JP4883701B2 - Content decoding apparatus, method and program thereof - Google Patents

Description

  The present invention relates to a content decryption apparatus, a method thereof, and a program thereof that decrypt and reproduce digital content in which the digital content is partially encrypted.

  In the so-called conditional access system (CAS), which broadcast programs in digital broadcasting are encrypted on the broadcaster side (transmission side) and the broadcast programs can be viewed only by limited viewers. Generally used by receivers that descramble (decode) scrambled (encrypted) broadcast programs (digital content, hereinafter referred to as content) based on key information generated by a viewer-specific security module (CAS card) Has been.

This content is generally encoded by MPEG-2 (Moving Picture Expert Group-2) and broadcast as a transport stream (TS).
In CAS, the payload part, which is the area of the data body of the packet (TS packet) constituting the transport stream, is encrypted, and this encryption can be decrypted only by the receiving apparatus with which a reception contract is made, The viewer can view the decoded video / audio.

On the other hand, in a receiving device that has not been subscribed to, since the encrypted transport stream cannot be decrypted, no video or the like is displayed. For example, a message such as “contract required” is displayed on the screen of the display device. Is displayed. This protects the copyright on the content.
However, in a receiving device that does not have a reception contract, since the viewer cannot see the video at all, the viewer's consciousness that he / she wants to view the video by making a reception contract may be impaired. Therefore, for the purpose of promoting content, it is desired to present a video (partial video, degraded video) that can be seen to some extent even in a receiving device that has not been subscribed to.

In response to such a request, as a technique for protecting the copyright of the content and presenting the viewer with a video that is visible to some extent, a plurality of slices that are data forming a slice layer in a data structure such as the MPEG-2 system Has been disclosed (see Patent Document 1).
According to this technique, in a receiving device (content decrypting device) with which a receiving contract is made, a partially encrypted slice is obtained by acquiring a content key (encrypting / decrypting key) corresponding to the encryption key as a license. Therefore, the original content can be reproduced as a normal video. On the other hand, in a receiving apparatus that has not been subscribed to, since the slice is displayed in an encrypted state, a partially degraded video is reproduced.
JP 2006-203671 A

  According to the prior art, since the content is encrypted in units of slices, the content decrypting apparatus restores only the unencrypted slice even if the license is not acquired. Can be played. Thus, the viewer can partially confirm the content, and the viewer's willingness to purchase the content can be enhanced while protecting the copyright of the content.

  However, when a conventional content decryption apparatus has not acquired a license, the encrypted slice is not decrypted and is directly decrypted by the decryption means (decoder). In this case, the encrypted slice data may include a code that cannot be recognized as encoded data by the decoder. As a result, there is no problem in the content decryption apparatus using the decoder designed to ignore the unrecognizable code, but depending on the decoder, a malfunction may occur due to the unrecognizable code. Therefore, there has been a demand for presenting partially encrypted content without causing malfunction even when an existing decoder is used.

  In addition, when a conventional content decrypting apparatus has not acquired a license, an encrypted slice is directly encoded / decoded as encoded data, so that an indefinite display pattern depending on the encoded code is displayed. Such an indefinite display pattern depending on the encoding code varies depending on the decoder. Therefore, there has been a request from a content provider (business operator) to generate a similar video effect (video disturbance) in all content decoding devices.

  The present invention has been made to solve the above-described problems, and prevents the decoder from malfunctioning when the encrypted content encrypted in units of slices is decrypted, and is further encrypted. It is an object of the present invention to provide a content decoding apparatus, a method thereof, and a program thereof capable of presenting slices in a unified pattern.

  The present invention was devised to achieve the above-mentioned object. First, the content decryption device according to claim 1, the plurality of slices which are data forming a slice layer in a data structure of digital content A content decryption device that decrypts encrypted content generated by partially encrypting each slice, and includes a license storage unit, a slice extraction unit, an encrypted slice determination unit, a decryption slice determination unit, An encrypted slice decrypting unit, a substitute slice replacing unit, and a code decrypting unit are provided.

According to this configuration, the content decryption apparatus stores in advance a license including an encryption / decryption key for decrypting an encrypted slice, which is an encrypted slice , in the license storage unit. This license is provided by a distributor (provider) who distributes encrypted content. The encryption / decryption key is a key corresponding to the encryption key obtained by encrypting the slice, and when the common key encryption method is used, the same encryption / decryption key as the encryption key can be used.

  Then, the content decryption apparatus sequentially extracts slices from the encrypted content by the slice extraction unit, and the encryption target information indicates whether the slice in the encrypted content is an encrypted slice by the encrypted slice determination unit. Thus, it is determined whether the slice extracted by the slice extracting means is an encrypted slice or an unencrypted slice.

