United States Patent
`
`1191
`
`[11] Patent Number:
`
`4,642,688
`
`Lowry et a1.
`
`[45} Date of Patent:
`
`Feb. 10, 1937
`
`.
`[1127572 4/1981 European Fat. 011'.
`82/01109 4/1982 World lnL Prop. 0. .
`Bil/03942 11/1983 World Int. Prop. 0. .
`1252332 11/1971 United Kingdom .
`1356193
`6/1974 United Kingdom .
`[356970 6/1974 United Kingdom .
`1382558
`2/1975 United Kingdom .
`1479717 7/1977 United Kingdom .
`1503051
`3/1978 United Kingdom .
`1521213 8/1978 United Kingdom .
`1528273 10/1973 United Kingdom .
`1557741 12/1979 United Kingdom .
`1602119 11/1981 United Kingdom .
`
`OTHER PUBLICATIONS
`
`Den Toonder et a], United Kingdom Patent Applica-
`tion No. 2,078,051, Dec. 23, ’81.
`Den Toonder et a}. United Kingdom Patent Applica-
`tion No. 2,077,547, Dec. 16, '81.
`W. Cheung, United Kingdom Patent Application No.
`2,042,846, Dec. 24, '30.
`Fondse et 211, United Kingdom Patent Application No.
`2,038,137, Jul. 16, ’80.
`
`Primaor Examineh—Stephen C. Buczinski
`Assistant Bummer—Linda J. Wallace
`Attorney, Agent, or Firm—Banner, Birch, McKic &
`Beckett
`
`[57]
`
`ABSTRACT
`
`A method and apparatus for creating a television signal
`and encrypting or decrypting the signal at the same
`time. Luminance and chrominance information are re-
`ceived by the apparatus and stored in separate television
`scan line stores. The stored liminance and chrominance
`informationisreadoutfromtheirrespectivestoresata
`frequency corresponding to a desired format or stan-
`daramcreatemetelevisionsignainrhesignalmaybe'
`simultaneously encrypted 01' decrypted by delaying the
`time at which the luminance and/or chrominanoe infor-
`mation is read out in accordance with an encryption or
`decryption key.
`
`24 Claims, 19 Drawing Figures
`
`FOREIGN PATENT DOCUMENTS
`642144 6/1962 Canada ................................ 358/119
`750074 1/ 1967 Canada .
`0004083 10/1979 European Pat. Off.
`(1321938 1/ 1981 Enmpean Pat. Off.
`
`.
`.
`
`
`
`PMC Exhibit 2141
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`Apple v. PMC
`|PR2016-00755
`
`Page 1
`
`[54] METHOD AND APPARATUS FOR
`CREdTING ENCRYP’I’ED AND DECRYP’I'ED
`TELEVISION SIGNALS
`
`[75]
`
`Inventors:
`
`John D. Lowry, Toronto; Keith
`Incas, Oak Ridges, both of Canada
`
`Scientific Atlanta, Inc, Atlanta, Ga.
`[73] Assigncc:
`[21] Appl. No: 736,301
`
`[22] Filed:
`
`May21,1985
`
`Related U.S. Application Data
`
`[63]
`
`Continuation-impart of Ser. No. 507,565, Jun. 24. 1983.
`
`Int. (31.4
`[51]
`[52] us. 01.
`
`-
`
`[58] Field ofSearch
`
`HMN 7/167; H0419 11/06
`330/11; 353/12;
`380/20
`
`358/120, 123, 12, 114,
`358/119
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`
`
`2,547,593 4/1951 Roechke ...............;............ .. 358/124
`2,673,237 3/1954
`..
`2,677,719 5/1954
`2,961,431 11/1960
`2,972,000
`2/1961
`3,735,027 5/1973
`4,070,693
`1/1973
`4,319,273 3/1982 Noesem
`4,325,079 4/1982 Little .. .......
`4,330,794 5/1932 Sherwood.
`453135.393 6/1982 Pearson
`4,338,628 7/1982 Payneetal. ..
`4,390,898 6/1983 Bond et al.
`4,396,946
`8/1983 Bond .............
`4,405,942 9/1983 Block et :11.
`4,466,017 8/1984 Banker
`
`
`
`
`353/123
`358/120
`.. .... 358/120
`.. 353/120
`358/4
`. 358/120
`...... 358/119
`..... 358/119
`...... 358/119
`358/120
`
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`

