CA1303208C - System for enabling descrambling on a selective-subscription basis in a subscriber communication network - Google Patents
System for enabling descrambling on a selective-subscription basis in a subscriber communication networkInfo
- Publication number
- CA1303208C CA1303208C CA000615869A CA615869A CA1303208C CA 1303208 C CA1303208 C CA 1303208C CA 000615869 A CA000615869 A CA 000615869A CA 615869 A CA615869 A CA 615869A CA 1303208 C CA1303208 C CA 1303208C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- subscriber
- line
- scrambled
- credit
- Prior art date
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- Expired - Lifetime
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Abstract
SYSTEM FOR ENABLING DESCRAMBLING ON A SELECTIVE-SUBSCRIPTION
BASIS IN A SUBSCRIBER COMMUNICATION NETWORK
ABSTRACT OF THE DISCLOSURE
A system in a subscriber television network for enabling descrambling of a received scrambled signal on a prepaid basis and/or an impulse-purchase basis. A received mask signal uniquely related to the scrambled signal is compared with a received authorization signal indicating whether the subscriber is authorized to receive the scrambled signal on a prepaid basis and a prepaid signal for enabling descrambling is provided when the compared signals match. A not-prepaid signal is provided when they do not match. A received cost signal indicating the charge for descrambling the scrambled signal and a received credit signal indicating the subscriber's accumulated credit are processed with reference to a stored record of the subscriber's prior accumulated charges to determine whether the subscriber has sufficient available credit to pay for descrambling of the scrambled signal. If a program is not prepaid and if sufficient credit is available, the subscriber is given the option of causing the signal to be descrambled on an impulse-purchase basis. To prevent a subscriber from obtaining descrambling through such deceit as changing the mask, authorization, cost and/or credit signals, these signals are processed with key signals which are used in scrambling and descrambling the television signal such that descrambling is prevented if any of the mask et al signals is changed.
BASIS IN A SUBSCRIBER COMMUNICATION NETWORK
ABSTRACT OF THE DISCLOSURE
A system in a subscriber television network for enabling descrambling of a received scrambled signal on a prepaid basis and/or an impulse-purchase basis. A received mask signal uniquely related to the scrambled signal is compared with a received authorization signal indicating whether the subscriber is authorized to receive the scrambled signal on a prepaid basis and a prepaid signal for enabling descrambling is provided when the compared signals match. A not-prepaid signal is provided when they do not match. A received cost signal indicating the charge for descrambling the scrambled signal and a received credit signal indicating the subscriber's accumulated credit are processed with reference to a stored record of the subscriber's prior accumulated charges to determine whether the subscriber has sufficient available credit to pay for descrambling of the scrambled signal. If a program is not prepaid and if sufficient credit is available, the subscriber is given the option of causing the signal to be descrambled on an impulse-purchase basis. To prevent a subscriber from obtaining descrambling through such deceit as changing the mask, authorization, cost and/or credit signals, these signals are processed with key signals which are used in scrambling and descrambling the television signal such that descrambling is prevented if any of the mask et al signals is changed.
Description
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BACKG~OUND OF THE INVENTION
The present invention generally pertains to descrambling systems for subscriber communication networks and is particularly directed to systems for enabling descrambling on a selective-subscription basis.
This application is a division of our Canadian application Serial No. 483,413 filed June 7, 1985.
S~lective-subscription subscriber communication net-works provide for descrambling of signals on a prepaid basis and/
or on an impulse-purchase basis.
In one type of prepaid descrambling system, a des-crambler at the subscriber terminal is adapted to descramble all communications received over a given communications channel, such as, for example, all oE the programs broadcast over a given television channel. When service is discontinued, the descrambler must be modified to preven~ descrambling of signals received over the given channel. In anothex type o~ prepaid descrambling system, descrambling is enabled by an enable signal addressed to the descrambler at the subscriber terminal.
Typical impulse-purchase subscriber communication net-work descrambling systems are described in United States Letters Patents Nos. 2,573,349 to Miller et al; 2,788,387 to Druz;
BACKG~OUND OF THE INVENTION
The present invention generally pertains to descrambling systems for subscriber communication networks and is particularly directed to systems for enabling descrambling on a selective-subscription basis.
This application is a division of our Canadian application Serial No. 483,413 filed June 7, 1985.
S~lective-subscription subscriber communication net-works provide for descrambling of signals on a prepaid basis and/
or on an impulse-purchase basis.
In one type of prepaid descrambling system, a des-crambler at the subscriber terminal is adapted to descramble all communications received over a given communications channel, such as, for example, all oE the programs broadcast over a given television channel. When service is discontinued, the descrambler must be modified to preven~ descrambling of signals received over the given channel. In anothex type o~ prepaid descrambling system, descrambling is enabled by an enable signal addressed to the descrambler at the subscriber terminal.
Typical impulse-purchase subscriber communication net-work descrambling systems are described in United States Letters Patents Nos. 2,573,349 to Miller et al; 2,788,387 to Druz;
2,864,885 to Morris; 2,866,962 to Ellett; 3,531,586 to Bass et al;
3,736,369 to Vogelman et al; 3,916,091 to Kirk/ Jr. et al; and
4,130,833 to Chomet.
Bass et al describes an impulse-purchase system for a subscriber television network in which a debit Icost) signal ~1~ .
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related to the viewing cost of a given television program i8 transmitted to each subscriber terminal and processed in relation to an indication of the subscriber'6 e~tablished credit to determine whether the subscriber i8 authorized to view the given program. In the ~ass et al ~ystem subscriber credit is established in response to the insertion of coins into a coin mechanism included in the ~ubscriber terminal.
If after a ~ubscriber ha~ accep~ed a given program for viewing the program is cancelled, ~uch as for technical reason~, a credit 3ignal i8 tran mitted to the ~ub~criber terminals to re~tore the sub~criberi~ establ~hed credit by an appropriate amount.
Druz describes an lmpul6e~purchase sy~tem for a ~ubscriber television network in which a C08t signal containing charging information related to the cost of viewing a given program i8 transmitted to the subscribers and upon acceptance by a subscriber o~ the program ~or viewingr the charging infoemation is recorded by a recording device at the subscriber terminal. The recorded charging information i~ collected or read from the recording device periodically and the subscriber subsequently i~ billed for the total co~t of programs selected for viewing during the previou~ period, Both of these prior art systems r~quire some type of post-viewing collection from the sub~criber. With the ~ass et al system coins must be collected from each individual ~ubscriber's coin mechanism; and with the Druz ~y~tem the recorded charging information must be collec~ed from each lndividual subscriber's recording device.
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One object of the present inven~ion iB to provlde an impulse-purchase descramhling system which enables other payment methods in addition, or alternative, to such post-viewing collection f rom each individual ~ubscriber terminal.
Another object of the present invention is to provide an impulse-purchase de~crambling sy~tem that will enable special event television programs ~ransmitted on a given pay-TV channel to be selected for viewing on an impulse-purchase basis by 6ubscriber~ who do not regularly subscribe to all of the programming on such channel.
Still another object of the present invention is to provide a descrambling system that can be controlled by received ~ignals to either descramble scrambled signals on a prepaid basi~ or to of~er descrambling on an impulse-purchase basis depending upon the subscription statu~ of the~ubscriber and whether the ~ignal is authorized for descrambling on an impul~e-purchase basis.
A further ob~ect of the present invention is to provide a system for preventing a subscriber from being able to enable descrambling in a ~elective-sub~cription subscriber aommunlcation network through such deceit as substituting other signals for transmitted B~ gnals, such as a cost signal, that are received and processed at the subscriber terminal to enable descrambling.
SUMMARY OF THE INVENTION
The present invention provides improved systems for enabling descrambling of a received scrambled signal on an lmpulse-purchase basi~ in a subscriber terminal of a 3ub~criber communication network. One improved system includes a circuit for processing a received c06t signal ~3~
", indicating the charge for descrambling the æcrambled signal and a received credit ~ignal indicating~ ~he accumulated credit attrlbuted to the subscriber to determine whether the subscriber has sufficient available credit to pay for descrambling of the æcrambled æignal, and for providing a credit-available slgnal when it ic determined that there i8 sufficient credit available; a device that is responsive to the credit-available signal for indicating that the subscri~er has the option of causing the scrambled signal ~o be descrambled on an impulse-purchase basis~ a device which is enabled in response to the credit-available signal~ for accepting sald option and for providing an accepted signal upon acceptance; and a circuit that is responsive to the accepted signal for enabling ~he ~crambled signal to be descrambled.
The cred~t signal may indicate accumulated payments made by the subscriber and/or credit extended to the subscriber in aavance of the signal being descrambled on an impulse-purchase basi~. This system does not require post-use collection of money or charge information from eachindividual subscriber terminal as wi~h the prior art systems described hereinabove.
In a separate aspect, the present invention provides a system for descrambling scrambled signals on a prepaid ba~is, This system include~ a circuit for comparing a received mask ~ignal related to ~he scrambled signal with a received authorization ignal addressed to the subscriber terminal and ~ndicating whether the subscriber iB authorized to deæcramble the scrambled signal on a prepaid basis and for providing a prepaid signal when the compared æignals ~3~3~
match to a prescribed degree~ and a circuit that is responsive to the prepaid signal for enabling the scrambled signal ~o be de~crambled, This prepaid descrambling system is compatible with the impulse-purchase descrambling system of the present invention such that both can be combined in a single sy~tem.