  Then, the content decryption apparatus determines whether or not the encryption slice decryption unit corresponding to the slice determined as the encrypted slice by the decryption slice determination unit is included in the license by the decryption slice determination unit. It is determined whether the generalized slice is a decoding target slice or a non-decoding target slice. As a result, only the slice having the encryption / decryption key as a license is subject to encryption decryption.

Then, the content decrypting apparatus decrypts the slice determined as the decryption target slice by the decryption slice determination unit by the encryption slice decryption unit using the encryption / decryption key.
In addition, the content decoding device includes a predetermined specific pattern in which the slice determined as the non-decoding target slice by the decoding slice determination unit by the substitute slice replacement unit is encoded by the same encoding method as the non-encrypted slice. Replace with a substitute slice. As a result, the non-decryption target slice (encrypted slice) is replaced with code data that can be decoded by the code decoding means.

Then, the content decrypting device decodes the substitute slice replaced by the substitute slice replacing unit, the slice determined to be an unencrypted slice by the encrypted slice determining unit, and the encrypted slice decoding unit by the code decoding unit The slices are code-decoded in the order of the slices.
As a result, the non-encrypted slice and the slice decrypted by the encrypted slice decrypting means are reproduced as video data that can be viewed by the viewer. On the other hand, the substitute slice is reproduced or skipped as specific pattern data that can be viewed by the viewer.

  Also, the content decrypting device according to claim 2 is the content decrypting device according to claim 1, wherein the encryption target information is included in the license.

  According to such a configuration, the content decryption apparatus stores in advance the encryption target information indicating whether or not the slice in the encrypted content is an encrypted slice in the license storage unit. The encryption target information is information for specifying a slice to be encrypted, and includes, for example, a picture type (NAL unit type), a slice type (slice type), a slice number, and the like. With this encryption target information, the encrypted slice determination unit can recognize which slice is encrypted.

Furthermore, the content decryption device according to claim 3 is the content decryption device according to claim 1, wherein the encryption target information is added to the encrypted slice.
According to such a configuration, the content decryption apparatus adds the encryption target information indicating whether or not the slice in the encrypted content is an encrypted slice to the encrypted slice. This makes it possible to recognize which slice is encrypted.

  Further, the content decoding device according to claim 4 is the content decoding device according to any one of claims 1 to 3, wherein the digital content is macroblock-based by a motion compensated prediction encoding method. P, which is encoded data, wherein the substitute slice replacing means generates an I slice, which is encoded data, with a macroblock indicating a specific color, and is encoded data indicating a difference from a reference picture. A slice and a B slice are generated with a skipped macroblock and replaced with the encrypted slice.

  According to such a configuration, the content decoding apparatus generates a substitute slice with a macroblock indicating a specific color (for example, gray) for an I slice that is a slice for which only intra-picture encoding is performed by the substitute slice replacement unit. To do. Also, the content decoding apparatus uses the substitute slice replacement means to convert the P slice (slice for performing inter-picture prediction and inter-picture encoding using one reference picture) or the B slice (intra-picture encoding and reference picture). Substitute slices are generated using skipped macroblocks for one or two slices for inter-frame predictive coding.

  Then, the substitute slice replacing means replaces the encrypted slice with the substitute slice. As a result, a slice having no actual data is generated for a slice without motion. As a result, the entire picture is formed while retaining the format of the original predictive coding scheme.

Furthermore, the content decryption device according to claim 5 is the content decryption device according to any one of claims 1 to 4, wherein the content decryption device includes an encryption count indicating the number of times the license has encrypted the slice. The encrypted slice decryption means decrypts the decryption target slice by the number of times of encryption using the encryption / decryption key.
According to such a configuration, the content decryption apparatus acquires the number of times of encryption when the encrypted slice is generated as a license, and the encrypted slice is decrypted by the number of times of encryption by the encrypted slice decryption unit. Data can be decrypted. This makes it possible to encrypt the slice at an arbitrary number of times on the side that encrypts the content.

  The content decryption device according to claim 6 is the content decryption device according to any one of claims 1 to 4, wherein the encrypted slice includes an encryption represented by a predetermined data length. The number of times of encryption is added, and the encrypted slice decryption means decrypts the decryption target slice by the number of times of encryption using the encryption / decryption key.

  According to such a configuration, the content decryption apparatus acquires the number of times of encryption when the encrypted slice is generated from the data added to the encrypted slice, and encrypts the encrypted slice by the encrypted slice decryption unit. By decoding the number of times, the data of the original slice can be decoded.

Furthermore, the content decryption method according to claim 7, the encrypted content generated by partially encrypting a plurality of slices, which are data forming a slice layer in the data structure of the digital content, for each slice. A content decrypting method in a content decrypting apparatus for decrypting, in the content decrypting apparatus comprising license storage means for storing a license including an encryption / decryption key for decrypting an encrypted slice, which is an encrypted slice, in a slice extracting step And an encrypted slice determination step, a decryption slice determination step, an encryption slice decryption step, a substitute slice replacement step, and a code decryption step.

