CA1194212A - Security system for sstv encryption - Google Patents
Security system for sstv encryptionInfo
- Publication number
- CA1194212A CA1194212A CA000415993A CA415993A CA1194212A CA 1194212 A CA1194212 A CA 1194212A CA 000415993 A CA000415993 A CA 000415993A CA 415993 A CA415993 A CA 415993A CA 1194212 A CA1194212 A CA 1194212A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- sequence
- key number
- receiver
- key
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N7/00—Television systems
- H04N7/16—Analogue secrecy systems; Analogue subscription systems
- H04N7/167—Systems rendering the television signal unintelligible and subsequently intelligible
- H04N7/1675—Providing digital key or authorisation information for generation or regeneration of the scrambling sequence
Abstract
ABSTRACT OF THE DISCLOSURE
In a secure communications system, a key number which is changed periodically, e.g. monthly, and a ran-dom number from a random number generator are combined and used as a seed to reset a Pn sequence generator, with the output of the generator being used to control encryption of transmission data in a signal processor.
The key is also provided to a first encipherer to en-cipher the random number for transmission with the en-crypted data. At the receiver, the key is provided in common to a deipherer for deiphering the random number and a Pn sequence generator which is periodically reset by the combination of the key and random number in the same manner as in the transmitter. The Pn sequence is then used to decrypt the information. User identifica-tion codes are stored in the transmitter and are used to encipher the key, with each employing its ID code to deipher the key. The user ID codes are known only to the system operator, so that not even a particular user can know the key.
In a secure communications system, a key number which is changed periodically, e.g. monthly, and a ran-dom number from a random number generator are combined and used as a seed to reset a Pn sequence generator, with the output of the generator being used to control encryption of transmission data in a signal processor.
The key is also provided to a first encipherer to en-cipher the random number for transmission with the en-crypted data. At the receiver, the key is provided in common to a deipherer for deiphering the random number and a Pn sequence generator which is periodically reset by the combination of the key and random number in the same manner as in the transmitter. The Pn sequence is then used to decrypt the information. User identifica-tion codes are stored in the transmitter and are used to encipher the key, with each employing its ID code to deipher the key. The user ID codes are known only to the system operator, so that not even a particular user can know the key.
Description
~L~9'~Z~2 The pres~nt invention is related t~ ~he confiden-tiality of television si~nal transmissions, and more particularly to the protection of TV signal trans-missions from unauthorized reception. The environmentin which the present invention may be widely applicable, and in the context of which the invention will be described herein, is that o subscriber television and TV program distribution.
1o Subscriber television systems are becoming increasingly widespread wherein TV signals are sent out via a cable network or over the air and are intended for reception and viewing by only those subscribers who have paid a monthly fee. Wi~h the increase in subscriber television systems has also come an increase in the number of people attempting to receive and display the premium television programs without payment. Thus, there is a need or more sophisticated secuxity techniques for preventing such unauthorized reception.
Many existing subscriber television systems utilize, directly or indirectly, signals transmitted via satellite, and it is becoming c~ite common for non-paying individuals to receive and display the premium television programs via te:levision receive only (TVR0) antennas, thus resulting in a substantial loss of revenue for the distributors of the subscrip-tion televi~ion programs. In addition, various direct satellite broadcast television ~ystems are currently being proposed wherein subscription television programs will be broadcast directly via satellite to , . - . . ..
4~
individual subscriber homes. These subscription satellite television (SSTV~ systems will be quite vulnerable to unau~horized reception/ and an effective security technique is therefore highly desirable.
The purpose of a security subsystem for an SSTV
system is to protect the distributor's business interest and, accordingly, the following objectives should be achieved:
(1) To prevent a non-subscriber from receiYing intelligible video ~nd audio ~ignals by using a regular home television set;
1o Subscriber television systems are becoming increasingly widespread wherein TV signals are sent out via a cable network or over the air and are intended for reception and viewing by only those subscribers who have paid a monthly fee. Wi~h the increase in subscriber television systems has also come an increase in the number of people attempting to receive and display the premium television programs without payment. Thus, there is a need or more sophisticated secuxity techniques for preventing such unauthorized reception.
Many existing subscriber television systems utilize, directly or indirectly, signals transmitted via satellite, and it is becoming c~ite common for non-paying individuals to receive and display the premium television programs via te:levision receive only (TVR0) antennas, thus resulting in a substantial loss of revenue for the distributors of the subscrip-tion televi~ion programs. In addition, various direct satellite broadcast television ~ystems are currently being proposed wherein subscription television programs will be broadcast directly via satellite to , . - . . ..
4~
individual subscriber homes. These subscription satellite television (SSTV~ systems will be quite vulnerable to unau~horized reception/ and an effective security technique is therefore highly desirable.
