Cryptography – Key management – Having particular key generator
Patent
1984-11-20
1988-07-12
Buczinski, Stephen C.
Cryptography
Key management
Having particular key generator
380 14, H04N 7167
Patent
active
047575310
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the transmission and reception of television signals in either digital or sampled analogue form. The preferred form of the invention is concerned with the encryption of a multiplexed analogue component (MAC) video signal.
Theoretically, with a digital or sampled analogue signal, the number of encryption methods is almost limitless. However, with video signals of finite bandwidth, care must be taken not to degrade the received picture due to the encryption. For this reason, the present invention proposes to leave unaltered the active picture time and to use the minimum specified by CCIR.
2. Prior Art
In our co-pending application published as International Publication No. WO83/03942 we have disclosed a multiplexed analogue component television signal which is encrypted for transmission and reception by authorised receipients only by dividing the signal into blocks and reordering the blocks prior to transmission. The signal within each block remains in its original order. The preferred arrangement does not split the blocks of analogue signals already present in the MAC signal.
The present invention is an improvement in or modification of the arrangement disclosed in No. WO83/03942 to the extent that it is now conceived that either or both of the original analogue blocks may be cut into a plurality of sections, and the order and/or timing of the commencement of sections altered.
Preferably, only the block containing chrominance signals is split, the block containing luminance signals being unsplit but its position in the line being altered with respect to the original signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of the present invention will become apparent from the following description of embodiments thereof when taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows diagrammatically one line of one form of MAC video waveform;
FIGS. 2 to 7 show the waveforms of various schemes for scrambling the waveform shown in FIG. 1;
FIG. 8 shows diagrammatically one line of another form of MAC video waveform;
FIGS. 9 to 11 show the waveforms of various schemes for scrambling the waveform shown in FIG. 8;
FIGS. 12(a) and 12(b) show two ways in which transitions may be achieved;
FIG. 13 shows in block diagram form a part of a receiver for receiving an encrypted television signal;
FIG. 14 shows in block diagram form a detail of part of the receiver shown in FIG. 13
DETAILED DESCRIPTION
The preferred method of encryption is called rotation scrambling in which the active picture time is left unaltered. FIG. 1 shows one C-MAC waveform. The portion `f` of eight samples (400 ns), has been reserved for encryption purposes. These samples will be redistributed depending upon the scrambling method used and in some circumstances may be combined with samples which allow for changes in the dispersal waveform (portion b and h). All resulting samples are used to form transitions which protect the cut edges of the scrambled waveform from distortion.
Furthermore, efficient use of the line time occurs when the luminance and chrominance `cuts` can be made to be continuous in the scrambled state. The two transitions which would normally take place can now be reduced to a single disturbance and a saving of samples results.
In order to determine the minimum number of samples required for a transition, two step functions passed through a software simulated linear satellite transmission channel. The edges of the input steps were designed to be 120 ns, 200 ns and 250 ns raised cosine edges respectively. The simulations show the following:
If a 120 ns edge was used 490 ns would be needed for the `cut` transition time.
If a 200 ns edge was used 260 ns would be needed to cope with the `cut`.
If a 250 ns edge was used only 250 ns would be needed for the `cut`.
This indicates that a very minimum of five samples should be used for the transition. Interpolation techniques can be optimised for the particular scrambling
REFERENCES:
patent: 4070693 (1978-01-01), Shutterly
patent: 4405942 (1983-09-01), Block et al.
patent: 4435393 (1982-06-01), Pearson
patent: 4563702 (1986-01-01), Heller et al.
patent: 4636851 (1987-01-01), Drury et al.
Flannigan Barry A.
Lodge Nicolas K.
Mason Arthur G.
Buczinski Stephen C.
Independent Broadcasting Authority
Wallace Linda J.
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