JP2004048256A - Encryption method, encryption system, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an encryption method, an encryption system, and a storage medium capable of reducing the processing time of encryption / decryption so as to enhance the versatility of protection strength without the need for exclusive hardware. <P>SOLUTION: The encryption system is configured such that information to be encrypted is format-converted, thereafter an error correction code is generated and part bits of the information after the format conversion are revised to generate encrypted information. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an encryption method for encrypting digital information, an encryption system, and a storage medium for storing encrypted digital information.
[0002]
[Prior art]
Conventionally, in order to perform high-speed encryption / decryption of digital information, it is necessary to perform complicated and enormous data processing, depending on the encryption algorithm employed. Needed. In addition, when dedicated hardware is used, the configuration is fixed, so the protection strength for protecting the encrypted digital information from unauthorized decryption depends on the encryption algorithm used, and the protection strength can be flexibly adjusted by the system. It is difficult to optimize the variable according to the required specifications.
[0003]
On the other hand, when digital information is encrypted by software in a device incorporating a microprocessor, the processing content is complicated and enormous, so that the program for processing must be large. Further, since the processing is performed by software, it takes an extremely long time as compared with the case of processing by dedicated hardware, which is not practical.
[0004]
[Problems to be solved by the invention]
As described above, in the conventional encryption / decryption of digital information, when dedicated hardware is used, the configuration becomes large, the cost increases, and it is difficult to easily introduce the configuration. In addition, the protection strength cannot be easily and flexibly changed, which causes a problem that it is difficult to optimize the protection strength.
[0005]
On the other hand, when the processing is performed by software, the processing program becomes enormous, and it takes an extremely long processing time to cause an unrealistic problem.
[0006]
Therefore, the present invention has been made in view of the above, and an object of the present invention is to reduce the processing time of encryption / decryption without using dedicated hardware and reduce the variability of protection strength. It is to provide an enhanced encryption method, an encryption system and a storage medium.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a first means for solving the problem includes a first step of converting the format of the information to be encrypted, and an error in the information obtained by the format conversion of the first step. A second step of generating an error correction code for detecting and correcting a bit error in the detection and correction function, and a part of information obtained by the format conversion of the first step within a correctable range of the error detection and correction function. A third step in which bits are changed, the changed information is used as encryption information, and decryption information when decrypting and decompressing the encryption information is used as the error correction code generated in the second step. It is characterized by.
[0008]
The second means is a control center of the system, and a host controller for format-converting the encrypted information by software, and a bit error in the error detection and correction function for the information obtained by the format conversion executed by the host controller. Generate an error correction code for detection and correction, change some bits of the information obtained by the format conversion performed by the host controller within the correctable range of the error detection and correction function, and encrypt the changed information. And an ECC & encryption / decryption block for decrypting and decompressing the encrypted information using the error correction code as decryption information, and encryption information obtained by the ECC & encryption / decryption block under the control of the host controller. Storage medium for providing stored encryption information to the ECC & encryption / decryption block Characterized in that it has a.
[0009]
The third means converts a format of the information to be encrypted, and generates a first error correction code for detecting and correcting a bit error in an error detection and correction function with respect to the information obtained by the format conversion. Encrypted information obtained by changing some bits of the information obtained by the format conversion within a correctable range of the correction function, and a first error generated for the information obtained by the format conversion. A correction code, a second error correction code generated for the encrypted information, and a third error correction code generated for the first error correction code are stored. I do.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is a diagram showing a procedure of an encryption method according to an embodiment of the present invention. In this embodiment, original data to be encrypted is subjected to format conversion such as compression and scrambling as simple encryption, and four symbols (1) based on, for example, the Reed-Solomon method, which is one of error detection and correction functions. Using an ECC (error correcting code) function of an error detection and correction function of a symbol (10 bits), an n-bit bit error (data change) is added to the format-converted data for encryption.
[0012]
In FIG. 1, first, original data DATA of information to be encrypted to be encrypted is compressed by a predetermined compression algorithm to generate compressed data DATA1 (step S11). Next, the compressed data DATA1 is scrambled by a predetermined scrambling algorithm to generate scrambled data DATA2 (step S12). In this manner, the original data DATA is subjected to compression and scrambling as simple encryption and format conversion. This format conversion is processed by software. Also, it is assumed that a plurality of compression and scrambling algorithms are prepared, respectively, and can be arbitrarily selected from the prepared ones. In order to identify the selected compression or scrambling algorithm, the identifiers of the respective algorithms are referred to as a compression key P_KEY and a scramble key S_KEY.
