Telegraphy – Systems – Printing
Patent
1981-06-10
1984-02-14
Cangialosi, Sal
Telegraphy
Systems
Printing
178 2219, 178 2209, H01K 100
Patent
active
044318650
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCES TO RELATED APPLICATIONS
Applicants hereby make cross references to their Patent Application PCT/FR 80/00 149, filed Oct. 10, 1980 and claim priority thereunder following the provisions of 35 U.S.C. 119.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for enciphering and deciphering a digital signal conveying n-bit words N.sub.i, wherein i denotes the rank of the word N.sub.i in the signal, into a digital enciphered signal having n-bit words R.sub.i, said system comprising, in an enciphering unit at the transmitting end, logic means for performing a logic function g applied to each word N.sub.i and to a predetermined n-bit word P.sub.i-1 to produce the corresponding enciphered word R.sub.i =g(N.sub.i, P.sub.i-1) and means further comprising a register receiving the enciphered word R.sub.i to produce the words P.sub.i-1 according to a predetermined algorithm based on the enciphered words R.sub.i, and, in a deciphering unit at the receiving end, logic means for performing a logic function h, called contrary to or the complement of the g operation, applied to each enciphered word R.sub.i and to the predetermined word P.sub.i-1 to produce the corresponding deciphered word N.sub.i =h(R.sub.i, P.sub.i-1) and means analogous to these of the enciphering unit for producing words P.sub.i-1.
2. Description of the Prior Art
The enciphering and deciphering terms are used in the present specification for the particular application to a signal conveying alphanumeric signals; however the invention is, generally speaking, related to any encrypting and decrypting, encoding and decoding or scrambling and unscrambling of a digital signal. Reference is made, hereinafter, as an examplary application, to the digital signal which is emitted from a teletext system and conveys, via a broadcasting network transmission medium, such as televized pictures network, pages of writing that will be visualized by conventional television receivers.
In a teletext system, the written pages are made up of alphanumeric characters which carry the information and characters required for the syntax and are generally transmitted in the form of 8-bit bytes. At the transmitting end, the digital signal conveying the characters is applied to multiplexing means which suitably insert it into the conventional video signal, for example into the frame synchronizing and blanking signals. After having been carried via the television link, the composition signal is received in the user's terminal and is demultiplexed to separate the digital signal from the video signal. By using a syntactical monitor, the written pages conveyed by the digital signal are reproduced for visualization by the television set.
The access controlling device embodied in a teletext system is of a conventional nature. The calling subscriber has an access means consisting of a data medium in which all the data characterizing the user and his accessible area are stored. The controlling device acquires this data and compares it, on the one hand, with the identified data which may perhaps be inside the terminal and, on the other hand, with the data characterizing the user's call. If the comparison is positive, the system "gives access" to the information.
In a broadcast teletext system, the information is received virtually everywhere and is thus accessible via straightforward technological means available to the general public. Transmission at frequencies specifically earmarked for this use would only constitute an illusory protection. The same goes for any device which would keep the information in a directly usable form. Moreover, the advent and the fast-growing spread of "house-hold or personal" computer set-ups is placing considerable computation powers at the hands of an increasing number of people. In view of all this, it would seem essential to encipher not only the teletext system order codes, but the whole data message. This solves, incidentally, the problem of the secrecy which may well be necessary for certain ins
REFERENCES:
patent: 3984668 (1976-10-01), Zetterberg et al.
patent: 4133974 (1979-01-01), Morgan
patent: 4323921 (1982-04-01), Guillou
patent: 4337483 (1982-06-01), Guillou
Article by Jeffery and Brandstad in Electro Conference Record, 1977, "Data Encryption", El Segundo, CA.
Communications of the ACM, vol. 17, No. 8 (8/74) pp. 437, 442, Evans et al.
Bernede Georges G.
Gregeois Jean M.
Cangialosi Sal
Telediffusion de France
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