JP2008003774A - Microcomputer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microcomputer which easily keeps an encryption key and a decryption key secret and has a high security level. <P>SOLUTION: A microcomputer 1 includes a secret key storage part 11 for storing a secret key pairing with a public key in a public key encryption system, a decryption part 12 for decrypting input data by using the secret key read out from the secret key storage part 11, and a nonvolatile memory 13 for storing data decrypted by a decryption part 12. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microcomputer, and more particularly to a microcomputer in which encrypted software is written.

  In a microcomputer that stores software in a built-in rewritable nonvolatile storage means, software is written to the microcomputer by using a writing device such as an EPROM writer.

  In some cases, the writing of the software is outsourced to a third party, and in order to prevent unauthorized reading of the software at the time of writing, the software is encrypted and written to the microcomputer (for example, see Patent Document 1). ).

  When such software is encrypted, encryption is performed using an encryption key. Therefore, the microcomputer is provided with a decryption key and decryption means corresponding to the encryption key, and the software inputted after encryption is decrypted inside the microcomputer.

Encrypting the software improves the security of the software against unauthorized reading, but it is important to maintain the confidentiality of the encryption key and the decryption key in order to maintain the security. In particular, since a general-purpose microcomputer is used by many users, it is desirable that the encryption key and the decryption key be kept secret and that the security level be high.
JP-A-8-185361 (3rd page, FIG. 1)

  SUMMARY OF THE INVENTION An object of the present invention is to provide a microcomputer having a high security level in which the encryption key and the decryption key are kept secret.

  According to one aspect of the present invention, a secret key storage unit that stores a secret key that is paired with a public key of a public key cryptosystem, and the secret key that is obtained by reading input data from the secret key storage unit There is provided a microcomputer characterized by having decoding means for decoding and non-volatile storage means for storing data decoded by the decoding means.

  According to another aspect of the present invention, a public key storage unit that stores a public key of a public key cryptosystem, a secret key storage unit that stores a secret key that is paired with the public key, and an input Decryption means for decrypting data using the secret key read from the secret key storage means, nonvolatile storage means for storing data decrypted by the decryption means, and the decryption stored in the nonvolatile storage means There is provided a microcomputer characterized by having encryption means for encrypting data decrypted by the means using the public key read from the public key storage means.

  According to the present invention, since the software is encrypted and written to the microcomputer, it is possible to prevent the software from being read illegally when writing to the microcomputer. At this time, since the public key is used as the encryption key, the microcomputer user is not bothered by storing the encryption key. In addition, since the decryption key for the encrypted software is stored inside the microcomputer as a secret key, it is difficult to decrypt the encrypted software, preventing infringement of intellectual property rights due to unauthorized copying of the software, etc. can do.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating an example of a configuration of a microcomputer according to the first embodiment of the invention.

  The microcomputer 1 of this embodiment uses a secret key storage unit 11 that stores a secret key that is paired with a public key of the public key cryptosystem, and a secret key that is read from the secret key storage unit 11 of input data. It has a decoding unit 12 for decoding, a nonvolatile memory 13 for storing data decoded by the decoding unit 12, and a boot ROM 14 for storing a control program for controlling the decoding operation.

  Further, the microcomputer 1 is input from the outside through the I / F (interface) unit 61 that interfaces data with the outside, the CPU 62 that controls the decoding operation based on the control program, and the I / F unit 61. RAM 63 for temporarily storing the data, and an internal bus 64 to which each block is connected and data is transmitted between the blocks.

  When writing software to the microcomputer 1, the software is encrypted using a public key by a PC (personal computer) 100 and input to the I / F unit 61 by the writing device 200.

  Here, the public key is created by, for example, a semiconductor manufacturer that manufactured the microcomputer 1 and is disclosed to the user of the microcomputer 1. On the other hand, a decryption key for decrypting data encrypted with the public key is stored as a secret key in the secret key storage unit 11 when the microcomputer 1 is manufactured. An encryption program is also provided by the semiconductor manufacturer, and a decryption circuit for the encryption program is mounted in the decryption unit 12.

  Next, a software writing operation to the microcomputer 1 of this embodiment will be described.

  When writing software, first, the software is encrypted on the PC 100 using a public key and an encryption program. Next, the encrypted software is transmitted to the writing device 200. The writing device 200 inputs the received encrypted software to the I / F unit 61 of the microcomputer 1.

