JP2001203652A - Contents information decoding method and medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system that can quickly inform a user that an erroneous key is in use when contents data re decoded by incorrect key. SOLUTION: In the case that contents data cannot have correctly be decoded within a preset period from start of decoding, the user is informed (by means of display) that the contents data cannot have correctly be decoded via a prescribed user interface such as an image or voice interface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a content key and a content information decryption method and medium for recording, transmitting, and reproducing encrypted content information encrypted using the content key. The present invention relates to a content information decryption method and a medium capable of detecting whether or not decrypted encrypted content information has been decrypted with valid encryption key information.

[0002]

2. Description of the Related Art With the development of encryption technology, Japanese Patent Application Laid-Open No. 10-269289 discloses a digital content distribution management method and a digital content reproduction method as useful methods for distributing digital data of audio and video using a network. A method and apparatus are disclosed. Japanese Patent Application Laid-Open No. 10-269289 discloses that on the distribution side of digital content, the digital content is encrypted, compressed and processed, and the processed digital content, the encrypted content key, and the encrypted billing information are communicated to the communication partner. Side, and the usage fee collected based on the content usage information transmitted from the communication partner is distributed to the right holders, while the digital content reproduction side transmits the processed digital The content is decrypted with the content key and decompressed and played back, and at the same time, the billing information is reduced according to the use of the content and the usage information is transmitted to the distribution side so that the recorded content can be carried. Things are disclosed.

[0003] Japanese Patent Application Laid-Open No. 10-283268 discloses an information recording medium, a recording device, an information transmission system, and a decryption device. JP-A-10-283268
Japanese Patent Laid-Open Publication No. H10-163873 discloses an information recording medium in which encrypted encrypted information and encryption key information obtained by encrypting key information for decrypting the encrypted information into original information are recorded.
Condition information for decrypting the encryption information in an unencrypted state is additionally recorded in the encryption key information, so that control information of the encryption key information includes device information and area information. Therefore, it is disclosed that the user can directly copy the encrypted information to an HDD or an optical disk to prevent unauthorized use.

[0004] MPEG, which is a conventional technique used in this patent, will be briefly described. MPEG in 1988, ISO /
Name of the organization (Moving Picture) that considers moving picture coding standards established in IEC JTC1 / SC2 (International Organization for Standardization / International Electrotechnical Commission / Technical Committee 1 / Subcommittee 2, current SC29)
s Expert Group). MPEG1 (MPEG phase
1) is a standard for storage media of about 1.5Mbps,
JPEG for still image encoding and video compression for low transfer rates of ISDN video conferences and video phones
It inherits the basic technology of H.261 (CCITT SGXV, standardized by the current ITU-T SG15) and introduces new technology for storage media. These are August 1993, ISO / IEC 111
72 holds.

[0005] MPEG2 (MPEG Phase 2) is an ISO / IEC 1381, November 1994, for the purpose of a general-purpose standard that can support various applications such as communication and broadcasting.
8, H.262.

[0006] The encoded part of MPEG is created by combining several techniques. The input image is reduced in time redundancy by taking the difference between the image decoded by the motion compensator and the input image. The direction of prediction is three from the past, the future,
Mode exists. These can be switched and used for each MB (macroblock) of 16 pixels × 16 pixels. The prediction direction is determined by the picture type given to the input image. P-pictures exist in two modes in which prediction from the past and independent coding of the MB without prediction are performed. B-pictures have four modes of prediction from the future, prediction from the past, prediction from both, and independent encoding. And it is I that all MBs encode independently
It is a picture. The motion compensation detects a motion vector with half-pel accuracy by performing pattern matching on a motion area for each MB, shifts the motion vector by the amount of motion, and predicts the motion vector. The motion vector has a horizontal direction and a vertical direction, and an MB (Motion Compensation) mode indicating where to predict from the MB.
Is transmitted as additional information. A GOP (Group Of Picture) refers to a GOP (Group Of Picture) from an I picture to a picture preceding the next I picture. In general, about 15 pictures are used.

Hereinafter, an example of the entire coding configuration will be described with reference to FIG. The difference image is DCT (Discrete Cosine Transfo
The rm) unit 100 performs orthogonal transformation. DCT is an orthogonal transform for discretely transforming an integral transform using a cosine function as an integral kernel into a finite space. In MPEG, MB is divided into four and two-dimensional DCT is performed on an 8 × 8 DCT block. Generally, since a video signal has many low-frequency components and few high-frequency components, when DCT is performed, coefficients concentrate on low frequencies.