  According to such a procedure, the content decryption method sequentially extracts slices from the encrypted content in the slice extraction step. Then, in the content decryption method, the slice extracted in the slice extraction step is encrypted based on the encryption target information indicating whether the slice in the encrypted content is an encrypted slice in the encrypted slice determination step. Whether the slice is an encrypted slice or a non-encrypted slice is determined.

  In the content decryption method, the decryption slice determination step determines whether the license includes an encryption / decryption key corresponding to the slice determined to be the encryption slice in the encryption slice determination step. It is determined whether the generalized slice is a decoding target slice or a non-decoding target slice.

  The content decryption method decrypts the slice determined as the decryption target slice in the decryption slice determination step using the encryption / decryption key in the encryption slice decryption step. In addition, the content decoding method includes a predetermined specific pattern in which the slice determined as the non-decoding target slice in the decoding slice determination step in the substitute slice replacement step is encoded by the same encoding method as the non-encrypted slice. Replace with a substitute slice. The execution order of the encrypted slice decryption step and the substitute slice replacement step is arbitrary, and may be the same timing.

  In the content decoding method, the substitute slice replaced in the substitute slice replacement step in the code decryption step, the slice determined as the non-encrypted slice in the encrypted slice determination step, and the decryption in the encrypted slice decryption step The slices are code-decoded in the order of the slices.

In addition, the content decryption program according to claim 8, the encrypted content generated by partially encrypting a plurality of slices that are data forming a slice layer in the data structure of the digital content for each slice. In order to perform decryption, a computer of a content decrypting apparatus having a license storage unit that stores a license including an encryption / decryption key for decrypting an encrypted slice that is an encrypted slice is converted into a slice extraction unit and an encrypted slice determination unit. The decryption slice determination unit, the encrypted slice decryption unit, the substitute slice replacement unit, and the code decryption unit function.

  According to such a configuration, the content decryption program sequentially extracts slices from the encrypted content by the slice extraction unit. Then, the content decryption program uses the encrypted slice determination unit to determine whether the slice extracted by the slice extraction unit is encrypted based on the encryption target information indicating whether the slice in the encrypted content is an encrypted slice. Whether the slice is an encrypted slice or a non-encrypted slice is determined.

  Then, the content decryption program determines whether or not the license includes a decryption key corresponding to the slice determined as the encrypted slice by the encrypted slice determination unit by the decryption slice determination unit. It is determined whether the generalized slice is a decoding target slice or a non-decoding target slice.

Then, the content decryption program decrypts the slice determined as the decryption target slice by the decryption slice determination unit by the encryption slice decryption unit using the encryption / decryption key. Further, the content decoding program includes a predetermined specific pattern in which the slice determined as the non-decoding target slice by the decoding slice determination unit by the substitute slice replacement unit is encoded by the same encoding method as the non-encrypted slice. Replace with a substitute slice.
Then, the content decryption program is decrypted by the coding / decrypting means by the substitute slice replaced by the substitute slice replacing means, the slice determined by the encrypted slice determining means as a non-encrypted slice, and the encrypted slice decrypting means The slices are code-decoded in the order of the slices.

The present invention has the following excellent effects.
According to the invention of claim 1, claim 2, claim 3, claim 7 or claim 8, even if the encryption / decryption key is not acquired, the partially encrypted digital content Can be reproduced as degraded content by restoring only the unencrypted portion (slice). Thus, the viewer can partially confirm the content, and the viewer's willingness to purchase the content can be enhanced.
In addition, when there is no encryption / decryption key, instead of the encrypted slice, the substitute slice encoded by the same encoding method as the non-encrypted slice is decoded. It is possible to prevent malfunction due to the inclusion of a code that has not been performed. Thus, an existing decoder (encoding / decoding means) can be used in the content decoding apparatus. In addition, since the encrypted slices can be presented in a unified pattern, it is possible to provide a viewer-friendly screen.

  According to the fourth aspect of the invention, since the encrypted slice is replaced with the substitute slice, it is possible to present a deteriorated screen in all the content decryption apparatuses. As a result, the content provider (business operator) can generate the same video effect in all the content decryption apparatuses. It is also possible to confirm the video effect in advance.

  According to the invention described in claim 5 or claim 6, the slice can be encrypted any number of times on the side of encrypting the content. Thus, for example, even when a slice is encrypted, a code that is prohibited from using the start code of the slice (prohibited code) is generated in the encrypted code multiple times. By performing encryption, the forbidden code can be removed, and problems such as erroneous recognition of the beginning of the slice can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Here, first, after describing the structure and the like of the slice, the structure and operation of the content decryption apparatus according to the embodiment of the present invention will be specifically described.

