Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1996-09-20
1998-11-03
Gregory, Bernarr E.
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 9, 380 44, 380 46, 380 49, 380 50, H04L 908, H04L 900
Patent
active
058320873
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to arrangements for the automatic encryption and decryption of electronically transmitted messages, particularly in the fields of telephone, facsimile or computer data transmission for example.
The present invention is concerned with providing arrangements for encrypting and decrypting messages at high speeds yet maintaining a high level of security.
SUMMARY OF THE INVENTION
In accordance with this invention, there is provided an encryption/decryption apparatus to enable encrypted communication between two stations each incorporating such an apparatus, the apparatus being arranged to generate a set of look-up tables in accordance with a session key and temporarily store said tables in memory, and to convert each successive element of a message to a code through use of said look-up tables.
It will be appreciated that a fresh session key is used for each transmission or session: a fresh set of look-up tables is therefore generated at the start of each transmission or session. The session key can in fact be changed (and a new set of look-up tables consequently generated) at intervals during the course of each transmission.
The set of look-up tables can be generated quickly, and the procedure to encode each element (e.g. character, bit or block) of the message can be carried out quickly yet maintaining a high level of security.
Each element of the message may be converted to its code by addressing one of the look-up tables, the output of which is used to address another of the look-up tables, and so on. The conversion procedure may involve at least two look-up tables being addressed simultaneously and their outputs being combined (e.g. added together). At least one of the tables may comprise a pseudo random sequence, the terms (or entries) of which are read consecutively, the pointer returning to the first term when the last term of the table has been read: the pointer may start at any predetermined position of the sequence.
It will be appreciated that for encryption of a message by the sender and correct decryption by the recipient, both sender and recipient apparatus must use the same session key for each transmission (or part thereof), so that the two stations can generate corresponding look-up tables. Our International patent application PCT/GB94/02004 describes one arrangement in which a sender apparatus generates a session key and the same session key is recreated at the recipient.
Embodiments of this invention will now be described by way of examples only and with reference to the accompanying Drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram of an encrypting/decrypting unit used at each sender/recipient station;
FIG. 2 is a schematic flow diagram to explain the operation of one form of high speed cypher in accordance with the invention;
FIG. 3 is a similar flow diagram to explain the operation of another form of high speed cypher in accordance with the invention;
FIG. 4 is a worked example of an encryption procedure performed by an apparatus in accordance with the invention; and
FIG. 5 is a worked example of another encryption procedure performed by an apparatus in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, there is shown an encryption/decryption unit 20 in accordance with this invention, in simplified diagrammatic form. Typically the unit 20 will form part of a communications machine (e.g. facsimile machine). The unit 20 includes an external port 10 for transmitting encrypted data to, and receiving encrypted data from, a corresponding unit at another station, with which it is desired to communicate. The unit also includes a port 12 for the flow of data to and from local host equipment. The unit 20 further includes a microprocessor 14 having a program memory 16 and a memory 18 for temporarily holding look-up tables which are used for encrypting data to be transmitted via the external port 10, and for decrypting data received via the external port 10
REFERENCES:
patent: 4776011 (1988-10-01), Busby
patent: 5063596 (1991-11-01), Dyke
patent: 5204901 (1993-04-01), Hershey et al.
Establishment of User Keys in a Multi-User Network, C.H. Meyer and W.L. Tuchman, IBM Technical Disclosure Bulletin, vol. 22, No. 2, Jul. 1979, pp. 629-631.
Chantilley Corporation Limited
Gallagher Thomas A.
Gordon David P.
Gregory Bernarr E.
Jacobson David S.
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