JPH11225140A - Data encryption device, decoder and its program recoding medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decode encrypted data by an access to an optional point on a time base of encrypted consecutive medium data in the output feedback OFB mode of a stream encryption. SOLUTION: A random number generator 11 generates a random number based on contents in a register 12 at an encryption side, the random number is fed back to the register to generate a succeeding random number, the random number series and input data are exclusively 0Red to obtain encrypted data, contents of the register 12 are extracted periodically and inserted to the encrypted data at a synthesizer 15 and insert identification information is inserted to the encrypted data without encrypting the information just before the insertion of the contents of the register 12 (Figure B). An extraction device 22 detects the inserted identification information from the received encrypted data at a decoder side (Figure C) and extracts the register contents, sets the contents to a register 23 to start generation of a random number by a random number generator 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a device for encrypting continuous information such as audio and moving images in a randomly accessible form, a decryption device and a program recording medium.

[0002]

2. Description of the Related Art Generally, an OFB (Output Feedback) mode of stream encryption is used for encrypting video data and the like. In this method, a random number is generated by a random number generator based on the value of a register, an exclusive OR of the random number sequence and plain text is obtained and encrypted, and the random number sequence is fed back to the register. Similarly, on the decryption side, a random number is generated, exclusive-ORed with the ciphertext, and decrypted (see, for example, Hideki Imai, “Cryptography”, pp. 64-70, published by the Japan Standards Association).

However, since the OFB mode requires synchronization between the encryption side and the decryption side, the data must be decrypted from the beginning. Stream Cipher CFB (Cipher
In the (Feedback) mode and the block cipher, synchronization between the encryption side and the decryption side is unnecessary, and decryption can be started from an arbitrary point of the encrypted data. However, these encryption modes have a disadvantage that the decryption error is increased. Furthermore, the order in which the keys are applied in decrypting data encrypted with a plurality of keys always depends on the order in which the keys are applied during encryption. Since the OFB mode performs encryption by addition to a random number sequence, encryption and decryption using a plurality of keys are independent of the order in which the keys are applied.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a random number sequence which enables random access to an arbitrary portion of continuous media data such as voice and moving image, starts decryption from that portion and enables reproduction. An object of the present invention is to provide an encryption device, a decryption device, and a program recording medium for enabling data conversion.

[0005]

The encryption device of the present invention has means for setting a synchronization point in data and inserting a random number output of a random number generator in the encrypted data at the synchronization point. The main feature of the decryption device is that it has means for extracting the random number output at the synchronization point inserted in the encrypted data and inputting the extracted random number to the random number generator. Action digitized audio data, continuous media data such as image data is fixed data format based on the coding rule is defined. Some of these formats include fields (hereinafter referred to as non-information fields) such as user fields, comment fields, and application fields for storing data not directly related to reproduced audio information and image information.

[0006] Only continuous media data stored in a format having a user field or the like is encrypted. That is, user fields, comment fields, and application fields not directly related to audio information and image information are not encrypted. Encrypting continuous media data can create fields whose data does not change (do not affect). In this way, even in the encrypted data of the continuous media data, the value of the data written in the non-encrypted field can be correctly read.

Access to continuous media is often performed using the time axis as an index. For example,
For example, how many seconds or frame from the start to play. Here, several synchronization points are defined in the time axis direction, and the value of the feedback register of the random number generator at the time of encrypting the synchronization point is recorded in a predetermined portion in the non-encrypted field. By using the value of the feedback register thus set as an initial value for random number generation, the same random number that has been continuously generated from the beginning can be generated for the synchronization point and thereafter.

The initial value of random number generation is I, and the conversion result of value v by the encryption algorithm for random number generation is E (v), E
(E (v)) = E ² (v), E (E ⁿ (v)) = E ^{n + 1}
Let us write (v). If the value used to convert the first data to be encrypted in the data after the synchronization point is within E ^m (v), E ^m (v)
Is recorded in the encrypted data at this synchronization point.