The purpose of a security subsystem for an SSTV
system is to protect the distributor's business interest and, accordingly, the following objectives should be achieved:
(1) To prevent a non-subscriber from receiYing intelligible video ~nd audio ~ignals by using a regular home television set;
(2) To prevent a delinquent subscriber from receiving intelligible video and audio signals by using the SS~V decoder,
(3) To prevent a legitimate subscriber from xeceiving intelligible video and audio signals of unsubscribed SS~V channels or programs;
(4) To discourage an average technician rom building his own rec~iver ca~able of obt~;ning acceptable ~uality video and audio signals;
(5) To discouragP a small unau~horized business concern from manufacturing and marketing devices which are capable of receivi~g and displaying acceptable ~uality video and audio signals from the SSTV channels; and
(6) To allow a legitimate subscriber to receive and display high quality video and audio signals from the subscxibed chAnn~ls or programs.
It would also be highly desirable tP achieve the above objectives at a reasonable cost.
A number of security systems for CATV exist, most of which involve the suppression or removal o the horizontal sync pulses from the video si~nal before transmission, and the recovery of the sync pulses at the receive end. These techni~ues will prevent people without the sync recovery circuits from receiving and displaying the progXams and may therefore achieve objectives (1) and (6) above, but these security systems do not achieve objectives (2) and (3) and, since sync recovery circuits are relatively easily designed and manuactured, als~ do not satisfy objectives ~4) and (5).
More sophisticated techniques may include additional intelligence in the subscriber's decoder box, including the capability of receiving commands from a control center which are specifically addre~sed to an individual subscriber and are used to turn on or off some or all of ~he channels~ These more sophis-ticated security techniques may succeed in achieving objectives (1)-(3) and (6), but still do not satisfy objectives ~4) and (5). For example, most o~ these ~echniques involve the checking of a password, and a particular channel is turned on only if the password is matched. This could be relati~ely easily by-passed by modifying the subscriber's decoder box or building a separate bo~ with all of the necessary faatures except the on/off switch. Further, subscribers may al~o be able to tamper wikh th~ decoder box to recei~e more programs than are actually paid for.
It is an object oE the present invention to pro-vide a security subsystem for a subsc:ription television system wherein at least some of -the above-mentioned objectives (1)-(6) are achieved.
The present invention provides, in a communications system includi-ng a transmi-tter and a receiver, the -trans-: . mitter including ~ program source for providing a program signal representing program information, a transmit ~;
~L9~
3asignal processor ~or encrypting the program signal in accordance with a transm.it con-trol signal and transmi-t means for transmitting the encryp-ted signal, the re-ceiver including receive means for receiving -the en-crypted signal, a receiver signal processor for decrypt-ing the encrypted signal in accordance with a receive control signal and means for receiving the decrypted signal and providing the program information, the im-provement comprising, first generator means at the trans-mitter for generating a first sequence of signals repre-senting a first sequence of numbers, key number means at the transmitter for providing a key number signal repre-senting a key number, second generator means at -the transmitter for generating a second sequence of signals representing a second sequence oE numbers, the second generator means being periodically reset by a reset sig-nal comprising the output of the first generator means to thereby generate a plurality of sequence segments each beginning with a reset signal, the output of the second generator means comprising the transmit control signal, means at the transmitter for enciphering the first sequence of signals with the key number signal and for providing -the enciphered first signal sequence to the transmit means for transmission wi-th the encrypted program signal, means at the receiver for providing -the key number signal, receive deciphering means at the re-ceiver for receiving the enciphered first signal sequence and the key number, deciphering the first signal sequence in accordance with -the key number and providing the deciphered first signal sequence as an output, and receive generatiny means for genera-ting a sequence of signals representing the first sequence of numbers, the receive generating means being periodically reset by a reset signal comprising the ou-tput of the receive deci-phering means to thereby generate the plurality ofsequence segments, the plurali-ty of sequence segments being provided by the receive generating means to the receive signal processor as the receive control signal.
When the sys-tem is in use it employs crypto-graphic scrambling and descrambling technlzues whiah utili~e a "key" which is changed on a regulax basis and is sent only to paid subscribers, and even this 5 "key" is sent in a different encrypted form to each subscriber so that delinquent subscribers cannnot learn the current key from others.
A record is kept of unique user ID codes corres-ponding to each subscriber, and in a transmitter according to the preferred embodiment of this inven~
tion, the key is ciphered with each subscriber's unique ID code prior to sending the key to that subscriber. A random number generator in the trans-mitter generates a new random number at regular inter~
vals, for example, every second, and this number is combined with ~he key, and the co~bined number is then used as a seed to reset a PN sequence generator every second. This PN sequence generator will thus generate a PN sequence with a random seed in one-second seg~
ments, and the segmented PN seguence is suppli~d to a signal processor where it is used to scramble the audio and video program signals. The random number generator is also ciphered with the key and the en-ciphered random number is continually transmitted with the scrambled video signal.
At the receiver, the enciphered key, which has been sent either via satellite ar mail, is deciphered in the receiver utilizing ~he particular ~ubscriber's unigue ID code, which ID code is internal to the receiver and is unknown to the subscriber. The de-ciphered key is then in turn used to decipher the enciphered random number received with the scrambled program si~nal. The deciphered key and random number are then combined as in the transmitter, and the A~' ~ 2 combined signal is used to continually resek a PN
sequence generator identical to tha-t in the trans-mitter so that a segmented PN sequence will be gener-ated in the receiver which is identical to ~hat s generated in ~he transmitter, and this segmented PN
se~uence can then be used to descramble the received signal. The descrambled signal will then be supplied to the subscriber television set.
