United States Patent
`Wechselberger et al.
`Jul. 23, 1985
`[45] Date of Patent:
` ___*__
`
`[11] Patent Number:
`
`4,531,020
`
`[19]
`
`4,464,678
`
`8/1984 Schiff et al.
`
`....................... .. 358/122
`
`FOREIGN PATENT DOCUMENTS
`
`W081/02961 10/1981 PCT Int’l Appl.
`W083/01881 5/1983 PCT Int‘1 Appl.
`
`............... .. 358/122
`...............
`358/122
`
`Primary Examz'ner—Salvatore Cangialosi
`Attorney, Agent, or Firm—Kinzer, Plyer, Dorn &
`McEachran
`
`[57]
`
`ABSTRACT
`
`A method of controlling the simultaneous broadcast of
`enciphered digital information signals, for example in a
`radio or television broadcast environment, to a plurality
`of subscribers provides several
`levels of enciphering
`keys. The broadcast digital information signal is in a
`broadcast common service enciphering key and com-
`munication between the transmitter and subscribers
`may take place in a box key or in a group enciphering
`key common to a group of subscribers having a com-
`mon interest in the reception of broadcast signals of a
`particular type. Each receiver will decipher the broad-
`cast digital information in a specific service key which
`is common to that broadcast. The service key may be
`changed at one or more subscribers by communicating
`the change in the service key to the subscribers by
`means of the group enciphering key. Further, the group
`enciphering key may be changed at one or more sub-
`scribers or new groups may be formed among subscrib-
`ers by communicating to the subscribers in one or more
`group enciphering keys.
`5 Claims, 3 Drawing Figures
`
`[54] MULTI-LAYER ENCRYPTION SYSTEM FOR
`THE BROADCAST OF ENCRYPTED
`INFORMATION
`
`[75]
`
`,Inventors: Anthony J. Wechselberger, San
`Diego; Leo I. Bluestein, Rancho
`Bernardo; Leo Jedynak, San Diego;
`David A. Drake, Escondido; Larry
`W. Simpson, Poway, all of Calif.
`
`[73] Assignee: Oak Industries Inc., Rancho
`Bernardo, Calif.
`
`[2]] Appl. No.: 401,258
`
`[22] Filed:
`
`Jul. 23, 1982
`
`[51]
`Int. Cl.3 ............................................. .. H04K 1/02
`
`[52] U.S. Cl. ........................... 178/22.08; 358/122;
`358/123
`178/22.08, 22.09, 22.13-22.16;
`[58] Field of Search
`375/2.2; 455/26-28; 358/114, 122, 123
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`................. .. 178/22.08
`3/1980 Lennon et al.
`4,193,131
`.... ..
`.. 178/22.09
`5/1980 Ehrsam et al.
`4,203,166
`9/1981 Atalla ............ ..
`.. 178/22.08
`4,288,659
`9/1981 Hendrickson
`358/114
`4,292,650
`4/1982 Guillou . . . . . . . .
`. . . .. 358/114
`4,323,921
`6/1982 Guillou
`...... .. 358/114
`4,337,483
`. . . .
`9/1982 Beier . . . . .
`. . . .. 358/114
`4,348,696
`4.354,201 10/1982 Sechet et al.
`358/114
`4,388,643
`6/1983 Aminetzeh . . . . . . .
`. . . .. 358/114
`4,460,922
`6/1984 Ensinger et al.
`.................. .. 358/114
`
`
`
`72
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`U.S. Patent
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`Jul. 23, 1985
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`U.S. Patent
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`Jul. 23,1985
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`1
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`4,531,020
`
`2
`placed in digital form and hence can be enciphered and
`deciphered by the control system described herein.
