Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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;
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
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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~
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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
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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
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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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8 72046-7D
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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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
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8b 72046-7P
signals.
Addltional features of the present invention are
described in relation to the des~ription of the preferred
embodiment.
A
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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
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-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
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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
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-14-
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
--17--
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~
-18-
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
-21- 72046-7
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
-23- 72046-7
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.