Such a combined system includes a circuit ~or comparing a received mask signal uniquely related to the scrambled s~gnal with a received authoriza~ion signal indicating whether the subscriber i~ authorized to descramble the scrambled signal on a prepaid ba~is, and for providiny a prepaid signal when the compared signals match to a prescribed degree and a not-prepaid ~ignal when they do not match, This combined system further includes a clrcuit for processing a received cost signal indicating the charge or descrambling the scrambled signal and a credit signal related to the subscriber's available credit to determine whether the subscriber has sufficient available credit to pay for descrambling of the scrambled signal, and for providing a credit-available signal when it i~ determined that there is sufficient credit available; a device that is responsive to both the not-prepaid siynal and the credit-available ~ignal for indlcating that the subscriber has the option of causing the signal to be de~crambled on an impulse-purchase basis$ a device which is enabled in response to both the not-prepaid signal and the credit available signal ~or the subscriber to operate to accep~
~uch option, and ~or providing an accepted signal upon acceptance; and a circuit that is responsive to the accepted signal for enabllng the scrambled signal to be descrambled.
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Thl~ system is particularly useful for enabling special event television programs tran~mitted on a given pay-TV
channel to be selected for viewing on an impulse-purchase basi6 by sub3cribers who do not regularly subscrlbe to all of the programm~ng on ~uch channel. For such an appl~cation the authorization signal addressed to a given 6ubscriber who regularly subscribe~ to all of the programming on the given pay-TV channel matches the mask ~ignal to the pre~cribed degree. Since the regular ~ubscriber receives all of the programs on the g~ven channel ~here i8 no need for the lmpulse-purchase option to be made available for 3uch sub~criber. To provide a service wherein only certain special event programs are made available to the nonregular subscribers on an impulse-purchase ba~, an impulse-purchase slsnal i~ included in the mask signal that isuniquely related to scrambled special event programs, and the option of causing the scrambled signal to be descrambled is indicated to the sub~criber and the acceptance device is enabled only when an impulse-purchase signal related to the scrambled signal i8 included in the ma~k signal that is received by the subscriber terminal~
Preferably, prepaid status i~ indicated by providing a "TRUE" bit in a given bit position of the authorization signal. Other bit po~ition may be used for other authorization functions. Since the bit-length of the authorization signal may be les~ than the number of authorization function~ and programs and/or channels for which prepaid service may be indicated, each subscriber terminal includes a memory for storing a plurality of the authorization signals and for providing a selected one of :~3~3;2q;~
the stored authoriæation signals for comparison with the mask signal in response to an address signal received with the ma~k signal.
Still another improved system prevents a sub6criber from being able to enable descrambling through such deceit as substitu~ing other signals for tran3mitted signals, such as cost and credi~ signals, that are received and processed at the subscriber terminal to enable descrambling. Thi~
system i8 particularly useful in a subscriber communication network in which selective remote descrambling o the scrambled signal is controlled through the use of key signals, including encrypted key signals that are tran~mitted to the subscriber ~erminal and that must be decrypted in the subscriber terminal to enable the ~crambled signal to be deAcrambled. This prevention system includes a circuit for encoding one or more of the key slgnals prior to encrypting a said key signal and/or prior to using a said key ~ignal to encrypt another said key signal by proces~lng said one or more said key ~ignals with the cost signal, and the credit signal and/or the mask signal and the authorizatlon signal prior to the transmi6sion of the encrypted key signals~ and a circuit in each subscriber terminal for decoding the one or more of the key signals ollowing decryption thereof r and/or prior to use thereof for k~ying decryption of a said encrypted key signal by processing said key signals with ~he respective cost signal and credit signal and/or mask signal and authorization ~ignal used to encode the one or more o the ~ey signals.
Changing any of the credlt slgnal, cost signal, mask signal or authorization signal prevents decryption of the key . .
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13(b32q~3 slgnals and thereby prevents descrambling.
Also disclosed is a system in a subscriber communication network for verifying charge information furnished to a broadcast company by a given subscriber and purported by the subscriber as having been displayed at the subscriber terminal. At the subscriber terminal there is generated a debit signal indicating the charges attributed to the subscriber terminal; and in response to the debit signal, a display of information indicating the accumulated charges is provided to the subscriber. An authentication signal is provided at the subscriber terminal by processing the debit signal in accordance with an encryption algorithm upon the algorithm being keyed by a key signal that ls unique to the subscriber terminal; and ln response to the authentication signal, a display o~ information representative of the authentication signal ls provided to the subscriber. The subscriber copies the displayed lnformatlon and sends lt to the broadcast company wlth his periodic bill payment. At the broadaast company the lnformation furnished by the given subscriber that purportedly is the displayed charges lnformation and the authentication in~ormation is en~ered in a processing system and converted into a received debit signal and a received authentication signal respectively. The received debit signal is processed with the received authentication signal to determine whether the in~ormation furnished by the given subscriber was authentic.
According to a broad aspect of the invention there is provided, in a subscriber communication ne~work, a sys~em ~or ' .,.
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enabling descrambling in a suhscriber terminal of a received scrambled signal, compris.ing maans in a subscriber terminal for determininq whether a first control siynal received by the subscriber terminal bears a predetermined relationship to a second control signal, and for providing an enable signal upon determining that sald first control signal bears said predetermined relationship to said second control signal;
means in the subscriber terminal for using a given key signal for descrambling the scrambled signal;
means in t~e subscriber tesmlnal responsive to said enable signal for enabllng the scrambled signal to be descrambled hy said given key signal; and means for preventing a subscriber from being able to enable descrambllng of the scrambled slgnal through such deceit as substituti.ng another slgnal for said received first control signal in order to cause said determining means to determine that said predetermined relationship with said second control signal exists, sald preventing means comprising means in the centxal station for encoding said given key signal by processing said given key signal with said ~irst control si~nal and means in the subscriber terminal for processing said given key signal with said received first control signal to enable said given key signal to be used to descramble said scrambled signal;
wherein said given key signal, said first control signal, said second control signal and said enable signal are separate A
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signals.
Addltional features of the present invention are described in relation to the des~ription of the preferred embodiment.
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_9_ 72046-7 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a combination functional and flow block diagram of an authorization processor embodying the systems of the present invention.
Figure 2 is a functional block diagram of a key signal encryption system included in broadcast terminal of a subscriber communication network including the system of the present invention.
Figure 3 is a functional block diagram of a key signal decryption system included in a subscriber terminal that includes the authorization processor of Figure l.
Figure 4 is a functional block diagram of an infor-mation processor which provides the credit signals that are transmitted to the respective subscriber terminals in the 5y s~em of the present invention~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention is included in an authorization processor which is described with reference to Figure 1. The authorization processor is included in a subscriber terminal in a subscriber television network, such as is described in Canadian Patent Application No. 454,444 filed May 16, 1984 by Klein S. Gilhousen and Charles F. Newby for "KEY SIGNAL ENCRYPTION AND ~ISTRIBUTION SYSTEM FOR CONTRO-LLING SCRAMBLING AND SELECTIVE REMOTE DESCRAMBLING OF TELEVISION
SIGNALS." ~he authorization processor of Figure l enables .
13~ 2~3 -9a- 72046-7 descram~ling of a received scrambled television signal on an impulse-purchase or a prepaid basis.
The authorization processor receives a program cost signal on line 10 and a credit signal on line 11. The cost ~3~3Z~
signal indicates the charge for de~crambling a given received scrambled television signal, and is provided to all of the sub~rriber terminals in the subscriber television network. Credit ~ignalR are unique to each subscriber and they are individually addre~ed to the respective subscriber terminals in the network. Each credit signal indicates the accumulated credit attri~uted to the respective individual sub~criber.
The authorization proces~or includes a credit register 12, an overflow detection device 13, a debit regis~er 14, an add register lS and a compari~on unit 16. The credit register 12 registers the credit signal received on line 11.
The debit register 14 registers the accumulated charges for scrambled signals accepted by the respective individual lS subscriber for descrambling. The add register 15 add~ and registers the sum of the charge indicated by the program cost ~ignal on line 10 and the accumulated charges regi~tered in the debit register 14. ~he comparison unit 16 compare~ the credit signal registered in the credit register 12 with the sum of the addition registered in the add register 15 to determine whether the ~ubscriber has ~uf~icient credit available to pay for descrambling of the ~crambled signal. If upon such comparison it is determined that the accumulated credit indica~ed by the credit signal registered in the credit register 12 i8 not less than the sum of the addition registered in the add register 15, a credit-available signal i8 provided on line 17 to a display driver and logic circuit 19. If upon such comparison i~ is determined that such accumulated credit is less than such sum, an insufficient credi~ signal i~ provid~d on line 20 to the display driver and logic circuit 19.
The display drlver and logic circuit 19 provides slgnals on line 21 for controlling the content of a display on a video monitor display device 22, ~uch as the television set that i~ attached to the ~ubscriber terminal.
Alternatively, the display device 2~ can be an alphanumeric display on the front panel of the descrambler unit.
The authorization proce~sor also receives a program mask signal on lines 23 and an authori2ation word ~ignal on lines 24. The program mask signal i~ a 56-bit digital ~ignal that is unique to each scrambled program that i8 broadcast over the subscriber televi~ion ne~work. The program ma~k signal is provided to all of ~he subs~riber terminals in the network. The authorization word signal is a 56-b~t word signal that is individually addre~3e~ to the respective individual subscriber ~erminals in the network, If the respective sub~criber regularly receives all of the scrambled programs on the given TV channel, the authorization word signal addre~8ed to the respective subscriber terminal will match the program mask signal that iB provided to all of the sub~criber terminalæ in the network to the prescrlbed degree. If the respective subscriber is not a regular subscriber to all of the scrambled programs on the given cbannel, the authorization word addressed to the respective subscriber term~nal and received on lines 2~ does not match the program mask signal that i8 received on lines 23.
The authorization proces~or includes a second comparison unit 25, which compare~ ~he received program ma~k signal on lines 23 with the received authorization word 3ignal on llne~ 24. When the compared slgnals do not match to the prescribed degree, a not-prepaid ~ignal is provided on line 26 to the display driver and logic circuit 19. When the compared signal6 do match, a prepaid ~ignal is provided on line 27 to an enable gate 29.