The present invention is not limited to the case where the register value is recorded in the non-information field, and a pair of the register value and the non-encrypted data indicating this immediately before the register value may be inserted into the encrypted data. Alternatively, a register value is inserted for every predetermined data amount or every time from the start on the encryption sending side, and a register value is taken out for every predetermined data amount or every time on the decryption side. The point is that the register value can be extracted on the decoding side.

In the OFB mode of the stream cipher, the next part of the random number sequence is generated by using the output of the cryptographic function as a part of the random number sequence and feeding the output back to the input of the cryptographic function. Here, at the synchronization point,
Since the value of the random number for encrypting the part after that can be read, the random number after this value can be generated without referring to the data before that.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1A shows an embodiment of the present invention, which is an apparatus for encrypting moving image data. The random number generator 11 converts the data in the register 12 to generate a random number, and feeds back the generated random number to the register 12 again to be used for the next random number generation. A data-formatted encrypted data from the information source 10 is supplied to a random number generator 11 through an input terminal 13.
Is converted by the exclusive OR circuit 13 with the output of.

For example, the writing timing of the value of the register 12 is set from the information source 10 to the synthesizer 15 at a fixed frame interval of a moving image, and the synthesizer 15 adds the value of the register 12 to the encrypted data according to this timing. .
At this time, in order to enable the decryption side to detect that the register value has been inserted, as shown in FIG. 1B, unencrypted insertion identification information indicating the insertion of the register value is also simultaneously inserted immediately before the register value. I do. Alternatively, it is determined in advance that the register value is to be inserted at the time of transmitting the cipher and at what byte the register value is to be inserted, so that the inserted register value can be detected on the decryption side.

FIG. 2A shows an apparatus obtained by adding a function of selecting an encrypted part to the encryption apparatus shown in FIG. 1A. Parts corresponding to those in FIG. 1A are denoted by the same reference numerals. A position designation generator 20 generates a signal for position designation, and a position designation input terminal 1
6 to the random number generator 11. That is, information source 1
0, for example, based on the data format information about the currently processed part in the moving image data, the frame number of the moving image, the elapsed time from the start of the data, and the like, determine whether to actually convert the currently processed data. I do.
The position designation signal is input from the terminal 16 to the random number generator 11. As a result, the random number generator 1
1 outputs a random number when the currently input moving image data is data to be converted, and outputs “0” when it indicates that data is not to be converted. The moving image data is converted by addition with the output of the random number generator 11.

1A, the encrypted data and the value of the register 12 are supplied to the synthesizer 15, and the value of the register 12 is added to the encrypted data by the synthesizer 15 at a predetermined timing. Therefore, even if the data encrypted in this way is a part or even from a certain designated point, the value of the register 12 can be correctly decrypted on the decryption side by inserting the register value as described above. .

In FIG. 3A, the data format of the data to be encrypted from the input terminal 13 is analyzed by the separation unit 17, and the data cannot be a part that can be encrypted, ie, non-information fields such as frame information and format information. The part to be encrypted is supplied to the exclusive OR circuit 14, and the part that cannot be encrypted is directly supplied to the synthesizer 15. In this case, register 12
Can be inserted into the non-information field, so that the inserted register value can be easily detected on the decoding side. Others are the same as those in FIG. 1A. Also in this case, a position designation signal for determining whether or not to perform conversion from the terminal 16 may be input to the random number generator 11 as shown by the broken line in FIG. 2A.

FIG. 4A is a schematic diagram of the apparatus of FIG.
5, a converter 18 for converting the value of the register 12 added to the encrypted data is added. Since the value of the register 12 is a part of a random number sequence used for data encryption, if this value is added to the encrypted data as it is,
Some ciphers can be decrypted using this data. In order to prevent this, when adding to the encrypted data, the converter 1
In step 8, conversion is first performed by a cryptographic function or the like. This makes it impossible to decrypt only the data added to the encrypted data. In order to perform decryption, an encryption key for converting the register value is required. However, it is the same as the description so far that the decryption side can detect the converted register value by inserting unencrypted data indicating the insertion immediately before the insertion.

