JPH1139156A - Enciphered data decoding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent encipherment-protected data from being illegally used due to an altered decoding support program. SOLUTION: Receiving a decoding instruction, a decoding device 100 temporarily stops operation of a CPU. An address detection part 103 monitors memory accessing of the CPU and acquires a store address Pr of an instruction code that issues the decoding instruction. A cipher authentication part 102 authenticates a cipher key. A decoding support program authentication part 104 acquires the authentication range designation (pre, post) from the cipher key, calculates a message summary number using a unidirectional hash function about an area covering Pr-pre through Pr+post, and compares the calculation result with the message summary number contained in the cipher key to authenticate the correctness of the decoding support program. When this authentication succeeds, a data decoding part 101 acquires a cipher decoding key from the cipher key and decodes the enciphered data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for decrypting encrypted data.

[0002]

2. Description of the Related Art Conventionally, when an encryption method is applied to a computer system and an encrypted program or data is decrypted and used, a decryption program (decryption calculation and support for the decryption program that operates on the system) is performed. Is generally executed (Japanese Unexamined Patent Publication No. 3-6802).
No. 4). By the way, in an open computer system in which specifications are disclosed, it is easy to analyze and modify a program. Therefore, by modifying a decryption support part (hereinafter also referred to as a decryption support program) of a decryption program, the original decryption is performed. Contrary to the specifications of the program, there is a problem that the decrypted data can be easily used illegally, and the security of the entire system is reduced. The progress of the encryption scheme has been remarkable, and many encryption schemes having strong encryption strength have been proposed. However, the problem due to the analysis and modification of the decryption program does not depend on the security of the encryption method used, and therefore cannot be solved even if an encryption method having a high strength is adopted.

[0003] As a proposal to solve this problem,
It is known to employ means for encrypting the decryption program itself, decrypting the decryption program only at the time of data decryption, and performing data decryption work, thereby making it difficult to analyze and modify the decryption program (Japanese Patent Application Laid-Open No. HEI 9-163572). 9-6232
No.). However, the decoding of the decryption program is ultimately performed by the program, and is not an essential solution. The only effect is that the cost required for analysis and modification is slightly increased. In addition, considering the recent improvement in computer performance, the increased cost cannot be a major obstacle, and thus there is a problem that analysis and alteration of the decryption program cannot be effectively prevented. Also,
Once the decryption program has been successfully modified, execution of the falsification program cannot be prevented, and there is a problem that the use of decrypted data for an unintended purpose cannot be prevented.

Further, as means for preventing the decryption program from being altered, the CPU monitors the address for accessing the memory and compares the address with the expected memory access pattern of the valid decryption program.
There is a proposal to permit memory access, but to prevent unauthorized use of unintended data by shutting off memory access when it is determined to be illegal (Japanese Patent Laid-Open No. 5-3).
No. 24483). However, in the case of a special small-scale system in which a program for embedding equipment is supplied by a ROM, the program exists at a fixed address position. However, in a general system, since the address at which a program is loaded is dynamically determined, there is a problem that a decryption program cannot be determined based on address information to be accessed. In addition, since the access pattern of the fraud criterion cannot be easily changed, the scalability is poor, and it is difficult to handle a large amount of encrypted data. Therefore, there is a problem that this method cannot be used in a general computer system.

As described above, in the conventional technology, it is not possible to authenticate at the time of decryption that the decryption program is legitimate without modification in a general computer system. Could not prevent the execution of the decryption program. For this reason,
Diversion of the decrypted data for unintended purposes by a falsified or altered decryption program cannot be effectively prevented.
Therefore, there is a problem that the security of the entire system is lowered regardless of the strength of the encryption method.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an open computer system in which specifications are disclosed.
An object of the present invention is to make it possible to authenticate the validity of a decryption program at the time of decryption of encrypted data, thereby preventing the use of the decrypted data for an unintended purpose by a falsified decryption program.

[0007]

According to the present invention, in order to achieve the above-mentioned object, an encrypted data decryption apparatus mounted on a computer system for decrypting encrypted data is provided. Data decryption means for decrypting data based on an encryption key, encryption key authentication means for authenticating that the encryption key is valid, and a decryption support program which, when receiving a decryption instruction from the CPU, includes Address detection means for detecting the memory address of the instruction code that issued the instruction, and decryption support program authentication means for verifying that the decryption support program is valid based on the memory address of the instruction code Like that.

