Browse Prior Art Database

Prevention of Unauthorized Use of a Credit Card

IP.com Disclosure Number: IPCOM000073403D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Gaston, CA: AUTHOR

Abstract

One of the ways of determining proper custody of a credit card is to have an N-digit secret number or word associated with the card. The secret number known only to the card holder must be presented with the card and is decoded to match a validation code on the card. With prior secret number systems, a thief with a stolen card and a validation machine can readily determine the secret number because there is an easily determined reverse transformation from the validation code to the secret number. The following system overcomes this deficiency. The new decoding system is a one-way transformation of the N-digit secret number to a validation code, the transformation has no pattern and there is no reverse transformation from the validation code back to the secret number.

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Prevention of Unauthorized Use of a Credit Card

One of the ways of determining proper custody of a credit card is to have an N-digit secret number or word associated with the card. The secret number known only to the card holder must be presented with the card and is decoded to match a validation code on the card. With prior secret number systems, a thief with a stolen card and a validation machine can readily determine the secret number because there is an easily determined reverse transformation from the validation code to the secret number. The following system overcomes this deficiency. The new decoding system is a one-way transformation of the N-digit secret number to a validation code, the transformation has no pattern and there is no reverse transformation from the validation code back to the secret number. The lack of a reverse transformation forces a thief to determine the secret number by trial and error. The lack of a pattern in a transformation means there is no indication of whether the trial secret number is close to the actual secret number. This prevents a person from determining the secret number quickly by following a trial and error path of increasing similarity between the validation code on the card and the validation code generated from the trial secret number. There are several ways of implementing this system.

An N-digit validation code is produced by the following transformation scheme, although a validation code having fewer or more digits can be produced in the same way. The figure is a table which produces the transformation. The table has N columns and 10 rows, one row for each of the numerals zero through nine. To accommodate those people who prefer to memorize a word, rather than a number, several letters of the alphabet are associated with each numeral. N, the number of columns, is determined by the degree of security desired and is equal to the number of digits in the secret number. To decode the secret number, the number in the row corresponding to the first digit of the secret number is extracted from the second column of the table; etc. The numbers extracted from the table are added, discarding carries. The number manipulation may be done by hand or automatically by machine. The decoding of SAFETY and SAFELY are show...