COMMERCIAL APPLICATIONS OF ENCRYPTED SIGNALS
`
`M. Davidov, V. Bhaskaran, T. Wechselberger
`
`OAK Industries Inc., Rancho Bernardo, California
`
`ABSTRACT
`The use of encryption technology in the delive-
`ry of premium television is described. Signal
`security concepts such as scrambling, encrypt-
`ion, key-management etc. as applied in the
`ORION and SIGMA systems are discussed*. In
`order to asess the effects of transmission link
`and system induced impairments, an analytical
`procedure is developed for the encryption met-
`hod used in ORION/SIGMA. System performance
`curves obtained from the analysis are present-
`ed. Finally, potential applications of ORION,
`SIGMA systems in the secure transmission of
`non-video information is discussed.
`
`1. INTRODUCTION
`In recent years, we have evidenced increasing
`concern for privacy and security of information.
`Information is now being viewed as a commodity
`with commercial value and hence, like material
`goods, security measures must be taken to protect
`it from theft. In the commercial arena, there are
`several instances, wherein, security measures are
`essential for the system to be commercially viable
`e.g. electronic funds transfer systems, software
`distribution, pay-TV broadcasts. Cryptographic
`techniques are being applied in such systems to
`realize high levels of information security.
`Development of such crypto-systems has been motiv-
`ated by recent technological advances in LSI/VLSI
`systems and this in turn has led to the implement-
`ation of cost-effective cryptographic protection
`schemes.
`Cryptographic methods used in ORION and
`SIGMA systems (for the secure transmission of TV
`programs) is the focus of this paper. By a judici-
`ous mix of analog scrambling, digital encryption
`and effective key-management, a high level of
`security at low-cost is achieved in these systems.
`This paper is organized as follows. In Section 2,
`factors affecting the design of secure transmiss-
`ion scheme for TV programs are discussed. Signal
`security methods used in ORION and SIGMA are des-
`cribed in Section 3. In Section 4, we provide a
`simple analysis which takes into account the
`specific encryption method used in ORION/SIGMA;
`this analysis is used to derive performance curves
`for ORION/SIGMA systems in the presence of typical
`*ORION and SIGMA are manufactured by OAK Ind.
`
`transmission link and system impairments. Examples
`of potential applications using ORION/SIGMA systems
`for secure transmission of non-video information
`are discussed in Section 5 and concluding remarks
`are made in Section 6.
`
`2. TV SIGNAL SECURITY CONSIDERATIONS
`In the past, TV systems transmitted only video and
`audio. TV systems today (e.g. ORION, SIGMA) however
`can handle diverse information sources such as
`program video, audio i(imonoaurallstereo/second-
`language), control data (is used to control the
`communication network and provide the receiver with
`the commands needed for it to function properly)
`and auxilary data services (e.g. video-text, home-
`banking, two-way interactive communications).
`There is considerable expense incurred in providing
`such diverse services; thus the system operator has
`to resort to direct subscriptions to pay for these
`services (referred to as "Pay-TV"). In order to
`ensure the revenue generating potential and to
`prevent unauthorized access to such services, a
`secure transmission scheme is needed.
`There are several considerations which stron-
`gly affect the design/selection of signal security
`methods for TV:
`1. Level of security
`2. Network attack scenarios
`3. Network compatibility
`4. Human factors, and
`5. Cost
`Let us briefly examine each of these issues.
`Level of security
`The type of information handled
`by the TV system and the medium over which the
`information is transmitted influence the level of
`security desired.
`Major objective of TV systems is to deliver
`video programs; for these sources, entertainment
`value is contained in video and audio. Hence, any
`security scheme which denies unauthorized access
`to any one of these signals is considered accept-
`able (a "medium" security video scheme and a "high"
`security audio scheme is used in several commer-
`cial systems today e.g. ORION, SIGMA). As observed
`earlier, TV systems also transmit control data;
`this channel contains decoder and program specific
`information and hence is a vital communication
`
`22.5.1
`84CH2069-3/84/0000-0307 $1.00 © 1984 IEEE
`
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`link. Its contents must be conveyed in a highly
`secure manner. If a TV system provides non-
`entertainment services, different levels of secur-
`ity may have to be applied to each of these servi-
`ces e.g. home banking may require a higher level
`of security than video-text.
