Browse Prior Art Database

ANALOG DTMF ENCRYPTION

IP.com Disclosure Number: IPCOM000007531D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-03
Document File: 1 page(s) / 47K

Publishing Venue

Motorola

Related People

Kristin Cramer: AUTHOR [+3]

Abstract

In current analog trunking systems, Motorola provides a secure l2kb 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 12kb 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 they may be transmitting their access numbers securely are not.

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Technical Developments

ANALOG DTMF ENCRYPTION

by Kristin Cramer, Mike Wirtjes and Jeff Jacobs

BACKGROUND

  In current analog trunking systems, Motorola provides a secure l2kb 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 12kb 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

they may be transmitting their access numbers securely are not.

SOLUTION

  A mobile can still fahback to non-secure mode to transmit the DTMF; digits, but the radio will encode the DTMF digits while 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 ftxed 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.

KEY w 1 I

KEY a

DTMF Tones From Radio To Phone Exchange

0 Motorola. 1°C. 19%

50 November1995

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