In this configuration, for example, based on the memory address of the instruction code in the decryption support program that issued the decryption instruction, the contents of the code in a predetermined area are verified, and the validity of the decryption support program is verified. Can be authenticated.
In this case, adaptation can be performed using the address of the detected instruction code regardless of which area of the memory the decoding support program is loaded.

[0009]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a computer system for decrypting encrypted data using the decryption device of the present invention. In this embodiment, encrypted data is decrypted by a decryption device 100 mounted on a computer system and a decryption support program executed by the computer system.

In FIG. 1, a CPU is connected to an internal bus 201.
The computer system is configured by connecting the 202, the I / O unit 203, the decoding device 100, and the memory 205. The CPU 202 is of a general stored program type, reads and interprets a program code stored in the memory 205 via the internal bus 201,
It operates according to the instruction of the read program code. The user of the system uses the system as intended by giving instructions to the CPU 202 via the internal bus 201 to access the data stored in the I / O unit 203 and the memory 205 by a program. be able to.

FIG. 2 shows an example of the configuration of the decoding device 100 shown in FIG. In this figure, a decryption device 100 includes a data decryption unit 101, an encryption key authentication unit 102, an address detection unit 10
3. It includes a decryption support program authentication unit 104 and an unauthorized access prevention unit 105. The data decryption unit 101 decrypts the encrypted data based on the encryption key. The encryption key authentication unit 102 outputs the encryption key 3
03 (FIG. 5) is authenticated as being valid. Upon receiving a decoding instruction from the CPU 202, the address detection unit 103 detects the memory address of the instruction code in the decoding support program 301 (FIG. 3) that issued the decoding instruction. The decryption support program authentication unit 104 authenticates that the decryption support program 301 is valid. Further, the unauthorized access prevention unit 105 detects an illegally deprived flow of processing due to an interruption or the like during execution of the decryption support program 301 and takes countermeasures.

FIG. 3 shows a data storage state in the memory when the encrypted data is decrypted.
In FIG. 3, the decryption support program 301 decrypts the encrypted data 302 and
4 is a program that issues a command to the decoding device 100 to store the data in the decoding device 4 and uses the decoded data for an intended purpose. The encryption key 303 (see FIG. 5) is key data necessary for decrypting the encrypted data. The storage addresses of the decryption support program 301, the encrypted data 302, the encryption key 303, and the decrypted data storage area 304 in the memory 205 are p, c, k, and d.

FIG. 4 is a conceptual diagram of a storage state of the decryption support program in the memory. In FIG. 4, addresses p to p _end on the memory 205 correspond to the decryption support program 3.
01 is an area for storing. Decryption support program 30
1 includes a decryption instruction issuing portion 402 for issuing a decryption instruction to the decryption device 204, and the address where this code is stored is pr. From the address pr of the decryption instruction issuance part 402, a block separated by a pre byte before and a post byte after is a decryption support program verification block 403. The validity of the decryption support program is determined using the number of message digests in the decryption support program verification block 403. pre and post are encryption keys 3
03 (see FIG. 5).

FIG. 5 is a configuration diagram of the encryption key 303. The encryption key 303 is digital data, and the encryption decryption key 50
1. The number of message digests 502 of the decryption support program, the verification area range designation 503, and the signature 504 of the entire encryption key
Consists of

FIG. 6 shows an example of the configuration of an encryption key generation device for generating the encryption key 303. In FIG. 6, the encryption key generation device includes a verification range designation section 505, a decryption support program input section 506, and a decryption key input section. Unit 507, message digest number generation unit 508, signature generation unit 509, and encryption key output unit 51
0 is included. The verification range designation unit 505
It receives the address of the decoding instruction code and the number of bytes pre and post specifying the verification block. The message digest count generation unit 508 generates the message digest count of the decryption support program within the range specified by the verification range specification unit 505. The signature generation unit 509 receives the decryption key input from the decryption key input unit 507 and the number of bytes pr of the verification block designation information.
e and post and message digest count generator 508
Generate a signature for the number of message summaries generated in.
The encryption key output unit 510 integrally outputs the decryption key, the number of message digests, pre and post of block designation information, and a signature.

Next, the decoding process of the embodiment will be described. In this embodiment, the decryption processing is performed by the decryption support program 3
01 and the decoding device 100. FIG. 7 is a flowchart of the decryption support program 301. FIG.
Is a flowchart showing the flow of the process of the decoding device 100. In FIG. 7, when the execution of the decryption support program 301 is started to decrypt the encrypted data,
First, preprocessing is performed (step 601). In the preprocessing, the encrypted data 302 and the encryption key 303 are stored in the memory 205.
And secures an area 304 for storing decrypted data, and performs a work of configuring a memory storage state as shown in FIG. 3 and other necessary preprocessing work. Next, the storage address k of the encryption key, the storage address c of the encrypted data, and the designated storage address d of the decrypted data are given to the decryption device 100. Specifically, the decoding device 10
This is performed by outputting k, c, and d to the I / O address mapped to 0 (step 602). Of course, the communication with the decoding device 100 may be performed by another method.