`TV signals are transmitted over terrestrial,
`cable and satellite links (C-band, Ku-band). There
`are differing opinions on the level of security
`needed in these links. The operator of a cable
`distribution network, in lieu of a high-cost, high
`security scheme,may opt for a low cost system that
`offers lower signal security. Selection of the
`lower security scheme may be justifiable; a cable
`system provides some protection against piracy
`because such a network is difficult to tap into
`without detection and in such a system, non-paying
`subscribers can be denied the service by having
`their link to the system isolated. In a-terrestr-
`ial link, risk of detection is low since there is
`no direct contact between subscriber and system
`operator unlike the cable distribution network;
`hence a high security scheme would be preferred in
`this environment. In distribution of TV signals by
`satellite, the signals are potentially available
`to a large number of homes and $ignal piracy on a
`large scale is feasible. Systems offering high
`security are preferred here.
`The security method must
`Network attack scenarios
`take into account possible system attacks. Poten-
`tial network attack scenarios in CATV transmissi-
`ons is shown in Fig. 1. These schemes include
`simple circuit changes in the receiver, local syn-
`thesis of valid control signals and add-on hard-
`ware to decode the signals and to tamper with the
`cable link. To thwart such network attacks, the
`security scheme should be devised in a manner such
`that (1) unauthorized access to transmitted sig-
`nals must offer no entertainment value, (2) one-
`time system defeats must not be possible - implies
`that a time-varying signal security scheme must be
`used, (3) observation of transmitted signals must
`not offer any clues about the actual signals, and
`(4) there must be contact between sender and rec-
`eiver via a control channel. The information in
`the control channel must be such that interruption
`of this channel must disable decoder and this
`channel must provide decoder with information not
`merely as to when to decode but how to decode.
`Network compatibility
`The security scheme must
`not impose excessive requirements on the network
`and for wider acceptability, it must posess the
`same bandwidth and other signalling requirements
`as conventional TV systems e.g. signals transmitt-
`ed using the secure transmission scheme must be
`capable of being transmitted in 6MHz RF bandwidth
`in CATV/terrestrial links employing VSB-AM, and
`must fit in a 27-36MHz (C-band) and 22-24MHz (DBS)
`satellite link employing FM modulation. The
`security scheme employed in these links must be
`resistant to the impairments dominant on the link
`e.g. in CATV links, multipath is dominant; hence
`signal security methods which rely on information
`smearing for its security (output feedback schemes)
`can result in degraded system performance when
`multipath is present.
`
`Human factors
`In a commercial environment, the end
`user must not be inconvenienced when system penetr-
`ations occur since long-term survival and profitab-
`ility are based on favorable consumer attitudes.
`Hence, Draconian methods such as closing down the
`link, changing security procedures and widespread
`investigations etc. in the event of suspected
`system intrusions must be avoided.
`Schemes offering very high security are pre-
`Cost
`sently being realized at high cost and thus are not
`amenable to commercial applications. In a TV envir-
`onment, cost constraints are very severe since the
`security scheme is only one aspect of the overall
`system required by the consumer. In a CATV system
`since risk of detection is high, desired level of
`security can be low and hence a low-cost security
`scheme is preferred (low-cost usually implies lower
`security). The signal security method should be
`such that the cost to derive useful information is
`low for an authorized user, whereas, the cost to
`derive useful information from the intercepted
`signal must be prohibitive.
`Prior to describing the signal security
`techniques used in ORION/SIGMA, let us examine
`basic signal security concepts.
`Signal security concepts
`Signal security methods
`which meet one or several of the design consider-
`ations can be realized with analog scrambling or
`digital encryption. Analog scrambling or digital
`encryption is an invertible transformation T
`T: A --
`S
`(1)
`Here, A is the scrambler(encryptor) input and S is
`the output. By analog scrambling, we imply A a-nd
`S to be analog signals and the transformation T
`is implemented in analog or digital domain. By
`digital encryption, we imply A and S to be digital
`signals and T is a digital process (typically a bit
`oriented process). Transformation T is controlled
`by another process and T is represented as T(k).
`For correct descrambling/decryption, decoder must
`posess k, transformation T and S.