[About slices]
First, the structure of the content slice will be described. Here, the content is encoded in units of band-like regions (slices) each having a predetermined width in the vertical direction and an arbitrary length in the horizontal direction for each time-series image (picture) constituting the video. It is assumed that the data is encoded by the encoding method. As encoding methods for performing encoding in units of slices, MPEG-2, MPEG-4, H.264, and the like are available. H.264 / AVC and the like exist here. H.264 / AVC is used.
This H. In H.264 / AVC, video as content is encoded in a six-layered structure including a sequence layer, a GOP (Group of Pictures) layer, a picture layer, a slice layer, a macroblock layer, and a block layer.

Here, the slice layer will be specifically described with reference to FIG. FIG. 2 is a data structure diagram showing a structure of a slice layer in H.264 / AVC. As shown in FIG. A video encoded by H.264 / AVC is composed of slices S (S _{1 to} S _N ) that are band-like regions obtained by dividing an image (screen) into a plurality of vertical directions. Each slice S includes a slice header SH and slice data SD composed of a plurality of macro blocks.

The head of the slice header SH includes a “slice start code” indicating the number of the slice S from the top in the vertical direction. In addition, the slice type and the like are written in the slice header SH.
This slice type is either an I slice (a slice that performs only intra-frame coding) or a P slice (a slice that performs intra-frame coding and inter-picture prediction coding using one reference picture). This is information indicating whether there is a B slice (intra-picture coding and inter-picture prediction coding using one or two reference pictures). If the picture is an I picture, the picture is composed of I slices. When the picture is a P picture, the picture is basically composed of P slices, but a plurality of types of slices may be mixed in the picture.
When the slice S is encrypted, the slice header SH is not encrypted and remains in plain text, and only the slice data SD is encrypted.

  H. In H.264 / AVC, the vertical length of the slice S is the size of a macroblock (for example, 16 bits). Further, the length in the horizontal direction may be the size of one or more macroblocks, and is the maximum width of the screen.

  H. In H.264 / AVC, each slice is abstracted with a predetermined data structure (NAL unit) by a network abstraction layer (NAL) in consideration of distribution in a network or broadcast.

  Specifically, as shown in FIG. 6, slices in the slice layer are divided into an access unit delimiter (AUD), a sequence parameter set (SPS), a picture parameter set (PPS). Video data is encoded and stored in a VCL (Video Coding Layer) unit having the same data structure as the NAL unit. This VCL unit includes types such as IDR (Instantaneous Decoding Refresh) and non_IDR (other than IDR).

  This VCL unit includes a header part (NAL unit header part) H of a NAL unit indicating header information of the network abstraction layer and a payload P (RBSP: Raw Byte Sequence Payload). The payload P stores a slice header SH indicating slice header information and slice data SD indicating slice data. If the slice data is less than the unique data length of the payload P, dummy data DD is stored. Further stored.

  Here, a display example of video (content) when encryption is performed in units of slices will be described with reference to FIG. FIG. 7 is a diagram showing an example of displaying the contents of a video, where (a) is the original video, and (b) is the encrypted slice when the original video is partially encrypted in units of slices. A video displayed without decryption, (c) shows a video obtained by decrypting the encrypted slice when the original video is partially encrypted in units of slices.

  Here, only odd-numbered slices in the original video in FIG. 7A are encrypted. As a result, in the state where the license including the encryption / decryption key for decrypting the slice is not acquired, only the unencrypted (even-numbered) slice is partially reproduced as shown in FIG. 7B. It becomes a deteriorated image. When the license is acquired, as shown in FIG. 7C, the encrypted odd-numbered slice is decrypted, and the same quality video as the original video in FIG. 7A is reproduced. It will be.

  Hereinafter, the configuration and operation of a content decrypting apparatus that decrypts content (encrypted content) encrypted in slice units will be described.

[Configuration of content decryption device]
First, the configuration of the content decryption apparatus according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a functional block diagram showing a configuration of a content decryption apparatus according to an embodiment of the present invention. The content decrypting apparatus 1 shown in FIG. 1 is an encrypted content generated by partially encrypting a plurality of slices that are data forming a slice layer in the data structure of content (digital content) for each slice. Is decrypted.
Here, the content decryption apparatus 1 includes a license storage unit 11, a slice extraction unit 12, a license determination unit 13, a substitute slice replacement unit 14, an encrypted slice decryption unit 15, and a code decryption unit 16. Yes.

  The license storage unit 11 stores a license distributed from a provider (provider) that provides content (encrypted content), and is a tamper-resistant module such as an IC card. Note that the license may be input via a recording medium by input means (not shown) or may be acquired via a network.

  This license includes encryption target information for specifying an encrypted slice (encrypted slice) and an encryption key (encryption / decryption key) for decrypting the encrypted slice. The encryption target information is information for specifying a slice to be encrypted, and includes, for example, a picture type (NAL unit type), a slice type (slice type), and a slice number (macro of the slice). Block start position).