`

`US. Patent
`
`Feb. 10,1987
`
`Sheet] of 10
`
`4,642,688
`
`FIG: Z
`
`
`
`5
`
`LINE
`
`LINE BLANKING
`INTERVAL
`
`SYNC
`PULSE
`
`STANDARD LINE BLANKINO
`INTERVAL LINE N+1
`
`Fla 2“
`
`DIOITAL
`DATA
`
`STANDARD
`LENOTI-I
`LINE
`
`
`ACTIVE
`VIDEO
`VIDEO
`(LINE N+1)
`
`
`
`MINIMUM
`LENGTH
`LINE
`
`
`
`
`AOTIVE
`VIDEO
`[LINE N)
`
`VIDEO
`
`FIG 21?.
`
`DIGITAL DATA
`
`EXTENDED
`LENGTH
`LINE
`
`PMC Exhibit 2141
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`Apple v. PMC
`IPR2016-00755
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`Page 2
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`
`
`
`
`ACTIVE
`VIDEO
`(LINE N+I)
`
`
`'
`' EXTENDED LINE
`BLANKING INTERVAL
`LINE N+I
`
`FIG: 2"-
`
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`
`

`

`US. Patent
`
`Feb. 10,1987-
`
`Sheet 2 'of 10
`
`4,642,688
`
`cw
`
`
`
`M.wxu‘
`
`ZD_._.n_>mowo
`
`>wv.
`
`.56”.Dzw
`
`D<MIm.ng
`
`PMC Exhibit 2141
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`Apple v._ PMC
`|PR2016-00755
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`Page 3
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`PMC Exhibit 2141
`Apple v. PMC
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`
`

`

`US. Patent
`
`Feb. 10, 1987.
`
`Sheet 3 of 10
`
`4,642,688
`
`FIG 4
`
`BLANKING
`RE GEN.
`
`22
`
`
`
`
`TV
`SlGNAL
`
`TRANSMITTER
`
`FIG: 6.‘
`
`
`PMC Exhibit 2141
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`|PR2016-00755
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`

`

`US. Patent
`
`Feb. 10,1987
`
`Sheet 4 of 10
`
`4,642,688
`
`mommwuommomgzE
`
`m.Gt
`
`.DonD
`
`19'...“—
`
`.2.u.
`
`'PMC Exhibit 2141
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`Apple v. PMC
`|PR2016-00755
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`Page 5
`
`PMC Exhibit 2141
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`
`

`

`US. Patent
`
`Feb. 10,1987
`
`Sheet 5 of 10
`
`4,642,688
`
`..._.D.w.mmZZDDU
`
`wz...
`
`-.
`
`15.92m...m2...
`
`mmjomhzou
`
`]
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`mat.wZS
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`0.00.—huwamm
`
`
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`rmx29.5.5.an—
`
`Ioozéénswmn.
`
`mmmzaz
`
`mah’uuwzmm
`
`J.00
`
`.m.“9k
`
`
`
`
`
`55:8gzoamoz‘.58
`
`.3.03wz:no9a
`
`museum-D
`
`
`
`m._<zw.m49”:an.wmohmMZD
`
`PMC Exhibit 2141
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`|PR2016-00755
`
`Page 6
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`PMC Exhibit 2141
`Apple v. PMC
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`
`
`
`

`

`US. Patent
`
`Feb. 10,1937
`
`Sheet6 of 10
`
`4,642,688
`
`FIG! xa
`PRIOR ART
`
`PICTURE CAI‘RRIER 56
`‘
`|
`\l
`
`50
`
`\
`
`zI
`
`'-
`
`I
`
`
`I
`
`0
`
`fCOLOR SWCAFHER 58
`
`I E
`
`I|
`
`I
`
`,AUDDCENTER
`r- FRmUENCY40
`iI
`
`
`I
`
`I25
`
`'
`
`5.75 60
`
`3.579545MHz———I
`4.5 MHz_-——-l
`
`6 MHz
`
`FIG. ll
`PRIOR ART
`
`CHRomm
`
`LUMINANCE 66
`
`
`
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`