`Note that analog scrambling can be achieved at RF
`or baseband. RF systems have traditionally been
`implemented at low-cost; however, presently, the
`trend is towards baseband systems due to the
`flexibility offered by baseband signals (such
`signals can be easily transmitted over different
`transmission media).
`The control process i.e. the mapping from k
`to T(k) is typically a digital process and k is
`referred to as the "key". Several factors must be
`considered in the design and handling of the key:
`1. The key must be used to inform decoder not
`merely when to descramble/decrypt but how to
`descramble/decrypt - this makes unauthorized key-
`less descrambling expensive.
`2. Key must be made time-varying to prevent one-
`time system defeats.
`3. Scrambling or encryption by itself does not
`ensure signal security. In order to maintain the
`integrity of the scrambling/encryption process,
`the key must be handled in a secure manner (refe-
`rred to as the "key-management" problem). The key
`must not be available via a fixed algorithm in the
`decoder. In a TV environment, due to the large
`number of subscribers, traditional means of
`
`308
`
`22.5.2
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`delivering keys e.g. courier, mail etc. are not
`feasible. Instead, an electronic-key distribution
`scheme could be used e.g. the keys can be made
`part of the information to be transmitted and by
`encrypting these keys under some master key, a
`secure key distribution scheme is achieved.
`In the next section we describe the ORION and
`SIGMA systems from a signal security viewpoint. A
`possible solution to the key management problem as
`implemented in ORION/SIGMA systems is also discu-
`ssed.
`
`3. ORION/SIGMA SYSTEM SECURITY
`ORION and SIGMA systems provide secure transmiss-
`ion of video, audio and control data. Block diagr-
`am of a transmission scheme employing the ORION
`system is shown in Fig. 2a; in Fig. 2b, use of
`the SIGMA system in a CATV scheme is shown. In
`general terms, ORION and SIGMA systems are similar;
`however, individual system parameters have been
`optimized for the specific transmission environ-
`ment.
`
`Signal security methods used in ORION/SIGMA
`is illustrated in Fig. 3. Digital encryption was
`ruled out for video due to bandwidth and cost
`constraints (bit rates around 80 - 120 MBps are
`generated when color signals are digitized. It is
`not possible to transmit this high rate informat-
`ion over 6MHz CATV/terrestrial links without some
`form of data compression.
`Compression schemes
`cannot be realized inexpensively). Instead, of
`digital encryption, a low-cost, analog scrambling
`method capable of offering good scrambling depth
`is used (for a discussion of the scrambling method
`see ref. 1). The scrambling function is controlled
`by a key as shown in Fig. 3.
`Audio security is achieved by encrypting the
`digitized audio signals. Digitization causes band-
`width expansion; however the encrypted audio
`signals can be easily transmitted in the available
`bandwidth of CATV/terrestrial/satellite links
`using a TDM scheme (encrypted audio bits are
`transmitted during video line blanking interval).
`A digital control channel is also transmitted.
`This control channel contains descrambling and
`decryption keys, decoder and video,.program speci-
`fic information. Control channel information is
`encrypted. In SIGMA, the control channel consists
`of two channels (1) a GLOBAL channel transmitted
`using FSK and all decoders tune to this channel,
`(2) a LOCAL channel transmitted using TDM by
`inserting this channel in the vertical blanking
`interval. In ORION, only the local channel is
`available.
`The encryption method used for audio and
`control data is the cipher-feedback scheme. This
`method is chosen over the bit-by-bit encryption
`method due to its good synchronization properties
`and its ability to provide message authentication
`(e.g. in a bit-by-bit encryption scheme for audio,
`if intruder has knowledge of sampling frequency,
`bits/sample etc., by merely altering few of the
`encrypted audio most significant bits, intelligible
`audio may be obtained). From a transmission view-
`point, a cipher-feedback scheme causes error
`
`propagation; a bit error probability analysis for
`the cipher-feedback scheme used in ORION/SIGMA is
`performed in Section 4.
`As observed earlier, keys used in scrambling
`and encryption are transmitted in the control
`channel. In Section 2, it was noted that these
`keys must be transmitted in a secure manner.
`The
`ORION/SIGMA solution to this key management problem
`is illustrated in Fig. 4. A multi-level key distr-
`ibution scheme is used in which there are three key
`variables. These include a decoder specific key
`(unique to each decoder), a variable second level
`key common to all legitimate users and the encrypt-
`ed service keys (used for descrambling/decryption).