  Here, the contents of the license will be described with reference to FIG. FIG. 2 is a data structure diagram showing an example of the contents of a license (license file). As shown in FIG. 2, each element of the license is given a meaning by the following tags.

The area indicated by the tag with the tag name “Key” includes the identification information of the encryption / decryption key corresponding to the encryption key and the encryption key data. Here, a plurality of identification information “000” and the like and encryption key data “112233” and the like are described in association with each other.
The encryption key is generated by an encryption algorithm such as DES (Data Encryption Standard) or AES (Advanced Encryption Standard) which is a common key encryption method. In the following description, it is assumed that the encryption / decryption key and the encryption key are the same.

The area indicated by the tag with the tag name “Cipher” includes the type of cipher method (CipherType) and the like. Here, the encryption method type is “A”.
In the area indicated by the tag with the tag name “CipherXXX”, the picture number (Picture) to which the slice identified by “XXX” belongs, the slice number (Slice), and the identification information of the encryption key that encrypted the slice ( KeyID) and the number of times the slice has been encrypted (encryption count: Count).

For example, the tag with the tag name “Cipher000” indicates that the picture number is “0”, the slice number is “0”, the identification information of the encryption key is “001”, and the number of times of encryption is “1”. Here, the picture number and the slice number become the encryption target information that identifies the encrypted slice. Note that the number of times of encryption is information indicating how many times the slice is encrypted with the encryption key. Here, when the encrypted content is generated on the content distribution side, the slice is encrypted a plurality of times until a unique prohibited code such as a start code is not included.
Returning to FIG. 1, the description of the configuration of the content decrypting apparatus 1 will be continued.

  The slice extracting unit 12 extracts a slice for each picture from the input encrypted content. The extracted slice is output to the license determination unit 13. The slice extracting means 12 separates and extracts a slice each time a “slice start code” is detected in a slice layer constituting the encrypted content.

  Whether the license determination unit 13 decrypts the encrypted slice among the slices extracted by the slice extraction unit 12 based on the license stored (obtained) in the license storage unit 11 Is determined. Here, the license determination unit 13 includes an encrypted slice determination unit 13a and a decryption slice determination unit 13b.

The encrypted slice determining unit 13a determines whether the slice extracted by the slice extracting unit 12 is an encrypted slice or an unencrypted slice. Here, the encrypted slice determination unit 13a determines that the NAL unit type, slice type, slice number, etc. of the slice matches the NAL unit type, slice type, slice number, etc., which is the encryption target information described in the license. The slice is determined to be an encrypted slice. Further, when the information does not match the encryption target information, the slice is determined as a non-encrypted slice.
When the encrypted slice determining unit 13a determines that the slice is an encrypted slice, the encrypted slice determining unit 13a outputs the encrypted slice to the decrypted slice determining unit 13b. When it is determined that the slice is a non-encrypted slice, the non-encrypted slice is output to the code decoding means 16 as it is.

  The decryption slice determination unit 13b determines whether the slice determined as the encryption slice by the encryption slice determination unit 13a is a decryption target slice or a non-decryption target slice. Here, the decryption slice determination unit 13b determines that the encryption slice is a decryption target slice when the license includes an encryption / decryption key corresponding to the encryption slice, and the encryption corresponding to the encryption slice is determined. If the decryption key is not included in the license, it is determined that the encrypted slice is a non-decryption target slice.

Then, the decryption slice determination unit 13b outputs the slice determined to be the decryption target slice to the encryption slice decryption unit 15, and outputs the slice determined to be the non-decryption target slice to the substitute slice replacement unit 14.
Note that the license determination unit 13 outputs all slices to the substitute slice replacement unit 14 when the license corresponding to the encrypted content is not stored in the license storage unit 11.

  The substitute slice replacing unit 14 encodes the encrypted slice (non-decryption target slice) determined by the license determining unit 13 as an encrypted slice without an encryption key (encryption / decryption key) using the same encoding method as the non-encrypted slice. It is replaced with a slice (substitute slice) including a predetermined specific pattern. The substitute slice replaced by the substitute slice replacing unit 14 is output to the code decoding unit 16.

  Here, the substitute slice replacement unit 14 generates and replaces a slice whose display color is gray, for example, as the specific pattern. Note that the substitute slice replacement unit 14 generates a slice with a macroblock indicating a specific color (in this case, gray) when the slice type of the encrypted slice is an I slice. Further, when the slice type of the encrypted slice is a P slice or a B slice, the substitute slice replacing unit 14 generates each slice with a skipped macroblock, for example.

  Here, with reference to FIG. 3 (refer to FIG. 1 as appropriate), the data structure of the slice generated by the substitute slice replacement means 14 will be specifically described. FIG. 3 is a diagram illustrating a data structure of a slice, where (a) illustrates an I slice, (b) illustrates a P slice, and (c) illustrates a B slice data structure.