The compari~on uni~ 25 i6 logically ANDI6 the corresponding bits from the program mask slgnal on line 23 with the authorization word signal on line 24 and then logically OR'~ the re~ult~ of the log~cal AND operation. A
match in any one o~ the correspondlng pair~ of bit3 results in the prepaid signal being provided on line 27. Typically the different bit positions in the authorization word ~ignal correspond to dlfferent TV channel~ and/or programs. Thus an authorization word signal for a given descrambler includes a "TRUE" blt in the bit po~ition deslgnated for each program and/or channel for which ~ervice has been prepaid. The program ma~k signal includes a TRUE bit in each po~ition corresponding to a given program and/or channel.
One of the bits of the program maEk signal on line 23 indicates whether the received scrambled television signal may be descrambled on an impul6e-purchase ba~is. When it may be ~o descrambled, an impul~e-purchase signal is provided in this bit position and i8 provided on line 30 to the display driver and logic circuit 19.
Certain bit~ of the program mask signal and the authori~ation word ~ignal may provide additional authorization unctions, such as 6tereo audio enabla, remote control enable and alternate language ~election.
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The display driver and logic 19 circuit contains logic circuitry which d~ctates the content of the ~ignals that are provided on line 21 to the display device 22. When a credit-available ~iynal is provided on line 17, a not-S prepaid signal iæ provided on line 26 and an impulse-purchase 6ignal i~ provided on 30, the display driver and logic circuit 19, provide~ an enabling signal on line 31 to an acceptance ~witch 3~ and ~ur~her provides a signal on line 21 that re3ults in the display device 22 di~playing an indication to the subscriber that the subscriber has the option of cau~ing the scrambled television signal to be di~played on an impulse-purchase basis.
The subscriber may indicate acceptance of the option by operating the ~witch 32 only when the ~witch 32 i8 enabled 1~ by the enabling ~ignal on line 31. If the sub~criber æo accepts the option, an accepted signal is provided on line 33 to the enable gate 29. The accepted signal on line 33 also i~ provided to the display driver and logic circuit 19, which responds thereto by causing the display device 22 to briefly indicate acknowledgement o the subscriber's acceptance. Thereafter, the de~crambled television signal i8 di~played on the given TV channel. If the subscriber indicates by operation of the switch 32 that the option is not accepted, a signal i8 provided on llne 34 to the display driver and logic circuit 19, which re~ponds thereto by causing the di6play device 22 to briefly indicate acknowledgement of the ~ubscriber's non-accep~ance.
Thereafter, only a blank screen signal is displayed on the glven TV channel The display driver and logic circuit 19 re~ponds to the in~ufficient credit signal on line 20 by :~3~32Pi.~3 causing the di~play device 22 to briefly indicate that the subscriber's credlt is insufficient to enable descrambling of the scrambled ~ignal~ Alternatively the display may provide a continuou~ indication that the program is not authorized because ei~her it i8 not prepaid or becau~e ~ufficient credit i~ not available.
The accepted signal on line 33 is further provided to the enter enable input of the debit register 14 and causes the ~um registered in the add regi~ter 15 to be entered into the debit register 14, thereby effectively incrementing the accumulated charges in the debit register 14 by the charge indicated by the program cost signal received on line 10.
The over~low detection device 13 is coupled to the add regi6ter 15 for detecting when the arithmetic limit of the deblt register 14 would be exceeded by incrementing the accumulated charges in the debit register 14 by the charge indicated by the program cost signal on line 10 and for providing an over~low signal on line 18 upon said detection.
~he di~play driver and logic clrcuit 19 responds to the overflow signal on line 18 by preventing an enabling ~ignal from otherwi~e being provided on line 31 in response to a credit-available ~lgnal on line 17. Thl~ feature is provided ln order to prevent a sub~criber from feeding ~alse cost and credit signals into the authentication proce~or in order to increment the debit regi~ter 14 until it overflows to thereby store an amount le~s than the actual accumulated charge~ attributed to the subscr~ber terminal.
Whenever either the prepaid s~gnal is provided on line 27 or the accepted signal iB provided on line 33 to the enable gate input line 35, the enable gate 29 provlde~ a :;L3~32~8 decrypted and de~oded channel key 6ignal ~rom line 36 onto line 37 and thereby enableR the scrambled television signal to be descrambled. The significance of passing this key signal onto line 37 is explained somewhat later below with S refexence to Figures 2 and 3.
Figure 2 and 3 respectively show the encryption and decryption ~ystem~ included ln the broadcast terminal and each subscriber terminal of a ~ubscriber television network with which the ~y~tem~ of the present invention are par~icularly useful~ The encryptlon and decryption systems o Figures 2 and 3 are e~pecially adapted to prevent a subscriber from being able to enable de~crambling of the ~crambled signal through deceit by ~ubstitutlng . other signals for one or more of the respective transmitted lS program mask ~ignal, authorization word signal, program cost signal and credit ~ignal rece~ved by the sub~criber terminal in order to obtain a match upon said comparison and/or to cau~e a credit-available signal to be provided when in fact the subscriber'~ credit iB inadequate.
~eferring to the encryption ~ystem of the broadcast terminal (Figure 2) a keystream generator 39 produce~ a keystream signal on line 40 that i~ used to scramble the televi~ion signal. An identical key~tream signal must be reproduced on line 42 by the keystream generator 44 in the decryption sy~tem of the sub~criber terminal (Figure 3) in order for the descrambler in the subscriber terminal to be able to descramble the scrambled televi~ion ~ignal.
Referring again to Figure 2, the key~tream generator 39 of the encryp~ion system generates the keystream signal on line 40 by processlng an initialization vector (IV) frame count ~ignal on line 45 in accordance with the Data Encryption Standard (DES) algorithm upon the algorithm being keyed by a working key signal on line 46.
A working key generator 47 generates the working key signal on line 46 by processing the frame count signal on line 45 in accordance with the ~E~ algorithm upon the algorithm being keyed by a channel key signal on line 49.
The channel key signal on line 49 is provided by a control computer ~not shown~ at the broadca~t terminal.
The channel key signal on line 49 is encrypted for transmission to the subscriber term~nalæ. ~ channel key generator 50 encrypts the channel key signal by generating an encrypted channel key signal on line 51 by processing an encoded channel key signal on llne 52 in accordance with the DES algorithm upon the algorithm being keyed by an encoded ca~egory key signal on line 54.
Incident to the scheme for preventing descrambling by deceit through substitution of one or more of the program mask signal, the authorization word signal, the program cost signal and the credit signal, the program mask signal on line 55 is used to encode the channel key signal on line 49 by exclusive- OR'ing the channel key signal on line 49 with the program mask signal on line 55 to provide the encoded channel key ~ignal on line 52. Incident to the same scheme the encoded category key signal on line ~4 is produc~d by exclusive-OR'ing a category key signal provided on line 56 by the control computer with a program C08t signal provided on line 57 by the control computer. The program coæt signal on line 57: also ~s provided by the control computer.
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The symbols 59, 60, 61 and ~2 in Figure 2 represent exclu~ive-OR logic elements.
The ca~egory key signal on line 56 also is encrypted for transmission to the ~ubscriber terminal~. Prior to such encryp~ion the category key ~ignal on line 56 is encoded by being exclllslve-OR'd with a credit ~i~nal provided on line 64 by the cGntrol computer to thereby provide an encoded category key ~ignal on line 65. Thi6 is incident to the aforementioned prevention ~cheme, The position of the bits of the category key signal on line 56 that ar~ exclusive-OR'd with the credit signal on line 64 must be different from the position of the bit~ of the category key ~ignal on line ~ that are exclusive-OR'd with the program çost signal on line 57. The derivation of the credit signal i8 described below with reference to Figure 4.
A category key generator 66 encrypt~ the category key signal by generating a plurality of unique encrypted cat~gory key signals on line 67 by proce~sing the encoded category key ~ignal on line 65 in accordance with the ~ES
algorithm upon the algorithm being keyed by a corre~ponding plurality o~ encoded unique ~ubscriber key signal~ on line 69. The subscriber key ~ignals are unique to the individual subscriber terminals.
A plurality of unique subscriber key signals are provided on line 70 from a sub3criber key storage memory 71 upon the memory 71 being accessed by a plurality of respective sub~criber addresses provided on line 72 by the control computer. The subscriber key s~gnals on line 70 are exclusive-OR'd with an authorization ~ord signal provided on 13~32~
line 74 by the control computer to provide the encoded subscriber key ~ignals on line 69. The authorization word signal on line 74 that is used for encoding the ~ubscriber key signal on line 70 either matches or doesn't match the program ma~k signal on line 55 in accordance with whether the subscriber terminal corresponding to the individual subscriber key signal being decoded iB assigned to a subscriber who is a regular ~ub~criber to all of the programs on the given TV channelO The use of the authorization word signal~ on ~ine 77 also is incident to the aforementioned prevention scheme.
The control computer also provides a subscriber key qeneration number on line 75 that is unique to the broadcaster.
The combination o the credit signal on line 64, the encrypted category key ~ignal on line 67, the subscriber address on line 72, and the authorization word signal on line 74 that all pertain to a given subscriber terminal are transmitted together as a category rekey message that is addressed to the given subscriber terminal by the subscriber address lncluded in such message. ~ccordingly, unique category rekey me~sages are transmitted to each of the subsariber terminalsc When the number of alternative authorization functions and the number of alternative programs an~/or channels that are provided to the subscribers over the network exceeds the 56 bit positions of the authorlzation word signals are provided and included in separate respective category rekey message addressed to each given subscriber terminal, where they are stored upon recelpt.
