Browse Prior Art Database

TIME DIVISION MULTIPLEXING IN CRYPTOGRAPHIC SYSTEMS

IP.com Disclosure Number: IPCOM000006249D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-18
Document File: 5 page(s) / 233K

Publishing Venue

Motorola

Related People

Dean E. Banwart: AUTHOR [+2]

Abstract

Digital voice and data encryption requirements con- tinue to grow in the industry The application of time division multiplexing techniques to high speed encryption key generator devices or algorithms can increase the flexibility and ease of management of cryptographic sys- tems with multiple key variables. This technique, coupled with newly emerging low bit-rate voice coding techniques and high speed processing capability, makes this technique especially useful for encrypted voice communication applications as well.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 26% of the total text.

Page 1 of 5

0 M

MOTOROLA INC. Technical Developments Volume 14 December 1991

TIME DIVISION MULTIPLEXING IN CRYPTOGRAPHIC SYSTEMS

by Dean E. Banwart and Michael L. Bushman

as well as the new burden to effectively manage the multi- ple encryption keys. The need for simultaneous encryption can be as simple as providing means to support a full- duplex exchange, or as complicated as providing unique encryption services to every user in a densely populated crypt0 network.

ABSTRACT

  Digital voice and data encryption requirements con- tinue to grow in the industry The application of time division multiplexing techniques to high speed encryption key generator devices or algorithms can increase the flexibility and ease of management of cryptographic sys- tems with multiple key variables. This technique, coupled with newly emerging low bit-rate voice coding techniques and high speed processing capability, makes this technique especially useful for encrypted voice communication applications as well.

BACKGROUND

   Common applications utilizing digital encryption for voice and data typically employ key generator circuits as depicted in Figure 1. In such systems, a key generator device is used to generate a sequence of values (binary, discrete, or continuous) known as a keystream. This key- stream is bit-wise modulated (using module-2 addition) on to an un-encrypted digital message (plaintext) to render a hxnsformation to ciphertext. Likewise, the keystream can be applied to ciphertext to produce plaintext.

  Because of complications including complexity, syn- chronization logistics, access times, and others, many voice and data applications use a single key generator source to provide crypt0 service for transmissions/receptions. However, within the scope of a single communications system, it is often desirable to encrypt multiple exchanges occurring simultaneously. In order to add increased com- munication security, it is often desirable to ensure that each exchange is encrypted with a unique keystream. Many current systems employ multiple key generator devices to produce this effect. This, however, adds cost to the system

Input Data JYtutput Data Figure 1. A typical Key Generator configuration. TlME DIVISION MULTIPLEXING

  A solution to this problem is obtained by applying the concept of Time Division Multiplexing to the Key Generator circuits. By generating a keystream with a data rate N times faster than the rate of the data to be encrypted/decrypted, the equivalent of N Key Genera- tors or crypto-variables is provided. Refer to Figure 2. In this example, N plaintext bit streams of rate X bits per second are encrypted form a source which produces keystream at a rate of N times X.

I

Shift Register

I

Key Variable

0 MofOr01a.

,nc 1991 1

[This page contains 14 pictures or other non-text objects]

Page 2 of 5

MOTOROLA INC. Technical Developments Volume 14 December 1991

\ Combiner / 'TDM Synchronization Information v Key Vary J

I L Time Division Multiplexer Keystream...