When generating the I slice, the substitute slice replacing unit 14 generates a slice by configuring a macro block as shown in FIG. In FIG. 3A, “I_16 × 16_2_0_0”, “I_16 × 16_1_0_0”, and “I_16 × 16_0_0_0” The type name of the macroblock in H.264 / AVC is shown. “Intra_chroma_pred_mode”, “mb_qp_delta”, and “coeff_token” indicate macroblock parameters, respectively.
Thus, it is possible to generate a slice in which the display pattern shows one color (here, gray) with the minimum data amount.

Further, when generating the P slice or the B slice, the substitute slice replacing unit 14 generates the P slice by configuring the macro block as shown in FIG. 3B, and as shown in FIG. A B slice is generated by configuring a macroblock. In FIG. 3B and FIG. 3C, “P_Skip” and “B_Skip” The model name of the skipped macroblock in H.264 / AVC is shown. Further, “mb_skip_run” indicates a parameter indicating how many skipped macroblocks are continuously arranged.
Returning to FIG. 1, the description of the configuration of the content decrypting apparatus 1 will be continued.

  The encrypted slice decryption unit 15 decrypts (encryption / decryption) the encrypted slice determined by the license determination unit 13 as the decryption target slice based on the license (encryption / decryption key) stored in the license storage unit 11. To do. The encrypted slice decrypting means 15 decrypts the encrypted slice by the number of times of encryption when there are a plurality of times of encryption described in the license. As a result, the original slice is decoded. The decoded slice is output to the code decoding means 16.

  The encoding / decrypting means 16 includes the slice determined as the non-encrypted slice by the encrypted slice determining means 13a, the substitute slice replaced by the substitute slice replacing means 14, and the slice decoded by the encrypted slice decrypting means 15. Code decoding is performed. The code decoding means 16 outputs reproduction content (video signal) which is display data that can be viewed by decoding the encoded data of each slice. The code decoding means 16 is, for example, H.264. This is a general decoder in H.264 / AVC.

Here, the encoding / decoding means 16 decodes the non-encrypted slice output from the license determination means 13 and the slice whose encryption has been decrypted by the encrypted slice decoding means 15, thereby enabling display data that can be viewed. To decrypt.
Also, the code decoding means 16 decodes the substitute pattern output from the substitute slice replacement means 14 to decode a specific pattern (here, a gray-colored display pattern) as display data.

As described above, the content decryption apparatus 1 can decrypt the encrypted content encrypted in units of slices based on the license.
At this time, if the content decrypting apparatus 1 has not acquired a license, the content of the encrypted slice is the same because the substitute slice is encoded / decoded instead of the encrypted slice without decoding / decoding the encrypted slice. Can be presented in the same pattern (same color). In addition, since the content decrypting apparatus 1 decodes the substitute slice instead of the encrypted slice, the content decrypting apparatus 1 decodes a code that is not defined by the encoding method included in the encrypted slice in the encoding / decoding unit (decoder) 16. There is no. As a result, malfunction of the code decoding means (decoder) 16 can be prevented.

  The content decrypting apparatus 1 can be realized by operating a general computer with a program that functions as each of the above-described units. This program (content decryption program) can be distributed via a communication line, or can be written on a recording medium such as a CD-ROM for distribution.

[Operation of content decryption device]
Next, the operation of the content decryption apparatus according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a flowchart showing the operation of the content decryption apparatus according to the embodiment of the present invention. Here, it is assumed that the license is stored in the license storage unit 11 in advance.

(Slice extraction step)
First, the content decryption apparatus 1 extracts a slice for each picture from the input encrypted content by the slice extraction unit 12 (step S1).

(Encryption slice judgment step)
Then, the content decrypting apparatus 1 determines that the slice extracted in step S1 is based on the license (encryption target information) stored in the license storage unit 11 by the encrypted slice determination unit 13a of the license determination unit 13. It is determined whether or not the slice is an encrypted slice (encrypted slice) (step S2).
Here, if the slice extracted in step S1 is not an encrypted slice, that is, if the slice is a non-encrypted slice (No in step S2), the content decrypting apparatus 1 advances the operation to step S6.

(Decoding slice judgment step)
On the other hand, when the slice extracted in step S1 is an encrypted slice (Yes in step S2), the content decryption apparatus 1 uses the decryption slice determination unit 13b of the license determination unit 13 to perform decryption corresponding to the encrypted slice. It is determined whether or not the encrypted slice is a decryption target slice based on whether or not the key is stored as a license in the license storage unit 11 (step S3).

(Encrypted slice decryption step)
Here, when the encryption / decryption key corresponding to the encrypted slice is stored in the license storage unit 11, that is, when the encrypted slice is the decryption target slice (Yes in step S3), the content decrypting apparatus 1 The encrypted slice decryption unit 15 decrypts (encrypts and decrypts) the encrypted slice using the license (encryption / decryption key) stored in the license storage unit 11 (step S4). Then, the operation proceeds to step S6.