~3t~32~3 -l9- 72046-7 The program mask signal on line 55, the encry~ted channel key signal on line 51 and the program cost signal on line 57 pertairl to all of the subscriber terminals and are transmitted together as a channel rekey message to all of the subscriber terminals. The channel rekey message also contains a category rekey address signal on line 76 for selecting one of th.e stored category rekey messages from stbrage in the subscriber terminal in accordance with which programs and/or channels and authorization functions are indicated by TRUE bits in the res pecti~e bit positions of the program mask signal on line 55.
The frame count signal on line 45 and the subscriber key generation number on line 75 also are transmitted to all of the subscriber terminals.
The encryption system of Figure 2, the manner in which the frame count signal, the channel rekey message, the category rekey messages and the subscriber key generation number are further processed prior to transmission; and the use of the keystream signal for scrambling the television signal are described in greater detail in the aforementioned Canadian Patent Application No. 454,444.
The decryption system of each subscriber terminal, as shown in Figure 3, includes an authorization processor 77, a rekey message memory 78 and the enable gate 29. The authorization processor 77 is as described above with reference to Figure l. The rekey message memory 78 stores all of the different rekey messages addressed to the given subscriber termin-al.
~3~Jt32~
-19a- 72046-7 The decryption system of each subscriber terminal receives the frame count signal on line 79, the program '' .
-20- ~.3~32~
mask ~ignal on llne 23, the encrypted channel key signal on line 80, the program C08t signal on line 10, the credit ~ignal on line 11, the encryp~ed category key ~ignal on line 81, the authorization word signal on line 24 and the subscriber key generation number on line 82, and the category rekey address signal on line 83. Tha credit signal on line 11, the encrypted category key signal on line 81 and the au~horization word signal on line 24 are retrieved from the storage location of the memory 78 that i~ acce~ed by the addre~s signal on line 83.
The rece~ved sub~criber key generation number on line 82 is combined with the Eub~criber addre~s on l~ne 84 ~rom a sub~criber addre~s memory 85 to provide a ~ubscriber key generation signal on line 86.
Two bit~ in a given position of ~he received sub criber key generation number on line 82 are also provided on line 87 to access a ~iv~n addre~s in a subscriber key seed memory 88, The memory 88 store~ four subscriber key seed OEignals that are unique to the ~ubscriber and provide~ a prescribed ~0 key seed signal on line 89 in accordance with the address on line 87.
A subscriber key generator 90 reproduce~ the ~ubscriber key signal on line 91 corre~ponding to the sub3criber key signal on line 70 in the sy~tem of Figure 2 that wa~ u~ed in 2~ encrypting the encrypted category key signal included in ~he category rekey message addressed to the given sub~criber and received on line 81.
The sub~criber key generator 90 generate~ the subscriber key ~ignal on 11ne 91 by proces6ing the ~ubscriber key qeneration signal on line 86 in accordance ~3~3Z~8 with the DES algorithm upon the algorithm being keyed by the prescribed key seed signal on line 89.
The above-described system for reproducing subscriber key signals through use o~ stored key seed signals is the subject of a Canadian Patent Application entitled "Descrambler Subscriber Key Production Util.izing Key Seeds Stored In Descrambler'l filed on March 14, 1985 by Kaxl E. Moerder, Serial No. 476,47~.
The subscriber key signal on line 91 is exclusive-OR'd with the received authorization word signal received on line 24 to provide an encoded subscriber key signal on line 92 corres-ponding to the subscriber key signal for the given subscriber on line 69 in the system of Figure 2.
A category key generator 94 decrypts the encrypted category key signal received on line 80 by generating an encoded category key signal on line 95 corresponding to the si~nal on line 65 in the system o~ Figure 2 by processing the encrypted category key signal on line 81 in accordance with the DES algorithm upon the algorithm being keyed by the subscriber key signal on line 92.
The encoded category key signal on line 95 is exclusive-OR'd with the received credit signal on line ll-to provide a decoded category key slgnal on line 96 corresponding to the category key signal on line 56 in the system of Figure 2.
The symbols 97, 98, 99 and 100 in Figure 3 represent exclusive-OR'd logic elements.
~3~3Z~
-21a- 72046-7 The decoded cateaory key signal on line 96 is exclusive-OR'd with the received program cost signal on line -~2~ 3~
to provide an encoded ca~egory key signal on line 101 corre~pondlng to the encoded category key ~ignal on line 54 in the system of Figure 2.
A channel key generator 102 decrypts the encrypted channel key signal received on l~ne 80 by generating an encoded channel key signal on line 104 corre~ponding to the siqnal on line 52 in the system of Figure 2 by processing the encrypted channel key signal on line 80 in accordance with the DES algorithm upon the algorithm being keyed by the encoded category key s~gnal on line 101.
The encoded channel key signal on line 104 is exclusive-O~'d with the program ma~k 6ignal on line 23 to provide a decoded channel key ~ignal on line 36 corresponding to the channel key signal on line 49 in the system of Figure 2.
The enable gate 29 pa~ses the channel key ~ignal from line 36 onto line 37 only when the input line 3~ of the enable gate 29 receives either a prepaid signal or an accepted siynal from the authorization processor 77, which is described above with reference to Figure 1.
A working key generator 106 generates a working key signal on line 107 corresponding to the working key 8~ gnal on line 46 in the system o~ Figure 2 by proce~sing the frame count ~ignal received on line 79 ~n accordance ~ith the DES algorithm upon the algorithm being keyed by the channel key signal on line 37.
The key~tream generator 44 generates a keystream signal on line 42 corre~ponding to the key~tream ~ignal on line 40 in the system of Figure 2 by proces~ing the frame count signal on line 79 in accordance with the DES algorithm upon ~3~32~3 the algorithm being keyed by the working key signal on line 107.
The subscriber key seed memory 88 and the debit register 14 of each subscriber terminal are included in a non-volatile ran-dom access memory (RAM) of an integrated circuit chip that has an architecture which prevents the debit register from being accessed from off the chip~ The chip must be capable of performing the computation, comparison and authorization functions of the authori-zation processor 77 described with reference to Figure 1 and the decryption and decoding functions of the key signal decryption systems of Figure 3. A model TMS70C40 chip manufactured by Texas Instruments is preferred. This chip is modified for use in the system of the present invention by disabling the capability for accepting instructions from off the chip, thereby preventing an instruction to read the secure memory from being accepted.
A more detailed description of the decryption system of Figure 3 and the use of the keystream for descrambling the received scrambled television signal is set forth in the above-referenced Canadian Patent Application No. 454,444.
Referring again to Figure 1, a debit signal on line 109 indicating the contents of the debit register is provided to the display driver and logic circuit 19, which upon operator command provides a signal on line 21 to the display 22 for enabling a display of an indication of the accumulated charges attributed to the subscriber terminal. This enables the subscriber to record the accumulated charges information -24-~ 3 ~ 3 Z ~ ~
tha~ is di~played and to transmit the ~ame to the broadcast company whenever called for, such as when service is d~continued, when the sub~criber term~nal equipment is transferred to another subscriber or upon payment of the subscriber's periodic billing. Thi~ accumulated charges information is used by the broadcaster to reæolve any bllling disputes that may ar~se with the sub~criber or to facilitate computation o~ a refund when service is discontinued or the equipment is transferred.
In order to verify the accumulated charge 1nformation provided to the broadcast company by the subscriber, authentication information al~o is displayed on the display 22 for copying and transm~ttal to the broadcast company by the subscriber, The authent~cation information is displayed ln response to an authentication ~ignal provided on line 110 to the display driven and logic circuit 19 by an authentication generator 111. The authentication generator 111 generates the authentication signal on line 110 by processing the debit signal on line 109 in accordance with the DES algorithm upon the algorithm being keyed by the subscriber key signal on line 91.
In a subscriber television network having a two-way communication link between the broadca~t terminal and the subscriber terminal the debit signal on line 109 and/or the authentication signal on line 110 could be ~tored in a memory (not shown) in the subscriber terminal and accessed from ~uch memory upon command for transmi~sion to ~he broadcast terminalO
Referring agaln to ~he system in which the sub~criber records and transmit~ the disp~ayed accumulated charges -25- ~ 3 ~ 3~
information and the authentication information, upon rPcelpt of what is purported by the subscriber to be the displayed accumulated charge information and the authentication information, the broadcast company enters the ~ame into the control computer. The control computer converts the entered informatîon into debit and authentication ~ignal~ having the same format as the signals provided to the displ~y driver and logic circuit 19 on lines 109 and 110 respectively.
Referring to Figure 4; the converted debit and authentication signal~ in the control computer are provided on lines 114 and 115 respectlvely. The debi~ ~ignal is entered in a debit register 116 and the authentication signal is entered in an authentication register 117. The debit signal from the debit regi~ter 116 is proces~ed by a debit generator 118 in accordance with the DES algorithm upon the algorithm being keyed by the sub~criber key ~ignal on line 70 that iB related to the ~ub~riber terminal belonging to the subscriber who transmltted the authentication information. ~he deblt generator 118 thereby generate~ an authenticating debit ~ignal on line 119 which is compared by a comparison unit 120 with the authentication signal registered in the authentication register 117. If thi~ comparison re~ult~ in a matchr the information provided by the subscriber is verified, and a ~ignal i8 provided on line 121 to enable entry of the contents of the debit register 116 into a debit memory 122.
Figure 4 further illustrates how a credit ~lgnal for a given subscriber is provided on line 64 (Figure 2) for transmission to the sub~criber terminal.
-26- ~3~3~8 An indication of the amount of each payment made by a given ~ub~criber is entered into the control computer to provide a payment signal on line 122 to an add register 124.
The add register 124 add6 and register~ the ~um of the amount indicated by the payment signal on line 124 and an amount stored in a payment memory 125, which i~ increm~nted by the amount of each payment. When ~ervice begins for the subæcriber, the amount ini~ially ~tored in the payment memory 12S is the amount then ~ored in the debit memory 122 for the corresponding sub~c~iber term~nal. Upon the amount of each new payment being entered into the control computer the sum registered in the add regi~ter 124 i8 stored in the payment memory 125 to thereby increment the stored payment record by the amount of the new payment.