  At this time, in the microcomputer 1, the CPU 62 reads out the control program from the boot ROM 14 and starts decrypting the encrypted software.

  When the encrypted software is input from the writing device 200 to the I / F unit 61, the microcomputer 1 sends the encrypted software to the RAM 63 via the internal bus 64 under the control of the control program. Memorize temporarily.

  Subsequently, under the control of the control program, the decryption unit 12 reads the encrypted software from the RAM 63 and decrypts it using the secret key read from the secret key storage unit 11.

  When the decryption is completed, the decrypted software is sent to the nonvolatile memory 13 via the internal bus 64 and written to the nonvolatile memory 13 under the control of the control program.

  The software input after being encrypted by the above-described series of operations is decrypted and stored in the nonvolatile memory 13.

  According to this embodiment, since the software is encrypted and written to the microcomputer, it is possible to prevent the software from being read illegally when writing to the microcomputer. At this time, since the public key is used as the encryption key, the microcomputer user does not need to store the encryption key. Also, since the decryption secret key is stored as hardware inside the microcomputer, it is difficult to analyze the secret key. Therefore, it is difficult to decrypt the encrypted software, and it is possible to prevent infringement of intellectual property rights due to an illegal copy of the software.

  FIG. 2 is a block diagram illustrating an example of a configuration of a microcomputer according to the second embodiment of the present invention.

  The microcomputer 2 of the present embodiment is different from the microcomputer 1 of the first embodiment in that it does not have the secret key storage unit 11 and the decryption unit 12 as hardware. Instead, a secret key as software and a decryption program are stored in the boot ROM 24.

  The boot ROM 24 stores a control program for controlling the decryption operation, and this control program controls the reading of the secret key and the decryption program and the series of decryption operations. 2, blocks having the same functions as the functional blocks shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof is omitted here.

  Also in this embodiment, the public key is created by, for example, a semiconductor manufacturer that manufactured the microcomputer 2 and is disclosed to the user of the microcomputer 2. Further, a decryption key for decrypting data encrypted with the public key is stored in the boot ROM 24 as a secret key when the microcomputer 2 is manufactured. Similarly, the encryption program is also stored in the boot ROM 24 when the microcomputer 2 is manufactured.

  Next, the software writing operation to the microcomputer 2 of this embodiment will be described.

  Also in this embodiment, when software is written, the software is first encrypted on the PC 100 using a public key and an encryption program. Next, the encrypted software is transmitted to the writing device 200. The writing device 200 inputs the received encrypted software to the I / F unit 61 of the microcomputer 2.

  At this time, in the microcomputer 2, the CPU 51 reads the control program from the boot ROM 24 and starts decrypting the encrypted software.

  When the encrypted software is input from the writing device 200 to the I / F unit 61, the microcomputer 2 sends the encrypted software to the RAM 63 via the internal bus 64 under the control of the control program. Memorize temporarily.

  Subsequently, the decryption program and the secret key are read from the boot ROM 24 under the control of the control program. The decryption program reads the encrypted software from the RAM 63 and decrypts it using the secret key read from the boot ROM 24.

  When the decryption is completed, the decrypted software is sent to the nonvolatile memory 13 via the internal bus 64 and written to the nonvolatile memory 13 under the control of the control program.

  The software input after being encrypted by the above-described series of operations is decrypted and stored in the nonvolatile memory 13.

  According to the present embodiment, by incorporating the secret key and the decryption program as software, even a microcomputer that does not have the secret key storage unit and the decryption unit as hardware can be encrypted with the public key. Can deal with written software.

  FIG. 3 is a block diagram illustrating an example of a configuration of a microcomputer according to the third embodiment of the invention.

  Unlike the microcomputer 1 of the first embodiment in which the decoding operation is controlled by the control program, the decoding operation of the microcomputer 3 of this embodiment is automatically executed continuously.

  For this purpose, the microcomputer 3 according to the present embodiment includes an I / F unit 31 dedicated for decoding processing, a decoding unit 32 directly connected to the I / F unit 31, and a decoding result output from the decoding unit 32 in a nonvolatile memory. 13 and a write control unit 33 for writing to 13.

  3, blocks having the same functions as the functional blocks shown in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof is omitted here.

  In the writing of the encrypted software in the present embodiment, when the encrypted software is input from the writing device 200 to the I / F unit 31, the encrypted software is immediately sent to the decryption unit 32. The decryption unit 32 decrypts the encrypted software using the secret key read from the secret key storage unit 11. The decrypted software is sent to the write control unit 33 and written into the nonvolatile memory 13 by the write control unit 33.