[0013]
Further, as the format conversion, only one of the compression and the scrambling may be performed without performing both. Further, the compression or scramble processing may be performed by hardware if it can be realized with a relatively small configuration by the adopted algorithm.
[0014]
Next, an ECC code having a function of automatically correcting a bit error in the ECC function is generated for the format-converted data DATA2 (step S13). The generated ECC code is set as a unique content key E_CODE_KEY unique to each content (original data). Next, an n-bit bit error (n = 4 symbols at maximum = 40 bits) is intentionally performed on the data field of the data DATA2 at random (step S14). Thus, the original data DATA is encrypted to generate the encrypted data DATA3. Here, the selection of a random data field involves the interposition of a random number, for example, using a count value of a free-running binary counter to generate a random number.
[0015]
In such an encryption procedure, the data owner (owner of the access right) uses a compression key P_KEY, a scramble key S_KEY, and a content unique key E_CODE_KEY as a decryption key. The compression key P_KEY and the scramble key S_KEY are used as device-specific system keys for implementing the encryption procedure, and the content unique key E_CODE_KEY is used as a unique key for each content.
[0016]
In the above encryption procedure, when a bit error is directly added to the original data without performing the format conversion, analogy of the original data and restoration / decompression can be easily performed. For this reason, in this embodiment, compression and scrambling are performed as the format conversion of the original data to prevent the protection strength of the data from being reduced.
[0017]
When an error of several bits occurs in the compressed data of the format conversion in the above encryption procedure, it becomes impossible to decompress and restore data after the bit position where the error occurred. By making use of this, by adding a bit error to the compressed data, it is possible to increase the difficulty of illegal decompression and restoration when there is no decompression key. Furthermore, for the purpose of increasing the protection strength of the data, as a pre-process of randomly adding a bit error to the format-converted data, a byte address is added to the compressed data in byte units, and scrambling is performed in the order of the byte addresses. Thereafter, a bit error of 4 symbols (= 40 bits) is added to the scrambled data, but one symbol is a continuous 10 bits.
[0018]
Here, for example, if a continuous 10-bit bit error is added to the 16-byte data without scrambling, the 2-byte portion to which the bit error has been added always becomes a continuous address, and four locations of the original data are added. The address area has been changed. On the other hand, if the original data is scrambled in byte units, a bit error can be added to 16-byte data having discontinuous addresses, so that the above-mentioned changed address area is distributed to eight locations. Can be. Further, when the original data is scrambled in 4-bit units, the changed address area can be dispersed in 12 places. When the original data is scrambled in 1-bit units, the changed address area is dispersed in 40 places. Will be able to As a result, when viewed from the address of the compressed data before scrambling, a 40-bit bit error (data change) can be dispersed over the entire address of the compressed data.
[0019]
As described above, in the above-described embodiment, since the format conversion is performed by software and the ECC function is realized by hardware, the configuration can be reduced in size and the processing time can be reduced. Further, since the ECC function can be realized using existing hardware, there is no need to prepare dedicated hardware. Further, by preparing and selecting a plurality of format conversion compressions and scrambles and changing the capability of the ECC function, it is possible to easily and flexibly change the protection strength against unauthorized decryption.
[0020]
Furthermore, since an encryption algorithm using a random number is employed, a large number of data correction patterns are used for unauthorized decryption, and therefore, highly reliable encryption with extremely high encryption protection strength can be realized. In addition, if the encryption system has hardware resources or software resources of the existing ECC code generator and decoder, the encryption system can be diverted to add a strong encryption / decryption function. The cost performance of the system can be significantly improved.
[0021]
In the above embodiment, compression and scrambling are performed before adding a bit error to the original data. However, if a format conversion method that makes it difficult to restore the data due to several bits of bit error, another format conversion method is used. Format conversion may also be used. For example, simple encryption using an algorithm using exclusive OR may be used.
[0022]
Also, a series of encryption procedures described in the above embodiment may be repeated a plurality of times. That is, the same processing is performed again using the encrypted data DATA3 as the original data DATA. In this case, the protection strength of data can be increased according to the number of repetitions without making any change in hardware or software.
[0023]
FIG. 2 is a diagram showing a restoration procedure for restoring and decompressing the encrypted data (DATA3) encrypted by the encryption method shown in FIG.