A signal indicating the amount of any credit extended to the given subscriber i8 provided on line 126 and stored in a credit memory 1~7. An add register 12~ sum~ and registers the amount of the credit advance from the credit memory 124 and the amount ~tored in the payment memory 125 to provide the credit signal on line 64 indicating the accumulated credit attributed to the given subscriber.
When service to the given subscriber i~ terminated, the amount of any refund due the subscriber iB determined by a difference register 129, which registers and provides on line 130 a 6ignal indicating the di~erence in the amounts ~tored in the payment memory 125 and the debit memory 122.
Bass et al describes an impulse-purchase system for a subscriber television network in which a debit Icost) signal ~1~ .
l~V3Z~
related to the viewing cost of a given television program i8 transmitted to each subscriber terminal and processed in relation to an indication of the subscriber'6 e~tablished credit to determine whether the subscriber i8 authorized to view the given program. In the ~ass et al ~ystem subscriber credit is established in response to the insertion of coins into a coin mechanism included in the ~ubscriber terminal.
If after a ~ubscriber ha~ accep~ed a given program for viewing the program is cancelled, ~uch as for technical reason~, a credit 3ignal i8 tran mitted to the ~ub~criber terminals to re~tore the sub~criberi~ establ~hed credit by an appropriate amount.
Druz describes an lmpul6e~purchase sy~tem for a ~ubscriber television network in which a C08t signal containing charging information related to the cost of viewing a given program i8 transmitted to the subscribers and upon acceptance by a subscriber o~ the program ~or viewingr the charging infoemation is recorded by a recording device at the subscriber terminal. The recorded charging information i~ collected or read from the recording device periodically and the subscriber subsequently i~ billed for the total co~t of programs selected for viewing during the previou~ period, Both of these prior art systems r~quire some type of post-viewing collection from the sub~criber. With the ~ass et al system coins must be collected from each individual ~ubscriber's coin mechanism; and with the Druz ~y~tem the recorded charging information must be collec~ed from each lndividual subscriber's recording device.
~3~
One object of the present inven~ion iB to provlde an impulse-purchase descramhling system which enables other payment methods in addition, or alternative, to such post-viewing collection f rom each individual ~ubscriber terminal.
Another object of the present invention is to provide an impulse-purchase de~crambling sy~tem that will enable special event television programs ~ransmitted on a given pay-TV channel to be selected for viewing on an impulse-purchase basis by 6ubscriber~ who do not regularly subscribe to all of the programming on such channel.
Still another object of the present invention is to provide a descrambling system that can be controlled by received ~ignals to either descramble scrambled signals on a prepaid basi~ or to of~er descrambling on an impulse-purchase basis depending upon the subscription statu~ of the~ubscriber and whether the ~ignal is authorized for descrambling on an impul~e-purchase basis.
A further ob~ect of the present invention is to provide a system for preventing a subscriber from being able to enable descrambling in a ~elective-sub~cription subscriber aommunlcation network through such deceit as substituting other signals for transmitted B~ gnals, such as a cost signal, that are received and processed at the subscriber terminal to enable descrambling.
SUMMARY OF THE INVENTION
The present invention provides improved systems for enabling descrambling of a received scrambled signal on an lmpulse-purchase basi~ in a subscriber terminal of a 3ub~criber communication network. One improved system includes a circuit for processing a received c06t signal ~3~
", indicating the charge for descrambling the æcrambled signal and a received credit ~ignal indicating~ ~he accumulated credit attrlbuted to the subscriber to determine whether the subscriber has sufficient available credit to pay for descrambling of the æcrambled æignal, and for providing a credit-available slgnal when it ic determined that there i8 sufficient credit available; a device that is responsive to the credit-available signal for indicating that the subscri~er has the option of causing the scrambled signal ~o be descrambled on an impulse-purchase basis~ a device which is enabled in response to the credit-available signal~ for accepting sald option and for providing an accepted signal upon acceptance; and a circuit that is responsive to the accepted signal for enabling ~he ~crambled signal to be descrambled.
The cred~t signal may indicate accumulated payments made by the subscriber and/or credit extended to the subscriber in aavance of the signal being descrambled on an impulse-purchase basi~. This system does not require post-use collection of money or charge information from eachindividual subscriber terminal as wi~h the prior art systems described hereinabove.
In a separate aspect, the present invention provides a system for descrambling scrambled signals on a prepaid ba~is, This system include~ a circuit for comparing a received mask ~ignal related to ~he scrambled signal with a received authorization ignal addressed to the subscriber terminal and ~ndicating whether the subscriber iB authorized to deæcramble the scrambled signal on a prepaid basis and for providing a prepaid signal when the compared æignals ~3~3~
match to a prescribed degree~ and a circuit that is responsive to the prepaid signal for enabling the scrambled signal ~o be de~crambled, This prepaid descrambling system is compatible with the impulse-purchase descrambling system of the present invention such that both can be combined in a single sy~tem.
Such a combined system includes a circuit ~or comparing a received mask signal uniquely related to the scrambled s~gnal with a received authoriza~ion signal indicating whether the subscriber i~ authorized to descramble the scrambled signal on a prepaid ba~is, and for providiny a prepaid signal when the compared signals match to a prescribed degree and a not-prepaid ~ignal when they do not match, This combined system further includes a clrcuit for processing a received cost signal indicating the charge or descrambling the scrambled signal and a credit signal related to the subscriber's available credit to determine whether the subscriber has sufficient available credit to pay for descrambling of the scrambled signal, and for providing a credit-available signal when it i~ determined that there is sufficient credit available; a device that is responsive to both the not-prepaid siynal and the credit-available ~ignal for indlcating that the subscriber has the option of causing the signal to be de~crambled on an impulse-purchase basis$ a device which is enabled in response to both the not-prepaid signal and the credit available signal ~or the subscriber to operate to accep~
~uch option, and ~or providing an accepted signal upon acceptance; and a circuit that is responsive to the accepted signal for enabllng the scrambled signal to be descrambled.
~ 3 ~ 3 ~
Thl~ system is particularly useful for enabling special event television programs tran~mitted on a given pay-TV
channel to be selected for viewing on an impulse-purchase basi6 by sub3cribers who do not regularly subscrlbe to all of the programm~ng on ~uch channel. For such an appl~cation the authorization signal addressed to a given 6ubscriber who regularly subscribe~ to all of the programming on the given pay-TV channel matches the mask ~ignal to the pre~cribed degree. Since the regular ~ubscriber receives all of the programs on the g~ven channel ~here i8 no need for the lmpulse-purchase option to be made available for 3uch sub~criber. To provide a service wherein only certain special event programs are made available to the nonregular subscribers on an impulse-purchase ba~, an impulse-purchase slsnal i~ included in the mask signal that isuniquely related to scrambled special event programs, and the option of causing the scrambled signal to be descrambled is indicated to the sub~criber and the acceptance device is enabled only when an impulse-purchase signal related to the scrambled signal i8 included in the ma~k signal that is received by the subscriber terminal~
Preferably, prepaid status i~ indicated by providing a "TRUE" bit in a given bit position of the authorization signal. Other bit po~ition may be used for other authorization functions. Since the bit-length of the authorization signal may be les~ than the number of authorization function~ and programs and/or channels for which prepaid service may be indicated, each subscriber terminal includes a memory for storing a plurality of the authorization signals and for providing a selected one of :~3~3;2q;~
the stored authoriæation signals for comparison with the mask signal in response to an address signal received with the ma~k signal.
Still another improved system prevents a sub6criber from being able to enable descrambling through such deceit as substitu~ing other signals for tran3mitted signals, such as cost and credi~ signals, that are received and processed at the subscriber terminal to enable descrambling. Thi~
system i8 particularly useful in a subscriber communication network in which selective remote descrambling o the scrambled signal is controlled through the use of key signals, including encrypted key signals that are tran~mitted to the subscriber ~erminal and that must be decrypted in the subscriber terminal to enable the ~crambled signal to be deAcrambled. This prevention system includes a circuit for encoding one or more of the key slgnals prior to encrypting a said key signal and/or prior to using a said key ~ignal to encrypt another said key signal by proces~lng said one or more said key ~ignals with the cost signal, and the credit signal and/or the mask signal and the authorizatlon signal prior to the transmi6sion of the encrypted key signals~ and a circuit in each subscriber terminal for decoding the one or more of the key signals ollowing decryption thereof r and/or prior to use thereof for k~ying decryption of a said encrypted key signal by processing said key signals with ~he respective cost signal and credit signal and/or mask signal and authorization ~ignal used to encode the one or more o the ~ey signals.
Changing any of the credlt slgnal, cost signal, mask signal or authorization signal prevents decryption of the key . .
.
13(b32q~3 slgnals and thereby prevents descrambling.
Also disclosed is a system in a subscriber communication network for verifying charge information furnished to a broadcast company by a given subscriber and purported by the subscriber as having been displayed at the subscriber terminal. At the subscriber terminal there is generated a debit signal indicating the charges attributed to the subscriber terminal; and in response to the debit signal, a display of information indicating the accumulated charges is provided to the subscriber. An authentication signal is provided at the subscriber terminal by processing the debit signal in accordance with an encryption algorithm upon the algorithm being keyed by a key signal that ls unique to the subscriber terminal; and ln response to the authentication signal, a display o~ information representative of the authentication signal ls provided to the subscriber. The subscriber copies the displayed lnformatlon and sends lt to the broadcast company wlth his periodic bill payment. At the broadaast company the lnformation furnished by the given subscriber that purportedly is the displayed charges lnformation and the authentication in~ormation is en~ered in a processing system and converted into a received debit signal and a received authentication signal respectively. The received debit signal is processed with the received authentication signal to determine whether the in~ormation furnished by the given subscriber was authentic.