FIG. 2A is similar to the converter 18 in FIG.
A, by adding to the apparatus shown in FIG. 3A, decoding using a part of the random number sequence can be disabled. An embodiment of a decryption device corresponding to the above-described encryption device will be described below. FIG. 1C is a decoding device corresponding to the device of FIG. 1A. The value of the register 12 inserted at the time of encryption is detected from the encrypted data from the input terminal 21 by the extractor 22 and stored in the register 23 of the decryption device. In this process, a flag described later is turned off as shown in FIG.
The register value is detected based on the non-encrypted insertion identification information indicating the insertion, that is, the insertion identification information is sequentially compared with the input encrypted data sequence (S2). When a match is detected, a predetermined number of bits immediately after the match is extracted as a register value (S3), or the processing can be performed from a position determined by a predetermined data amount value from the start of encryption reception. The random number generator 24 starts generating random numbers based on the value of the register 23 (S
5). Further, the extractor 22 has a flag indicating that a value has been stored in the register 23, and turns ON the flag when the value is stored in the register 23 (S4). Flag is ON
, The value of the register 12 added to the encrypted data is not extracted (S1). When the input of the moving image data to the decoding device is interrupted (S6), the flag is turned off (S6).
7). In other words, it is up to the user to determine from which timing the decoding side should start decoding, and the transmitting side can use any of the register values inserted at regular intervals.

The value stored in the register 23 from the extractor 22 is the value in the register 12 at the time when the data currently being decrypted in the encryption device is encrypted. Therefore, the random number generator 24 of the decryption device thereafter generates the same random number as the random number generated by the encryption device. That is,
After the value is stored in the register 23 from the extractor 22,
Decoding is performed correctly.

Further, the extractor 22 once stores the register 23
When the subsequent moving image data is continuously accessed, there is no need to extract the value of the register 12 added to the encrypted data again. When the processing target is changed to data at another position in the moving image data, that is, once stored encrypted data, or data in the database,
For example, in the case of decrypting the data after 7 minutes after the lapse of 3 minutes, or re-decoding the data before decryption from the one currently being decrypted, the random number generation is again defined as the time of encryption. Since it is necessary to synchronize, register 1 in the encrypted data
2 is extracted.

FIG. 2B shows an example of a decoding apparatus corresponding to FIG. 2A. Parts corresponding to those in FIG. 1C are denoted by the same reference numerals. In this example, a signal similar to the position designation signal from terminal 16 in FIG. 26 to a random number generator 24. Others are the same as FIG. 1B. FIG. 3B shows a decryption device corresponding to the encryption device of FIG. 3A by attaching the same reference numerals to parts corresponding to FIG. 1C. In this case, the input signal from the terminal 21 is separated by the separator / extractor 27 into encrypted data and unencrypted data, and should be stored in the register 23 from a predetermined location in the non-information field. The exclusive OR circuit 25 extracts only the encrypted data from which the value has been extracted.
The non-encrypted data that has been supplied and separated is combined by the combiner 28 with the output of the exclusive OR circuit 25 and output.
As shown by a broken line in FIG. 3B, a position designation signal may be input to the random number generator 24 from the terminal 26.

FIG. 4B shows a decryption device corresponding to the encryption device shown in FIG. 4A. For the decryption device shown in FIG. 1B, the value of the register 12 is obtained from the data extracted from the encrypted data by the extractor 22. A converter 29 is added. The converter 29 performs the inverse conversion of the conversion of the value of the register 12 performed by the converter 18 in the encryption device shown in FIG. 4A. When an encryption device is used as the converter 18, the converter 29 is a corresponding decryption device, and a decryption key corresponding to the encryption key used in the converter 18 of FIG. It works.