(Substitute slice replacement step)
On the other hand, if the encryption / decryption key corresponding to the encrypted slice is not stored in the license storage unit 11, that is, if the encrypted slice is a non-decryption target slice (No in step S3), the content decrypting apparatus 1 uses the substitute The slice replacement unit 14 generates a slice (substitute slice) including a predetermined specific pattern encoded by the same encoding method as that of the non-encrypted slice, and replaces the encrypted slice with the substitute slice (step S5). ).

(Code decoding step)
Then, the content decrypting apparatus 1 performs the processing for the slice determined as the non-encrypted slice in step S2, the slice decrypted from the encrypted slice in step S4, or the encrypted slice in step S5 by the code decrypting unit 16. The substituted substitute slices are code-decoded in the order of the slices (step S6).
Although illustration is omitted, after this step S6, when there is a slice, the content decrypting apparatus 1 returns to step S1 and continues the operation.
Note that the operations of step S4 (encrypted slice decryption step) and step S5 (substitute slice replacement step) may be performed in a different order or may be performed in parallel.

  With the above operation, the content decrypting apparatus 1 can decrypt the encrypted content partially encrypted in units of slices based on the license. If the license has not been acquired, or even if the license has been acquired, if the encryption key (encryption / decryption key) for each slice has not been acquired, the content decryption device 1 can decrypt the encrypted content. Can be reproduced as partially degraded video.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this embodiment. Here, the encoding method is H.264. Although an example of H.264 / AVC has been described, the present invention can be applied to an encoding method having a slice layer as a data structure, such as MPEG-2.

Here, the number of encryptions is described in the license, but the number of encryptions may be added to the encrypted slice with a predetermined data length. For example, as shown in FIG. 8, immediately after the slice data, for example, the number of times the slice data SD is encrypted with a data length of 1 byte (encryption count CNT) is added. At this time, for example, “1” is set in the first bit of the encryption count so that the encryption count CNT does not become a prohibition code such as a start code.
Then, the encrypted slice decrypting means 15 decrypts the encrypted slice with the encryption / decryption key by the number of times of encryption added to the encrypted slice.

At this time, the license can have a simple configuration as shown in FIG. 9, for example. 9, in the region _{L 1,} and identification information of the decryption key (Key Canada), describe the cipher key data (Value). Further, in the region _{L 2,} slice type of the slice to be encrypted and (Type), a slice number (Num), describe the identification information decryption key (Key Canada) for that slice.
Thus, by adding the number of times of encryption to the slice to be encrypted, it is not necessary to describe the license for each slice, and the license file can be made smaller.

Here, in order to specify the encryption slice, the encryption target information is included in the license. However, the encryption target information may be added to the encryption slice itself.
In this case, as long as the encryption target information is information that can distinguish whether the slice is an encryption slice or a non-encryption slice, the content is not particularly limited.

  For example, in the encrypted slice, a code (encryption target information) other than the type of the NAL unit, for example, Reserved (nal_unit_type = 23) is set in the header of the NAL unit. When the encrypted slice determination unit 13a recognizes that the NAL unit type of the slice extracted by the slice extraction unit 12 is Reserved, the content decryption apparatus 1 encrypts the NAL unit (encrypted slice). Judge as a slice. In this case, the license storage unit 11 does not need to store the encryption target information as a license.

It is a functional block diagram which shows the structure of the content decoding apparatus which concerns on embodiment of this invention. It is a data structure figure which shows the example of the content of a license file. It is a figure which shows the data structure of a slice, (a) is I slice, (b) is P slice, (c) has shown the data structure of B slice, respectively. It is a flowchart which shows operation | movement of the content decoding apparatus which concerns on embodiment of this invention. H. 2 is a data structure diagram showing a structure of a slice layer in H.264 / AVC. It is a data structure figure which shows the structure of a slice layer at the time of abstracting a slice with a network abstraction layer. It is a figure which shows the example which displayed the content of the image | video, Comprising: (a) is an original image, (b) is a case where the original image is partially encrypted in units of slices, without decrypting the encrypted slice The displayed video, (c), shows the video obtained by decrypting the encrypted slice when the original video is partially encrypted in units of slices. It is a data structure figure which shows the structure which added the frequency | count of encryption to the data of the slice. It is a data structure figure which shows the example of the content of the other license file.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Content decryption apparatus 11 License memory | storage means 12 Slice extraction means 13 License determination means 13a Encrypted slice determination means 13b Decryption slice determination means 14 Substitute slice replacement means 15 Encrypted slice decryption means 16 Encoding decryption means

Claims (8)