According to a broad aspect of the invention there is provided, in a subscriber communication ne~work, a sys~em ~or ' .,.
~3Z~
8a 72046-7D
enabling descrambling in a suhscriber terminal of a received scrambled signal, compris.ing maans in a subscriber terminal for determininq whether a first control siynal received by the subscriber terminal bears a predetermined relationship to a second control signal, and for providing an enable signal upon determining that sald first control signal bears said predetermined relationship to said second control signal;
means in the subscriber terminal for using a given key signal for descrambling the scrambled signal;
means in t~e subscriber tesmlnal responsive to said enable signal for enabllng the scrambled signal to be descrambled hy said given key signal; and means for preventing a subscriber from being able to enable descrambllng of the scrambled slgnal through such deceit as substituti.ng another slgnal for said received first control signal in order to cause said determining means to determine that said predetermined relationship with said second control signal exists, sald preventing means comprising means in the centxal station for encoding said given key signal by processing said given key signal with said ~irst control si~nal and means in the subscriber terminal for processing said given key signal with said received first control signal to enable said given key signal to be used to descramble said scrambled signal;
wherein said given key signal, said first control signal, said second control signal and said enable signal are separate A
~L3~32~8 8b 72046-7P
signals.
Addltional features of the present invention are described in relation to the des~ription of the preferred embodiment.
A
~IL3~
_9_ 72046-7 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a combination functional and flow block diagram of an authorization processor embodying the systems of the present invention.
Figure 2 is a functional block diagram of a key signal encryption system included in broadcast terminal of a subscriber communication network including the system of the present invention.
Figure 3 is a functional block diagram of a key signal decryption system included in a subscriber terminal that includes the authorization processor of Figure l.
Figure 4 is a functional block diagram of an infor-mation processor which provides the credit signals that are transmitted to the respective subscriber terminals in the 5y s~em of the present invention~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the present invention is included in an authorization processor which is described with reference to Figure 1. The authorization processor is included in a subscriber terminal in a subscriber television network, such as is described in Canadian Patent Application No. 454,444 filed May 16, 1984 by Klein S. Gilhousen and Charles F. Newby for "KEY SIGNAL ENCRYPTION AND ~ISTRIBUTION SYSTEM FOR CONTRO-LLING SCRAMBLING AND SELECTIVE REMOTE DESCRAMBLING OF TELEVISION
SIGNALS." ~he authorization processor of Figure l enables .
13~ 2~3 -9a- 72046-7 descram~ling of a received scrambled television signal on an impulse-purchase or a prepaid basis.
The authorization processor receives a program cost signal on line 10 and a credit signal on line 11. The cost ~3~3Z~
signal indicates the charge for de~crambling a given received scrambled television signal, and is provided to all of the sub~rriber terminals in the subscriber television network. Credit ~ignalR are unique to each subscriber and they are individually addre~ed to the respective subscriber terminals in the network. Each credit signal indicates the accumulated credit attri~uted to the respective individual sub~criber.
The authorization proces~or includes a credit register 12, an overflow detection device 13, a debit regis~er 14, an add register lS and a compari~on unit 16. The credit register 12 registers the credit signal received on line 11.
The debit register 14 registers the accumulated charges for scrambled signals accepted by the respective individual lS subscriber for descrambling. The add register 15 add~ and registers the sum of the charge indicated by the program cost ~ignal on line 10 and the accumulated charges regi~tered in the debit register 14. ~he comparison unit 16 compare~ the credit signal registered in the credit register 12 with the sum of the addition registered in the add register 15 to determine whether the ~ubscriber has ~uf~icient credit available to pay for descrambling of the ~crambled signal. If upon such comparison it is determined that the accumulated credit indica~ed by the credit signal registered in the credit register 12 i8 not less than the sum of the addition registered in the add register 15, a credit-available signal i8 provided on line 17 to a display driver and logic circuit 19. If upon such comparison i~ is determined that such accumulated credit is less than such sum, an insufficient credi~ signal i~ provid~d on line 20 to the display driver and logic circuit 19.
The display drlver and logic circuit 19 provides slgnals on line 21 for controlling the content of a display on a video monitor display device 22, ~uch as the television set that i~ attached to the ~ubscriber terminal.
Alternatively, the display device 2~ can be an alphanumeric display on the front panel of the descrambler unit.
The authorization proce~sor also receives a program mask signal on lines 23 and an authori2ation word ~ignal on lines 24. The program mask signal i~ a 56-bit digital ~ignal that is unique to each scrambled program that i8 broadcast over the subscriber televi~ion ne~work. The program ma~k signal is provided to all of ~he subs~riber terminals in the network. The authorization word signal is a 56-b~t word signal that is individually addre~3e~ to the respective individual subscriber ~erminals in the network, If the respective sub~criber regularly receives all of the scrambled programs on the given TV channel, the authorization word signal addre~8ed to the respective subscriber terminal will match the program mask signal that iB provided to all of the sub~criber terminalæ in the network to the prescrlbed degree. If the respective subscriber is not a regular subscriber to all of the scrambled programs on the given cbannel, the authorization word addressed to the respective subscriber term~nal and received on lines 2~ does not match the program mask signal that i8 received on lines 23.
The authorization proces~or includes a second comparison unit 25, which compare~ ~he received program ma~k signal on lines 23 with the received authorization word 3ignal on llne~ 24. When the compared slgnals do not match to the prescribed degree, a not-prepaid ~ignal is provided on line 26 to the display driver and logic circuit 19. When the compared signal6 do match, a prepaid ~ignal is provided on line 27 to an enable gate 29.
The compari~on uni~ 25 i6 logically ANDI6 the corresponding bits from the program mask slgnal on line 23 with the authorization word signal on line 24 and then logically OR'~ the re~ult~ of the log~cal AND operation. A
match in any one o~ the correspondlng pair~ of bit3 results in the prepaid signal being provided on line 27. Typically the different bit positions in the authorization word ~ignal correspond to dlfferent TV channel~ and/or programs. Thus an authorization word signal for a given descrambler includes a "TRUE" blt in the bit po~ition deslgnated for each program and/or channel for which ~ervice has been prepaid. The program ma~k signal includes a TRUE bit in each po~ition corresponding to a given program and/or channel.
One of the bits of the program maEk signal on line 23 indicates whether the received scrambled television signal may be descrambled on an impul6e-purchase ba~is. When it may be ~o descrambled, an impul~e-purchase signal is provided in this bit position and i8 provided on line 30 to the display driver and logic circuit 19.
Certain bit~ of the program mask signal and the authori~ation word ~ignal may provide additional authorization unctions, such as 6tereo audio enabla, remote control enable and alternate language ~election.
~3~3~
The display driver and logic 19 circuit contains logic circuitry which d~ctates the content of the ~ignals that are provided on line 21 to the display device 22. When a credit-available ~iynal is provided on line 17, a not-S prepaid signal iæ provided on line 26 and an impulse-purchase 6ignal i~ provided on 30, the display driver and logic circuit 19, provide~ an enabling signal on line 31 to an acceptance ~witch 3~ and ~ur~her provides a signal on line 21 that re3ults in the display device 22 di~playing an indication to the subscriber that the subscriber has the option of cau~ing the scrambled television signal to be di~played on an impulse-purchase basis.
The subscriber may indicate acceptance of the option by operating the ~witch 32 only when the ~witch 32 i8 enabled 1~ by the enabling ~ignal on line 31. If the sub~criber æo accepts the option, an accepted signal is provided on line 33 to the enable gate 29. The accepted signal on line 33 also i~ provided to the display driver and logic circuit 19, which responds thereto by causing the display device 22 to briefly indicate acknowledgement o the subscriber's acceptance. Thereafter, the de~crambled television signal i8 di~played on the given TV channel. If the subscriber indicates by operation of the switch 32 that the option is not accepted, a signal i8 provided on llne 34 to the display driver and logic circuit 19, which re~ponds thereto by causing the di6play device 22 to briefly indicate acknowledgement of the ~ubscriber's non-accep~ance.
Thereafter, only a blank screen signal is displayed on the glven TV channel The display driver and logic circuit 19 re~ponds to the in~ufficient credit signal on line 20 by :~3~32Pi.~3 causing the di~play device 22 to briefly indicate that the subscriber's credlt is insufficient to enable descrambling of the scrambled ~ignal~ Alternatively the display may provide a continuou~ indication that the program is not authorized because ei~her it i8 not prepaid or becau~e ~ufficient credit i~ not available.
The accepted signal on line 33 is further provided to the enter enable input of the debit register 14 and causes the ~um registered in the add regi~ter 15 to be entered into the debit register 14, thereby effectively incrementing the accumulated charges in the debit register 14 by the charge indicated by the program cost signal received on line 10.
The over~low detection device 13 is coupled to the add regi6ter 15 for detecting when the arithmetic limit of the deblt register 14 would be exceeded by incrementing the accumulated charges in the debit register 14 by the charge indicated by the program cost signal on line 10 and for providing an over~low signal on line 18 upon said detection.
~he di~play driver and logic clrcuit 19 responds to the overflow signal on line 18 by preventing an enabling ~ignal from otherwi~e being provided on line 31 in response to a credit-available ~lgnal on line 17. Thl~ feature is provided ln order to prevent a sub~criber from feeding ~alse cost and credit signals into the authentication proce~or in order to increment the debit regi~ter 14 until it overflows to thereby store an amount le~s than the actual accumulated charge~ attributed to the subscr~ber terminal.
