JPH0241051A - Recording system - Google Patents

Abstract

PURPOSE:To attain the decoding of recording information for a specific cryptographic decoder only by ciphering a key Kt to decode cryptographic information by a key Ki specific to each decoder so as to form a key EKi (Kt) and recording it together with cryptographic information. CONSTITUTION:Suppose that a video signal and a voice signal are scrambled by using a function f(Kt) decided definitely with a key Kt changing as time elapses, then in the case of sending the key Kt from the sender side to the receiver side, since the possibility of interception exists without any modification, the key is ciphered by other key Ki to form a key EKi and it is recorded on a VTR or the like together with cryptographic information. When the recorded information is reproduced, since the key EKi (Kt) is obtained, the result DKi (Kt) being the decoding of the EKi (Kt) is decoded by using further the key Ki to obtain the key Kt, and then the reproduced scrambling information signal is decoded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a recording system that encrypts and records information so that it can be reproduced only by a specific reproduction device.

Conventional technology It has long been known to encrypt and transmit information (video, audio, data) and receive it, but when encrypting, information that is to be kept secret and information that can only be shown to those who have paid the fee have been known. There is. If you want to keep it secret, you can record the information in its encrypted state, but in that case, it is not desirable that any encryption/decryption device can decode it.

In addition, if there is a fee, it is undesirable for the decrypted information to be copied.

The present invention is a technology related to a recording system that solves these problems.

Problems to be Solved by the Invention In conventional recording systems, there has been a problem in that even if the encrypted data is recorded, any decryption device can decrypt it.

Furthermore, when encrypted information is decrypted and recorded, for example, the secret number of the device is encoded and recorded at the same time, but there is a problem in that the decrypted information cannot be prevented from being copied.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to solve such conventional problems and provide a recording system that can decrypt recorded information only with a specific decryptor and also prevent copying of the decrypted information. With the goal.

Means for Solving the Problem In order to achieve this object, in the present invention, as a key for decrypting encrypted information, or by encrypting c with a key Ki unique to each decryption device, EK, (Kx) and is characterized in that it is recorded together with the encrypted information.

Therefore, even if recorded information is reproduced as is, it remains encrypted and can only be decrypted by a decryption device that has the key Kt used for recording.

According to the present invention, since the key or Kx generally changes over time, it is possible to change the key or Kx of the decryption device at the time of reproduction to be different from when the information signal was recorded. However, according to the recording system of the present invention, when the recorded information signal is played back, the encrypted information such as scrambled video and audio cannot be recovered.
(K, ) or E, (K) is obtained, and the scrambled information is reproduced by decoding DKi (Kt) or DKi (K) using the key. The signal can be decoded (descrambled).

Embodiment An embodiment of the present invention is shown in FIG. In the figure, parts 1 to 5 are recording and reproducing units (for example, VTR), and parts 11 to 21.
A portion 29 indicates a part of the paid decoder including a decryption function and an encryption function.

In Figure 1, input buffer 1 circuit 1.3, video recording head 4
, the audio recording head 5 is a circuit etc. that is common to the corresponding part of a normal VTR. ~Also, the data extraction circuit 14, the encryption/decryption circuit 16, the key, and the memory 16 are used for paid broadcasting (for example, video) that has already been put into practical use.

This circuit is functionally the same as the corresponding part of the paid decoder of C1pher 11, BMAC, etc.).

First, an overview of the entire encryption system that is the basis of the recording system of the present invention will be explained with reference to FIGS. 2 and 3. Here, it is assumed that the video signal and the audio signal are scrambled using f(Kt), a function uniquely determined by the key Kt that changes over time. When transmitting the key Kt from the sending side to the receiving side. Since there is a risk of eavesdropping if the data is left as is, it is encrypted using a different key Ki. A separate key may be assigned to each terminal, a key may be assigned to several terminals at once, or a common key may be used for all terminals. For such a layered structure of keys, for example, −
“Research on data protection and encryption” supervised by Matsunobu, page 63, Figure 1-
27, etc. A key Kx, which is updated at a longer cycle than the key Kt, may be used between the key Kt and the key Kt. This is also shown in the same document. Figure 3 is an example.