When a device similar to the converter 18 is added to the encryption device shown in FIGS. 2A and 3A, FIGS. 2B and 3B
The converter 29 may be added to the decoding device shown in FIG. FIG. 5A
FIG. 1 shows an example of an encryption device for encrypting a plurality of keys. This device comprises a register 12i and a random number generator 11i (i
= 1, 2, ..., n), the outputs from all the random number generators 11i are added by the exclusive OR circuit 19, and this and the data from the input terminal 13 are exclusive. In the logical OR circuit 14, encryption is performed by addition. The value of each register 12i is added to the encrypted data by the synthesizer 15.

FIG. 5B shows a decryption device corresponding to the encryption device of FIG. 5A. The extractor 22 reads the value of each register 12i from the encrypted data input from the terminal 21 and stores it in the corresponding register 23i. Each output of each random number generator 24i is added by the exclusive OR circuit 31 and supplied to the exclusive OR circuit 25 to decrypt the input encrypted data. FIG. 5A
5A and 5B, the converters 18 and 29 for disturbing the register values in FIGS.
8i and 29i can be added as indicated by solid lines.

FIG. 6A shows an example of an apparatus for performing DCT (discrete cosine transform) conversion, variable length conversion, and encryption of video data. Digital video data from input terminal 13 is D
The sign of the DCT (frequency domain) coefficient quantized by the CT / quantizer 31 and the value of the category by quantization (in this example, a value indicating how many bits the absolute value of the coefficient value can be expressed, for example) are output. Is done. The category value is the variable length encoder 3
2 converts it into a variable length code. The sign of the coefficient is input to the adder 14 which is the output of the random number generator 11. The combiner 15 combines the output of the adder 14, the variable-length code, and the register value, and outputs encrypted, quantized DCT encoded video data.

FIG. 6B shows a decryption device corresponding to the encryption device shown in FIG. 6A. The separator / extractor 27 stores the
The code of the encrypted quantized DCT coefficient and the variable length code are separated, and the register value is stored in the register 23. The output of the random number generator 24 is added to the sign of the encrypted quantized DCT coefficient, and the sign of the coefficient is decoded. The variable length decoder 34 decodes the category from the separated variable length code,
The category and the code of the decoded coefficient are input to the inverse DCT / inverse quantum 35, and the video signal is decoded. In FIG. 6A, the DCT coefficient value quantized by the DCT / quantizer 31 and the category value by quantization can be used as an output encoding method. In this case, the coefficient value is transmitted to the exclusive OR circuit 14. It is supplied and encrypted, and the category value is converted by the variable length encoder 32 into a variable length code.

On the decoding side, in FIG.
7, a variable length decoder 34 is juxtaposed, the category value is decoded, and the number of bits for one code is separated from the encrypted data in accordance with the category value. , The bit string of the coefficient value is decoded. The decoded category value is sent to the inverse DCT / inverse quantizer. Both the encryption device and the decryption device described above,
It can also be configured so that it can be operated by decoding and executing a program.

[0027]

As described above, according to the present invention, in the OFB mode of the stream cipher, the encryption device can
By periodically inserting register values into encrypted data, it is possible to decrypt continuous media data, such as encrypted video and audio, from any point on the time axis without having to constantly synchronize with the decryption device. Become.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a functional configuration of an embodiment of an encryption device according to the present invention; FIG. 1B is a diagram illustrating an example of encrypted data into which a register value is inserted; and C is a diagram of the present invention corresponding to FIG. It is a figure showing functional composition of an example of a decoding device.

FIG. 2A is a diagram showing a functional configuration of another embodiment of the encryption device of the present invention, and FIG. 2B is a diagram showing a functional configuration of the decryption device of the present invention corresponding to FIG. 2A;

FIG. 3A is a diagram showing a functional configuration of still another embodiment of the encryption device of the present invention, and FIG. 3B is a diagram showing a functional configuration of the decryption device of the present invention corresponding to FIG. 3A;

4A is a diagram showing a functional configuration of still another embodiment of the encryption device of the present invention, and FIG. 4B is a diagram showing a functional configuration of the decryption device of the present invention corresponding to FIG. 4A.