The quantized image data (DCT coefficients) is quantized by a quantizer 101. In the quantization, the DCT coefficient is quantized by using a value obtained by multiplying an 8 × 8 two-dimensional frequency called a quantization matrix by a visual characteristic by a value called a quantization scale for multiplying the whole by a scalar, as a quantization value. Divide by value. When inverse quantization is performed by the decoder, a value close to the original DCT coefficient is obtained by multiplying by the quantization value.

[0009] The quantized data is subjected to variable length coding in a VLC unit 102. A signal relating to a motion vector and a prediction mode is supplied to the VLC unit 102 from a motion compensator predictor 107 described later, and the VLC unit 102 operates in a mode corresponding to the supplied signal. Of the quantized values, DC (D
The C) component is a DPCM (diffe
Use rential pulse code modulation). In addition, the alternating current (AC) component has a zigzag scan (z
igzag scan), Huffman coding is performed in which a run length of zero and an effective coefficient value are regarded as one event, and codes having a short code length are assigned from those having a high occurrence probability. The variable-length coded data is stored in a temporary buffer (BUFFER) 103 and output as coded data at a predetermined transfer rate.

The generated code amount for each macro block of the output data is supplied to a code amount controller (not shown in FIG. 2), and an error code amount between the generated code amount and a target code amount is quantized. The code amount is controlled by feeding back to the device 101 and adjusting the quantization scale.

[0011] The quantized image data is supplied to an inverse quantizer 10.
4, inverse DCT by the inverse DCT unit 105, and is supplied to one input terminal of the adder 106.
6 is supplied with a prediction signal from a motion compensation predictor 107 as described later. These signals are added by an adder 106 and temporarily stored in an image memory 10.
After that, it is supplied to the motion compensation predictor 107 and used as a reference decoded image for calculating a difference image. A difference image is calculated using an input image signal supplied to the motion compensation predictor 107 and a signal (reference decoded image) supplied from the image memory 108, and this signal is added to the other terminal of the subtracter 109 and to the addition. To the other terminal of the vessel 106. The subtractor 109 subtracts the predicted image signal supplied from the motion compensation predictor 107 from the input image signal, and supplies a signal in which the time redundancy is reduced by taking the difference between the two signals to the DCT unit 100 described above.

Next, an example of the structure of the decoding will be described with reference to FIG. The transmitted or reproduced variable-length coded digital signal is input to a VLD unit 20, is subjected to variable-length decoding, is converted into the original fixed-length data, and is then supplied to an inverse quantizer 22 to be supplied with a quantization width and a quantization width. By multiplication, it is replaced with a representative value that is a value approximating the original DCT coefficient,
The signal is supplied to the T unit 23, subjected to an orthogonal inverse transformation process, locally decoded, and a prediction error signal is output. Next, the prediction error signal is supplied to one terminal of the adder 25 from the inverse DCT unit 23, and the prediction signal from the motion compensation prediction unit 24 is supplied to the other input terminal of the adder 25. The device 25 outputs a reproduced image signal obtained by adding these signals as decoded data. The adder 25 supplies the output to the image memory 26, where the output is temporarily stored.
The temporarily stored data is supplied to the motion compensation predictor 24 together with the signal from the inverse quantizer 22 to generate a prediction signal. The prediction signal is output to the other terminal of the adder 25. The motion vector and the prediction mode extracted from the inverse quantizer 22 are supplied to the motion compensation predictor 24 together with the decoded data from the image memory 26, thereby outputting the motion compensated and predicted image data. Adder 25
Decodes the image data equivalent to the image data input to the encoding device by adding the data from the inverse DCT unit 23 and the image data subjected to the motion compensation prediction from the motion compensation prediction unit 24, While supplying it to the image memory 26 and outputting it to the outside.

[0013]

However, in the above-mentioned conventional method, when the content is encoded by a predetermined compression method and the content is encrypted, the encryption can be decrypted only with a valid key. Although some contrivances have been devised, when actually decrypting with an invalid key, many playback devices cannot reproduce reproduced images and sounds for a long period of time, or even if they can do so, many blocks will fail due to compression / decoding failure. The problem of noise generation is not considered.

[0014]

According to the present invention, there is provided a content information decoding method for transmitting encoded content information encrypted with a predetermined content key and decoding the encoded content information. If the content information has not been correctly decoded within a preset period from the start of the decoding of the content information, it is notified using a predetermined user interface that the content information was not correctly decoded, and It provides a method of stopping decoding. Also,
In order to solve the above-described problem, the present invention relates to a medium used when transmitting encoded content information encrypted with a predetermined content key, wherein the content information and a decoding start of the content information are started. MP that defines the point
A medium that encodes an EG start code and encrypts the EG start code with the predetermined content key is provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The concept of the present invention will be described with reference to FIG. First, the recording side or the transmission side will be described. The content information 1 is compression-encoded by the MPEG encoder 2. The compressed content information is encrypted by the encryption device 3. For the content information to be encrypted, a key 6 is created using the one-way function 5 from the information 4 serving as the key, and the content information is encrypted using the key.