Here, in order to simplify the explanation, the case shown in FIG. 2 will be explained. As a broadcasting format, control signals such as keys can be encrypted (scrambled) by adding a PN signal to a broadcasting satellite that can send digital signals. Therefore, the initial value of the PN signal becomes the key, and if this is known, it can be decrypted (descrambled). It is sufficient to encrypt (scramble) the data using this key Kt and send it, and decrypt it on the receiving side using the key 1. The video signal may be encrypted (scrambled) by fin rotation, and the cutting point on each line of the signal may be given using the PN signal, and a known technique can be used for this purpose.

Now, in FIG. 1, Pl is an input terminal for a received signal on the receiving side, and for example, the FM detection composite video output signal of a BS tuner may be input as is. 11 is an input buffer circuit, 12 is a separation circuit that separates a 5.73 MHz audio carrier wave component and a video signal component, and 13 is a demodulation circuit that demodulates a 5.73 MH2 QPSK signal to obtain a 2,048 Mbps digital signal. 14 is a QPSK demodulation circuit 13
16 is a decoding circuit for decoding the encrypted key Kt and other signals from the control signal data; 16 is a sampling circuit for extracting control signal data other than audio data from the output of the decoding circuit 16; In addition to the memory A16 that stores the key Kt, it goes without saying that there is another memory that stores control signals other than the key Kt.

On the other hand, 17 transmits 4.5MHz continuous carrier wave to 20482O
The modulated audio output of the modulating circuit 17 and the video signal component output of the separation circuit 12 are mixed in the mixing circuit 18 and outputted from the output terminal P2. Therefore, the output signal of output terminal P2 is similar to the NTSC television signal of terrestrial television broadcasting, and A
This signal contains an M-modulated 4.5MHz audio data signal.
The video is recorded on tape by the video recording head 4 via the video recording head 4. In this case, it goes without saying that the video recording head 4 can record up to a high frequency of 4.5 MHz or higher. Note that if the recording band of the VTR is narrow, it is sufficient to record the audio data signal in baseband, but in order to scramble and record the baseband audio data signal, an audio scrambling circuit is required on the paid decoder side. become. This means that
Since this is not the subject of the present invention, we will discuss the 4.5
It should be capable of recording up to MHz.

On the other hand, the key Kt stored in the memory 16 is stored in the encryption circuit 19.
Then, the terminal-specific key from the memory 29 is encrypted with 1 (here, the key is different for each terminal), and is output from the output terminal P3 via the output buffer 1 circuit 2o. The encryption circuit 19 and the output buffer circuit 20 each have a buffer memory therein.

Now, when the recording start control circuit 2 of the VTR instructs to start recording at time t0 shown in FIG. 4, φ. The control signal is 1.3
, 4.5, and output terminal P2 . of the pay decoder. The output signal from P3 is recorded on the same tape.

Next, when the changeover switch 22 is operated at time t1 on the paid decoder side, the control signal φ1 (φ
11), φ2 (φ12) is output, the key Kt is read from the memory 16, inputted to the encryption circuit 19, encrypted by the key Ki in the encryption circuit 19, and transmitted as EK4 (Kt) to the output buffer circuit 2°. , write to that buffer memory. This action ends between t1 and t2, and then between t2 and t
3, the EKI (Kt) is read from the output buffer circuit 20 at a low speed of 1200 bps and output from the output terminal P3. The format of the signal is the same packet structure as the output extracted by the data extraction circuit 14, and one packet consists of 272
Make it pit. Here, from the output buffer circuit 2o
If t(Kt) is phase-encoded and read out at 1200 bps, 272 pits of data can be output in about 0.23 seconds.