[0024]
In FIG. 2, first, the bit error of the encrypted data DATA3 is corrected using the content unique key E_CODE_KEY to obtain data DETA2 in which the bit error has been corrected (step S21). Next, the data DATA2 is descrambled (descrambled) using the scramble key S_KEY to obtain the descrambled data DATA1 (step S22). Subsequently, the compression of the data DATA1 is decompressed using the compression key P_KEY to obtain the original data DATA (step S23).
[0025]
FIG. 3 is a diagram showing a procedure for storing the encrypted data obtained by the encryption method shown in FIG. 1 in various storage media 31, for example, a flash memory card or the like. The feature of this embodiment is that, in order to store the encrypted data DATA3 on the storage medium 31 by the encryption method shown in FIG. Then, an ECC code is generated (steps S31 and S32), and an ECC code ECC_CODE (DATA) of the encrypted data DATA3 and an ECC code ECC_CODE (KEY) of the content unique key are obtained. Then, the encrypted data DATA3, the content unique key E_CODE_KEY, the ECC code ECC_CODE (DATA), and the ECC code ECC_CODE (KEY) are stored in the storage medium 31.
[0026]
In such an embodiment, even if the encrypted data DATA3 and / or the content unique key E_CODE_KEY has changed due to, for example, data corruption, the data is restored using the ECC code stored in the storage medium 31. This makes it possible to protect data when the data is stored in the storage medium.
FIG. 4 is a diagram showing a procedure for reading out data stored in the storage medium and restoring and decompressing the data in the procedure shown in FIG.
[0027]
In FIG. 4, when the encrypted data DATA3 and the content unique key E_CODE_KEY stored in the storage medium 31 are changed to, for example, DATA3 ′ and E_CODE_KEY ′, the encrypted data DATA3 ′ read from the storage medium 31 The bit error is corrected using the ECC code ECC_CODE (DATA) (step S41), the correct encrypted data DATA3 before being stored is obtained, and the content unique key E_CODE_KEY ′ read from the storage medium 31 The bit error is corrected using the ECC code ECC_CODE (KEY) to be performed (step S42), and a correct content unique key E_CODE_KEY before being stored is obtained. After that, the procedure is the same as the decoding and decompression procedure shown in FIG.
[0028]
FIG. 5 is a diagram showing a procedure of an encryption method according to another embodiment of the present invention.
[0029]
The feature of this embodiment is that, in comparison with the embodiment shown in FIG. 1, the compression processing in step 11, the scrambling processing in step 12, and the addition of bit errors in step S 14 shown in FIG. Is divided into a plurality of, for example, four blocks, and each block is independently processed.
[0030]
Here, a case is considered where bit errors (data changes) of four symbols are concentrated in a specific byte address area of data and the address is at the end of the data. When attempting to decrypt and decompress such encrypted data without a legitimate key, by giving all combinations of compression key and scramble key, most data except for the end address area of the data can be obtained without the content unique key. It will be decrypted and the protection strength will be degraded.
[0031]
This embodiment has been proposed for the purpose of preventing such deterioration. For example, when the size of the original data is 512 bytes, this data is divided into 4 blocks each having 128 bytes, and the data is compressed for each block (step S51). Scrambling is performed for each block (step S52). Subsequently, an ECC code E_CODE_KEY of the data DATA2 obtained by merging four blocks of the obtained data is obtained (step S53). Next, a bit error of one symbol (= 10 bits) is randomly added to the data DATA2 for each block, and a bit error of four symbols is added to the entire data of the four blocks to obtain encrypted data DATA3 ( Step S54).
[0032]
In such an embodiment, since the data change area of the bit error is distributed in the divided four blocks, data other than the data end is illegal without the content unique key as described above. Can be prevented. Also, by repeating the procedure shown in FIG. 5 a plurality of times as in the embodiment of FIG. 1, the protection strength of data can be further increased.
[0033]
FIG. 6 is a diagram showing a configuration of an encryption system according to an embodiment for performing the encryption / decryption method shown in the embodiment of FIGS.
[0034]
In FIG. 6, the encryption system according to this embodiment includes a host controller 61, an ECC & encryption / decryption block 62, and a storage medium 63. The host controller 61 is composed of, for example, a microcomputer system having a CPU and a memory, functions as a control center for controlling the ECC & encryption / decryption block and the storage medium 63, and performs format conversion of original data by software. The host controller 61 uses the write protect signal (WP), the address latch enable signal (ALE), the command latch enable signal (CLE), the read enable signal (RE), and the write enable signal (WE) to perform the ECC & encryption / decryption block 61. Also, the operation of the storage medium 63 is controlled, and data, addresses, and commands are input and output between the host controller 61, the ECC & encryption / decryption block 62, and the storage medium 63 via the I / O bus 64.