The one-way function 5 can also be expressed as a one-way hash function. Given a function h and a certain value x in its domain, find y such that h (x) = h (y). It is a function that is difficult. As the encryption method, for example, encryption such as DES is used. The DES encryption system, which was adopted in the United States Federal Government standard in 1977, is a typical common key encryption system and is a block encryption system that performs encryption and decryption in 64-bit units using a 56-bit key. . Encryption is 6
The 4-bit data is divided into 32 bits each, and is composed of transposition, permutation, nonlinear function, and exclusive OR.
In the case of DES, the encryption key is about 56 bits. Therefore, the information that forms the key such that the number of output bits of the one-way function is 56 bits is, for example, 5 bits specific to a specific system.
This is stored as 6-bit information.

The encrypted content information 7 is recorded on a recording medium or transmitted to a transmission path or a transmission medium. Next, the reproduction side or the reception side will be described. On the reproducing side or the receiving side, a key 10 is generated by using a one-way function 9 for the information 8 which is a source of the shared key. By using the key 10 to decrypt the transmitted encrypted content information 7 by the decryption device 11, it is possible to obtain compression-encoded content data. This data is decompressed and decoded by the MPEG decoder 12, and
The content data information 13 thus decrypted is obtained, and the content data 13 is reproduced and displayed on the content display device 14. Also, at the time of MPEG decoding, the reproduction start signal 15 is output from the content display device 14 to the MPEG decoder 1.
Send to 2. In the MPEG decoder 12, the reproduction start signal 15
Based on the above, it is determined whether a start code is input within a predetermined time, or whether a predetermined number of error concealments are continuously performed during decoding after the start code is input. If it is determined that an unauthorized key has been used in accordance with the result, an unauthorized key use display signal 16 is generated, and the content display device 14
When the unauthorized key use display signal 16 is detected, a message to the effect that the correct content data could not be decrypted is displayed to the user using an image or sound or a predetermined user interface.

Next, a case will be described with reference to FIG. 4 where it is determined whether a start code is input within a predetermined time and it is determined that an unauthorized key has been used according to the result. FIG. 6 shows the entire MPEG2 video syntax. FIG.
The function called next # start # code () is set at the beginning of. This function is an MPEG that acts to ignore the input data until the start code comes
Is stipulated. The start code is the sequence shown in Fig. 7.
ce # header # code, which is defined as 0x000001B3, for example.

When the user starts reproduction, a reproduction start signal 15 is sent from the content display device 14 to the detection time measuring device 17.
And the elapsed time is reset to zero. afterwards,
The encoded data 18 is input from the decoding device 11 shown in FIG. 1, and the start code detector 19 outputs the encoded data 18
It is detected whether or not the above-mentioned start code exists therein. When the start code is detected, it is interpreted that the encrypted content signal input to the decoding device 11 on the reproducing side or the receiving side shown in FIG. The data is transmitted (transmitted) to the VLD device 20 and MPEG decoding is started. Regarding the processing after the VLD unit 20, for example, the configuration example of the decoding shown in FIG. 3 can be used, and the description thereof will be omitted.

If the encryption is decrypted with an unauthorized key, no start code is input. Therefore, the start code cannot be detected by the start code detector forever. Therefore, even if a predetermined time, for example, 5 seconds has elapsed since the reproduction start signal 15 arrived at the detection time measuring device 17, the start code is not detected. If the start code cannot be detected by the detector 19, the detection time measuring device 17 sends a predetermined start code non-detection signal to the unauthorized key use display signal generator 21. When the detection signal is received, it is interpreted that an unauthorized key has been used, and an unauthorized key use display signal 16 is generated. The unauthorized key use display signal 16 is supplied to the content display device 14 shown in FIG. Using the interface, for example, the user can obtain the correct content data in the form of images or sound, or a combination thereof. Notification to the effect that could not issue (display) is performed.

Next, a case will be described with reference to FIG. 5 in which it is determined whether or not a predetermined number of error concealments have been continuously performed, and it is determined that an unauthorized key has been used in accordance with the result. .

The concealment means that, for example, when an error occurs in the data and a bit pattern that cannot be solved as a VLC code occurs in the VLD unit 20, if it is decoded as it is, in order to prevent any image disturbance from occurring, the output is normally performed. This is a function that uses the previous video frame as it is and displays it, so that the user does not see the distorted screen.

