DE3427286A1 - METHOD AND ARRANGEMENT FOR ENCRYPTION OR DECREASING TELEVISION SIGNALS - Google Patents

Description

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EGA 79 972 Ks / Ri
US Serial No. 517
Filed: July 25, 1983

ROA Corporation New York, N.Y., V.St.v.A.

Method and arrangement for encryption or decryption of television signals

The invention relates to the transmission and reception of video signals and, more particularly, relates to a technique for Encryption and decryption of video signals, the components of which are interleaved as analog signals in the multiplex are.

Encryption of television signals may be desirable be to broadcast in cases such as cable television, satellite broadcast, and subscriber television broadcasting secure against unauthorized reception. Known encryption devices are either amplitude encoders or time sequence encoders, i.e. they work either with a change in amplitude or with a change in time Episode. Among the amplitude encoders there are e.g.

those in which the amplitude of the vertical or horizontal. sync pulse is changed or in which the video signal is modulated with an encoding waveform (e.g. a sine wave). Such devices have the advantage that the decoders needed to decode the signals can be relatively simple and inexpensive. A disadvantage of amplitude coding is that the codes are relatively easy to see and decipher, which creates the risk of a

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there is a "black market" for nielit-authorized decoders. From a technical point of view, it is disadvantageous that the amplitude distortion imparted to the video signal is not always complete is made to disappear by the decoder and critical decoder adjustments are necessary to correct the remaining Distortion of the decoded signal to an acceptable level to reduce. Another problem that can arise with the use of amplitude encoders is deterioration the signal-to-noise ratio and the reduction in dynamic range.

Time sequence encoders rearrange the sequence of the video signal to form a non-standard signal sequence, the can be changed indiscriminately so as to obtain a very high level of security. Examples of such coders are devices which reverse the sequence of picture elements within a horizontal line, devices for moving or swapping lines within a partial image and devices for moving or rearranging of portions of each line of the video signal as suggested by H.B. Shutterly is described in U.S. Patent No. 4,070,693 the disclosure of which is incorporated herein by reference.

This last-mentioned principle from Shutterly, in each case a television line is scrambled at once (intra-line scrambling), has the advantage that less memory is required in the encoder and in the decoder than with those coders that change the line sequence within blocks of lines (interline scrambling). At the Shutterly system, in short, every active line of the composite video signal rearranged in such a way that the segments on both sides of a predetermined Points are exchanged for each other (an exchange principle also known as "rotation"), whereby the position this "exchange point" (width or degree of rotation) is changed indiscriminately from time to time. Information about the "exchange point" is used during a selected line of the

Transmitted at a vertical interval. This exchange code itself does not show the exchange point directly, it just becomes used to match a random number generator in the decoder with a similar random number generator in the encoder Synchronize so that the exchange point is protected from detection.

The present invention is based in part on the finding that the encryption method of intra-line interchange of picture elements as applied to video signals of the conventional composite format to one has a code that is easy to decipher if you use it without looking at video signals of the so-called MAC format *), in which the components of the video signal are multiplexed as analog signals.

In the MAC video signal transmission, a F _a rbbildsignal is (a satellite transponder, a cable or broadcasting system, a video tape recorder, for example, etc.) over a channel transmitted serially appearing in shape and time compressed analog signal components. Serial transmission is preferable because only one channel is required. The use of time-compressed components to represent the color signal (e.g. the components Y, RY, BY or Y, U, V or Y, I, Q or R, G, B, etc.) leads to a desirable reduction in crosstalk between luminance and Chromaticity. Compare US Pat. No. 4,376,957 and US Pat. Application No. 509,786, which issued on June 30, 1983 under the title "A Worldwide Compatible Synchronizing Signal For Accurate Time Base Correction In An Analog Component Interface Standard" in the name of TM Gurley was filed. Reference is made here to these two literature references.

An object of the invention is to take advantage of the intra-line interchanging coding method described above in a video transmission system of the

*) Abbreviation for "Multiplex Amplitude Component Format" "

using the MAC format described without the Encryption security suffers. Methods and arrangements according to the invention for solving this Task are characterized in the claims.