[0035]
The ECC & encryption / decryption block 62 executes processing other than the format conversion processing shown in FIGS. As the storage medium 63, various forms such as a flash memory, a smart media, and a memory stick can be applied.
[0036]
In this embodiment, the content unique key E_CODE_KEY is also stored in the storage medium 63 as a pair with the encrypted data. Also, since the system keys of the compression key P_KEY and the scramble key S_KEY are unique for each system, they are held by the system and kept private. For the access right of the content unique key E_CODE_KEY, a protection mechanism is provided at an application level, and another key for accessing the content unique key E_CODE_KEY is generally separately prepared.
[0037]
【The invention's effect】
As described above, according to the present invention, after the information to be encrypted is format-converted, an error correction code is generated, and some bits of the information after the format conversion are changed to generate the encrypted information. Therefore, the processing time for encryption / decryption can be reduced without using dedicated hardware, and the protection strength can be easily and flexibly changed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a procedure of an encryption method according to an embodiment of the present invention.
FIG. 2 is a diagram showing a procedure for decrypting the encrypted data encrypted by the procedure shown in FIG.
FIG. 3 is a diagram showing a procedure for saving the encrypted data encrypted by the procedure shown in FIG. 1 in a storage medium.
FIG. 4 is a diagram showing a procedure for reading and decoding data stored in a storage medium according to the procedure shown in FIG. 3;
FIG. 5 is a diagram showing a procedure of an encryption method according to another embodiment of the present invention.
FIG. 6 is a diagram showing a configuration of an encryption system according to an embodiment for performing the encryption / decryption method shown in the embodiment of FIGS. 3 and 4;
[Explanation of symbols]
S11 to S14, S21 to S23, S31 to S32, S41 to S42, S51 to S54 Processing steps 31, 63 Storage medium 61 Host controller 62 ECC & encryption / decryption block

Claims (8)

A first step of converting the format of the encrypted information;
A second step of generating an error correction code for detecting and correcting a bit error in the error detection and correction function with respect to the information obtained by the format conversion in the first step;
Within the correctable range of the error detection and correction function, some bits of information obtained by the format conversion in the first step are changed, the changed information is used as encryption information, and the encrypted information is decrypted and decompressed. And a third step in which the decryption information at the time of decryption is used as the error correction code generated in the second step. 2. The encryption method according to claim 1, wherein a series of processes including the first step, the second step, and the third step is repeatedly performed a plurality of times. 3. The encryption method according to claim 1, wherein the format conversion in the first step is selected from a plurality of algorithms. 3. The cipher according to claim 1, wherein the encrypted information is divided into a plurality of blocks, and format conversion and partial bit change are executed independently for each of the plurality of divided blocks. Method. 3. The encryption method according to claim 1, wherein the format conversion in the first step is a compression process for compressing information, a scramble process for changing a bit arrangement, or the compression process and a scramble process. . 5. The encryption method according to claim 1, wherein some bits changed in the third step are determined based on random numbers. A host controller that becomes the control center of the system and converts the format of the encrypted information by software;
For the information obtained by the format conversion performed by the host controller, an error correction code for detecting and correcting a bit error in an error detection and correction function is generated, and the host controller is controlled within a correctable range of the error detection and correction function. An ECC & encryption / decryption block for changing some bits of the information obtained by the format conversion performed by the above, making the changed information into encryption information, and using the error correction code as decryption information to decrypt and decompress the encryption information; ,
A storage medium for storing the encryption information obtained by the ECC & encryption / decryption block under the control of the host controller, and providing the stored encryption information to the ECC & encryption / decryption block. Encryption system. A format of the information to be encrypted is converted, and a first error correction code for detecting and correcting a bit error in the error detection and correction function is generated for the information obtained by the format conversion, and a correction range of the error detection and correction function is generated. Within, encryption information obtained by changing some bits of the information obtained by the format conversion,
A first error correction code generated for the information obtained by the format conversion,
A second error correction code generated for the encrypted information;
A storage medium storing a first error correction code and a third error correction code generated for the first error correction code.

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