When the user starts reproduction, a reproduction start signal 15 is input from the content display device 14. This signal is input to the concealment frequency measuring device 27 in FIG. 5, and the frequency is reset to zero. Thereafter, when the encoded data 18 is input and the Huffman code cannot be decoded by the VLD unit 20, concealment is performed. If the encryption is decrypted with an incorrect key, a pattern that does not occur in MPEG is input, so that the Huffman code cannot be decrypted by the VLD device 20. When the encoded data 18 decoded with the genuine key is decoded, concealment due to an error or the like is performed at most once or several times. Therefore, the concealment number detector 27 sets the concealment to 10 or more times, for example. In such a case, the unauthorized key use indication signal generator 2
7, it is interpreted that an unauthorized key has been used, and an unauthorized key use display signal 16 is generated. The unauthorized key use display signal 16 is supplied to the content display device 14 shown in FIG. Using a predetermined user interface, notification (display) that correct content data could not be decrypted is performed.

If the number of concealments occurring within a predetermined period (time) from the start of reproduction is equal to or less than a predetermined value, the reproduction side or reception side decoding device 11 shown in FIG. , The encoded data 18 is transmitted (transmitted) to the VLD device 20, and MPEG decoding is started. Regarding the processing after the VLD unit 20, for example, the configuration example of the decoding shown in FIG. 3 can be used, and the description thereof will be omitted.

As described above, according to the present invention, when a content is encoded by a predetermined compression method, and the content is encrypted, if the content is decrypted by an unauthorized key, many playback devices use a long format. Prevents the playback of images and sounds during the period, and prevents noise on the block caused by many compression / decoding failures even if done, and allows the user to quickly confirm that the wrong key is being used. A communication system can be built.

[0026]

As described above, according to the present invention, the time required to detect the start code from the start of reproduction or the number of error concealments can be counted, and the result can be immediately notified to the user. In the case of decryption with a simple key, the playback device prevents playback images and sounds from being unable to be played back for a while, and prevents the occurrence of noise on blocks caused by many compression / decoding failures even if possible. , You can build a system that quickly informs the user that the wrong key is being used.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of an MPEG encoder.

FIG. 3 is a block diagram of an MPEG decoder.

FIG. 4 is a block diagram showing an example of a decoder according to the embodiment of the present invention.

FIG. 5 is a block diagram showing another example of the decoder according to the embodiment of the present invention.

FIG. 6 is a diagram showing the entire MPEG video syntax.

FIG. 7 is a diagram showing an MPEG2 video Sequence header.

[Explanation of symbols]

 1, 13 content information, 2 MPEG encoder, 3 encryption, 4, 8 information for the first key, 5, 9 one-way function, 6, 10 key, 7 ... Encrypted content information, 11 ... Decoding device, 12 ... MPEG decoder, 14 ... Content display device, 15 ... Reproduction start signal, 16 ... Illegal reproduction key use display signal, 17 ... Detection time measuring device, 18 Coded data 19 Start code detector 20 VLD device 21 Incorrect key use indication signal generator 22 Inverse quantizer 23 Inverse DCT device 24 Motion compensated predictor 25 Adder 26, image memory 27: concealment frequency measuring device

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenjiro Ueda 3-12-12 Moriyacho, Kanagawa-ku, Yokohama-shi, Kanagawa Japan F Co., Ltd. F-term (reference) 5B017 AA03 BA07 BB09 CA16 5C059 KK43 MA00 MA02 MA05 MA14 MA23 MC15 ME01 NN15 NN21 PP05 PP06 PP07 RC01 RF01 SS06 SS11 UA02 UA05 5J104 AA06 AA41 NA02 NA11

Claims (4)

[Claims] 1. A content information decoding method for transmitting encoded content information encrypted with a predetermined content key and decoding the encoded content information, wherein the content information is transmitted within a predetermined period from the start of the decoding of the content information. A content information decoding method characterized by notifying that content information was not correctly decoded using a predetermined user interface and stopping decoding of the content information when the information was not correctly decoded. 2. A content information decoding method according to claim 1, wherein said content information is correctly decoded when a start code defining a decoding start point is detected within a preset period from the start of decoding. A content information decoding method, characterized in that it is determined that 3. The content information decoding method according to claim 1, wherein when the execution of the error concealment does not exceed a predetermined number of times within a preset period from the start of the decoding, the content information is correctly decoded. A content information decoding method characterized by determining. 4. A medium used for transmitting coded content information encrypted with a predetermined content key, wherein the content information and an MPEG start code defining a decoding start point of the content information are stored in a medium. Encoding,
A medium characterized by being stored by being encrypted with the predetermined content key.