`US. Patent
`
`Feb. 10,1987
`
`Sheet"! oflO
`
`4,642,688
`
`F16‘. I2;
`
`CLOCK 30
`
`
`
`CLOCK 3|
`
`SELECT
`
`PMC Exhibit 2141
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`
`
`33
`
`MEMORY ELEMENT
`
`FIG“. 13. _
`
`34
`MEMORY ELEMENT
`
`30
`
`
`
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`

`

`US. Patent
`
`Feb. 10,1937
`
`Sheet 8 of 10
`
`4,642,688
`
`.Vxfixnx
`
`:56
`
`ma8.
`
`m0.
`
`
`
`co.:5389
`
`ES:
`
`«3......E4%
`
`Ifig6980.
`
`m9.
`
`0N0.
`
`000.
`
`PMC Exhibit 2141
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`|PR2016-00755
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`

`

`US. Patent
`
`Feb. 10,1987
`
`Sheet9 oflO . 4,642,688
`
` STORE
`
`
`
`FIG.l5.
`
`CHROMINMCE
`
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`

`

`US. Patent
`
`Feb. 10,1937
`
`Sheet 10 of 10 4,642,688
`
`FIG. I60.
`
`DEW
`
`DELAY
`
`ELEMHNIT
`33
`
`_
`
`_
`
`52m:
`
`6495
`
`I
`
`34usL-
`
`521-6
`
`L2
`
`——l 341.13 L—l-
`
`641.35
`
`I
`
`?6us
`
`64115
`
`1?
`
`'
`
`76us
`
`F[6. I66.
`
`DELAY
`
`W34 m Wj 1 m mj
`1:54115$52115 L
`--|
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`52113
`us
`F7615
`
`.
`
`76
`
`6;“
`
`64“
`f 5
`
`I
`
`76115
`
`PMC Exhibit 2141
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`