`It is important in broadcast systems of the type re-
`ferred to above to insure secrecy or privacy of the com-
`munications, as customarily such broadcasts are on a‘
`subscription basis and it is mandatory that privacy be
`retained or the concept of a subscription broadcast
`system is destroyed. To that end various schemes have
`been proposed to insure the security of those portions of
`the signals which can be placed in digital form. The
`present invention provides a first level of security by
`enciphering the digital information signals in what is
`termed a service key, which key is provided to all sub-
`scribers who are to receive a specific broadcast or a
`specific type of broadcast. For example, the service key
`may be peculiar to a specific program, but more com-
`monly it will be used for a specific channel when the
`system is used in a television environment. To insure
`privacy and security the service key must be periodi-
`cally changed. To change the service key it is necessary
`to communicate with each of the subscribers and this
`communication takes place in what is called the group
`key which is common to a group of subscribers, all of
`whom are to receive a specific type of broadcast. There
`may be a substantial number of groups associated with a
`specific communication system and an individual sub-
`scriber may itself belong to more than one or a plurality
`of groups. Specifically, to change the service key for a
`particular type of broadcast, the broadcaster will com-
`municate to all of the subscribers in the group key and
`the group key is used to change the service key. As an
`alternative, a large number of service keys may be
`stored in each decoder and the broadcast station selects
`a specific service key by communicating with the sub-
`scriber in the group key.
`From time to time subscribers’ tastes and desires in
`programming change and thus it is necessary to change
`groups, to reform groups and to add or delete subscrib-
`ers from a particular group. Again, this may be accom-
`plished by communicating to the subscribers in the
`group key. The group key itself may be changed and
`subscribers may be added or deleted from the group, or
`in fact new groups may be formed by communicating to
`the subscribers in the group key.
`In addition to communicating in the group key, it is
`necessary to have addresses which are peculiar to an
`individual subscriber and peculiar to a group. For exam-
`ple, each subscriber may have its own individual ad-
`dress which is peculiar to that subscriber. That address
`will be stored in the subscriber’s decoder. In addition,
`the subscriber may belong to one or more groups, each
`of which will have a specific address for that group
`with these addresses being temporarily stored in the
`subscribers decoder. Thus, the broadcaster may com-
`municate to the subscriber by providing the subscriber’s
`group address or the subscriber’s individual address and
`by communicating to the subscriber in the group key
`peculiar to the group with which the broadcaster is
`specifically concerned at that moment.
`As a final means for insuring security and privacy,
`each subscriber will have what is known as a box key
`and that is a key peculiar to a specific subscriber. If the
`broadcaster wishes to communicate in complete pri-
`vacy with an individual subscriber, it may do so in the
`subscriber’s box key. For example, if the broadcaster
`feels that one or more groups of keys have been com-
`promised and the only way to reform groups is to com-
`municate to each individual subscriber in its box key,
`
`MULTI-LAYER ENCRYPTION SYSTEM FOR THE
`BROADCAST OF ENCRYPTED INFORMATION
`
`SUMMARY OF THE INVENTION
`
`The present invention relates to a system for enci-
`phering and deciphering digital information signals and
`has application in the field of broadcast television, al-
`though the principles disclosed herein should not be so
`limited. Specifically, audio information and/or text
`information for display on a video screen may be placed
`in digital form and enciphered. Such signals may be part
`of a cable television system (CATV), a subscription
`television system (STV) or a direct broadcast satellite
`television system (DBS).
`A primary purpose of the invention is a system for
`enciphering digital information signals in the environ-
`ment described in which there are multiple layers of
`enciphering keys to insure security of the broadcast
`information.
`
`Another purpose is an enciphering and deciphering
`system of the type described in which communication
`between the broadcast station and a plurality of sub-
`scribers may take place in a box key peculiar to an
`individual subscriber, a group key peculiar to a group of
`subscribers having a common interest, or in a service
`key which is common for a specific broadcast and
`which may be changed from time to time through either
`the group or box keys.
`Another purpose is a simply reliable and completely
`secure enciphering and deciphering system for use in
`the broadcast of digital information signals.
`Another purpose is a method for controlling the
`broadcast of digital information signals in which there
`are layers or levels or tiers of keys to insure system
`security and in which the keys may be changed by
`communication to subscribers in one or more of the
`layers of keys.