BRIEF DESCRIPTION OF ~HE DRAWING
lo The invention will be more clearly understood with reference to ~he following description in con-junction with the accompanying drawing wherein the single figure is a block diagram of the essential components of the SSTV ~ecurity sy~tem embodying the present invention.
DETAILED DESCRIPTION OF T~E PREFERRED EMBODIMENT
The drawing illustrates a functional block dia~
gram of the SSTV security system ~mbodying this invention, The SSTV transmitter will typically in-clude or have access to a billing system computer 10 which will store subscriber information including a list of paid subscribers and their corresponding unique user ID codes. This information may typically be stored in a user data base 12 within the computer.
Also within the computer will be a register 14 or the like cont~;n;ng a key which will be changed on a regular basis, e.g. monkhly. In preparation or sending this "key of the month" to each current sub-scriber, the key is enciphered in cm encipherer 16 with the user ID code unique to that particular cur-rent subscriber, and the enciphered key is then sent -to the subscriber.
The transmitter includes a pseudo-random number (PN) seguence generator 18 and a random number gener-ator 20. The random number generator 20 periodically generates'a new random number, e.g. once every second, 1, and the outputs of the random number generator 20 and key regis~er 14 are combined and loaded into the PN
~equence generato~ 18 to periodically reset or "seed' ~he PN sequence generator 18 in a m~nner well ~nown in the a.rt. Each seeding of th2 seguence generator 18 will begin a new segment of the PN sequence. The program signal from source 22 is supplied to a signal processor 24 where it is encrypted with the se~mented PN sequence from generator 18. The encryption tech nique used may be any one of a variety o~ well known techniguPs and need not be discusse~ in detail herein.
The e~crypted, or ~crambled, signal is then provided to a transmitter 26 for transmission over link 100 to the various subscriber recPivers.
The random number from generator ~0 is enciphered with the key of the month in an encipher~r 28, and ~he enciphered random number is transmitted wi~h the scrambled ~ideo signal over the link 100.
At ~he receiver, a register 30 or the like internal to the subscriber TV receiver contains a subscriber specific secret user ID code which is set priox to installation and is stored in the user data base 12 of the billing computer at the transmitter.
Thus, when the subscriber receiver receives the en~
ciphered key or when the user receives the enciphered key by mail and enters the enciphered key into the receiver, a decipherer 32 in the receiver deciphers the enciphered key with the sec:ret user ID code specific to that particular subscriber, and the deciphered key is provided to a decipherer 34. A
receiver 36 separates the scrambled signal from ~he enciphered random number received.over li~k 100 and provides the enciphered random number to the de-cipherer 34 where it is deciphered with the key - 35 received from the decipherer 32. The deciphered rand~m number and key are then combined and loaded into ~he PN sequence generator 38 to xeset or "seed"
the sequence generator in ~he s~me manner as in the transmitter, to thereby result in the same segmented PN seguence as was used ~or scrambling in the SSTV
transmitter signal processor ~4. This segmented PN
sequence is ~hen provided to signal processor 40 where it is used to descramble ~he received program signal.
The descrambled sig~al is then provided to the sub~criber television ~et 42.
The above-de~cribed security ~ystem provides a no~el technique for g~nera~ing and synchronizing a se~mented pseudo-random number ~PN3 seguence, and a secure key distribution method. The se~mented PN
seguence generated is used to contro~ the video and audio signal processors that scramble and descramble the program signals. Since a different se~mented PN
sequence will b~ generated by each distinct key, the scrambling sequence is diferent for each key, and by periodically changing th2 key the scrambling and descrambling sequences will change. Thus, it i~ not possible for anyone wi~hout exact knowledge of the current key to descramble the received program signal with or wi~hout a descrambling de~ice.
For each given duration of time, a particular chAnnel is scrambled by a PN se~uence that is generated by a randomly selected number and the key of the month. To prevent subscribexs of different chAnnels from exchanging the keys ~nong ~hemselves, it is essential that the key for a given ch~nnel distri-buted to each subscriber look different, and thi~
accomplished by enciphering the key with each subscriber's unique user ID code. In ~his way, although a single key is provided by the regi~ter 14 at any one time, a di~erent key is required by each subscriber. It is only when the subscriber-specific ~ 9 ~
key is entered into the receiver that the true key of the mon~h contained in reqister 14 can be provided to the decipherer 34 and seguence generator 38, and ~he deciphering sf ~his true key of the month in the decipherer 32 i~ performed internally of the subscriber receiver and without the subscriber's knowledge.