  According to the present embodiment as described above, since the decoding process is entirely executed by the dedicated circuit, the execution speed is high and the time required for the decoding process can be shortened.

  When data is written to a microcomputer, there is a case where it is desired to verify whether the data has been written correctly. Therefore, in general, the writing device 200 has a write verification function. Write verification in the writing device 200 is performed by reading back data once written to the microcomputer from the microcomputer and comparing whether the data matches the original input data.

  Therefore, the microcomputer according to the present embodiment uses the write verification function of the writing device 200 to verify whether the encrypted software has been written correctly.

  FIG. 4 is a block diagram showing an example of the configuration of a microcomputer according to Embodiment 4 of the present invention.

  The microcomputer 4 of this embodiment is obtained by adding a read control unit 42, an encryption unit 43, and a public key storage unit 44 to the microcomputer 3 of the third embodiment. In addition, an I / F unit 41 that bidirectionally interfaces data with the writing device 200 is provided.

  In FIG. 4, blocks having the same functions as those shown in FIG. 3 are denoted by the same reference numerals as those in FIG. 3, and detailed description thereof is omitted here.

  When there is a write verification request from the writing device 200, the read control unit 42 reads the decrypted software stored in the nonvolatile memory 13 and sends it to the encryption unit 43.

  The encryption unit 43 performs encryption using the same encryption algorithm as that used for encryption in the PC 100.

  The public key storage unit 44 stores the same public key as that used for encryption in the PC 100.

  In this embodiment, a series of decryption operations from the input of the encrypted software to the I / F unit 41 to the writing of the decrypted software to the nonvolatile memory 13 is the same as that of the third embodiment. Then, the explanation is omitted.

  When there is a write verification request from the writing device 200 to the microcomputer 4 of this embodiment, the decrypted software stored in the nonvolatile memory 13 is read from the nonvolatile memory 13 by the read control unit 42. To the encryption unit 43.

  The encryption unit 43 encrypts the sent decrypted software using the public key read from the public key storage unit 44.

  The encrypted software is output to the writing device 200 via the I / F unit 41. At this time, if writing by the writing device 200 is performed normally, the encrypted software output from the I / F unit 41 should be the same as the original encrypted software input to the microcomputer 4. It is.

  Thus, by comparing the two using the write verification function of the writing device 200, it is possible to verify whether the encrypted software has been correctly written in the microcomputer 4.

  According to this embodiment, since the decrypted software stored in the nonvolatile memory can be encrypted again and output, it is verified whether the software has been correctly written to the microcomputer. be able to.

  FIG. 5 is a block diagram showing an example of the configuration of a microcomputer according to Embodiment 5 of the present invention. The microcomputer 5 of the present embodiment basically has the same configuration as the microcomputer 2 of the embodiment 2 shown in FIG. Therefore, in FIG. 5, blocks having the same functions as the functional blocks shown in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and detailed description thereof is omitted here.

  The microcomputer 5 of the present embodiment is different from the microcomputer 2 of the second embodiment in that it has an I / F unit 51 that can be bidirectionally interfaced with the writing device 200, and that the boot ROM 54 has a control program and a decoding program. In addition to the program and private key, the encryption program and public key are stored.

  Using this encryption program and public key, the microcomputer 5 of the present embodiment also encrypts the decrypted software stored in the non-volatile memory 13 again, similarly to the microcomputer 4 of the fourth embodiment. It can be executed and output to the writing device 200 via the I / F unit 51.

  That is, when there is a write verification request from the writing device 200 to the microcomputer 5 of this embodiment, the CPU 62 reads the control program stored in the boot ROM 54 and starts the decryption process of the decrypted software. .

  When encryption is started, the microcomputer 1 reads the decrypted software from the nonvolatile memory 13, sends it to the RAM 63 via the internal bus 64, and temporarily stores it in the RAM 63 under the control of the control program.

  Subsequently, the encryption program and the public key are read from the boot ROM 54 under the control of the control program. The encryption program reads the decrypted software from the RAM 63 and encrypts it using the public key read from the boot ROM 54.

  When the encryption is completed, the encrypted software is sent to the I / F unit 51 via the internal bus 64 and output to the writing device 200 under the control of the control program.

  Thereby, also in the microcomputer 5 of the present embodiment, whether or not the encrypted software has been correctly written in the microcomputer 5 using the write verification function of the writing device 200 as in the fourth embodiment. Can be verified.