`The service keys are time-varying.
`
`4. ORION/SIGMA SYSTEM PERFORMANCE
`Due to transmission link and system imperfections
`received control and/or audio bits- (encrypted) will
`be in error. In this section, it is our intent to
`estimate the effects of these bit errors on descr-
`ambled video, decrypted control and decrypted
`audio.
`Error enhancement due to cipher-feedback
`The
`cipher-feedback scheme causes error propagation (a
`bit in error at decryptor input can cause several
`bit errors at decryptor output). The encryption/
`decryption system is modelled as shown in Fig. 5.
`Due to transmission errors E(i), B(i) < (i). If
`For the decryptor,_we can write
`B(i) = B(i) ® E(i)
`eis Mod-2 addition
`E(i) = E(i)e)ET(j)E(i-j)
`Kis Mod-2
`J
`addition
`
`(2)
`(3)
`
`OR
`
`Pr [B(i) E B(i)] = Pr[E(i)=l]
`= Pr[E(i)=l]Pr[ET(j)E(i-j)=O]
`Pr[E (i )=O]Pr[Y,T(j )E(i-j )=1]
`(4)
`Note that T(j) is binary valued and time-varying.
`At any given instant, let N be the number of '1'
`valued T(j) and let P be the probability that
`E(i-j)='1'. Then,
`Pr[ET(j)E(i-j)=O] = Pr[# of E(i-j)=1 is even
`among N E(i-j)=1]
`(5) can be shown to be
`1 + (1 - 2p)N
`-2
`
`5)
`
`Using (5) in (4), we obtain
`Pr[decrypted bit error] = (P/2)[1÷(1-2P) ] +
`N
`=(112)[1-(1-2P)N]
`(6)
`Decrypted control channel errors, video descrambl-
`ing errors due to wrong descrambling key and decry-
`pted audio error probabilities can be derived from
`(6) as will be shown now.
`Control channel errors
`Control channel informati-
`on including decryption keys is transmitted in
`encrypted form (cipher-feedback encryption). A
`6 x 8 row-column parity scheme is used on the encr-
`*
`
`Pr is abbreviation for Probability.
`
`22.5.3
`
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`5. APPLICATIONS FOR NON-VIDEO SOURCES
`The basic ORION/SIGMA transmission scheme can be
`used to handle non-video sources. One can envision
`a host of applications, wherein, the signal securi-
`ty methods and the transmission schemes as embodied
`by the ORION/SIGMA systems can be radily used.
`Video-text for instance, can easily be incorporated
`as part of the control channel. Other digital data
`sources depending on their bit rate can also be
`time-division multiplexed with the existing control
`channel data. In an application where there is no
`need to transmit video, the entire video signal
`duration can be used to handle non-video informat-
`ion. For instance, in a commercial application
`concerning the secure delivery of music (a pay-
`music analogue of pay-TV), analog music channels
`could be digitized and encrypted as per the ORION/
`SIGMA method and be transmitted using these systems
`so that secure transmission of music is achieved -
`upto 11 stereo channels can be transmitted using
`such a scheme .
`
`6. CONCLUSIONS
`In this paper, we have described the signal secur-
`ity methods applied to the transmission of TV
`programs. Signal security methods used in two
`commercially available systems ORION and SIGMA were
`described. An analysis was developed to asess the
`effects of transmission errors on decrypted
`signals. From the performance curves derived from
`the analysis, it was concluded that the cipher-
`feedback scheme causes only marginal degradations
`under normal operating conditions; synchronization
`and message authentication benefits
`of such an
`encryption method make it more desirable than the
`simpler bit-by-bit encryption method. Potential
`uses of the ORION/SIGMA secure transmission format
`for non-video sources were briefly discussed.
`
`REFERENCES
`-[1] V. Bhaskaran, M. Davidov , "Video-Scrambling,
`Overview", Intnl. Conf. Consumer Electron.,
`1984.
`[2] M. Davidov, V. Bhaskaran, "Scrambled C-band
`DBS-Like Services", Intnl. Conf. Consumer
`Electron., 1984.