Whenever either the prepaid s~gnal is provided on line 27 or the accepted signal iB provided on line 33 to the enable gate input line 35, the enable gate 29 provlde~ a :;L3~32~8 decrypted and de~oded channel key 6ignal ~rom line 36 onto line 37 and thereby enableR the scrambled television signal to be descrambled. The significance of passing this key signal onto line 37 is explained somewhat later below with S refexence to Figures 2 and 3.
Figure 2 and 3 respectively show the encryption and decryption ~ystem~ included ln the broadcast terminal and each subscriber terminal of a ~ubscriber television network with which the ~y~tem~ of the present invention are par~icularly useful~ The encryptlon and decryption systems o Figures 2 and 3 are e~pecially adapted to prevent a subscriber from being able to enable de~crambling of the ~crambled signal through deceit by ~ubstitutlng . other signals for one or more of the respective transmitted lS program mask ~ignal, authorization word signal, program cost signal and credit ~ignal rece~ved by the sub~criber terminal in order to obtain a match upon said comparison and/or to cau~e a credit-available signal to be provided when in fact the subscriber'~ credit iB inadequate.
~eferring to the encryption ~ystem of the broadcast terminal (Figure 2) a keystream generator 39 produce~ a keystream signal on line 40 that i~ used to scramble the televi~ion signal. An identical key~tream signal must be reproduced on line 42 by the keystream generator 44 in the decryption sy~tem of the sub~criber terminal (Figure 3) in order for the descrambler in the subscriber terminal to be able to descramble the scrambled televi~ion ~ignal.
Referring again to Figure 2, the key~tream generator 39 of the encryp~ion system generates the keystream signal on line 40 by processlng an initialization vector (IV) frame count ~ignal on line 45 in accordance with the Data Encryption Standard (DES) algorithm upon the algorithm being keyed by a working key signal on line 46.
A working key generator 47 generates the working key signal on line 46 by processing the frame count signal on line 45 in accordance with the ~E~ algorithm upon the algorithm being keyed by a channel key signal on line 49.
The channel key signal on line 49 is provided by a control computer ~not shown~ at the broadca~t terminal.
The channel key signal on line 49 is encrypted for transmission to the subscriber term~nalæ. ~ channel key generator 50 encrypts the channel key signal by generating an encrypted channel key signal on line 51 by processing an encoded channel key signal on llne 52 in accordance with the DES algorithm upon the algorithm being keyed by an encoded ca~egory key signal on line 54.
Incident to the scheme for preventing descrambling by deceit through substitution of one or more of the program mask signal, the authorization word signal, the program cost signal and the credit signal, the program mask signal on line 55 is used to encode the channel key signal on line 49 by exclusive- OR'ing the channel key signal on line 49 with the program mask signal on line 55 to provide the encoded channel key ~ignal on line 52. Incident to the same scheme the encoded category key signal on line ~4 is produc~d by exclusive-OR'ing a category key signal provided on line 56 by the control computer with a program C08t signal provided on line 57 by the control computer. The program coæt signal on line 57: also ~s provided by the control computer.
~L3~3Z~B
The symbols 59, 60, 61 and ~2 in Figure 2 represent exclu~ive-OR logic elements.
The ca~egory key signal on line 56 also is encrypted for transmission to the ~ubscriber terminal~. Prior to such encryp~ion the category key ~ignal on line 56 is encoded by being exclllslve-OR'd with a credit ~i~nal provided on line 64 by the cGntrol computer to thereby provide an encoded category key ~ignal on line 65. Thi6 is incident to the aforementioned prevention ~cheme, The position of the bits of the category key signal on line 56 that ar~ exclusive-OR'd with the credit signal on line 64 must be different from the position of the bit~ of the category key ~ignal on line ~ that are exclusive-OR'd with the program çost signal on line 57. The derivation of the credit signal i8 described below with reference to Figure 4.
A category key generator 66 encrypt~ the category key signal by generating a plurality of unique encrypted cat~gory key signals on line 67 by proce~sing the encoded category key ~ignal on line 65 in accordance with the ~ES
algorithm upon the algorithm being keyed by a corre~ponding plurality o~ encoded unique ~ubscriber key signal~ on line 69. The subscriber key ~ignals are unique to the individual subscriber terminals.
A plurality of unique subscriber key signals are provided on line 70 from a sub3criber key storage memory 71 upon the memory 71 being accessed by a plurality of respective sub~criber addresses provided on line 72 by the control computer. The subscriber key s~gnals on line 70 are exclusive-OR'd with an authorization ~ord signal provided on 13~32~
line 74 by the control computer to provide the encoded subscriber key ~ignals on line 69. The authorization word signal on line 74 that is used for encoding the ~ubscriber key signal on line 70 either matches or doesn't match the program ma~k signal on line 55 in accordance with whether the subscriber terminal corresponding to the individual subscriber key signal being decoded iB assigned to a subscriber who is a regular ~ub~criber to all of the programs on the given TV channelO The use of the authorization word signal~ on ~ine 77 also is incident to the aforementioned prevention scheme.
The control computer also provides a subscriber key qeneration number on line 75 that is unique to the broadcaster.
The combination o the credit signal on line 64, the encrypted category key ~ignal on line 67, the subscriber address on line 72, and the authorization word signal on line 74 that all pertain to a given subscriber terminal are transmitted together as a category rekey message that is addressed to the given subscriber terminal by the subscriber address lncluded in such message. ~ccordingly, unique category rekey me~sages are transmitted to each of the subsariber terminalsc When the number of alternative authorization functions and the number of alternative programs an~/or channels that are provided to the subscribers over the network exceeds the 56 bit positions of the authorlzation word signals are provided and included in separate respective category rekey message addressed to each given subscriber terminal, where they are stored upon recelpt.
~3t~32~3 -l9- 72046-7 The program mask signal on line 55, the encry~ted channel key signal on line 51 and the program cost signal on line 57 pertairl to all of the subscriber terminals and are transmitted together as a channel rekey message to all of the subscriber terminals. The channel rekey message also contains a category rekey address signal on line 76 for selecting one of th.e stored category rekey messages from stbrage in the subscriber terminal in accordance with which programs and/or channels and authorization functions are indicated by TRUE bits in the res pecti~e bit positions of the program mask signal on line 55.
The frame count signal on line 45 and the subscriber key generation number on line 75 also are transmitted to all of the subscriber terminals.
The encryption system of Figure 2, the manner in which the frame count signal, the channel rekey message, the category rekey messages and the subscriber key generation number are further processed prior to transmission; and the use of the keystream signal for scrambling the television signal are described in greater detail in the aforementioned Canadian Patent Application No. 454,444.
The decryption system of each subscriber terminal, as shown in Figure 3, includes an authorization processor 77, a rekey message memory 78 and the enable gate 29. The authorization processor 77 is as described above with reference to Figure l. The rekey message memory 78 stores all of the different rekey messages addressed to the given subscriber termin-al.
~3~Jt32~
-19a- 72046-7 The decryption system of each subscriber terminal receives the frame count signal on line 79, the program '' .
-20- ~.3~32~
mask ~ignal on llne 23, the encrypted channel key signal on line 80, the program C08t signal on line 10, the credit ~ignal on line 11, the encryp~ed category key ~ignal on line 81, the authorization word signal on line 24 and the subscriber key generation number on line 82, and the category rekey address signal on line 83. Tha credit signal on line 11, the encrypted category key signal on line 81 and the au~horization word signal on line 24 are retrieved from the storage location of the memory 78 that i~ acce~ed by the addre~s signal on line 83.
The rece~ved sub~criber key generation number on line 82 is combined with the Eub~criber addre~s on l~ne 84 ~rom a sub~criber addre~s memory 85 to provide a ~ubscriber key generation signal on line 86.
Two bit~ in a given position of ~he received sub criber key generation number on line 82 are also provided on line 87 to access a ~iv~n addre~s in a subscriber key seed memory 88, The memory 88 store~ four subscriber key seed OEignals that are unique to the ~ubscriber and provide~ a prescribed ~0 key seed signal on line 89 in accordance with the address on line 87.
A subscriber key generator 90 reproduce~ the ~ubscriber key signal on line 91 corre~ponding to the sub3criber key signal on line 70 in the sy~tem of Figure 2 that wa~ u~ed in 2~ encrypting the encrypted category key signal included in ~he category rekey message addressed to the given sub~criber and received on line 81.
The sub~criber key generator 90 generate~ the subscriber key ~ignal on 11ne 91 by proces6ing the ~ubscriber key qeneration signal on line 86 in accordance ~3~3Z~8 with the DES algorithm upon the algorithm being keyed by the prescribed key seed signal on line 89.
The above-described system for reproducing subscriber key signals through use o~ stored key seed signals is the subject of a Canadian Patent Application entitled "Descrambler Subscriber Key Production Util.izing Key Seeds Stored In Descrambler'l filed on March 14, 1985 by Kaxl E. Moerder, Serial No. 476,47~.
The subscriber key signal on line 91 is exclusive-OR'd with the received authorization word signal received on line 24 to provide an encoded subscriber key signal on line 92 corres-ponding to the subscriber key signal for the given subscriber on line 69 in the system of Figure 2.
A category key generator 94 decrypts the encrypted category key signal received on line 80 by generating an encoded category key signal on line 95 corresponding to the si~nal on line 65 in the system o~ Figure 2 by processing the encrypted category key signal on line 81 in accordance with the DES algorithm upon the algorithm being keyed by the subscriber key signal on line 92.
The encoded category key signal on line 95 is exclusive-OR'd with the received credit signal on line ll-to provide a decoded category key slgnal on line 96 corresponding to the category key signal on line 56 in the system of Figure 2.
The symbols 97, 98, 99 and 100 in Figure 3 represent exclusive-OR'd logic elements.
~3~3Z~
-21a- 72046-7 The decoded cateaory key signal on line 96 is exclusive-OR'd with the received program cost signal on line -~2~ 3~
to provide an encoded ca~egory key signal on line 101 corre~pondlng to the encoded category key ~ignal on line 54 in the system of Figure 2.