`~
`Other purposes will appear in the ensuing specifica-
`tion, drawings and claims.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention is illustrated diagrammatically in the
`following drawings wherein:
`FIG. 1 is a block diagram of a transmitter for use in
`the control system described herein,
`FIG. 2 is a block diagram of the receiver, and
`FIG. 3 is a diagrammatic illustration of typical mes-
`sage structures used in the system disclosed herein.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`The present invention has utility in CATV, STV and
`DBS television systems in which the video signal is
`coded. The specific enciphering and deciphering sys-
`tem disclosed herein is primarily applicable to the audio
`portion of the video signal as the audio signal is readily
`susceptible of being placed in a digital format. It is also
`applicable to those video signals in which alphanumeric
`text information is transmitted, such as the VIDEO-
`TEXT system now in commercial use by Oak Industries
`Inc., assignee of the present application or other types
`of digital or digitized data such as computer software,
`games, radio programs, computer data bases, etc. which
`may be delivered via such communication system. Sig-
`nals of that type are also readily susceptible to being
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`the broadcaster may do so, although this may be a time
`consuming operation taking several hours. In any event,
`by having a hard-wired box key available in each sub-
`scriber’s box, the broadcaster may communicate to each
`individual subscriber in that specific key to provide
`changes in group keys or formation of new groups, etc.
`In the general sense, there need not be a logical distinc-
`tion between group keys and box keys, or group ad-
`dresses and box addresses. The box address/box key
`pair
`simply constitutes another
`subscriber
`subset
`(group) to which there happens to be only a single
`member.
`There are normally two channels of communication
`between the broadcaster and the subscribers. The ser-
`vice channel provides the digital information signals
`and these are enciphered in the service key. The other
`channel
`is the control channel necessary to change
`service keys, change or reform group keys, etc., and this
`channel may be independent of the channel carrying the
`digital information signals, or it may be inserted into
`gaps in the service channel. For example, in a television
`environment the service channel may be at aural carrier
`frequencies and the control channel may be on an alter-
`nate FM frequency. Another system provides that the
`control channel is inserted as data in the vertical or
`horizontal blanking intervals of the accompanying
`video signal.
`In FIG. 1 the network control computer is indicated
`at 10 and will normally be programmed to handle all of 30
`the functions of the overall control system as described.
`A service data encryptor 12 receives digitized service
`data at its data port 14. This may be digitized audio or
`text information as described above. The current ser-
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`vice key is provided at key port 16 from a current ser-
`vice key source 18. A key generator 20 will provide a
`constant supply of enciphering keys. Key generator 20
`provides keys to the service key source 18 and also to a
`network group identification and group and box key
`data base 22. Computer 10 also provides an input to data
`base 22 so that group identifications may be added or
`changed or replaced.
`One output from data base 22 goes to a receiver
`group key source 24 which provides the input for key
`port 26 of control channel encryptor 28. Data port 30 of 45
`encryptor 28 receives its input from a selector 32 which
`in turn receives one input from service key source 18
`and a second input from a new group key source 34.
`Thus, the selector provides either a change in service
`key or a change in group key to the data port of the
`control channel encryptor, which data will be encoded
`in the then current group key for transmission to com-
`biner 36. Combiner 36 will be connected to a modulator
`which will provide a modulated signal appropriate for
`the particular communication medium, e.g., CATV,
`STV or DBS.
`An additional input to combiner 36 comes directly
`from network control computer 10 and will provide
`miscellaneous control information such as error correc-
`tion, etc.
`In addition to the encrypted key information which is
`a part of a control message, each message includes iden-
`tification numbers or addresses peculiar to a subscriber
`or to a group. This information is provided by data base
`22 to combiner 36 through a new group identification
`38 which is utilized when a group ID is to be changed
`or through a receiver group identification 40 which is
`utilized when a particular group is to be addressed.
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`FIG. 3 illustrates typical control messages which may
`be sent by combiner 36 as the control channel data. In
`the upper message there will be, as the first field of a
`message various command and control signals peculiar
`to the protocol of the specific system. The next field of
`the message is the receiver group identification or ad-
`dress of all of the subscriber boxes in a particular group
`which are to receive the message. This is necessary to
`inform the subscriber boxes that a message is on the
`way. Assuming that a new group key is to be provided,
`that will be the next field of the message and that infor-
`mation will be encrypted in the current group key. If a
`new group identification or address is to be provided
`because the group is being changed or reformed in some
`manner, then that information will also be provided,
`however, it need not be in encrypted form. Finally, the
`message will conclude with such miscellaneous com-
`mand information as error correction, etc.