`

`1
`
`4,642,688
`
`METHOD AND APPARATUS FOR CREATING
`ENCRYPTED AND DECRYPTED TELEVISION
`SIGNALS
`
`REFERENCE TO PRIOR. APPLICATION
`
`This application is a continuation-in-part of appli-
`cants’ application Ser. No. 507,565 filed June 24, 1983.
`BACKGROUND OF THE INVENTION
`
`The present invention relates to the field of television
`signal transmission and, more particularly, is directed to
`a method and apparatus for creating a television signal
`and encrypting or decrypting the signal at the same
`time.
`
`10
`
`IS
`
`20
`
`25
`
`30
`
`35
`
`Television signals are produced and displayed as a
`result of a line scanning process. The picture infoma—
`tion is scanned using a progressive series of horizontal
`lines which are transmitted sequentially in time. The
`transmitted signal
`is a continuous analogue of the
`brightness intenty corresponding to each point of the
`line. Such a signal is shown in FIG. 1 from which it may
`be seen that in a series of standard lines, any two adja-
`cent active line periods (periods during which video
`information is transmitted) are'separated by a period in
`which no video informatiOn is transmitted. This latter
`period is known as the line blanking interval and is
`introduced to allow the scanning device in the receiver
`to reset to the linestart position.
`In typically color television signals, the active line
`period includes one signal which simultaneously repre-
`sents the instantaneous values of three hidependt
`color components. The method by which the three
`color components are coded into one signal is standard-
`ized throughout North America, Canada and Japan.
`This method is known as the NTSC standard. Alterna-
`tive standards known as PAL and SECAM have been
`adopted in other countries but these standards have the
`same basic format as the NTSC standard, including a
`line-blanking interval and an active line period in each 4D
`scan line.
`Other types of analogue video signals which are par—
`ticularly adapted to transmission by satellite and cable,
`and which lead to improved picture quality in compari~
`son with existing standards, are presently being studied.
`These signals are based on a time multiples of the three
`independent color components during the active line
`period of the scan line. Instead of coding the three com-
`ponents into one signal using the NTSC, PAL or
`SECAM standard, the components are sent sequentially
`using a time-compression'technique. One version of this
`type of signal is know as MAC (Multiplexed Analogue
`Components). Signals generated by a time comparison
`technique also adhere to the same basic format as the
`NTSC, PAL and SBCAM standards,
`including the
`presence of a line-blanking interval and an active line
`period in each scan line. It should be noted that when a
`MAC signal is employed, digital data may also be trans-
`mitted during the line-blanking interval as shown by the
`dotted lines in FIGS. 26 and 2c.
`_ Color video signals broadcast under. the NTSC stain-
`dard require that picture information be separated into
`two components: luminance. or brightness, and chromi-
`nance, or color. FIG. 10 is an amplitude-vs.-frequency
`diagram illustrating, in simplied form, a typical NTSC
`composite color television gnal 50 comprising a lumi-
`nance signal 52 and a chrominance signal 54. (A com-
`posite television signal is one in which chrominance
`
`45
`
`50
`
`55
`
`65
`
`2
`information is carried on a subcarrier.) The signal occu-
`pies a nominal bandwidth of 6 MHz with the picture
`carrier 56 being 1.25 MHz above the lower end of the
`band. Luminance information is modulated directly
`onto picture carrier 56, while chrominance informatiOn
`is modulated onto color subcarrier 58 which is in turn
`used to modulate picture carrier 56. Color subcarrier 58
`has a frequency of 3.519545 MHz. a standard estab-
`lished by the NTSC. (Audio information is carried on
`another subcarrier 40 lying near the upper edge of the
`band.)
`The region labeled A in FIG. 10 is of particular im-
`portance for it represents overlap between the lumi—
`nance 52 and chrominance 54 signals. Since Separation
`of luminance and chrominance is accomplished by lil-
`tering a frequency—division multiplexed signal, overlaps
`such as A between the two signals lead to several prob-
`lems. If, upon reception, complete separation between
`luminance and chromiuance is desired, the necessary
`filtering will cause the loss of some of the information in
`both signals. 0n the other hand, if no loss of informatiOn
`can be tolerated, then one must accept interference
`between the luminance and chrominance signals. More-
`over, since the various parts of the NTSC television
`signals are transmitted at different frequencies, plume
`shifts occurring during transmission will affect them
`differently, causing the signal to deteriorate. Also, the
`available color information is severely limited by the
`small color bandwidth permitted.
`As discussed in commonly assigned pending applica-
`tion Ser. No. 652,926 filed Sept. 21, 1984, and herein
`incorporated by reference, the above-mentioned MAC
`standard was developed to overcome the problems
`associated with the NTSC standard. A MAC color
`television signal is illustrated in FIG. 11, which is an
`amplitude-vs-time diagram of a single video line of
`63.56 pa duration. The first 10.9 its is in the horizontal
`blanking interval (HPI) 62, in which no picture informa-
`tion is transmitted. Following RBI 62 are chrominance
`signal 64 and luminance signal 66, either of which may
`be time-compressed. Behvcen chrominance signal 64
`and luminance signal 66 is a 0.28 1.1.5 guard band 68, to
`assist in preventing interference between the two sig-
`nals.
`The MAC color television signal of FIG. 11 is ob-
`tained by generating conventional luminance and chro-
`minance signals (as would be done to obtain a conven~
`tional NTSC or other composite color television signal)
`and then sampling and storing them separately. Lumi-
`nance is sampled at a luminance sampling frequency and
`stored in a luminance store, while chrominance is sam—
`pled at a chrominanoe sampling frequency and stored in
`a chrominance store. The luminance or chrominance
`samples may then be compressed in time by writing
`them into the store at their individual sampling fre-
`quency and reading them from the store at a higher
`frequency. A multiplexer selects either the luminance
`store or the chrominance store, at the appropriate time
`during the active line period, for reading, thus creating
`the
`signal of FIG. 11. If. desired, audio samples
`may be transmitted during the H13]; these .‘are multi-
`plexed (and may be compressed) in the same manner as
`the video samples. The sample rate at which all samples
`occur in the multiplexed MAC signal is called the MAC
`sampling frequency.
`Although the MAC format of FIG. 11 overcomes the
`problems of the composite television signal of FIGS. 1
`
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`

