Browse Prior Art Database

Verification of Message Blocks and the Detection of Transmission Errors by a Step Cipher

IP.com Disclosure Number: IPCOM000075310D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Related People

Notz, WA: AUTHOR [+2]

Abstract

This is a method for verifying the integrity of messages of indefinite length within a cryptographic system by a step cipher.

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Verification of Message Blocks and the Detection of Transmission Errors by a Step Cipher

This is a method for verifying the integrity of messages of indefinite length within a cryptographic system by a step cipher.

In a block cipher system, it is desirable to include within each message block one or more bytes to be used for the purpose of verification. This verification field can be utilized as a password in a challenge-reply authentication procedure, to ensure the continuity and validity of each block of a message, and also to ensure that identical stereotyped messages will be enciphered in a different way, each instance, through use of a unique initial verification field.

A step cipher is one in which a clear text block to be enciphered is made to consist of X message bytes and Y bytes for verification; after encipherment, X bytes of the cryptogram are transmitted and Y bytes are saved to be appended to X new message bytes to make up the second block to be enciphered, etc. At the receiver, blocks of cipher text so prepared are deciphered in the reverse order, and the last one deciphered will contain the verification field.

In the Fig. there is shown a method for carrying out the step cipher so that, instead of transmitting only X bytes of each cryptogram block, the entire block (X + Y bytes) is transmitted. By this procedure, the entire cipher text is greater in length than the message by the factor (X + Y)/X, but the cryptogram blocks may be deciphered at the receiving station in the same order as they are received. For purposes of illustration, X has the value 4, and Y the value 2. Clear text messages originating at the CPU are shown in upper-case roman, and clear text originating at a terminal is shown in lower-case roman; cipher text is in lower- case Greek.

The initial clear text message to be sent from the CPU is represented to be ABCDEFGHJKLM. The first block to be enciphered is ABCD to which is appended PQ, here denoting the unique date and time. Encipherment produces the...