Thereafter, an instruction is issued to the decryption device 100 to perform decryption processing (step 603). At this time, the address where the instruction code corresponding to step 603 is stored is Pr. Issuance of this instruction, specifically,
This is performed by outputting an instruction command to the I / O address mapped to the decoding device 100 via the internal bus 201.

The decoding device 100 that performs decoding uses the internal bus 2
01, it is possible to monitor what access the CPU 202 is making. In addition, the memory is directly accessed without going through the CPU (DMA: Direct
Memory Access). In addition, the operation of the CPU 202 is controlled, and the CPU
202 can be kept in a paused state or the operation can be resumed.

In FIG. 8, the decryption apparatus 100 having received the decryption instruction immediately proceeds to
02 is temporarily stopped, and the storage address k of the encryption key 303, the storage address c of the encrypted data 302, and the designated storage address d of the decrypted data are read (step 701).
As a result, the decryption support program 301 executes step 603
Will be in a pause state. The following access to the memory 205 of the decoding device 100 uses DMA.

The processing of the decoding device 100 proceeds to step 702. In step 702, the memory 20 of the CPU 202
The storage address Pr of the instruction code for issuing the decryption instruction is obtained by monitoring the access to No. 5.

Next, at step 703, the encryption key 30
Perform 3 authentication. The encryption key 303 is provided with a signature 504 of the entire encryption key, and the electronic signature verification technique is used to authenticate whether the key is valid. Specifically, a signature authentication key is prepared in the decryption device, and RSA (Rivest
-Shamir-Adelman) public key cryptography,
Authentication is performed using a message digest generation technique using a one-way hash function. Of course, other methods may be used for authentication.

If the authentication fails, the encryption key 303
May have been tampered with. The decryption device 100 determines that the encryption key 303 is not valid and
Go to 5. In step 705, the CPU operation is restarted, and an error code meaning "failure of encryption key authentication" is returned to the CPU. Specifically, by accessing the I / O address mapped to the decoding device 100, the CP
The error code is stored in a register that can be read by U202. Of course, the communication with the CPU 202 may be performed by another method. Decryption support program 3 that resumed operation
In step 01, it is determined that an error has occurred in the branch of step 605, and error processing is performed in step 606, and the processing ends without decoding.

If the authentication of the encryption key 303 is successful in step 703, the process proceeds to step 704.
In step 704, the verification range designation 503 is obtained from the encryption key 303, and the number of message digests using the one-way hash function is calculated for the region from Pr-pre to Pr + post.

Then, in step 706, the number of message digests 502 in the verification area of the decryption support program in the encryption key 303 is compared with the number of message digests calculated in the previous step 704. If they do not match, the decryption support program 3
01 means different from what the issuer of the encryption key 303 intended. The decryption device 100 determines that the decryption support program 301 has been tampered with, and proceeds to step 707.
Proceed to. In step 707, the operation of the CPU 202 is restarted, and an error code meaning "authentication of the decryption support program failed" is returned to the CPU. Specifically, an error code is stored in a register that can be read by CPU 202 by accessing an I / O address mapped to decoding device 100. Of course, the communication with the CPU 202 may be performed by another method. The decryption support program 301 that has resumed operation determines that an error has occurred in the branch of step 605 in FIG. 7, performs error processing in step 606, and ends without decoding.

If the authentication of the decryption support program is successful in step 706 of FIG. 8, the process proceeds to step 708. In step 708, the decryption device 100 acquires the decryption key 501 of the encryption from the encryption key 303, and performs decryption processing of the encrypted data. Specifically, the DES (Data Encrypt) is obtained from two of a decryption key for encryption and a secret key prepared separately for each decryption device.
A decryption key of a block cipher such as Tion Standard) is generated, the data encrypted by the DMA is read to the block cipher decryptor, and the decryption result is written to the decrypted data area by the DMA. Of course, any method of encryption / decryption may be used.

After completion of the decryption processing, step 709
To use the decrypted data. After use, the decrypted data is deleted from the memory 205 as needed, thereby preventing the use of the decrypted data for an unintended purpose.