`

`3
`and 10, there also exists in the prior art a need for secure
`encryption of video signals, such that only designated
`users may decrypt and display the information. In typi-
`cal encryption systems. one or more parameters of the
`signal to be encrypted are modified according to a pat— 5
`tern which is determined at the transmitter. The pattern
`generally is a member of a large class of similar patterns,
`such that discovery of the pattern through exhaustive
`search is extremely unlikely. A precise description of
`the pattern used for encryption is delivered to desig- IO
`nated receivers which then are able to recover the origi-
`nal information. The description of the pattern is known
`in the art as the “encryption key" and the process of
`informing designated users of the encrytion key is
`known as “key distribution.“
`With reference to FIG. 1, various encryption tech-
`niques known in the art will be described. As shown in
`FIG. I, the video signal during the active line period
`may be represented by:
`
`15
`
`20
`
`y=fl0
`
`where
`y = amplitude (voltage) and
`t = time
`Knowledge of both the signal’s amplitude (y) and the
`time at which it occurs (t) is necessary for accurate
`reconstruction of the video signal in a line scan system.
`Encryption techniques may be classified as follows:
`(1) Those which modify the amplitude (y) of the
`transmitted signal according to a prescribed pat-
`tern.
`
`.v‘=s0'}.
`
`where
`.
`.
`f=f(r)
`Examples of this technique include amplitude reversal
`of randomly chosen lines:
`
`.v’=s(fl-= -r
`
`(2) Those which modify the time at which the signal
`is transmitted through the channel:
`
`Y=fi!')
`
`Examples of this technique include the reordering of
`television lines according to a prescribed pattern:
`
`y'=}lt—d)
`
`25
`
`30
`
`35
`
`40
`
`50
`
`55
`
`(3) Those which modify both amplitude and transmis-
`sion time.
`It has been found that encryptiOn techniques from the
`first category (variation of amplitude) cause distortion
`when the channel through which the signal is to be
`passed is non—linear. In this case, an amplitude (y) will
`be represented in the scrambled channel by various
`amplitudes according to the scrambling function in use
`at that instant. Channel non-linearity, therefore, causes 50
`imperfect reconstruction of the video. information at the
`receiver. Since amplitude non-linearity is very com—
`mon, it has been found that an optimum encryption
`algorithm should be selected from the second category,
`and, in particular, from the subset:
`
`y'=fi-'—dJ
`
`4, 642,683
`
`4
`where d is constant during each standard line. In this
`case, the channel is subjected to an undistorted signal
`and only the time at which the signal occurs is scram-
`bled. Since almost all channels are essentially 'time
`invariant,’ this technique introduces little distortion.
`This system is known as time-base scrambling.
`An obvious method of time-hue scrambling which
`has been used, is to reorder the television lines within
`the picture. This method, which results when d in the
`previous equation is an integral number of line periods,
`is complex, expensive and difficult to implement be-
`cause recovery of the picture in the receiver demands
`storage of many television lines.
`SUMMARY OF THE INVENTION
`
`It is, therefore, the overall object of the present in-
`vention to provide a method and apparatus for creating
`a television signal while at the same time encrypting and
`decrypting the signal.
`It is a specific object of the present invention to pro-
`vide a method and apparatus for time-base scrambling
`of television signals which is relatively simple and
`which can be readily implemented.
`It is another specific object of the present invention to
`provide a method and apparatus for time-base scram-
`bling of television signals which can be implemented at
`low cost while at the same time being reliable in opera-
`tion.
`It is a still further specific object of the present inven-
`tion to provide a method and apparatus for time-base
`scrambling of television signals which requires storage
`of only a very small number of televisiOn lines in the
`receiver.
`It is another specific object ofthe present invention to
`provide a method and apparatus for creating an en-
`crypted MAC standard television signal for transmis-
`sion and for creating a decrypted NTSC standard tele-
`vision signal for display on a television receiver.
`These and other objects of the present invention are
`achieved by using the same apparatus to create a televi-
`sion signal and to encrypt and decrypt the signal at the
`same time. In accordance with the present invention, a
`MAC standard television signal may be created and
`encrypted for transmission to a remote receiver. At the
`receiver end. the MAC signal may be used to create a
`decrypted signal, as for example an NTSC signal, for
`display on a television receiver. The MACsigna] is
`created at the transmitter end by sampling and storing
`the luminance and chrominance signals separately. Lu-
