H - Electricity
04
L
340/70
H04L 9/00 (2006.01)
Patent
CA 1133086
ABSTRACT OF THE DISCLOSURE Apparatus for use in a secure data communicaton system includes a microcomputer that controls a cipher process by which sensistive data is encrypted before trans- mission. When activated, the apparatus accepts either clear- text or ciphertext and transforms the text to its opposite form according to an algorithm that is past dependent and which is also dependent on a pseudo random cipher key. Ciphertext may then be stored in an information retrieval system or transmitted to a destination terminal where the text is deciphered in real time by a corresponding second apparatus that stores the same key. In either case, security of transmitted and stored data is maintained since the sensi- tive data is in encrypted form. A set of logical instructions according to the algorithm is stored in a read only memory of the microcomputer which includes an EPROM unit having a data field of predetermined characters. The cipher process is initiated by a control character and starts with predeter- mined seeds that establish a first origin in the data field for each line of text to be encrypted. This origin is then translated to a second origin of the data field in response to four characters that are randomly generated by a counter. A variable sequence of iterative logical operations trans- forms cleartext to ciphertext and provides a key stream that is non-linear, random-like and which possesses an encryption period that is substantially longer than the period of any line so that the periodicity of the key stream is never indicated. The cipher keys for each line of text are tempo- rarily stored in a read/write memory to permit editing operations and are erased at the onset of the next line.
310805
Eberle Gernot
Goodchild William
Humbert-Droz Patrice L.d.
Walker Anthony R.
Michaels & Associates
Northern Telecom Limited
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