`A second type of message structure is indicated in the
`lower portion of FIG. 3 and in this case differs from the
`top message in that a new service key is provided to all
`of the members of the group. This specific service key
`is encrypted in the then current group key.
`A typical receiver is illustrated in FIG. 2. The en-
`crypted service data is provided on the service channel
`and provides an input for data port 42 of service data
`decryptor 44. The output will be the decrypted service
`data.
`The control channel data is directed to a receiver
`
`data processor 46 in which the receiver group identifi-
`cation field, routed through a selection circuit 48, will
`pass through the processor and be compared in a com-
`parison circuit 50 with the group identification stored in
`a memory table or memory storage means 52. Assuming
`that the particular subscriber is to receive the message
`on the control channel, data processor 46 will be en-
`abled which in turn will cause the memory table to
`provide the required key information to the decryptors.
`If a new group identification is to be provided, re-
`ceiver data processor 46 will pass this information,
`which is separated by a new group ID selection circuit
`54, directly to the group identification portion of the
`memory table so that the group ID may be changed in
`the required manner.
`The command information is passed directly through
`a separating circuit 56 to the receiver data processor, to
`perform a portion of the enabling function to permit the
`processor to handle the group identification address or
`a change in group identification address, as required in
`accordance with a specific message. Thus, the group
`identification which may be peculiar to a single sub-
`scriber or peculiar to one of the groups to which the
`subscriber belongs,
`is stored in memory table 52 and
`may be changed periodically as the tastes and require-
`ments of a specific subscriber change.
`The encrypted key portion of a control channel mes-
`sage is separated by encrypted group or service key
`detector 58 and is sent directly to data port 60 of control
`channel decryptor 62. The key port of decryptor 62,
`indicated at 64, is connected to the group and box key
`portion of the memory table. Thus, when enabled by
`data processor 46, the required key will be drawn from
`the memory and provided at the key port of control
`channel decryptor 62. In this connection, the memory
`table may be a non-volatile storage area for the collec-
`tion of the group identifications and the group keys
`resident within the box. The permanent box key for a
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`specific subscriber box is permanently stored in the
`memory table and is not subject to revision or change.
`The output from control channel decryptor 62 which
`may be a change in service key or a change in group key
`is connected to the memory table and to the service key
`source 68 with the output from the service key source
`being connected to key port 70 of service data decryp-
`tor 44. Accordingly, a change in service key is provided
`to the service data encryptor to decrypt the information
`bearing signals from the broadcast station. A change in
`group key is communicated to the memory table so that
`the group key information may be added to or deleted
`or changed as requirements dictate.
`In a typical broadcast situation, and assuming audio
`signals as a portion of a subscription television broad-
`cast are the information signals in question, such audio
`signals will be digitized and encrypted in a specific
`service key and broadcast on the particular medium
`whether it be a CATV, STV or DBS system. The ser-
`vice key will be available at each subscriber eligible to
`receive that broadcast and may be periodically changed
`as the broadcaster deems necessary to maintain system
`security. Whenever there is to be a change in the service
`key, this information is provided through the control
`channel to all subscribers who are to receive that broad-
`cast. The change in service key is encrypted in the
`group key peculiar to the group which is to receive the
`specific broadcast. For example, there may be a group
`composed of those interested in adult movies,
`those
`interested in opera, those interested in specific types of
`sports programs. The group may be formed of those in
`a specific geographical area. The number and types of
`groups are almost infinite and normally each subscriber
`will be able to belong to a plurality of groups and will
`have a group key and group ID associated with each
`such group.
`If a specific subscriber desires to belong to a new
`group, that fact is communicated to the broadcast sta-
`tion and if only a single subscriber is to join the group,
`the broadcaster may communicate the group ID and
`group key to that subscriber through the subscriber’s
`individual box key. On the other hand, if a substantial
`portion of a current group is to be involved in a new
`group, the broadcaster may address those subscribers to
`form the new group in the current group key but with
`the message being preceded by the individual IDs of
`those particular subscribers. Thus, the broadcaster may
`form new groups, delete subscribers from a particular
`group, etc., all by communicating to the subscribers
`within the concept of the group identification and the
`group key. Group keys may be changed without a
`change in the subscribers as from time to time the
`broadcaster may consider that it is possible that the
`group key has been compromised.