`minance is sampled at a luminance sampling frequency
`and stored in a luminance store while chrominance is
`sampled at a chromiuance sampling frequency and
`stored in a chrominance store. The luminance and chro-
`minance samples are compressed in time by writing
`them into the store at their individual sampling fre—
`quency and reading them from the store at a higher
`frequency. A multiplexer selects either the luminance
`store or the chrominance store, at the appropriate time
`during the active period of the video scan line, for read-
`ing, thus creating the MAC signal. The signal may be
`encrypted by varying the starting time at which the
`luminance and/or chrominance signals are read out
`from their respective stores in accordance with an en-
`cryption key.
`At the remote or receiver end, a decrypted signal,
`e.g., an NTSC signal, may be created for display on a
`television receiver using the same method and appara-
`tus as used to create the encrypted signal at the televi-
`
`PMC Exhibit 2141
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`|PR2016-00755
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`4,642,688
`
`6
`blanking interval or the period of digital data transmisr
`step.
`
`5
`sion transmitter end. This is accomplished by also stor-
`ing the incoming luminance and chrominance signals in
`individual stores. The signals are read out from the
`stores at a frequency corresponding to the desired for-
`mat, i.e., the NTSC standard. The signal is decrypted by
`varying the starting time at which the luminance and/or
`chrominance signals are read out from their respective
`stores in accordance with a decryption key.
`Thus, the method and apparatus of the present inven-
`tion may be used for creating an encrypted television
`signal for transmission to a remote receiver and for
`creating a decrypted signal at the receiver for display.
`Accordingly, a television broadcast system which em-
`bodies the present
`invention uses fewer component
`parts. is simplier in construction, more reliable in opera-
`tion and is lower in cost.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 shows a standard NTSC television signal;
`FIGS. 2a, 2b and 2c illustrate the encryption tech-
`nique employed in the present invention;
`FIG. 3 shows one form of an encryption/decryption
`system which may be used with the present invention;
`FIG. 4 shows an alternative system to that shown in
`FIG. 3;
`FIG. 5 illustrates another embodiment of an encryp-
`tion system which may be used with the present inven-
`tion;
`FIGS. 6 and '7 illustrate two different decryption
`systems which may be used with the present invention;
`FIG. 8 shOws a decryption system embodying an
`aspect of the invention and surrounding equipment;
`FIG. 9 illustrates apparatus that may be employed for
`the encryption and decryption of video signals by a
`technique embodying the present invention;
`FIG. 10 is an amplitude-vs-frequency diagram illus-
`trating in simplified form a typical NTSC color televi-
`sion signal;
`.
`FIG. 11 is an amplitude-vs.-time diagram of a single
`video line of a typical MAC color television signal;
`FIG. 12 is a block diagram of a line store which may
`be used to compress or decompress television scan lines
`in accordance with the present inventiOn;
`FIG. 13 is a block diagram of the clock signals used to 45
`control the line store shown in FIG. 12;
`FIG. 14 is a block diagram of an encoder which may
`be used with the present invention;
`FIG. 15 is a block diagram of a decoder which may
`be used with the present invention; and
`FIGS. 16:: and 16!) are diagrams illustrating the sig-
`nals input to and output from the line store of FIG. 12.
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`PREFERRED EMBODIMENT
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`The encryption and decryption method of the present
`invention is based on the derivation and use of a variable
`scan line period as shown in FIGS. Za—Zc. Referring to
`FIG. 2a, portions of the active video components of
`lines N and N+l are shown along with the line-blank-
`ing interval of line N+1. The line shown in FIG. 2a is
`of standard length and this includes a standard line-
`blanking interval. As discussed previously, and as
`shown in dotted outline in FIG. 2a. instead of there
`being a line—blanking interval, there may be a period of 65
`standard length for transmission of digital data.
`A line of minimum length is shown in FIG. 2b and is
`obtained by virtually eliminating the standard line-
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`A line of extended length is shown in FIG. 2c and is
`obtained by increasing the standard line-blanking inter-
`val or the period of digital data transmission shown in
`FIG. 20. the dotted outline in FIG. 2: also indicating
`digital data.
`An extended length line of the type shown in FIG. 2c
`can be derived with simple hardware in the case where
`the line—blanking interval is double the line-blanking
`interval of FIG. 2a. In fact, the extended length line of
`FIG. 2: is such a line and has twice the line blanking