`
`ypted bits. In the decoder, a 2 out of 3 majority
`voting scheme is used to accept/reject control
`channel messages. Thus,
`P = Pr[bit error at decryptor input]
`= Pr[2 out 3 control channel messages in error]
`
`(9
`
`Pr[message in error] = 42
`(1-Pb)46
`)Pb
`(7)
`Pb is the transmission link bit error probability.
`Depending on the modulation format, transmission
`link carrier-to-noise ratio versus Pb relationship
`is usually available. Decrypted control channel
`bit error probability (henceforth denoted as Pd)
`can be easily computed using (7) in (6) for given
`Pb and N.
`.Video descrambling errors
`Erroneous descrambl-
`ing keys can result in descrambled video errors.
`Using (7) in (6), descrambling key error probabi-
`lity Pd can be computed. Assuming one descrambling
`key controls upto 30 frames of video descrambling
`and assuming a key change every second, number of
`seconds between video frame errors can be computed
`as
`1/(30 x Pd)
`(8)
`Decrypted audio errors
`Audio errors are caused
`by wrong decryption key and/or wrong decryptor
`input audio bits. Using (6), decrypted audio bit
`error probability can be written as
`[(1-Pd)/2][1-(1-2Pb)N+1] + (PdI2)[1-(1-2Pd)N+1]
`+ (Pd/2)[1-(1-2Pb)N+1]
`Calculated error probabilities
`Various error pro-
`determined from (6 )-(9) are summarized
`babilities
`in Fig. 6,7. For the calculations, we account for
`the time-varying nature of T(j) by assuming a
`uniform distribution on N, where the N values are
`distributed between 2 and 32 (determined from the
`key-size and decryptor shift register size).
`Calculations in Fig. 6 were performed for a
`SIGMA system. Here, curve labelled IDEAL is for
`the case of no encryption and no multipath. Curve
`labelled ACTUAL includes multipath effects,
`receiver imperfections (5deg RMS phase error in
`demodulator, data detector peak timing jitter = 5%
`of bit duration) and no encryption. In all cases,
`gaussian noise effects are included. Curve for
`Pd (control channel decrypted bit error probabili-
`ty; also descrambling/decryption key error
`probability) is derived using ACTUAL, (7) and (6).
`Decrypted audio bit error probability is derived
`using (9) with Pb as per ACTUALand Pd as computed.
`From these curves, it is seen that cipher-feedback
`degrades audio performance by atmost 1.5dB at
`error probabilities around 1E-5. In CATV systems,
`worst case C/N (around 34dB) and poor multipath
`yields acceptable performance in audio and
`control channels even with the error propagating
`cipher feedback scheme.
`In Fig. 7, we show performance results for
`the ORION system with discriminator and PLL type
`demodulation (ref. 2 contains details on these
`demodulators). Typical operating conditions are
`C/N
`10dB for discriminator and
`8dB for PLL. From
`Fig. 7 and actual observations, it is concluded
`that the cipher-feedback scheme yields negligible
`degradations while ensuring high levels of
`security.
`
`310
`
`22.5.4
`
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`

`FIXED
`DEFEAT
`
`CABLE
`TAMPERING
`
`CAITV
`CABLE
`
`SCRAMBLED VIOtD
`
`SCRAMBLED AUDIO
`
`CONTROL DATA
`
`-
`
`~-.---- -
`
`/ ANTI JAM
`FILTER(S),
`ETC
`
`TAMPERING
`\DEVICE
`
`.rv
`.TV
`
`"SPOOFING"
`
`Fig. 1:
`
`CATV Network Attack Scenarios
`
`1)
`
`FM Mod
`
`C-Band or
`Ku-Band
`
`ORION
`ENCODER |
`
`. Video
`Audio
`Control
`
`---
`
`Scrambled
`Video
`. Encrypted
`Audio
`. Encrypted
`Control
`
`Fig. 2a: ORION System In Satellite Link
`
`GLOBAL Control Channel. Encrypted. FSK Mod.