A content decrypting device for decrypting encrypted content generated by partially encrypting a plurality of slices, which are data forming a slice layer in a data structure of digital content, for each slice,
License storage means for storing a license including an encryption / decryption key for decrypting an encrypted slice which is the encrypted slice;
Slice extracting means for sequentially extracting the slices from the encrypted content;
Whether the slice extracted by the slice extraction unit is an encrypted slice or an unencrypted slice based on encryption target information indicating whether a slice in the encrypted content is an encrypted slice Encrypted slice determining means for determining
By determining whether or not an encryption / decryption key corresponding to a slice determined to be an encrypted slice by the encrypted slice determination unit is included in the license, whether the encrypted slice is a decryption target slice or not decrypted Decoding slice determination means for determining whether the slice is a target slice;
Encrypted slice decryption means for decrypting a slice determined to be a decryption target slice by the decryption slice determination means, using the encryption / decryption key;
Substitute slice replacement means for replacing a slice determined as a non-decoding target slice by the decoded slice determination means with a substitute slice including a predetermined specific pattern encoded by the same encoding method as the non-encrypted slice; ,
Coding / decoding means for coding / decoding the substitute slice replaced by the substitute slice replacing means, the slice determined as an unencrypted slice by the encrypted slice determining means, and the slice decoded by the encrypted slice decoding means When,
A content decryption apparatus comprising:   The content decryption apparatus according to claim 1, wherein the encryption target information is included in the license.   The content decryption apparatus according to claim 1, wherein the encryption target information is added to the encrypted slice. The digital content is data encoded in units of macroblocks by a motion compensated predictive encoding method,
The substitute slice replacement means generates an I slice as encoded data with a macroblock indicating a specific color, and skips a P slice and a B slice as encoded data indicating a difference from a reference picture. The content decrypting apparatus according to any one of claims 1 to 3, wherein the content decrypting apparatus generates the data and replaces the encrypted slice. The license includes an encryption count indicating the number of times the slice has been encrypted,
The encrypted slice decryption means comprises:
5. The content decryption apparatus according to claim 1, wherein the decryption target slice is decrypted by the encryption / decryption key by the number of times of encryption. In the encrypted slice, the number of times of encryption represented by a predetermined data length is added,
The encrypted slice decryption means comprises:
5. The content decryption apparatus according to claim 1, wherein the decryption target slice is decrypted by the encryption / decryption key by the number of times of encryption. A content decrypting method in a content decrypting apparatus for decrypting encrypted content generated by partially encrypting a plurality of slices, which are data forming a slice layer in a data structure of digital content, for each slice,
In a content decrypting apparatus comprising license storage means for storing a license including an encryption / decryption key for decrypting an encrypted slice which is the encrypted slice,
A slice extraction step for sequentially extracting the slices from the encrypted content;
Whether the slice extracted in the slice extraction step is an encrypted slice or an unencrypted slice based on encryption target information indicating whether a slice in the encrypted content is an encrypted slice An encrypted slice determination step for determining
By determining whether or not an encryption / decryption key corresponding to the slice determined to be an encrypted slice in this encrypted slice determination step is included in the license, whether the encrypted slice is a decryption target slice or not decrypted A decoding slice determination step for determining whether the slice is a target slice;
An encrypted slice decryption step for decrypting the slice determined to be a decryption target slice in the decryption slice determination step with the encryption / decryption key;
A substitute slice replacement step of replacing the slice determined as the non-decoding target slice in the decoding slice determination step with a substitute slice including a predetermined specific pattern encoded by the same encoding method as the non-encrypted slice; and ,
Code decoding step for decoding and decoding the substitute slice replaced in the substitute slice replacement step, the slice determined as the non-encrypted slice in the encrypted slice determination step, and the slice decoded in the encrypted slice decoding step When,
A content decryption method comprising: In order to decrypt encrypted content generated by partially encrypting a plurality of slices, which are data forming a slice layer in a data structure of digital content, for each of the slices, the encrypted slices A computer of a content decrypting apparatus including a license storage unit that stores a license including an encryption / decryption key for decrypting an encrypted slice ,
Slice extraction means for sequentially extracting the slices from the encrypted content;
Whether the slice extracted by the slice extraction unit is an encrypted slice or an unencrypted slice based on encryption target information indicating whether a slice in the encrypted content is an encrypted slice Encrypted slice determination means for determining
By determining whether or not an encryption / decryption key corresponding to a slice determined to be an encrypted slice by the encrypted slice determination unit is included in the license, whether the encrypted slice is a decryption target slice or not decrypted Decoding slice determination means for determining whether it is a target slice,
An encrypted slice decryption means for decrypting a slice determined by the decryption slice determination means with the encryption / decryption key;
Substitute slice replacement means for replacing the slice determined as the non-decoding target slice by the decoded slice determination means with a substitute slice including a predetermined specific pattern encoded by the same encoding method as the non-encrypted slice,
Coding / decoding means for coding / decoding the substitute slice replaced by the substitute slice replacing means, the slice determined as an unencrypted slice by the encrypted slice determining means, and the slice decoded by the encrypted slice decoding means ,
A content decryption program that is allowed to function as:

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