
Security Check is allowed 15secs
to generate KEY
KEY comparison
Correct comparison
= Action Complete
3
Transmits KEY
4
Transmits Comfirmation
BASE
Fig.10 An Over-Air Security Transaction
CM1481
On reception of an over-air request [1] the CM1481 will produce, and transmit, a random
SEED (random number) [2] which will set the start-count position for both pseudo-random
generators; under the control of the configured “Iterations” parameter both generators will
produce the KEY.
Over-Air
Functions
Correct KEY comparison will allow the over-air operation to be completed and confirmed
[3].
Each over-air operation requires its Security Check to be completed within a preset time
period of 15 seconds.
Failure to complete the transaction in the pre-determined time or an incorrect KEY
comparison will result in the cancellation and failure of the relevant operation.
Due to the covert manner of this operation the CM1481 will not produce an “OPEN” or
“Selcall Received” alert during these transactions.
Neither ANI or Transpond functions are available during Over-Air operations.
18
CMLMICRO [ CML MICROCIRCUITS ]