A method according to the invention for encrypting a television signal for transmission makes use of a source a television signal to be encrypted, each of which Line a luminance component and at least one chrominance component contains. Via a first and a second signal path, the luminance component or the chrominance component coupled to an output terminal while selected, non-overlapping Time intervals. The luminance component in the first signal path is time-compressed by a given amount, and the chrominance component in the second signal path is time compressed to a greater extent. The signal sequence of the Luminance component in the first signal path and the signal sequence of the chrominance component in the second signal path are interchanged ("rotates") depending on each other in order to encode the luminance and chrominance components, without their temporal position in the encrypted line of the television signal supplied to the output terminal will be changed.

The invention is illustrated below using exemplary embodiments explained in more detail by drawings.

Figures 1Δ and 1B show simplified waveforms for illustrative purposes the coding of a video signal appearing in MAC format by intra-line rearrangement;

Figures 2A and 2B are simplified waveforms for illustrative purposes an intra-line rearrangement according to the invention for coding a video signal appearing in MAC format;

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-ιοί Figures ⁷ jk and 3B are more detailed waveforms ^ eranschaulichung the principle of the invention in a video transmission with three components in each row;

Pig. 4- is a block diagram of one embodiment of a encoder according to the invention;

Figure 5 is a block diagram of one embodiment of a decoder according to the invention.

The -Pig. 1A shows a line in a simplified representation a video signal appearing in MAC format with two components (The synchronizing signals and the timing signals for the receiver are not shown). An area A contains the clamp level of the video signal preceding the chrominance component. In the two-component version dealt with here the chrominance components U and V are transmitted alternately in alternating lines, differently than a "three component system" where the luminance ecomponents and both chromaticity components within the duration of one horizontal line each (approx. 63 microseconds) be transmitted. A range B corresponds to the clamp level interval between the chrominance component (U or V) and the Luminance component Y.

Figure 1B shows the effect of "rotating" the signal components 1A around the exchange point K. It is instructive to point out that by rearranging the areas A and B have been shifted from the beginning of the line (an arbitrary reference point Ti) and that this shift directly indicates how the rotation of the picture elements of the line took place. The exchange point K in Fig. 1A is delimited on both sides by points N and 0 in the Y signal. After the rotation (Fig. 1B) the new one begins Line at point 0 of the Y signal and proceeds as shown via points P, M and N to create a new

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- Form 11 ordered signal sequence for the line sent.

The problem illustrated with Figures 1Δ and 1B exists in that one can easily determine the "degree of rotation" of the signal elements of the rearranged row by one simply counts the time from the last horizontal sync pulse (not shown) to one of the easily recognizable ones Measures terminal level intervals A or B. Consequently is this scrambling code easy to crack, what set in motion a black market in "pirate" decodem could. This may illustrate the hitherto unrecognized problem of intra-line rearrangement that occurs in composite video signal transmission systems of the type described by Shutterly is very effective in video transmissions of the MAC format is not effective.

Figures 2A and 2B are similar to Figures 1A and 1B, but show an encryption technique using intra-line shuffling in accordance with the present invention. As can easily be seen, the clamp level intervals A and B in the unencrypted line (FIG. 2A) and in the encrypted (rotated) line (FIG. 2B) bring absolutely no information about the degree of rotation. That is, the clamp level areas A and B are not shifted by the rearrangement process and are not otherwise changed in any way. This undesirable result, which means a high degree of security for the encrypted signal, is achieved according to the invention in that each component is ^{rearranged individually by its own exchange point (K and K 1} ). A continuation of this principle to a three-component system means that each component (e.g. Y, I, Q or Y, U, V or Y, RY, BY, etc.) individually for its own exchange point (K, K ¹ and K " ) is rearranged.

Figures 3A and 3B illustrate the principles in detail of the invention in a video transmission in one

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* 3427236

MC format with three components, such as in the above U.S. patent application by T.M. Gurley described is. It can be seen that similar to the example according to the Figures 2A and 2B show the "marks" of the signal (i.e. the clamp levels) the same positions in the scrambled signal (Fig. 3B) as in the unscrambled signal (Fig. 3A) and that there are no fixed, identifiable patterns on the basis of which the signal can be deciphered.

In the case shown, the "unscrambled" (i.e. unencrypted) signal (Fig. 3A) with a horizontal sync pulse, whose amplitude is -4-0 IRE units and is followed by a timing signal burst (T). Of the Burst T has a peak-to-peak amplitude ranging from -20 to +20 IRE units and is used in the receiving and decoding equipment used to synchronize a phase locked loop (PLL), the timing signals for the decoder. The burst T is not the usual color burst, as it is in a conventional composite coloration signal is used.