This is recorded on the audio track by the audio recording head via the input buffer circuit 3 of the VTR. The recording band of the VTR audio track is 5KHz or more, 1200bpt
Since the frequency range is sufficiently higher than the highest frequency component of the output signal obtained by phase encoding the data read out by r, there is no problem in recording. When recording Exl (Kt) on the audio track of a VTR tape in this way, the first time is as follows: φ2<t2~7. When recording only between tn2 and tn at regular intervals such as φ12
There is a method of recording repeatedly during 3, but either method is fine. The recording control signal φ 2 or φ11 is generated by the R/W control circuit 21 and switched according to the setting of the changeover switch 22 .

With the above configuration, the recording control signal φ shown in FIG. While the signal is at a high level, the encrypted video signal (including the audio code signal) is recorded on the VTR by the video recording head 4, and the key Kt4 is encrypted and the audio is recorded on the VTR's audio track as EKi(t)t). Recording can be performed using the recording head 6. In this case, the existing VTR as the recording and reproducing section
You can use TR.

Note that if the recording bandwidth of the video signal in the VTR is wide, the output of the input buffer circuit 11 is directly outputted to the output terminal P2 without using the modulation circuit 17, and the output is directly output to the video recording head 4.
It is also possible to convey the information to and record it.

Next, reproduction of the video/audio signal and key recorded in this manner will be explained with reference to FIG. 5. As explained in FIG. 4, there is a case where Ext (Kt) is recorded only in the beginning part t2 to t3 of the reproduced signal, and a case where Ext (Kt) is recorded only in the beginning part of the reproduced signal, and
Although it may be recorded repeatedly in tn3, it works the same way either way. First, when the playback start control circuit 1o of the recording/playback unit controls the start of playback, the audio playback head 7 plays back the encrypted EKI (Kt) phase encoded signal from the audio track, and outputs it to the paid decoder via the output buffer circuit 9. input terminal P6. The input buffer circuit 2 phase-decodes the output signal and generates a 1200 bps 272-bit digital signal Exi (
K't). The output EK of the human buffer circuit 27
i(Kt) is decoded using the terminal-specific key Ki stored in the memory 29 to obtain the key K.

get. This key Kt is then written into the memory B30.

On the other hand, at this time, a reproduction instruction signal is issued from the VTR reproduction instruction circuit 31 to the memory A1θ, the selector 2, and the Kt memory B30. The signal is supplied to the descrambling processing section 32. With this, Kt memo! The output of JA16 becomes high impedance and becomes a holding state, and the other Kt memo IJ B
30 becomes active. Also, at this time, the selector 2θ
is the audio detection circuit 2 instead of the output of the QPSK demodulation circuit 13.
6 is applied to the data processing circuit 14. Therefore, the output of the audio detection circuit 26 having the same format as the output of the 0PSK demodulation circuit 13 is added to the data processing circuit 14. This data processing circuit 14 processes the output of the QPSK demodulation circuit 13 and the output of the audio detection circuit 26 in the same way. Then, the encryption/decryption circuit 15 decrypts some of the control signals in the data. These 15 operations will be described later. Encryption/decryption circuit 1
The information other than the key Kt being outputted in No. 6 is transmitted to the descrambling processing section 32.

The descrambling processing unit 32 uses the key Kt to decrypt a part of the output of the data extraction circuit 14 (the part that has not been decrypted by the encryption/decryption circuit 15), and obtains the information necessary for decryption (descrambling). The reproduced signal is descrambled based on this information.

The decoding (descrambling) of the audio data signal is performed using a predetermined PN initial value, that is, the key Kt, at the beginning of the audio data frame period.
This is done by generating a PN sequence by giving , and adding the PN value to the audio data signal output from the data processing section 14 .

Regarding video signals, when encrypting the video signal, the cut position of the line rotation is specified by the PN value, for example, the force return position of the 22nd line is specified as the key, that is, the initial value of PN,
Thereafter, one fin of the video signal is cut and rotated at the position indicated by the PN sequence up to the 23rd, 24th, and 262nd lines of the song. At this time, the same fin in every field or frame is cut at the same position. If the waveform of a line video signal before line rotation is as shown in Figure 8A, the waveform encrypted by cutting and rotating at a position indicated by a predetermined PN value is as shown in Figure 8. It will be something like B. Therefore, if the initial PN value can be determined using the key Kt, it is easy to decode the encrypted video signal in FIG. 8B and return it to A.

