ANALOG DTMF ENCRYPTION
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-19
In current analog trunking systems, Motorola provides a secure 12kb option. This option will give a user secure voice communications. A current prob- lem with many 12kb secure systems is that the DTMF tones can not be encoded into I2kb secure. The analog systems today solve this problem by "fall- ing back" to non-secure mode to transmit the DTMF tones. Anyone "listening" to the communications can "pick" the DTMF tones up and decode them with off the shelf equipment into numbers. These numbers can be phone numbers, credit card num- bers, calling card numbers, or access numbers. With no way to secure this information, users who think A mobile can still fallback to non-secure mode to transmit the DTMF digits, but the radio will encode the DTMF digitswhile in a secure call. The mobile can use the same encoding algorithm and key that is used for the voice encoding, but the DTMF tones are encoded across a DTMF alpha- bet. The fixed end will then decode the DTMF tones using the same algorithm and key. The algorithm used can be any known or new algorithm, as long as a DTMF alphabet is used.