Further, the decryption apparatus 100 monitors the access of the CPU 202 to the internal bus 201, and detects an operation that steals the processing flow due to an illegal interrupt or the like while the decryption support program 301 is being executed by the CPU 202. it can. If it is detected that the processing flow has been illegally taken, the decoding operation is immediately stopped, and the data decoded so far is also destroyed by the DMA. With this function, it is possible to eliminate interference with the operation of the program due to a hardware interrupt, and further improve safety.

[0028]

As described above, the present invention prevents the use of decrypted data for an unintended purpose by a falsified decryption support program by checking the validity of the decryption support program at the time of decryption. This allows
The alteration resistance of the decryption support program can be improved, and the security of the system corresponding to the encryption strength can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a computer system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a decoding device according to the above embodiment.

FIG. 3 is a diagram illustrating a data storage state in a memory when decrypting encrypted data.

FIG. 4 is a diagram conceptually showing a storage state of a decryption support program in a memory.

FIG. 5 is a diagram illustrating a configuration of an encryption key.

FIG. 6 is a block diagram illustrating a configuration example of an encryption key generation device that generates an encryption key.

FIG. 7 is a flowchart illustrating the operation of a decryption support program.

FIG. 8 is a flowchart illustrating a flow of a process performed by the decoding device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 decryption device 101 data decryption unit 102 address detection unit 103 decryption support program authentication unit 104 unauthorized access prevention unit 201 bus 202 CPU 203 I / O unit 205 memory

Claims (11)

[Claims] 1. An encrypted data decryption device mounted on a computer system for decrypting encrypted data, comprising: data decryption means for decrypting the encrypted data based on an encryption key; Encryption key authentication means for authenticating that the decryption instruction has been received; address detection means for detecting, when a decryption instruction is received from the CPU, a memory address of the instruction code in the decryption support program which issued the decryption instruction; Decryption support program authentication means for verifying that the decryption support program is valid based on the memory address of the code. 2. The encryption system according to claim 1, further comprising an unauthorized access prevention means for detecting and taking a countermeasure when the flow of the processing is illegally taken by an interrupt or the like during execution of the decryption support program. Data decoding device. 3. The decryption support program authentication means verifies whether or not the contents of a code in a predetermined memory address range determined by the memory address of the instruction code are genuine. An encrypted data decryption device according to the above. 4. A method for verifying that the contents of the code in the predetermined memory address range are genuine based on a calculation result of the contents of the code in the predetermined memory address range by a predetermined function. An encrypted data decryption device according to the above. 5. The encrypted data decryption device according to claim 4, wherein said predetermined function is a predetermined one-way function. 6. The encryption key holds a reference value generated from a genuine decryption support program, and compares the calculation result by the decryption support program verification means with the calculation result held by the encryption key. 6. The encrypted data decryption device according to claim 4, wherein the validity of the decryption support program is authenticated. 7. The encryption method according to claim 6, wherein the encryption key further holds information for specifying the predetermined memory address range, and the reference value is generated based on the specified memory address range. Data decoding device. 8. An encrypted data decryption device mounted on a computer system for decrypting encrypted data, comprising: data decryption means for decrypting the encrypted data based on an encryption key; Is transferred to the bus, an address detecting means for detecting a memory address of an instruction code which has transferred the predetermined information to the bus in the decoding support program, and is determined by a memory address of the instruction code. Decryption support program authentication means for verifying that the decryption support program is valid based on the contents of the decryption support program in a predetermined memory address range. 9. An encryption key body for decrypting encrypted data,
An encryption key for generating encryption key information including a calculation result of a predetermined function of a code in a predetermined range of a decryption support program used for decrypting the encrypted data, the encryption key body, and a signature for the calculation result; Information generation device. 10. An encryption key body for decrypting encrypted data, a result of calculation of a code in a predetermined range of a decryption support program used for decrypting the encrypted data by a predetermined function, the encryption key body, Receiving encryption key information including a signature for the calculation result; and, when decrypting the encrypted data, extracting a code developed in a memory area corresponding to the predetermined range of the decryption support program used for decryption. Generating a calculation result of the extracted code by the predetermined function; comparing the generated calculation result with the calculation result in the encryption key information; based on the comparison result Verifying the authenticity of the decryption support program used for the decryption. Method. 11. A bus, a CPU connected to the bus, a memory connected to the bus, and an authentication device connected to the bus, wherein the authentication device transmits encrypted data from the CPU. Address detection means for detecting the memory address of the instruction code that issued the decoding instruction when the decoding instruction is transferred via the bus, based on the memory address of the instruction code. Computer means for authenticating that the decryption support program is legitimate.