The burst T is followed by the luminance component Y, the color difference component R-Y and the color difference component B-Y in that order. However, the order of the components is not essential to the invention. It is important that each individual component is rearranged around its own separate exchange point, and the component Y around the point K1, the component R-Y around the point K2 and the component B-Y around the point K3.

All clamping levels remain in the encrypted signal (Fig. 3B) with the corresponding levels in the unencrypted Siganl (Fig. 3A) aligned.

In detail, the unencrypted component Y begins at point A, goes through the exchange point K at location B, B ¹ and ends at point C. After its rearrangement (rotation) around the exchange point K1, the component Y begins with point B ', then

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This is followed by section B ^f to C, then point K 'and then section A to B. In the example described here, component Y begins with section B' to C, followed by point A (the starting point of the unencrypted component) and from point B. During this "rotation" the rear (ie later) signal elements of component Y are placed at the beginning of component Y in the encrypted signal, but the order of the picture elements within each offset section remains unchanged. Each of the components Y, RY and BY has its own separate exchange or rotation point. It can be seen that the clamping levels between the components (eg 0 IRE and +50 IRE) all keep exactly the same position in the encrypted signal as in the unencrypted signal.

The principles of the present invention can generally be applied to any system that ^{transmits video signals in the MAC-I 1} Ormat. FIG. 4 shows an example of the application of the encryption technique according to the invention in a MAC transmission coder, as is described in the above-mentioned US patent application by TM Gurley. This is a system with a single channel over which the components Y, RY and BY are transmitted during each line interval.

The encoder of Fig. 4 includes a source of video signal components 4-00, which sends a luminance component Y to an analog / digital converter (A / D converter) 402, a first larbdiff er en zkomp on en te R-Y to an A / D converter 404 and a second color difference component B-Y to an A / D converter 406 supplies. The source 400 may, for example, be a matrix circuit which converts the output signals R, G and B of a color television camera, or any other suitable Source for the components Y, R-Y and B-Y. The A / D converters 402, 404 and 406 can be conventional 8-bit flash converters be. Such converters, which are designed to operate with the data

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speed of video signals are well known and are commercially available.

The digitized output signals of the converters 402, 404 and 406 are given to a multiplexer 410 via three separate paths (lying no. 1, path no. 2 and path no. 3), which selectively couples the paths to an output terminal 408. The multiplexer 410 receives the three at its inputs Signals Y, R-Y and B-Y via the corresponding paths and delivers selected copies of these signals to the output terminal 408, via a digital / analog converter (D / A converter) 412 and a circuit 414 arranged in series therewith for inserting timing and code signals.

A timing signal source 416 provides clock signals to the A / D converters (and also to shuffling circuits and compression circuits that are included in the mentioned signal paths and are described further below). the Source 416 also provides selection signals over a rail to multiplexer 40 and horizontal and vertical sync signals (HS, VS), a reference frequency burst signal, and clamp level enable signals via rail 420 to insert circuit 414. Any of the three above mentioned signal paths includes a reorder circuit and a time compression circuit (422, 424 in path # 1; 426, 428 in path # 2; 43O, 432 in path no. 3), each arranged in series with one another are. Digital and analog time compression circuits as well as circuits for rearranging a signal sequence are known (examples of this can be found in the patents and patent applications mentioned above). The insertion circuit 414 also receives reorder code signals K1, K2 and K3 which come from a code signal source 450 and each of which also has an associated copy of the reorder circuits 422, 426 and 430 applied. the Time compression circuits 424, 428 and 432 time compression (gathering) of the video components in each a certain ratio. In detail the gathers

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Compression circuit 424 the component Y in proportion 2: 1, circuit 428 gathers component R-T in a ratio of 4: 1, and circuit 432 gathers the component B-Y in a ratio of 4: 1. The time signal source 416 "is actuated the multiplexer 410 in such a way that this successively the output signals of the path no. 1, the path no. 2 and the Path no. 3 to act on the D / A converter 412 selects. The inserting circuit 414 inserts the horizontal and vertical sync signals (HS, VS) and the reference frequency signal and ensures the clamping under control by the Time signal source 416.