5A is a diagram showing a functional configuration of still another embodiment of the encryption device of the present invention, and FIG. 5B is a diagram showing a functional configuration of the decryption device of the present invention corresponding to FIG. 5A;

6A is a diagram showing a functional configuration of still another embodiment of the encryption device of the present invention, and FIG. 6B is a diagram showing a functional configuration of the decryption device of the present invention corresponding to FIG. 6A.

FIG. 7 is a flowchart showing a processing procedure for register value extraction and setting in the embodiment of the decoding device of the present invention.

Claims (26)

[Claims] 1. A register value in a register is input to random number generating means, a random number sequence is generated, and the random number sequence is fed back to the register and used for generating a next random number sequence. A cryptographic device that outputs exclusive-OR with the arithmetic means and outputs encrypted data, characterized by comprising a synthesizing means for periodically extracting a register value in the register and inserting the register value into the encrypted data. Cryptographic device. 2. The encryption apparatus according to claim 1, wherein non-encrypted insertion identification information indicating a place where the register value is inserted is included in the encrypted data. 3. The input data is data-formatted, separated into a data field in the data format and a non-information field not directly related to data, and supplies the data field to the arithmetic means. 2. The encryption apparatus according to claim 1, further comprising a separating unit that supplies the non-information field to the synthesizing unit, wherein the synthesizing unit is a unit that stores the register value in the non-information field. 4. The encryption device according to claim 1, further comprising a conversion unit that converts the register value into data and supplies the data to the synthesizing unit. 5. A plurality of combinations of the register and random number generating means for receiving the register value to generate a random number sequence, and feeding the random number sequence back to the register for generating the next random number sequence, Means are provided for taking the exclusive OR of each of the random number sequences from each of the combinations as the random number sequence to the arithmetic means. The synthesizing means converts a register value in each register of each of the combinations into the encrypted data. 5. The encryption device according to claim 1, wherein the encryption device is an insertion unit. 6. A position designation signal indicating a part to be encrypted in the input data is input to the random number generation means, and the random number generation means generates a random number when the position specification signal is input, The encryption device according to any one of claims 1 to 5, wherein the device is configured to output 0 when not input. 7. A register value in a register is input to a random number generating means to generate a random number sequence, and the random number sequence is fed back to the register and used for generating a next random number sequence. In a decryption device which outputs exclusive OR with encrypted data by arithmetic means and outputs decrypted data, a non-encrypted register value periodically inserted from the input encrypted data is extracted and set in the register. A decoding device for starting the operation of the random number generating means. 8. The apparatus according to claim 1, wherein said extracting means detects unencrypted insertion identification information in the input encrypted data, and extracts a predetermined data amount immediately thereafter as the register value. 8. The decoding device according to 7. 9. The input encrypted data is data-formatted, and non-information fields that are not directly related to data, such as user fields, are not encrypted. And a means for separating the data field and the data field to the arithmetic means, and a means for extracting data at a predetermined position in the non-information field as the register value. 8. The decoding apparatus according to claim 7, further comprising a synthesizing means for synthesizing the decoded data and the non-information field in a predetermined data format. 10. The decoding device according to claim 7, further comprising a conversion unit that performs inverse data conversion of the register value extracted by the extraction unit and sets the data in the register. . 11. A plurality of combinations of the register and random number generation means for receiving the register value to generate a random number sequence, and feeding the random number sequence back to the register for generating the next random number sequence, Means are provided for taking the exclusive OR of each random number sequence from each of the combinations as the random number sequence to the arithmetic means, and extracting means for extracting the plurality of register values in the register of the combination. 11. The decoding device according to claim 7, wherein the decoding device is a means for setting each of the corresponding items. 12. A flag means which is turned on when the register value is set in the register, and which is turned off when the input encrypted data is cut off, and an operation of the extracting means when the flag means is on. The decoding device according to claim 7, further comprising a prohibition unit. 13. A position designation signal indicating a part to be decrypted in the input encrypted data is input to the random number generation means, and the random number generation means generates a random number when the position specification signal is input. 