Cryptography – Cryptanalysis
Patent
1992-09-04
1994-08-02
Buczinski, Stephen C.
Cryptography
Cryptanalysis
380 20, 380 33, 380 36, H04N 7167
Patent
active
053352750
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the broadcasting and transmission of signals such as television signals, which are to be encoded for commercial or other purposes.
In the transmission of programmes for subscription systems such as satellite or cable television, it is desired to encode the signal in such a way that it cannot be properly received without a suitable decoder so that the viewer is obliged to pay for reception of the programmes. Various methods of encoding are known, one common method being to rearrange parts of the video signal. However many of the known methods suffer from technical overcomplexity and in particular it is desirable to reduce the complexity of the decoder which must be provided at the receiver or receiving station. Accordingly the present invention provides apparatus for encrypting or decrypting a signal comprising a series of values or groups of values, comprising a memory having a predetermined number of storage locations or groups of locations;
means for reading output values or groups of output values from, and writing new input values or groups of input values into, each of said locations or groups of locations in a first predetermined order until the said predetermined number is reached, and further
reading output values or groups of output values from, and writing new input values or groups of values into, each of said locations or groups of locations in a second predetermined order until the said predetermined number is reached;
and control means for causing the reading and writing operations to be repeated alternately in the two said predetermined orders.
The invention also provides a method of encrypting or decrypting a signal comprising a series of values or groups of values, using a predetermined number of storage locations or groups of locations in a block of memory, the method comprising the steps of: (a) reading output values or groups of output values from, and writing new input values or groups of input values into, each of said locations or groups of locations in a first predetermined order until the said predetermined number is reached;
(b) reading output values or groups of output values from, and writing new input values or groups of values into, each of said locations or groups of locations in a second predetermined order until the said predetermined number is reached; and
(c) subsequently repeating steps (a) and (b) alternately.
Preferably one order is sequential and the other order is random or pseudo-random. Particularly in the decoder the same block of RAM can thus be used for both storage and retrieval, rather than moving the line data between different RAMs, with the actual storage and retrieval process causing the "scrambling" rather than some additional intermediate process so as to provide a simplified and economical construction. However, for additional flexibility of operation, the encoder may utilise a shuffling memory comprising two blocks of RAN memory. Preferably, means are also provided for shifting the lines by a small percentage horizontally to further scramble the transmission.
Preferably the randomly variable order is determined by supplying a "seed" to a random or pseudo-random number generator, which may be changed periodically to provide a different random sequence. The random seed may be independently programmed into the coder and decoder or it may be regularly retransmitted so as to frequently "reprogram" the decoder.
One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:
FIG. 1 is a schematic block diagram of a signal encoder in accordance with the invention,
FIG. 2 is a schematic block diagram of a decoder; and
FIG. 3 is a more detailed block diagram of the decoder of FIG. 2.
ENCODER (FIG. 1)
General
The system will be described with reference to a PAL television broadcasting system, but it will be appreciated that it could also be applied to other systems such as NTBC.
The system digitises and stores 32 or 128 lines of normal video information and retrieves th
REFERENCES:
patent: 4275265 (1981-06-01), Davida et al.
patent: 4563702 (1986-01-01), Heller et al.
patent: 4663659 (1987-05-01), Blatter
patent: 4691352 (1987-09-01), Arragon et al.
patent: 4910772 (1990-03-01), Matias et al.
Greenhalgh Stephen J.
Gregory Richard P.
Millar David J.
Buczinski Stephen C.
DCE Voice Processing Limited
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