An impor~ant feature o any security system is that a legitimate subscriber mus-t be capa`ble of 10 obt~in;ng synchronization within a shor~ period of time. In the system according to the present invention, the PN seguence used for scxambling and descr~mbling the siynal in si~nal processor~ 24 and 40, respectively, is separated into short segments each of which is seeded by ~he combination o~ khe key of the month and a random number which changes, for example, once every second. Thus, assuming ~hat a legitimate subscriber does have his appropriate key, the time required to acquire synchronization will be substantially equal to the du:ration o:f each random number so that synchronization can be acquired rapidly : in case of loss of sync due to power outages, rainstorms, changing of channels, e~c.
The individuial components in ~he security system according to the present invention are known in the art and need not be described in detail herein since the internal details of ~hese cc,mponents do not constitute a part of the present i~vention. The encipherers u~ed to encipher the key of the month and 3~ ~he random number can be two different encipherers, but for the sake of hardware simplicity at the receive side, and conseguent cost savings in mass production of the subscriber receivers, it is preferable that the same enciphPrers be used~ The encipherer may employ any enciphering method as long as it has a suffi-ciently high level of security.
~ ' > ~1 ' ' g The PN sequence generator can be any general PN
sequence generator as long as it also has sufficient security strengt~, e.g. a proper~y selected non-linear ~eedback shit register may suffice.
The random number ge~erator in the transmitter may be a well known thermal noi~e generator which generate~ "true" random number~, or it may be a pseudo-random number generator similar to the seguence generator 18, implemented in a well known manner with digital electronics or computer sof~ware. Similarly, ~he technique for combining ~he key of the month and the random number generator to produc2 the "seed" for the PN sequence generators 18 and 38 is not ~ritical, with the simplest technique being a bik by-bit modulo-2 addition of th~ two num~ers.
In general, each of the functional blocks in the drawing can be implemented with existing techniques, with system complexity and cost and security st~eng~h depending on the particular implementation of each of the functional blocks.
The transformation of th simple cipherer is specified by a variable which is different for each ~h~nnel or special pxogram, and is changed every month.
The user ID code 30 within each subscriber set may be a set of binary switches or a bit pattern programmed into a read-only memory in a sealed box to prevent the subscriber from seeing or changing the number.
The use of a simple cipherer in addition to the non-linear feedback shift-register may seem to increase the system complexity unnecesarily. However, since only a small amou~t of data, namely the "seed", need be handled each time, and since the statistical properties of the cipherer do not impact to the output of the PN sequence yenerator, ~he cipherer can be very simple. One possible approach, for ex~mple, is a ROM
table of random bits with or without cipher feedback.
The use of this simple cipherer greatly simplifies the problem of cryptosynchronization and key distribution, and therefore reduces the overall system complexity.
Suitable alternatives for the scramblin~ of the program signals includP conven~ional scrambling techniques such as on-off switching, r~n~o~ly invert-ing lines, fields or frames, and delaying horizontal lines or fields by certain randomly fixed steps. In any case, ~he technigue used will require the genera-tion of a PN sequence which must be synchroni~ed at both the transmit and receive sides.
It would also be highly desirable tP achieve the above objectives at a reasonable cost.
A number of security systems for CATV exist, most of which involve the suppression or removal o the horizontal sync pulses from the video si~nal before transmission, and the recovery of the sync pulses at the receive end. These techni~ues will prevent people without the sync recovery circuits from receiving and displaying the progXams and may therefore achieve objectives (1) and (6) above, but these security systems do not achieve objectives (2) and (3) and, since sync recovery circuits are relatively easily designed and manuactured, als~ do not satisfy objectives ~4) and (5).
More sophisticated techniques may include additional intelligence in the subscriber's decoder box, including the capability of receiving commands from a control center which are specifically addre~sed to an individual subscriber and are used to turn on or off some or all of ~he channels~ These more sophis-ticated security techniques may succeed in achieving objectives (1)-(3) and (6), but still do not satisfy objectives ~4) and (5). For example, most o~ these ~echniques involve the checking of a password, and a particular channel is turned on only if the password is matched. This could be relati~ely easily by-passed by modifying the subscriber's decoder box or building a separate bo~ with all of the necessary faatures except the on/off switch. Further, subscribers may al~o be able to tamper wikh th~ decoder box to recei~e more programs than are actually paid for.
It is an object oE the present invention to pro-vide a security subsystem for a subsc:ription television system wherein at least some of -the above-mentioned objectives (1)-(6) are achieved.