13. The decoding device according to claim 7, wherein the decoding device is configured to output 0 when no input has been made. 14. A method of generating a random number sequence by converting a register value in a register in a random number generation process, and feeding the random number sequence back to the register for use in generating a next random number sequence. A storage medium storing a program for operating a cryptographic device that outputs cryptographic data by calculating an exclusive OR of the cryptographic data, wherein the program periodically extracts a register value from the register, A computer-readable recording medium having a synthesizing step of inserting it into the medium. 15. The recording medium according to claim 14, wherein said synthesizing step includes a step of inserting non-encrypted insertion identification information indicating an insertion point immediately before said register value. 16. The method according to claim 16, wherein the input data is data-formatted, and the input data is separated into a data field in the data format and a non-information field not directly related to data. 15. The recording medium according to claim 14, further comprising a step of supplying the register value to the operation step, and wherein the combining step is a step of storing the register value in the separated non-information field. 17. The encryption device according to claim 14, wherein a conversion step of converting the register value into data is performed prior to the synthesizing step. 18. A combination of the register and a random number generation step of receiving the register value to generate a random number sequence and returning the random number sequence to the register for generating a next random number sequence, The above program causes the exclusive OR of each of the random number sequences from each of the combinations to be taken as the random number sequence in the above-described arithmetic process, and the synthesizing process sets the register value in each register of each of the combinations to 18. The recording medium according to claim 14, wherein the recording medium is inserted into encrypted data. 19. The random number generation step is a step of generating a random number based on a position designation signal indicating a part to be encrypted in the input data, and outputting 0 if the position designation signal is absent. 19. The method according to claim 14, wherein:
The recording medium according to any one of the above. 20. A register value in a register is converted in a random number generation process to generate a random number sequence, and the random number sequence is fed back to the register and used for generating a next random number sequence. What is claimed is: 1. A recording medium storing a program for operating a decryption device that outputs decrypted data by calculating exclusive OR with encrypted data in an arithmetic process, wherein the program is a non-transitory computer that periodically inserts from the input encrypted data. A computer-readable recording medium comprising: an extraction step of extracting an encrypted register value; and a setting start step of setting the extracted register value in the register and starting execution of the random number generation step. 21. The extracting step includes a step of detecting non-encrypted insertion identification information in the input encrypted data, and a step of extracting a predetermined data amount immediately after the detected insertion identification information as the register value. 21. The recording medium according to claim 20, comprising: 22. The input encrypted data is data-formatted, and non-information fields not directly related to data, such as user fields, are not encrypted, and the extracting process detects the non-information fields. Separating the non-information field and the data field, and using the data field as one of the inputs of the operation process, and extracting data at a predetermined position in the non-information field as the register value. 21. The program according to claim 20, further comprising a step of combining the decoded data obtained in the operation step and the separated non-information field in a predetermined data format. Recording medium. 23. The recording medium according to claim 20, wherein, prior to the setting start step, a conversion step of performing a data reverse conversion on the register value extracted in the extraction step is executed. 24. A combination of the register and a random number generation step of receiving the register value to generate a random number sequence, and returning the random number sequence to the register for generating the next random number sequence, An exclusive OR of each of the random number sequences from each of the combinations described above has a process of forming the random number sequence as one input of the arithmetic process, and the setting start process includes combining the extracted plurality of register values with the combination of the extracted register values. 24. The recording medium according to claim 20, wherein the setting is performed for each of the corresponding ones of the registers. 25. A process for setting a flag in the register when the register value is set to ON, a process for turning off the flag when the input encrypted data is cut off, 25. The recording medium according to claim 20, further comprising a step of prohibiting execution. 26. The random number generating step, wherein a random number is generated by a position designation signal indicating a part to be decrypted in the input encrypted data, and 0 is output without the position designation signal. The recording medium according to any one of claims 20 to 25.