  According to such a present embodiment, by incorporating a public key and an encryption program as software in addition to a secret key and a decryption program, a secret key storage unit, a decryption unit, a public key storage unit, and a cipher as hardware Even a microcomputer that does not have an encryption unit can write software encrypted with a public key, and can output the written software as encrypted software.

  In addition, since the public key, encryption program, secret key, and decryption program are built in as software, the semiconductor manufacturer that manufactured the microcomputer can change the public key and secret key, or change the encryption algorithm at any time. it can. Thereby, the security of the microcomputer can be further increased.

  FIG. 6 is a block diagram showing an example of the configuration of a microcomputer according to Embodiment 6 of the present invention.

  Similarly to the microcomputer 5 of the fifth embodiment, the microcomputer 6 of the present embodiment again encrypts the decrypted software stored in the nonvolatile memory 13 and passes through the I / F unit 51. To the writing device 200.

  The microcomputer 6 of the present embodiment is different from the microcomputer 5 of the fifth embodiment in that decryption and encryption are executed by hardware. For this purpose, the microcomputer 6 of this embodiment includes a secret key storage unit 11, a decryption unit 12, a public key storage unit 44, and an encryption unit 73. Further, a boot ROM 74 is provided instead of the boot ROM 54.

  The secret key storage unit 11 and the decryption unit 12 have the same function as the block with the same code shown in FIG. 1, and the public key storage unit 44 has the same function as the block with the same code shown in FIG. Since it is a thing, the description is abbreviate | omitted here.

  The boot ROM 74 stores a control program for controlling the decryption operation and a control program for controlling the encryption operation.

  The encryption unit 73 of the present embodiment is different from the encryption unit 43 of the fourth embodiment in that bidirectional data transmission is performed with the internal bus 64, but functionally, the encryption in the PC 100 is similar to the encryption unit 43. Encryption is performed using the same encryption algorithm as that used in encryption.

  Also in this embodiment, the decrypted software stored in the nonvolatile memory 13 is encrypted again by the encryption unit 73 and output to the writing device 200 via the I / F unit 51. be able to.

  Thereby, also in the microcomputer 6 of the present embodiment, whether or not the encrypted software has been correctly written in the microcomputer 6 using the write verification function of the writing device 200 as in the fifth embodiment. Can be verified.

  According to the present embodiment, by performing decryption and encryption with hardware, write verification by the writing device can be performed at high speed.

1 is a block diagram showing an example of the configuration of a microcomputer according to Embodiment 1 of the present invention. FIG. 5 is a block diagram illustrating an example of a configuration of a microcomputer according to a second embodiment of the invention. FIG. 9 is a block diagram showing an example of the configuration of a microcomputer according to a third embodiment of the invention. FIG. 9 is a block diagram showing an example of the configuration of a microcomputer according to a fourth embodiment of the invention. FIG. 9 is a block diagram showing an example of the configuration of a microcomputer according to a fifth embodiment of the invention. FIG. 9 is a block diagram showing an example of the configuration of a microcomputer according to Embodiment 6 of the present invention.

Explanation of symbols

1-6 Microcomputer 11 Secret key storage unit 12, 32 Decryption unit 13 Non-volatile memory 14, 24, 54, 74 Boot ROM
31, 41, 51, 61 I / F unit 33 Write control unit 42 Read control unit 43, 73 Encryption unit 44 Public key storage unit 62 CPU
63 RAM
64 Internal bus

Claims (5)

A secret key storage means for storing a secret key paired with a public key of a public key cryptosystem;
Decryption means for decrypting input data using the secret key read from the secret key storage means;
A microcomputer having nonvolatile storage means for storing data decoded by the decoding means.   2. The microcomputer according to claim 1, wherein data input to the decryption means is software encrypted with the public key. Public key storage means for storing the public key of the public key cryptosystem;
Secret key storage means for storing a secret key paired with the public key;
Decryption means for decrypting input data using the secret key read from the secret key storage means;
Nonvolatile storage means for storing data decoded by the decoding means;
A microcomputer having encryption means for encrypting data decrypted by the decryption means stored in the nonvolatile storage means, using the public key read from the public key storage means.   4. The microcomputer according to claim 3, wherein data input to the decryption means is software encrypted with the public key.   It is possible to verify that data is correctly written in the nonvolatile storage means by comparing data input to the decryption means and data output from the encryption means The microcomputer according to claim 3.

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