The present invention provides, in a communications system includi-ng a transmi-tter and a receiver, the -trans-: . mitter including ~ program source for providing a program signal representing program information, a transmit ~;
~L9~
3asignal processor ~or encrypting the program signal in accordance with a transm.it con-trol signal and transmi-t means for transmitting the encryp-ted signal, the re-ceiver including receive means for receiving -the en-crypted signal, a receiver signal processor for decrypt-ing the encrypted signal in accordance with a receive control signal and means for receiving the decrypted signal and providing the program information, the im-provement comprising, first generator means at the trans-mitter for generating a first sequence of signals repre-senting a first sequence of numbers, key number means at the transmitter for providing a key number signal repre-senting a key number, second generator means at -the transmitter for generating a second sequence of signals representing a second sequence oE numbers, the second generator means being periodically reset by a reset sig-nal comprising the output of the first generator means to thereby generate a plurality of sequence segments each beginning with a reset signal, the output of the second generator means comprising the transmit control signal, means at the transmitter for enciphering the first sequence of signals with the key number signal and for providing -the enciphered first signal sequence to the transmit means for transmission wi-th the encrypted program signal, means at the receiver for providing -the key number signal, receive deciphering means at the re-ceiver for receiving the enciphered first signal sequence and the key number, deciphering the first signal sequence in accordance with -the key number and providing the deciphered first signal sequence as an output, and receive generatiny means for genera-ting a sequence of signals representing the first sequence of numbers, the receive generating means being periodically reset by a reset signal comprising the ou-tput of the receive deci-phering means to thereby generate the plurality ofsequence segments, the plurali-ty of sequence segments being provided by the receive generating means to the receive signal processor as the receive control signal.
When the sys-tem is in use it employs crypto-graphic scrambling and descrambling technlzues whiah utili~e a "key" which is changed on a regulax basis and is sent only to paid subscribers, and even this 5 "key" is sent in a different encrypted form to each subscriber so that delinquent subscribers cannnot learn the current key from others.
A record is kept of unique user ID codes corres-ponding to each subscriber, and in a transmitter according to the preferred embodiment of this inven~
tion, the key is ciphered with each subscriber's unique ID code prior to sending the key to that subscriber. A random number generator in the trans-mitter generates a new random number at regular inter~
vals, for example, every second, and this number is combined with ~he key, and the co~bined number is then used as a seed to reset a PN sequence generator every second. This PN sequence generator will thus generate a PN sequence with a random seed in one-second seg~
ments, and the segmented PN seguence is suppli~d to a signal processor where it is used to scramble the audio and video program signals. The random number generator is also ciphered with the key and the en-ciphered random number is continually transmitted with the scrambled video signal.
At the receiver, the enciphered key, which has been sent either via satellite ar mail, is deciphered in the receiver utilizing ~he particular ~ubscriber's unigue ID code, which ID code is internal to the receiver and is unknown to the subscriber. The de-ciphered key is then in turn used to decipher the enciphered random number received with the scrambled program si~nal. The deciphered key and random number are then combined as in the transmitter, and the A~' ~ 2 combined signal is used to continually resek a PN
sequence generator identical to tha-t in the trans-mitter so that a segmented PN sequence will be gener-ated in the receiver which is identical to ~hat s generated in ~he transmitter, and this segmented PN
se~uence can then be used to descramble the received signal. The descrambled signal will then be supplied to the subscriber television set.
BRIEF DESCRIPTION OF ~HE DRAWING
lo The invention will be more clearly understood with reference to ~he following description in con-junction with the accompanying drawing wherein the single figure is a block diagram of the essential components of the SSTV ~ecurity sy~tem embodying the present invention.
DETAILED DESCRIPTION OF T~E PREFERRED EMBODIMENT
The drawing illustrates a functional block dia~
gram of the SSTV security system ~mbodying this invention, The SSTV transmitter will typically in-clude or have access to a billing system computer 10 which will store subscriber information including a list of paid subscribers and their corresponding unique user ID codes. This information may typically be stored in a user data base 12 within the computer.
Also within the computer will be a register 14 or the like cont~;n;ng a key which will be changed on a regular basis, e.g. monkhly. In preparation or sending this "key of the month" to each current sub-scriber, the key is enciphered in cm encipherer 16 with the user ID code unique to that particular cur-rent subscriber, and the enciphered key is then sent -to the subscriber.
The transmitter includes a pseudo-random number (PN) seguence generator 18 and a random number gener-ator 20. The random number generator 20 periodically generates'a new random number, e.g. once every second, 1, and the outputs of the random number generator 20 and key regis~er 14 are combined and loaded into the PN
~equence generato~ 18 to periodically reset or "seed' ~he PN sequence generator 18 in a m~nner well ~nown in the a.rt. Each seeding of th2 seguence generator 18 will begin a new segment of the PN sequence. The program signal from source 22 is supplied to a signal processor 24 where it is encrypted with the se~mented PN sequence from generator 18. The encryption tech nique used may be any one of a variety o~ well known techniguPs and need not be discusse~ in detail herein.
The e~crypted, or ~crambled, signal is then provided to a transmitter 26 for transmission over link 100 to the various subscriber recPivers.
The random number from generator ~0 is enciphered with the key of the month in an encipher~r 28, and ~he enciphered random number is transmitted wi~h the scrambled ~ideo signal over the link 100.
At ~he receiver, a register 30 or the like internal to the subscriber TV receiver contains a subscriber specific secret user ID code which is set priox to installation and is stored in the user data base 12 of the billing computer at the transmitter.