According to the present invention, the code signal source 450 supplies the rearrangement codes K1, K2 and K3 to the rearrangement circuits 422, 426 and 430, so that these circuits independently of one another the signal el em en te of the component Rearrange Y in path no. 1, component R-Y in path no. 2 and component B-Y in path no. 3. The consequence of this is that the components or the clamp levels of the component signals do not change their relative position to one another during the rearrangement, as described above in connection with FIG. 3 has been. As a result, the position of the components in the encrypted signals at terminal 408 does not give any Clue for decryption.

Code signal source 450 also provides reorder codes K1, K2 and K3 to inserter circuit 414 for transferring the codes to terminal 408 during the vertical interval of the video output signal. The security of the rearrangement codes can be improved by the Shutterly technique described above or by transmitting these codes via other devices (e.g. via a separate transmission channel, a permanently programmed read-only memory or some other secure transmission system). As mentioned above, it is important for the invention that each transmitted component is rearranged or otherwise encrypted in such a way that it does not change its position in time. .r-

That in Pig. 4- illustrated system for secure encryption video signals in MAC format can be transmitted via a Satellites, a direct cable connection, or any coupled with a decoder.

The Pig. 5 shows an example of a decoder that is in connection with the coding device according to Pig. 4- use leaves.

According to FIG. 5, the encrypted signal is applied to an input terminal 502 which is coupled to a time signal regenerator 504, an A / D converter 506 and a code detector 5OS. The timing signal regenerator 504 · includes a ^v phase-locked loop (PLL) and counters and is responsive to the reference frequency component of the closure-line input signal, tunge to the clock signals for time expansion scarf to generate rearranging circuits and Bigitalwandler in the decoder. The regenerator 504 also samples the code detector 508 during the relevant line of the vertical interval to decode the reorder codes K1, K2 and KJ.

The output of the A / D converter 506 is sent to a demultiplexer 510 given, that of the regenerator 504 · such is controlled to have the output of transducer 506 selectively couples to signal paths no. 1, no. 2 and no. 3, synchronously with the transmission of the signal components I, R-I and B-Y. The way he. 1 contains a first D / A converter 514, the output of which is connected to a Y output terminal 508 and its input via the series connection of a rearrangement circuit 516 and a 1: 2 time expansion circuit 518 with is coupled to the Y output of the demultiplexer 510. Path No. 2 and Path No. 3 are in a similar fashion, respectively a D / A converter 520 or 526, a shuffling circuit 522 and 528 and time expansion circuits 524 and 530, respectively. The time expansion circuits for the color difference signals However, R-Y and B-Y cause an expansion over time in a ratio of 1: 4, unlike the stretch ratio of 1: 2

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The decoder after. Pig. 5 works in essential parts as described in the aforementioned U.S. patent application by Gurley is described, only that in the present EaIl the Code detector 508 and the individual rearrangement circuits provided 516 »522 and 528 play along. The three order codes, which are transmitted during the vertical interval of the input signal fed to terminal 502, are detected by the god detector 508 and sent to the three in the Due to No. 1, No. 2 and No. 3 provided rearrangement circuits 516, 522 and 528, which the respective Signal elements within the component T, the component Rearrange E-Y and component B-Y in a sense opposite to that which occurred in the encoder is. This decodes the individual components Y, R-Y and B-Y.

The application of the principle of the invention to the with Gurley's system using the three components Y, R-Y and B-Y is only one example. An individual rearrangement the chrominance and luminance components in transmission systems that carry analog video signals in multipliers (MAV systems), brings the same simplification as that Intra-line scrambling in component transmission systems, however, avoids the above-mentioned problem that the components are in proportion to the intra-row rearrangement can be shifted in time and thus give an indication of how the time shift or rearrangement is to be Would be decoding. Thus, the present invention brings the technique of component sequential transfer to the same level of security as the conventional technology of mixed signal transmission with intra-line rearrangement. The principles of the invention are generally applicable and can be applied to transmission systems that use work with two or three components (as described above), which are components Y, I and Q

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or the components Y, U and V or the in Components I, R-I and B-I used in the example described above.