`interval of the standard line of FIG. 2a.
`Encryption is achieved according to the present in-
`vention by varying the line-blanking intervals of some
`of the lines to derive minimum and extended lgth
`lines. The transmitted television signal is then composed
`of lines of all three different lengths in accordance with
`an encryption key.
`It will be appreciated that over some specified period
`of time it is necessary for the average line length to be
`equal to the length of a standard line, i.e., that the long
`and short lines must cancel or balance each other out.
`This period is not critical. It may be one field, for exam-
`ple, or one frame, or it may be even a longer period. The
`longer this period is, however, the longer it will take for
`the recver to lock in on the signal.
`While FIGS. 2a-2c illustrate an embodiment of the
`invention where the line-blanking interval is standard,
`zero and two times standard, line-blanking intervals
`between zero and standard can be employed as well as
`line-blanking intervals more than twice standard and/or
`between one and two times standard. There may also be
`a number of different line-blanking intervals greater
`than standard. Generally speaking, however. play-
`ing a standard and more than two other line blanking
`intervals can be done only at the expense ofmore so-
`phisticated hardware.
`In another embodiment of the invention, no standard
`length line is employed, i.e., the line-blanking intervals
`of all lines are lengthed or shortened. Thus. in the
`practice of the present invention a television signal is
`modified in accordance with an encryption key to pro-
`duce a signal in which all active video lines are transnat-
`ted unchanged except for a time delay equal to the
`accumulated variance in the line-blanking periods.
`More specifically, and as determined by the encryption
`key. some lines may be lefi with unchanged line-blank-
`ing intervals. the line-blanking intervals of other lines
`are increased and the line-blanking intervals of still
`other lines are decreased. The encrypted television
`signal is composed of all of these lines and is what is
`transmitted, the encryption key
`which lines
`are standard lines, which lines are long lines and which
`lines are short lines to enable decryption of the received
`signal-
`_One additional condition is require to ensure a low-
`cost receiver. This condition is that the accumulated
`change of the line-blanking periods at any given time
`should remain within the range of from 0-1 line. With
`this constraint, the lines which arrive at the receiver do
`not require more than one line of delay before they are
`used in reconstructing the original signal. i.e., the signal
`prior to encryption. It is to be understood clearly, how-
`ever, that this is not a limitation of the present invention.
`If the accumulated change in the line-blanking periods
`at any given time will be more than one line, all that is
`required is to ensure that apparatus capable of storing
`
`PMC Exhibit 2141
`
`Apple v. PMC
`-|PR2016-00755
`
`Page 14
`
`PMC Exhibit 2141
`Apple v. PMC
`IPR2016-00755
`Page 14
`
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`the accumulated change is available. This requirement
`simply introduces greater cost and complexity.
`Because certain of the line-blanking periods have
`been completely or partially removed, it is necessary to
`regenerate the blanking waveforms in the receiver. This
`can be achieved simply using electronic memories.
`More specifically, in the case of an NTSC signal, for
`example, regeneration of the line-blanking intervals will
`require regeneration of the line synchronizing signals
`and the color burst signals. This can be done using prior
`art techniques, however, and is not a part of the present
`invention. Thus, once the decryption key, which is the
`same as the encryption key, has been employed to re-
`store the active video components to their proper time
`relationship with respect to each other, sync and color
`burst signals correctly timed with respect to the video
`signals can be added readily and by known means.
`In the case where digital data is present during what
`would otherwise appear to be a line-blanking interval, it
`might appear from FIG. 2!) that the digital data would
`be lost by the practice of this invention. The data is not
`lost, however, but rather is transmitted during longer
`than standard digital data periods, as shown in FIG. 2c
`for example.
`The
`encryption/decryption technique described
`herein can be implemented in a large number of ways
`using known techniques, equipment and components.
`Thus, referring to FIG. 3, for example. the television
`signal produced by TV camera 12 is supplied to an
`optional analogue to digital converter (ADC) 13, the
`digital output of which is supplied to a line storage
`device 1‘. The output of line storage device 14 is sup-
`plied to an optional digital
`to analogue converter
`(DAC) 15 whose output, which is an encrypted televi-