Thus, when the subscriber receiver receives the en~
ciphered key or when the user receives the enciphered key by mail and enters the enciphered key into the receiver, a decipherer 32 in the receiver deciphers the enciphered key with the sec:ret user ID code specific to that particular subscriber, and the deciphered key is provided to a decipherer 34. A
receiver 36 separates the scrambled signal from ~he enciphered random number received.over li~k 100 and provides the enciphered random number to the de-cipherer 34 where it is deciphered with the key - 35 received from the decipherer 32. The deciphered rand~m number and key are then combined and loaded into ~he PN sequence generator 38 to xeset or "seed"
the sequence generator in ~he s~me manner as in the transmitter, to thereby result in the same segmented PN seguence as was used ~or scrambling in the SSTV
transmitter signal processor ~4. This segmented PN
sequence is ~hen provided to signal processor 40 where it is used to descramble ~he received program signal.
The descrambled sig~al is then provided to the sub~criber television ~et 42.
The above-de~cribed security ~ystem provides a no~el technique for g~nera~ing and synchronizing a se~mented pseudo-random number ~PN3 seguence, and a secure key distribution method. The se~mented PN
seguence generated is used to contro~ the video and audio signal processors that scramble and descramble the program signals. Since a different se~mented PN
sequence will b~ generated by each distinct key, the scrambling sequence is diferent for each key, and by periodically changing th2 key the scrambling and descrambling sequences will change. Thus, it i~ not possible for anyone wi~hout exact knowledge of the current key to descramble the received program signal with or wi~hout a descrambling de~ice.
For each given duration of time, a particular chAnnel is scrambled by a PN se~uence that is generated by a randomly selected number and the key of the month. To prevent subscribexs of different chAnnels from exchanging the keys ~nong ~hemselves, it is essential that the key for a given ch~nnel distri-buted to each subscriber look different, and thi~
accomplished by enciphering the key with each subscriber's unique user ID code. In ~his way, although a single key is provided by the regi~ter 14 at any one time, a di~erent key is required by each subscriber. It is only when the subscriber-specific ~ 9 ~
key is entered into the receiver that the true key of the mon~h contained in reqister 14 can be provided to the decipherer 34 and seguence generator 38, and ~he deciphering sf ~his true key of the month in the decipherer 32 i~ performed internally of the subscriber receiver and without the subscriber's knowledge.
An impor~ant feature o any security system is that a legitimate subscriber mus-t be capa`ble of 10 obt~in;ng synchronization within a shor~ period of time. In the system according to the present invention, the PN seguence used for scxambling and descr~mbling the siynal in si~nal processor~ 24 and 40, respectively, is separated into short segments each of which is seeded by ~he combination o~ khe key of the month and a random number which changes, for example, once every second. Thus, assuming ~hat a legitimate subscriber does have his appropriate key, the time required to acquire synchronization will be substantially equal to the du:ration o:f each random number so that synchronization can be acquired rapidly : in case of loss of sync due to power outages, rainstorms, changing of channels, e~c.
The individuial components in ~he security system according to the present invention are known in the art and need not be described in detail herein since the internal details of ~hese cc,mponents do not constitute a part of the present i~vention. The encipherers u~ed to encipher the key of the month and 3~ ~he random number can be two different encipherers, but for the sake of hardware simplicity at the receive side, and conseguent cost savings in mass production of the subscriber receivers, it is preferable that the same enciphPrers be used~ The encipherer may employ any enciphering method as long as it has a suffi-ciently high level of security.
~ ' > ~1 ' ' g The PN sequence generator can be any general PN
sequence generator as long as it also has sufficient security strengt~, e.g. a proper~y selected non-linear ~eedback shit register may suffice.
The random number ge~erator in the transmitter may be a well known thermal noi~e generator which generate~ "true" random number~, or it may be a pseudo-random number generator similar to the seguence generator 18, implemented in a well known manner with digital electronics or computer sof~ware. Similarly, ~he technique for combining ~he key of the month and the random number generator to produc2 the "seed" for the PN sequence generators 18 and 38 is not ~ritical, with the simplest technique being a bik by-bit modulo-2 addition of th~ two num~ers.
In general, each of the functional blocks in the drawing can be implemented with existing techniques, with system complexity and cost and security st~eng~h depending on the particular implementation of each of the functional blocks.
The transformation of th simple cipherer is specified by a variable which is different for each ~h~nnel or special pxogram, and is changed every month.
The user ID code 30 within each subscriber set may be a set of binary switches or a bit pattern programmed into a read-only memory in a sealed box to prevent the subscriber from seeing or changing the number.
The use of a simple cipherer in addition to the non-linear feedback shift-register may seem to increase the system complexity unnecesarily. However, since only a small amou~t of data, namely the "seed", need be handled each time, and since the statistical properties of the cipherer do not impact to the output of the PN sequence yenerator, ~he cipherer can be very simple. One possible approach, for ex~mple, is a ROM
table of random bits with or without cipher feedback.
The use of this simple cipherer greatly simplifies the problem of cryptosynchronization and key distribution, and therefore reduces the overall system complexity.
