Browse Prior Art Database

Stream Block Cipher Scheme

IP.com Disclosure Number: IPCOM000084646D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Ehrsam, WF: AUTHOR [+3]

Abstract

This cryptographic scheme combines a stream cipher technique with a block cipher technique to provide an enhanced resultant cryptographic method. The resultant cryptographic method has the advantage of expanding the block size b of the block cipher to a new block size B, which is variable in size and determined by line control mechanism used. The stream cipher unit could, for example, include a linear N-stage shift register SR of the type shown in the article Enciphering Data for Secure Transmission by C. R. Meyer, Computer Design, April 1974, pages 129-134.

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Stream Block Cipher Scheme

This cryptographic scheme combines a stream cipher technique with a block cipher technique to provide an enhanced resultant cryptographic method. The resultant cryptographic method has the advantage of expanding the block size b of the block cipher to a new block size B, which is variable in size and determined by line control mechanism used. The stream cipher unit could, for example, include a linear N-stage shift register SR of the type shown in the article Enciphering Data for Secure Transmission by C. R. Meyer, Computer Design, April 1974, pages 129-134.

An initializing vector Z, which may be changed for each transmission, is set into the N stages of the linear shift register, and feedback switches of the register are set in accordance with a key K1. The output R from the first stage of the shift register is a pseudo-random number which is then added (indicating a modulo - 2 addition or, equivalently, an exclusive OR operation) to the clear text X on a bit- by-bit basis to obtain an ciphered text Y1.

The enciphered message is fed back to the feedback switches of the shift register SR, to assure intersymbol dependence between the ciphered text and the clear text. While such a crypto scheme is weak, it can be strengthened by applying the ciphered text as an input, on successive block b bases, to a block cipher unit BC which may be of the type shown in U. S. patent No. 3,798,359.

The block cipher unit BC further enciphers the text Y1 i...