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Claims (6)

RCA Corporation
New York, NY, V.St.vA Method and arrangement for encrypting or decrypting TV signals Claims Method for encrypting a color television signal for its transmission, characterized a) that a color television signal is taken from a source (400) of color television signals to be encrypted, each line of which has a luminance component and contains at least one chrominance component; b) that during selected, non-overlapping time intervals, the luminance component selectively (Y) via a first signal path and the or each chrominance component (R-Y, B-Y) via at least a further signal path can be coupled to an output (4-08); c) that the luminance component in the first signal path temporally compressed by a predetermined amount (424) and the or each chrominance component in the or each further signal path is temporally compressed by a higher predetermined amount (4-28, 4-32);
d) that the signal sequence of the luminance component in the first signal path and the signal sequence of the or each chrominance component in the or each further signal path are rearranged in time individually and independently of one another, in particular according to a rotation reversal (422, 4-26, 4-30 , 4-50) so that the luminance and Chroma components are encrypted without their temporal position within the encrypted To change the line of the television signal delivered at output (4-08). 2. method for decoding a color television signal, which contains a luminance component and at least one chrominance component which are consecutive in time appear and each of them through temporal rearrangement of ■ 20 signal ele- ments within the relevant component is separately encrypted, characterized in that a) that the luminance component (Y) of the television signal over a first period of time a first signal path to an output (508) is coupled; b) that the or each chrominance component (R-Y, B-Y) of the television signal during an associated second time period via a respectively assigned further signal path to an assigned Output (510, 512) is coupled, the second time period from the first time period spaced by a predetermined interval during which the television signal is on a given one Clamp level is clamped; c) that the signal elements of the luminance component (Y) within the first time period in the sense a restoration of their original time sequence are rearranged (516) and that the Signal elements of the or each chrominance component (R-Y, B-Y) within the respective second time period separately in the sense of a restoration be rearranged in their original timing (522, 528). 3. Arrangement for encrypting a color television signal for transmission, characterized by: a) a source (400) for supplying a color television signal to be encrypted, each of which Row contains a luminance component (Y) and at least one chrominance component (R-Y, B-Y); b) a first signal path and at least one further Signal path for the selective coupling of the luminance component and the or each chrominance component while respective, not themselves overlapping time intervals to an output (408) j c) devices (424, 428, 432) for temporal compression the luminance component by a predetermined amount in the first signal path and at the time Compressing the or each chrominance component by a greater predetermined amount in that or any other signal path; d) devices (422, 426, 430), which the signal sequence of the luminance component in the first signal path and, independently of this, the Rearrange the signal sequence of the or each chrominance component in the further signal path (s) in terms of time, so that the luminance and chrominance components are encoded without the temporal position of the components within the encrypted line of the television signal delivered at the output (408) to change. - 4 - 4. Arrangement for decoding a color television signal, which contains a luminance component and at least one chrominance component which are consecutive in time appear and each of which is encrypted separately by the temporal rearrangement of its signal elements by: a) a first signal path for coupling the luminance component (Y) of the television signal during a first time period on an output (508); b) at least one further signal path for coupling the or {each chrominance component (R-Y, B-Y) of the Television signal for a second time period on an associated output (510, 512), the second time period being spaced from the first time period by a predetermined interval is during which the television signal is clamped to "a given clamp level;" c) devices (516, 522, 528), which the signal elements of the luminance component within the rearrange the first time period in the sense of a restoration of their original time sequence and separately therefrom the signal elements of the or each Chroma component within the respective second time period in the sense of a restoration rearrange their respective original timing. 5. Television system, characterized by an encryption arrangement according to claim 3 and a decryption arrangement according to claim 4. 6. Color television transmission system, characterized by: a) a source (4-00) for supplying a color television signal in component form; b) a device (424-, 428, 432) for temporally compressing the components of the television signal by a certain amount each time, so that a se- rial transmission of the components of each television line is possible within each line interval; c) a device (422, 426, 430) for temporal rearrangement the signal sequence separated within each Component of each line; d) a transmission device (410, 412, 414, 416, 408) for the serial transmission of the time-compressed and in each case temporally rearranged components to a receiving device (502 to 530); e) a device (510) contained in the receiving device for separating the serially transmitted and components that are temporally rearranged in each case; f) a device (516, 522, 528 and 518, 524, 530) contained in the receiving device for the temporal Rearranging and stretching each of the separate components in a manner that is complementary is to the previous temporal rearrangement and temporal compression.