Cryptography – Particular algorithmic function encoding – Nbs/des algorithm
Patent
1985-03-15
1989-01-31
Cangialosi, Salvatore
Cryptography
Particular algorithmic function encoding
Nbs/des algorithm
380 20, 380 47, H04L 904, H04N 7167
Patent
active
048022152
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a security system for television signal encryption, usable in the transmission and reception of television signals in either digital or sampled analogue form. In particular, the invention relates to such a security system which can provide an effective payment monitoring facility whereby relevant information can be transmitted, for example, in a satellite broadcasting channel. The invention may be used in the encryption of a multiplexed analogue component (MAC) television signal.
The present invention is a development of certain aspects of the system described in our co-pending application U.S. Ser. No. 317796, and reference is directed thereto.
PAY-PER-VIEW
Pay-per-view is a very important feature which all subscription television services should contain. Typically, the decision to watch a programme is made in the few minutes before a service is broadcast. This factor of human behaviour could be very important to the economics of providing a new type of public service broadcasting. If the customer has to decide well in advance which programmes he will watch the viewer will tend to make a conservative estimate for his entertainment budget. Pay-per-view can be offered quite simply by including a meter in the receiver. A payment is made by the viewer to the broadcaster who then transmits the payment to the customer's receiver in the form of `electronic` over-air credit. The over-air credit is sent with the viewers validation signal and it is entered into the meter in his receiver. A money store is provided for each television channel and the store is decremented by a cost code which accompanies the television signal. In this way a viewer is able to gain immediate access to programmes and furthermore, he only pays for those programmes that he watches.
Over-air credit provides a convenient and economical means of transferring credit units into a store in the receiver. However, in order that the system operates securely certain facts have to be taken into account: quantity of credit units when the same quantity is being repeatedly transmitted; have been received correctly in the presence of noise; and a standing order, when the customer leaves the receiver switched off for a time longer than the payment period (such as when the customer goes away on holiday).
The present invention is able to cope effectively with factors (i) to (iii). Factor (iv) is catered for provided a very large number of credit units are not missed.
Features and advantages of the invention will become apparent from the following description of a preferred embodiment thereof, given by way of example, and when taken in conjunction with the accompanying drawings, in which:
FIG. 1 shows a block diagram of the signal paths in a transmitter/receiver system in accordance with one embodiment of the invention;
FIG. 2 is a diagram for explaining the statistics for validation of non-unique information; and
FIGS. 3a and 3b show a technique for producing cipher text that has certain properties which are desirable in the invention.
The arrangement to be described, specifically with reference to FIG. 1, involves a technique by which over-air credit information may be sent securely under conditions of low signal-to-noise ratio, such as in a noisy satellite channel. A predetermined quantity of credit units (hereinafter referred to as "money") are sent to each customer per payment interval, encrypted in the transmitted signal, and entered in a meter in the receiver. The meter is decremented upon reception of a programme cost code in the transmitted signal. In this way, a full pay-per-view service can be made available to all categories of customer. The service can be organised on a pre-payment basis by transmitting appropriate credit units upon payment in advance by the customer.
In accordance with the preferred technique, the following steps must be made in order to transmit securely money to each receiver for entry in the meter. The techniques described may also be applied when the system is used for tiering or a basic
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Cangialosi Salvatore
Independent Broadcasting Authority
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