`At times it may be necessary for the broadcaster to
`communicate individually with all subscribers in the
`‘ system. Perhaps the broadcaster considers that in some
`manner the group key concept has been compromised
`and it is necessary to completely change the group keys
`throughout the system. In that instance the broadcaster
`would communicate to each subscriber utilizing the
`subscriber’s individual box key. This would be a time
`consuming process, for example several hours, and
`would normally be done in the nighttime hours when
`there are few if any subscribers watching television
`programming.
`The present system provides great flexibility for the
`broadcast station. Boxes which are stolen or in the
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`houses of non paying subscribers may be electronically
`detected or rendered ineffective. Subscribers may select
`different types of programming. The system is secure in
`that there are layers or tiers of keys available to the
`broadcaster for enciphering information and communi-
`cating with subscribers.
`Although the service data encryptor and control
`channel encryptor have been described as physically
`separate, it will be understood by those skilled in the art,
`that these circuits may be physically the same, but func-
`tionally responsive to different instructions to perform
`both service and control encrypting functions. The
`same applies to the receiver decryptors.
`Whereas the preferred form of the invention has been
`shown and described herein, it should be realized that
`there may be many modifications, substitutions and
`alterations thereto.
`The embodiments of the invention in which an exclu-
`sive property or privilege is claimed are as follows:
`1. A method of controlling the simultaneous broad-
`cast of enciphered digital information signals to a plu-
`rality of subscribers in which each subscriber has a
`permanent box enciphering key; in which the broadcast
`digital information signal is in a service enciphering key;
`and in which communication to subscribers may take
`place in a group enciphering key common to a group of
`subscribers having a common interest in the reception
`of broadcast signals of a particular type, including the
`steps of:
`(a) simultaneously broadcasting digital information sig-
`nals in a specific service key, which digital informa-
`tion signals are deciphered by subscribers having the
`service key,
`(b) changing the service key at subscribers by simulta-
`neously communicating the change in service key to
`subscribers in at least a portion of a group, such com-
`munication being in the group enciphering key,
`(c) changing the group enciphering key in at least a
`portion of the subscribers in a group by communicat-
`ing such change in the group enciphering key to the
`selected subscribers in the group, with each commu-
`nication to a subscriber in the group being preceded
`by an address to designated subscribers in the group.
`2. The method of claim 1 further characterized by
`and including changing the group key and/or forming a
`new group of subscribers by communicating to each
`subscriber, individually and sequentially, a new group
`key, with such communication to each subscriber being
`in the subscriber’s box key.
`3. The method of claim 1 further characterized by
`and including changing the group key and/or forming a
`new group of subscribers by communicating to each
`group of subscribers, in whole or in part, a new group
`key, with such communication being in group encipher-
`ing keys.
`4. A receiver for deciphering broadcast digital infor-
`mation signals enciphered in a broadcast common ser-
`vice enciphering key including:
`(a) a service data decryptor using a broadcast common
`service deciphering key to decipher broadcast digital
`information signals,
`(b) memory storage means for retaining an individual
`subscriber box deciphering key, at least one change-
`able group deciphering key, and one or more ad-
`dresses specific to a subscriber and its specified group
`or groups,
`(c) and a control channel decryptor having a control
`channel input and being connected to said memory
`
`
`
`7
`
`

`
`4,531,020
`
`8
`sage as to a change in the service deciphering key or
`a change in or formation of a group deciphering key.
`5. The receiver of claim 4 further characterized by
`and including a receiver data processor connected to
`said memory storage means for adding and/or deleting
`and/or replacing addresses in said memory storage
`means.
`*
`*
`*
`*
`*
`
`7
`\
`storage and service data decryptor, comparison
`
`means for determining if a control channel message is
`
`addressed to a specific subscriber, said control chan-
`
`nel decryptor using the box deciperhing key or a
`
`group of deciphering key to decipher a control mes-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`
`
`8