A channel key generator 102 decrypts the encrypted channel key signal received on l~ne 80 by generating an encoded channel key signal on line 104 corre~ponding to the siqnal on line 52 in the system of Figure 2 by processing the encrypted channel key signal on line 80 in accordance with the DES algorithm upon the algorithm being keyed by the encoded category key s~gnal on line 101.
The encoded channel key signal on line 104 is exclusive-O~'d with the program ma~k 6ignal on line 23 to provide a decoded channel key ~ignal on line 36 corresponding to the channel key signal on line 49 in the system of Figure 2.
The enable gate 29 pa~ses the channel key ~ignal from line 36 onto line 37 only when the input line 3~ of the enable gate 29 receives either a prepaid signal or an accepted siynal from the authorization processor 77, which is described above with reference to Figure 1.
A working key generator 106 generates a working key signal on line 107 corresponding to the working key 8~ gnal on line 46 in the system o~ Figure 2 by proce~sing the frame count ~ignal received on line 79 ~n accordance ~ith the DES algorithm upon the algorithm being keyed by the channel key signal on line 37.
The key~tream generator 44 generates a keystream signal on line 42 corre~ponding to the key~tream ~ignal on line 40 in the system of Figure 2 by proces~ing the frame count signal on line 79 in accordance with the DES algorithm upon ~3~32~3 the algorithm being keyed by the working key signal on line 107.
The subscriber key seed memory 88 and the debit register 14 of each subscriber terminal are included in a non-volatile ran-dom access memory (RAM) of an integrated circuit chip that has an architecture which prevents the debit register from being accessed from off the chip~ The chip must be capable of performing the computation, comparison and authorization functions of the authori-zation processor 77 described with reference to Figure 1 and the decryption and decoding functions of the key signal decryption systems of Figure 3. A model TMS70C40 chip manufactured by Texas Instruments is preferred. This chip is modified for use in the system of the present invention by disabling the capability for accepting instructions from off the chip, thereby preventing an instruction to read the secure memory from being accepted.
A more detailed description of the decryption system of Figure 3 and the use of the keystream for descrambling the received scrambled television signal is set forth in the above-referenced Canadian Patent Application No. 454,444.
Referring again to Figure 1, a debit signal on line 109 indicating the contents of the debit register is provided to the display driver and logic circuit 19, which upon operator command provides a signal on line 21 to the display 22 for enabling a display of an indication of the accumulated charges attributed to the subscriber terminal. This enables the subscriber to record the accumulated charges information -24-~ 3 ~ 3 Z ~ ~
tha~ is di~played and to transmit the ~ame to the broadcast company whenever called for, such as when service is d~continued, when the sub~criber term~nal equipment is transferred to another subscriber or upon payment of the subscriber's periodic billing. Thi~ accumulated charges information is used by the broadcaster to reæolve any bllling disputes that may ar~se with the sub~criber or to facilitate computation o~ a refund when service is discontinued or the equipment is transferred.
In order to verify the accumulated charge 1nformation provided to the broadcast company by the subscriber, authentication information al~o is displayed on the display 22 for copying and transm~ttal to the broadcast company by the subscriber, The authent~cation information is displayed ln response to an authentication ~ignal provided on line 110 to the display driven and logic circuit 19 by an authentication generator 111. The authentication generator 111 generates the authentication signal on line 110 by processing the debit signal on line 109 in accordance with the DES algorithm upon the algorithm being keyed by the subscriber key signal on line 91.
In a subscriber television network having a two-way communication link between the broadca~t terminal and the subscriber terminal the debit signal on line 109 and/or the authentication signal on line 110 could be ~tored in a memory (not shown) in the subscriber terminal and accessed from ~uch memory upon command for transmi~sion to ~he broadcast terminalO
Referring agaln to ~he system in which the sub~criber records and transmit~ the disp~ayed accumulated charges -25- ~ 3 ~ 3~
information and the authentication information, upon rPcelpt of what is purported by the subscriber to be the displayed accumulated charge information and the authentication information, the broadcast company enters the ~ame into the control computer. The control computer converts the entered informatîon into debit and authentication ~ignal~ having the same format as the signals provided to the displ~y driver and logic circuit 19 on lines 109 and 110 respectively.
Referring to Figure 4; the converted debit and authentication signal~ in the control computer are provided on lines 114 and 115 respectlvely. The debi~ ~ignal is entered in a debit register 116 and the authentication signal is entered in an authentication register 117. The debit signal from the debit regi~ter 116 is proces~ed by a debit generator 118 in accordance with the DES algorithm upon the algorithm being keyed by the sub~criber key ~ignal on line 70 that iB related to the ~ub~riber terminal belonging to the subscriber who transmltted the authentication information. ~he deblt generator 118 thereby generate~ an authenticating debit ~ignal on line 119 which is compared by a comparison unit 120 with the authentication signal registered in the authentication register 117. If thi~ comparison re~ult~ in a matchr the information provided by the subscriber is verified, and a ~ignal i8 provided on line 121 to enable entry of the contents of the debit register 116 into a debit memory 122.
Figure 4 further illustrates how a credit ~lgnal for a given subscriber is provided on line 64 (Figure 2) for transmission to the sub~criber terminal.
-26- ~3~3~8 An indication of the amount of each payment made by a given ~ub~criber is entered into the control computer to provide a payment signal on line 122 to an add register 124.
The add register 124 add6 and register~ the ~um of the amount indicated by the payment signal on line 124 and an amount stored in a payment memory 125, which i~ increm~nted by the amount of each payment. When ~ervice begins for the subæcriber, the amount ini~ially ~tored in the payment memory 12S is the amount then ~ored in the debit memory 122 for the corresponding sub~c~iber term~nal. Upon the amount of each new payment being entered into the control computer the sum registered in the add regi~ter 124 i8 stored in the payment memory 125 to thereby increment the stored payment record by the amount of the new payment.
A signal indicating the amount of any credit extended to the given subscriber i8 provided on line 126 and stored in a credit memory 1~7. An add register 12~ sum~ and registers the amount of the credit advance from the credit memory 124 and the amount ~tored in the payment memory 125 to provide the credit signal on line 64 indicating the accumulated credit attributed to the given subscriber.
When service to the given subscriber i~ terminated, the amount of any refund due the subscriber iB determined by a difference register 129, which registers and provides on line 130 a 6ignal indicating the di~erence in the amounts ~tored in the payment memory 125 and the debit memory 122.
Claims (3)
AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED
ARE DEFINED AS FOLLOWS:
1. In a subscriber communication network, a system for enabling descram-bling in a subscriber terminal of a received scrambled signal, comprising means in a subscriber terminal for determining whether a first control signal received by the subscriber terminal bears a predetermined relationship to a second con-trol signal, and for providing an enable signal upon determining that said first control signal bears said predetermined relationship to said second control signal;
means in the subscriber terminal for using a given key signal for descram-bling the scrambled signal;
means in the subscriber terminal responsive to said enable signal for ena-bling the scrambled signal to be descrambled by said given key signal; and means for preventing a subscriber from being able to enable descrambling of the scrambled signal through such deceit as substituting another signal for saidreceived first control signal in order to cause said determining means to determine that said predetermined relationship with said second control signal exists, said preventing means comprising means in the central station for encoding said given key signal by processing said given key signal with said first control signal; and means in the subscriber terminal for processing said given key signal with said received first control signal to enable said given key signal to be used todescramble said scrambled signal;
wherein said given key signal, said first control signal, said second control signal and said enable signal are separate signals.
means in the subscriber terminal for using a given key signal for descram-bling the scrambled signal;
means in the subscriber terminal responsive to said enable signal for ena-bling the scrambled signal to be descrambled by said given key signal; and means for preventing a subscriber from being able to enable descrambling of the scrambled signal through such deceit as substituting another signal for saidreceived first control signal in order to cause said determining means to determine that said predetermined relationship with said second control signal exists, said preventing means comprising means in the central station for encoding said given key signal by processing said given key signal with said first control signal; and means in the subscriber terminal for processing said given key signal with said received first control signal to enable said given key signal to be used todescramble said scrambled signal;
wherein said given key signal, said first control signal, said second control signal and said enable signal are separate signals.
2. A system according to Claim 1, wherein the control signals include a mask signal uniquely related to said scrambled signal and an authorization signal indicating whether the subscriber is au-thorized to descramble the scrambled signal; and wherein the determining means compare the mask signal with the authoriza-tion signal, and provide said enable signal when the compared signals match to aprescribed degree.
3. A system according to Claim 1, wherein the control signals include a cost signal indicating the charge for descrambling said scrambled signal and a credit signal indicating credit available to the subscriber; and wherein the determining means process the cost signal with the credit signal to determine whether the subscriber has sufficient credit available to pay for descram-bling of said scrambled signal, and for providing said enable signal when it is deter-mined that there is sufficient credit available.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US618,917 | 1984-06-08 | ||
| US06/618,917 US4712238A (en) | 1984-06-08 | 1984-06-08 | Selective-subscription descrambling |
| CA000483413A CA1277764C (en) | 1984-06-08 | 1985-06-07 | System for enabling descrambling on a selective- subscription basis in a subscriber communication network |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000483413A Division CA1277764C (en) | 1984-06-08 | 1985-06-07 | System for enabling descrambling on a selective- subscription basis in a subscriber communication network |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1303208C true CA1303208C (en) | 1992-06-09 |
Family
ID=25670704
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000615869A Expired - Lifetime CA1303208C (en) | 1984-06-08 | 1990-09-19 | System for enabling descrambling on a selective-subscription basis in a subscriber communication network |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1303208C (en) |
-
1990
- 1990-09-19 CA CA000615869A patent/CA1303208C/en not_active Expired - Lifetime
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