Here, the key Kt used for decryption (descrambling) is 1
Assuming that the key Kt is changed on a weekly basis, even if the key Kt is played back from a VTR using the paid decoder used for reception and recording as described above, the key Kt will have been changed after - weeks and the key Kt will be changed as shown in Fig. 6. , the key Kt of memo 1JA16 is different from the one at the time of recording. Therefore, in such a case, it is necessary to obtain Kt from the reproduced signal of the VTR. Also, as mentioned above, since the key Kt is encrypted using the key Ki during recording, even if a paid decoder other than the paid decoder used during recording is used, the key KL is no longer available because it does not have the key KL. Unfortunately, the reproduced signal cannot be descrambled.

Note that when it is known that the key Kt has not changed, the Memo! JB30
By modifying the descrambling processing section 32 to descramble the reproduced signal using the output of the KtZ memory A1e instead of using the output of It becomes possible to descramble the reproduced signal without using the converted Kt, that is, without using Ki. Even a paid decoder that does not have a unique key Ki can reproduce a signal encrypted and recorded with the key Ki, as long as it can extract Kt from the transmitted signal. Tsumashi, it becomes possible to actually watch the video in secret. To prevent this, it is necessary to change the key Kt in a relatively short period of time, and to change the key Kt when a VTR playback instruction is given in the paid decoder shown in Fig. 6.
tKey K read from memory A1s.

By making this switching part a structure that cannot be modified so that it cannot be easily descrambled by
This makes it possible to prevent anything other than personal recording and playback using the same paid decoder, thereby preventing the creation of illegal duplicate tapes. FIG. 9 shows an example of such a configuration. VTR
The reproduction instruction circuit 31 is composed of a switch 318 and a memory 31M that holds the input thereof, and the memory 31M, the key Kt memory A16, the key Kt memory B30, and the selector 3.
By integrating ゜ into one package or resin molding j5. Modification can be prevented by physically preventing switching such as using the key Kt taken from the receiver when playing back the VTR.

Next, the specific contents of the encryption (scrambling) of the key Kt as described above and the operation of the encryption/decryption circuit 16 will be supplementarily explained using FIG. 6.7. Here, it is assumed that the update cycle of the key is once a week and is performed at night. Note that if the paid decoder terminal is powered off, Kt in memory A16 in the paid decoder cannot be updated, so just to be safe, encrypt the key Kt with the key Ki and send it to the paid decoder of each terminal at midnight every day. shall be taken as a thing. Assume that various data are sent using a 0PSK modulation modulator of an audio data signal, and that 500 bits out of the 2.048 Mbits per second are used for delivering the key Kt. Further, if the key Kt per terminal is 32 bits and the address is 24 bits, 56 bits are required per terminal (see FIG. 7). Also, one packet to be transmitted, including the header, is
As shown in the figure, it is assumed to be 288 bits. A is a packet for various control information to which an identification signal 1 is attached, and B is a packet for control signals including Kt to which an identification signal 2 is attached. If the 272 bits are encoded using the BEST error correction method used in teletext broadcasting, the data will be 190 bits out of 272 bits. Therefore, assuming 966 bits per terminal, 168 bits of data for three terminals can be transmitted in one packet. 500 bits ÷ 288
Bit 4-p1736 is the number of terminals that can be accessed per second. If the address is composed of 24 bits, the number of terminals that can be specified is approximately 16.78 million terminals, so 16,780.000 ÷ 1
It is possible to access all terminals and deliver the key Kt in 736+0.966 million seconds, or about 2.7 hours. Therefore, for example, a method can be selected in which the key Kt is delivered once on Monday morning from 2:00 to 6:00, and thereafter, the key is handled individually each time according to the request from the terminal side.

When receiving QPSK modulated data in the signal format (packet) shown in FIG.

is sent, decrypts it with its own key Ki, and decrypts the encrypted key Kt, which matches the terminal address, with the new direction Ki. That is, since the key is doubly encrypted, it is doubly decrypted. to the key,
There is also a method of encrypting only the address but not encrypting the address, or a method of encrypting the key Kt with 1/ (Ki/ is a key other than Ki that differs for each terminal).