Suitable alternatives for the scramblin~ of the program signals includP conven~ional scrambling techniques such as on-off switching, r~n~o~ly invert-ing lines, fields or frames, and delaying horizontal lines or fields by certain randomly fixed steps. In any case, ~he technigue used will require the genera-tion of a PN sequence which must be synchroni~ed at both the transmit and receive sides.
Claims (13)
1. In a communications system including a transmitter and a receiver, said transmitter including a program source for providing a program signal repre-senting program information, a transmit signal processor for encrypting said program signal in accordance with a transmit control signal and transmit means for transmitting said encrypted signal, said receiver including receive means for receiving said encrypted signal, a receiver signal processor for decrypting said encrypted signal in accordance with a receive control signal and means for receiving said decrypted signal and providing said program informa-tion, the improvement comprising:
first generator means at said transmitter for generating a first sequence of signals repre-senting a first sequence of numbers;
key number means at said transmitter for providing a key number signal representing a key number;
second generator means at said transmitter for generating a second sequence of signals representing a second sequence of numbers, said second generator means being periodically reset by a reset signal comprising the output of said first generator means to thereby generate a plurality of sequence segments each beginning with a reset signal, the output of said second generator means comprising said transmit control signal;
means at said transmitter for enciphering said first sequence of signals with said key number signal and for providing said enciphered first signal sequence to said transmit means for transmission with said encrypted program signal;
means at said receiver for providing said key number signal;
receive deciphering means at said receiver for receiving said enciphered first signal sequence and said key number, deciphering said first signal sequence in accordance with said key number and providing said deciphered first signal sequence as an output; and receive generating means for generating a sequence of signals representing said first sequence of numbers, said receive generating means being periodically reset by a reset signal comprising the output of said receive deciphering means to thereby generate said plurality of sequence segments, said plurality of sequence segments being provided by said receive generating means to said receive signal processor as said receive control signal.
first generator means at said transmitter for generating a first sequence of signals repre-senting a first sequence of numbers;
key number means at said transmitter for providing a key number signal representing a key number;
second generator means at said transmitter for generating a second sequence of signals representing a second sequence of numbers, said second generator means being periodically reset by a reset signal comprising the output of said first generator means to thereby generate a plurality of sequence segments each beginning with a reset signal, the output of said second generator means comprising said transmit control signal;
means at said transmitter for enciphering said first sequence of signals with said key number signal and for providing said enciphered first signal sequence to said transmit means for transmission with said encrypted program signal;
means at said receiver for providing said key number signal;
receive deciphering means at said receiver for receiving said enciphered first signal sequence and said key number, deciphering said first signal sequence in accordance with said key number and providing said deciphered first signal sequence as an output; and receive generating means for generating a sequence of signals representing said first sequence of numbers, said receive generating means being periodically reset by a reset signal comprising the output of said receive deciphering means to thereby generate said plurality of sequence segments, said plurality of sequence segments being provided by said receive generating means to said receive signal processor as said receive control signal.
2. A communications system as defined in claim 1, further comprising:
means for providing an identification number signal uniquely identifying said receiver;
means for enciphering said key number signal with said identification signal;
means at said receiver for providing said identification number signal; and means at said receiver for receiving said identification number signal and said enciphered key number signal and for deciphering said key number signal, said deciphered key number signal being provided to said receive deciphering means.
means for providing an identification number signal uniquely identifying said receiver;
means for enciphering said key number signal with said identification signal;
means at said receiver for providing said identification number signal; and means at said receiver for receiving said identification number signal and said enciphered key number signal and for deciphering said key number signal, said deciphered key number signal being provided to said receive deciphering means.
3. A communications system as defined in claim 1, wherein each of said reset signals provided to said second generator means comprises a combination of said key number signal and a signal of said first signal sequence, and wherein each of said reset signals provided to said receive generator means comprises a combination of said key number signal and a signal of said deciphered first signal sequence.
4. A communications system as defined in claim 3, wherein said key number signal is changed at predetermined time intervals.
5. A communications system as defined in claim 4, wherein said second generator means is a non-linear pseudorandom sequence generator.
6. A communications system as defined in claim 3, wherein a plurality of receivers receive the encrypted signal transmitted by said transmitter, each of said receivers having a corresponding unique identification number and said enciphered key number received at each receiver being enciphered with the user identification number unique to said each receiver.
7. The communications system as defined in claim 6, wherein said first signal sequence represents a substantially random number sequence.
8. In a method of providing security in a signal transmission system, said method including the steps of encrypting in accordance with an encryption control signal a program signal representing informa-tion, transmitting said encrypted signal, receiving said encrypted signal, decrypting said received encrypted signal in accordance with a decryption control signal and providing said information repre-sented by said decrypted signal the improvement comprising:
generating a key number signal representing a key number;
generating a first signal sequence repre-senting a first sequence of numbers;
generating a second signal sequence repre-senting a second sequence of numbers, said second signal sequence being periodically reset by a reset signal comprising a signal of said first signal sequence to thereby generate a plurality of second sequence segments;
providing said second sequence segments to said transmit signal processor as said encryption control signal;
enciphering said first signal sequence with said key number and providing said enciphered first sequence to said transmitter for transmission with said encrypted signal;
decrypting said enciphered first sequence at said receiver in accordance with said key number signal;
generating said second sequence segments at said receiver by resetting a receive number signal generator with a reset signal comprising said deciphered first signal sequence; and providing said second sequence segments to said receive signal processor as said decryption control signal.