`sion signal in analogue form, is supplied to a transmitter
`16 for broadcast to a satellite 17, for example. An en-
`cryption key for encrypting the television signal in line
`storage device 14 is supplied to encoding and timing '
`networks which vary the line-blanking intervals of the
`television signal.
`The encrypted signal is received by a cable head end
`receiver 19 and is supplied to an optional ADC 20
`whose digital output is supplied to a line storage device
`21. The output of line storage device 21 is supplied to an
`optional DAC 2 whose output, which is a decrypted
`TV signal the same in all respects as that derived at the
`output of camera 12, is supplied via cable to cable sub-
`scribers. A decryption key, which is the same as the
`encryption key, for decrypting the television signal in
`line storage device 21 is supplied to decoding and tim-
`ing networks 23 which restores the shortened and ex-
`tended link-blanking intervals to the standard length
`shown in FIG. 2a.
`In the case where the TV signal is an NTSC signal,
`for example, it may be necessary to restore line and field
`synchronizing signals and color burst signals. This func-
`tion is performed by blanking interval regenerating
`network 24._
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`The TV signal may be processed in either analogue
`or digital form. The nature of line storage devices 14
`and 21 will depend upon the format of the signal. Thus,
`if the TV signal is in analogue form, line storage devices
`14 and 21 may be set-called bucket—brigade devices,
`while, if the TV signal is in digital form. line storage
`devices 14 and 21 may be shift registers or may be RAM
`with at least one line memory capacity or CCD storage
`devices.
`
`8
`FIG. 8 shows a decryption system embodying the
`present invention in somewhat greater detail.
`FIG. 9 shows how the decryption (or encryption)
`key is used to vary the line lengths. The decryption key
`(which in the embodiment shown, is updated once a
`frame) is used as a starting vector for a pseudo-random
`number generator circuit. This circuit produces (for the
`NTSC standard) a sequence of 525 random numbers
`based on the decryption key. These random numbers
`then are combined with information derived from a
`counter, which is incremented once per line. in a line
`type selection circuit. This circuit Selects the type of
`line (i.e., determines the length of the blanking interval)
`for the next line. This information is then fed to the line
`length controller which monitors the aggregate devia-
`tion in line lengths referenced to the start of the current
`frame and ensures that for this particular embodiment
`the following two conditions are met:
`1. The aggregate deviation never exceeds one full
`video line (63.5631. see for an NTSC signal);
`2. The aggregate deviation at the end of the frame is
`zero.
`
`The line controller then provides inforrnatiOn to the
`horizontal counter and its associated decoder which
`enables this counter/decoder to produce the correct
`line store control signals for the current line.
`As pointed out above, use of the MAC standard for
`transmission of televisiOn signals eliminates many of the
`problems associated with the NTSC standard. FIG. 12
`is a block diagram of a line store which may be used to
`compress or decompress luminance and chrominance
`signals to create a MAC standard television signal. The
`store comprises a pair of memory elcnts 33 and 34
`coupled to a common input 35 which recieves either
`luminance or chrominance, i.e.. color different signals.
`Memory elements 33 and 34 may be selected from
`among a number of merrrory elements known in the art
`and are shown in FIG. 12 as being CCD memory ele-
`ments. Memory elements 33 and 34 are coupled to re-
`spective clock signals 31} and 31 and to selector switch
`36. Switch 36 is an electronic switch or multiplexer well
`known in the art and which has a double-pole-single-
`throw (DPST) function. Each respective output line of
`memory elements 33 and 34 are coupled to switch 36
`and selectively passed to output line 37 as controlled by
`output select signal 32.
`Though the line store of FIG. 12 may he used to both
`compress and decompress signals,
`the device is de-
`scribed hereafter as performing compression. When a
`signal, as for example a luminance signal, arrises at input
`35, clock 30 writes a predetermined number of lumi-
`nance samples into memory element 33 at a predeter-
`mined ineoming sampling frequency. It has been found
`that a suitable number of samples is 750 and that a suit-
`able incoming sampling frequency is 14.32 MHz for a
`luminance signal in accordance with, for example, the
`NTSC standard. At the same time that memory element
`33 is storing the incoming luminance signal, clock 31 is
`causing the contents of memory element 34 (luminance
`signals from the previous scan line) to be read onto
`output line 37 through switch 36 at a'predetermined
`outgoing sampling frequency. It has been found that a
`suitable outgoing sampling frequency is 21.48 MHz.
`During th