On the other hand, when a signal in the signal format shown in FIG. 6A is received, the encryption circuit 16 decrypts the control information using the key Kt to obtain information necessary for decoding (descrambling).

The above is a case where the key structure is double layered as shown in FIG. 2, but if the key structure is three-layered as shown in FIG. 3, the security will be even higher. The operation is similar in this case as well, except that the keys are stored in the memories 16 and 30. In this case, the key Kt is changed every minute or every second, and the key strength is changed every week, month, or year. Since the key is included in the output of the QPSK demodulation circuit 13 in FIG. 1, it is recorded together with the audio data signal and reproduced together with the audio data signal. in this case,
The control information in FIG. 6A is encrypted using a key, and the key, that is, a predetermined PN initial value is included in the control signal shown in FIG. ing. The descramble processing unit 32 shown in FIG. 6 decodes (descrambles) the video signal and the audio data signal using this PN initial value.

Effects of the Invention As described above, according to the present invention, an encrypted video signal and
The key, which is updated over time, is encrypted using a unique key and recorded on the same recording medium using a VTR, etc., so it can only be played back by a decryption device that has the unique key used for recording. can be decrypted. Therefore, even if you copy a recording medium such as a VTR tape that has been illegally recorded, it cannot be reproduced and decrypted (descrambled) unless you use the paid decoder or other decryption device that was used for recording. It is possible to prevent unauthorized copying.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the recording part of a recording system in an embodiment of the present invention, FIGS. 2 and 3 are block diagrams showing the basic principle of encryption and decryption, and FIG. 4 is the recording timing. Fig. 6 is a block diagram showing the playback part of the recording system, Figs.
8 is a waveform diagram showing an encrypted signal, and FIG. 9 is a block diagram showing a main part of a recording system in another embodiment of the present invention. 4...Video recording head, 6...Audio recording head, 13...QPSK demodulation circuit, 14...
...Data extraction circuit, 16... Encryption/decryption circuit, 16... Kt memory A, 19...
...Encryption circuit, 25...Sound detection same number, 2e
...Selector, 28...Decoding circuit,
29...Ki memory, 3o...K, memory B132...descramble processing section. Name of agent: Patent attorney Shigetaka Awano and 1 other person EKL (Kt) Figure Figure

Claims (7)

[Claims] (1) A recording system that encrypts and decrypts recorded data using multiple keys in a hierarchical structure, and the key K_t is updated when a certain amount of time has elapsed from the encrypted video signal.
E_(_K_i)(K_t) which is obtained by encrypting the key K_t using a key K_i unique to the decryption device in the system.
A recording system characterized by recording as follows. (2) The key K_x with a longer update cycle than the key K_t is the key K_t
E_(K_i)(
2. The recording system according to claim 1, wherein the recording system records in the form of K_x). (3) E_(K_i)(K
2. The recording system according to claim 1, wherein the recording system outputs D_(K_i)(K_t)=K_t obtained by decoding D_(K_i)(K_t)=K_t, and simultaneously reproduces and outputs a video signal and an audio signal. (4) In the same format as the key K_x sent from the signal sending side, E_(K_i)(K
3. The recording system according to claim 2, wherein the recording system outputs D_(K_i)(K_x)=K_x obtained by decoding _x), and simultaneously reproduces and outputs a video signal and an audio signal. (5) The recording system according to claim 1 or 3, wherein the recorded signal is encrypted using a key K_t. (6) The recording system according to claim 2 or 4, wherein the recorded signal is encrypted using a key K_t. (7) In the paid viewing decoder, a processing circuit for decoding control signals obtained by reproducing recorded signals, and a processing circuit for decoding control signals in signals sent from broadcasting stations. 6. The recording system according to claim 1, wherein the recording system has a structure in which both the circuits are partially shared, and switching between the two circuits is physically prevented from being performed from the outside.