`
`IN CATV Li nk
`
`-) VSB-AM
`
`CATV Link
`
`SIGMA
`ENCODER
`
`Video
`Audi o
`. Control
`
`. Scrambled
`Vi deo
`. Encrypted
`Audio
`. Encrypted
`Control
`
`Fig. 2b: SIGMA System In CATV Link
`
`Analog Video
`
`Analog Audio
`
`Control Data
`
`Scrambled
`Video
`
`Encrypted
`Audio
`
`Encrypted
`Control
`
`Fig. 3: ORION/SIGMA Signal Security Scheme (Encoder)
`
`22.5.5
`
`311
`
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`

`STORED. UNIDU,
`SECRET BDX KEY
`
`BOX SPECFE
`DE-CRTPTION
`ALGORITHM
`
`DOWNLOADED,
`ENCRYPTED
`CONITROL
`CHANNEL
`IPFORMATON
`
`ENCRYPTED
`SERVICE
`DATA
`RDO RAMMI)
`
`CONTROL DATA
`DECRYPTION
`KEY
`I VARBLE)
`
`K
`
`DECRYPTED
`CONTOL DATA
`
`CONTROL DATA
`* DECRYPTS
`ALCOTTO
`
`OTHE CONTROL RIPRATIN AND
`b- AUTHORTION DATA (TIE
`CODES, SYSTEM CODES. ETC.)
`
`SERVEICE
`K KEY K
`4 VARIABLE)
`
`DEIIC
`
`SECRVEO
`
`DECRYPTIO
`
`CRYPTED
`SERVIEE
`DATA
`
`CLEAR AUD, VIEO. ETC.)
`
`Fig. 4:
`
`Multilevel Key Distribution in ORION/SIGMA
`
`B(i )
`(Bits)
`
`ENCRYPTOR
`
`I
`
`>.66
`
`Encryptor Transfer Function :
`
`E(i ) [Transmission Link]
`Errors
`
`(Bits)
`
`I
`
`+fT9j)SfJ
`
`Mod-2 operations
`in g domain
`
`Decryptor Transfer Function: Inverse of Encryptor Function
`
`T(j), B(i), B(i), E(i)
`
`:
`
`'O' or '1'
`
`Fig. 5: Encryptor/Decryptor System ModeL. Cipher-Feedback.
`
`ORION SYSTEM PERFORMANCE
`
`Baseband Format: same as SIGMA
`Transmission Format: FM. Peak
`deviation of 1V signal = 7.8MHz.
`24MHz IF Bandwidth.
`
`Receiver Imperfections Ignored.
`
`DISCRIMINATOR
`---Decrypted Audio Performance
`Audio Performance. No
`Encryption.
`Control Channel Performance.
`Error control scheme effects
`included (refer equation 7)
`
`\
`
`\
`
`Decrypted Audio Performance
`.Audio Performance. No
`Encryption.
`-Control Channel Performance.
`Error control scheme effects
`included (refer equation 7).
`
`~
`
`~
`
`X
`
`-.
`
`.I
`
`2SA
`
`v
`35
`30
`Video Carrier/Noise Ratio, dB
`6: SIGMA System Performance For Decrypted Signals.
`
`*
`
`v
`
`I
`
`40
`
`45
`
`Fig. 7: ORION System Performance For Decrypted Signals
`
`22.5.6
`
`SIGMA SYSTEM PERFORMANCE IN THE PRESENCE OF
`14dB, 500Nsecs MULTIPATH
`Baseband Signals: Binary PAM,
`Pulse-shaped, 30/140 volts,
`4.09MBps.
`Transmission Format: VSB-AM, 6MHz
`Bandwidth.
`
`\ \
`
`-2
`
`I-
`
`Decrypted Audio Performance.
`\Multipath, Gaussian Noise,
`Receiver imperfections included.
`
`\\ \*\
`
`\
`
`\
`
`ACTUAL. Multipath, Gaussian Noise,
`Receiver imperfections included.
`-IDEAL System. Gaussian noise only.
`Multipath effects, receiver
`imperfections ignored. Signals not
`encrypted.
`
`\
`
`Control Channel Performance at
`Decryptor output. Multipath, Noise,
`Receiver imperfections included.
`Error control scheme (Equation 7)
`effects included.
`
`-4-
`
`-5-
`
`-6 -
`
`-7
`
`-6-
`
`-9-
`
`.,,.
`
`-IU
`20
`
`Fig.
`
`312
`
`APPLE EXHIBIT 1073
`APPLE v. PMC
`IPR2016-01520
`Page 6
`
`