Cryptography – Key management – Having particular key generator
Patent
1993-02-02
1994-06-14
Barron, Jr., Gilberto
Cryptography
Key management
Having particular key generator
380 46, 375115, 371 471, H04L 926, H04L 710
Patent
active
053217543
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of pseudo random sequence generation and apparatus for use therein and comprises extensions of the methods and apparatus described in our U.S. Pat. No. 5,237,593 the contents of which are incorporated herein by reference.
In U.S. Pat. No. 5,237,593 there is described a method for scrambling a data sequence by the modulo addition at the transmitter of a pseudo random sequence, descrambling being achieved by the modulo subtraction at the receiver of the same pseudo random sequence, the receiver PRS generator being synchronised to that in the transmitter by means of conveying samples over the same transmission channel as the data from the transmitter PRS to a synchronisation mechanism in the receiver PRS.
According to one aspect of the present invention there is provided an apparatus for transmitting a data sequence from a transmitter to a receiver, including means at the transmitter for scrambling the data sequence by modulo addition thereto of a pseudo random sequence (PRS) output from a PRS generator at the transmitter, and means at the receiver for unscrambling the received scrambled data sequence by modulo subtraction therefrom of the same PRS, the PRS at the receiver being generated by a respective PRS generator thereat, the receiver PRS generator being synchronised to the transmitter PRS generator by means of samples taken from the transmitter PRS and conveyed to synchronisation means at the receiver, and wherein the transmitter includes a PRS sample mapping block and the receiver includes a functionally complementary sample mapping block and the time of transmission of the conveyed samples is decoupled from the points in the PRS for which they were selected, the conveyed samples being skewed with respect to the PRS, thereby to optimise the performance of the apparatus.
According to another aspect of the present invention there is provided a method of transmitting a data sequence from a transmitter to a receiver including the steps of scrambling the data sequence by modulo addition thereto of a pseudo random sequence (PRS) output from a PRS generator at the transmitter, and unscrambling the received scrambled data sequence at the receiver by modulo subtraction therefrom of the same PRS, the PRS at the receiver being generated by a respective PRS generator thereat, the receiver PRS generator being synchronised to the transmitter PRS generator by taking samples from the transmitter PRS and conveying the samples to synchronisation means at the receiver, the samples taken being added with predetermined skew to the data sequence for transmission whereby the time of transmission of the conveyed samples is decoupled from the points in the PRS for which they were selected.
According to a further aspect of the present invention there is provided a method of synchronising a first sequence generator, obeying a generator polynomial whose coefficients and operators are defined over a Galois Field, disposed at a data receiver with a second identical sequence generator disposed at a data transmitter, including the steps of selecting samples from the source sequence produced by the second generator and adding these with predetermined skew to a data stream for transmission from the transmitter to the receiver, which data stream includes a predictable data value at intervals, framing the received data and thus determining the interval and the positions of the predictable data values, and sampling the received data at said positions, the resultant sequence of samples comprising a sampled version of the selected and skewed samples of the sequence produced by the second generator, determining the phase of the second generator from the selected sequence samples and adjusting the phase of the first generator to correspond to that of the second generator, which method serves also for automatically determining at said data receiver whether said data transmitter has applied its sequence generator.
The present application thus relates to an extension of the mechanism of U.S. Pat. No. 5,237,593 i
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Brueckheimer Simon D.
Fisher David A.
Barron Jr. Gilberto
Northern Telecom Limited
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