generating a key number signal representing a key number;
generating a first signal sequence repre-senting a first sequence of numbers;
generating a second signal sequence repre-senting a second sequence of numbers, said second signal sequence being periodically reset by a reset signal comprising a signal of said first signal sequence to thereby generate a plurality of second sequence segments;
providing said second sequence segments to said transmit signal processor as said encryption control signal;
enciphering said first signal sequence with said key number and providing said enciphered first sequence to said transmitter for transmission with said encrypted signal;
decrypting said enciphered first sequence at said receiver in accordance with said key number signal;
generating said second sequence segments at said receiver by resetting a receive number signal generator with a reset signal comprising said deciphered first signal sequence; and providing said second sequence segments to said receive signal processor as said decryption control signal.
9. A method as defined in claim 8, further comprising:
enciphering said key number signal at said transmitter with a user identification number signal uniquely identifying said receiver;
transmitting said enciphered key number signal to said receiver;
deciphering said enciphered key number signal at said receiver in accordance with said user identification number signal uniquely identifying said receiver; and providing said deciphered key number signal to said deciphering means.
enciphering said key number signal at said transmitter with a user identification number signal uniquely identifying said receiver;
transmitting said enciphered key number signal to said receiver;
deciphering said enciphered key number signal at said receiver in accordance with said user identification number signal uniquely identifying said receiver; and providing said deciphered key number signal to said deciphering means.
10. The method as defined in claim 9, further comprising the steps of:
combining said key number signal and a signal in said first sequence to obtain said reset signal in said transmitter; and combining said key number signal and a signal in said deciphered first sequence in order to obtain said reset signal in said receiver.
combining said key number signal and a signal in said first sequence to obtain said reset signal in said transmitter; and combining said key number signal and a signal in said deciphered first sequence in order to obtain said reset signal in said receiver.
11. The method as defined in claim 8, further comprising the step of periodically changing said key number signal.
12. The method as defined in claim 11, wherein said second generator means in said transmitter and said generator means in said receiver each generate non-linear pseudo-random signal sequences.
13. The method as defined in claim 12, wherein said first signal sequence represents a substantially random number sequence.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/322,833 US4484027A (en) | 1981-11-19 | 1981-11-19 | Security system for SSTV encryption |
| US322,833 | 1981-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1194212A true CA1194212A (en) | 1985-09-24 |
Family
ID=23256635
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000415993A Expired CA1194212A (en) | 1981-11-19 | 1982-11-19 | Security system for sstv encryption |
| CA613072A Expired - Lifetime CA1328501B (en) | 1981-11-19 | 1982-11-19 | Security System for SSTV Encryption |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA613072A Expired - Lifetime CA1328501B (en) | 1981-11-19 | 1982-11-19 | Security System for SSTV Encryption |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4484027A (en) |
| EP (1) | EP0094423B1 (en) |
| JP (2) | JPS58501982A (en) |
| AT (1) | ATE56333T1 (en) |
| CA (2) | CA1194212A (en) |
| DE (1) | DE3280237D1 (en) |
| WO (1) | WO1983001881A1 (en) |
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| NL6906145A (en) * | 1968-05-15 | 1969-11-18 | ||
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-
1981
- 1981-11-19 US US06/322,833 patent/US4484027A/en not_active Ceased
-
1982
- 1982-11-19 WO PCT/US1982/001631 patent/WO1983001881A1/en active IP Right Grant
- 1982-11-19 AT AT83900222T patent/ATE56333T1/en not_active IP Right Cessation
- 1982-11-19 EP EP83900222A patent/EP0094423B1/en not_active Expired - Lifetime
- 1982-11-19 CA CA000415993A patent/CA1194212A/en not_active Expired
- 1982-11-19 CA CA613072A patent/CA1328501B/en not_active Expired - Lifetime
- 1982-11-19 DE DE8383900222T patent/DE3280237D1/en not_active Expired - Fee Related
- 1982-11-19 JP JP83500335A patent/JPS58501982A/en active Pending
-
1992
- 1992-11-19 JP JP4332267A patent/JPH06125554A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS58501982A (en) | 1983-11-17 |
| JPH06125554A (en) | 1994-05-06 |
| CA1328501E (en) | 1985-09-24 |
| US4484027A (en) | 1984-11-20 |
| EP0094423B1 (en) | 1990-09-05 |
| EP0094423A1 (en) | 1983-11-23 |
| WO1983001881A1 (en) | 1983-05-26 |
| CA1328501B (en) | 1994-04-12 |
| DE3280237D1 (en) | 1990-10-11 |
| EP0094423A4 (en) | 1986-11-27 |
| ATE56333T1 (en) | 1990-09-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MZSU | Surrender | ||
| MZSU | Surrender |
Effective date: 19940412 |