JP3396634B2 - Data encryption / decryption device and its program recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to encryption / decryption of data on a computer, and more particularly to the configuration of keys used during encryption / decryption, the configuration of an encryption / decryption device, and a program recording medium. In business activities that use computers, such as electronic commerce, electronic payments, and office automation of office work, communication data between computers and data stored in a database may be encrypted and electronically signed. Many.

Data encryption / decryption is performed by converting data to be encrypted with secret information called an encryption key / decryption key. The encryption key / decryption key corresponds to the common key in the symmetric key encryption system and the encryption public key / decryption private key in the asymmetric key encryption system. In any encryption system, if a single key is used for various types of data, the risk of decryption increases, so it is necessary to properly select and use a plurality of keys. Also, since the encryption key and the decryption key need to correspond to each other, the decryption side needs to know which encryption key was used by some method.

The present invention reduces the risk of decryption by automatically selecting different encryption keys for different data, and eliminates the need for explicit notification of the used encryption key to the decryption side. The present invention relates to a decoding device. In particular, it is assumed to be used for encryption / decryption at the time of backing up a file system in which a large amount of data is stored.

[0004]

2. Description of the Related Art A method for automating the selection of an encryption key is as follows.
Type to derive the encryption key to use from a single key (KP
S) and a type (PGP, etc.) of selecting an encryption key to be used from a plurality of encryption keys. More specifically, the former assumes that a single key called a master key is shared by the encryption side and the decryption side. For key selection at the time of encryption, a common key is generated from the master key and the ID on the decryption side. At the time of decryption, the master key and the I on the encryption side
The same common key is generated from D.

The latter is premised on that the encryption side and the decryption side have a plurality of keys. The key selection at the time of encryption is obtained by searching the key in the key file from the ID of the communication partner. Regarding the selection of the key at the time of decryption, a method of setting the ID of the key used for encryption on the encryption side in the header of the ciphertext data and notifying the decryption side is adopted. Both methods are characterized in that the encryption key is selected according to the ID on the decryption side.

The latter is further characterized in that the encryption side notifies the decryption side of the ID of the encryption key in a fixed format. As for the digital signature method, the digital signature using the RSA encryption method is currently the mainstream. The RSA digital signature calculates a message digest (MD) by applying a one-way function called a hash function with little collision to plaintext data (data before encryption), and encrypts this MD with the private key for signature of RSA. It is done by The verification of the signature is performed by collating the result obtained by decrypting the electronic signature with the RSA signature public key and the result obtained by applying the hash function to the plaintext data obtained as a result of the decryption. These processes are performed independently of data encryption / decryption.

[0007]

In the conventional data encryption / decryption device, the encryption key to be used is determined by the other party, that is, the ID of the decryption side so that the other party can decrypt the data. The same key will be used. In particular, if you generate a key for your data, you will always get the same key. As a result, a single encryption key is used for various kinds of data, which increases the risk of decryption by known attack methods such as selective plaintext attack.

In the conventional technique of selecting from a plurality of keys, data is regarded as a communication partner and an ID is added to the data to solve the problem of generating a key for own data. However, since the ID of the encryption key must be explicitly notified by the ciphertext header information,
It is not general because it requires the establishment of a unique notification format. The present invention has been made in view of the above points. The same encryption key is not used for various types of data, and the encryption key I
An object of the present invention is to provide a data encryption / decryption device and a program recording medium for the data encryption / decryption device, which solves the problem that it is not necessary to explicitly notify D to the decryption side.

[0009]

In order to achieve the above object, according to one aspect of the present invention, in encryption, a set of keys (metakey) to which a sequence number is given is input to an encryption device. And the output of the MD generation component from the signature generation device (plain text message digest: hereinafter referred to as MD)
And a key selector for selecting an encryption key to be an input of a data encryption component from a plaintext MD, and in decryption, a set of keys (metakey) to which a sequence number is added is a decryption device. Input, taking out the output of the MD decryption component (plaintext MD) from the signature verification device, and having a key selector for selecting the decryption key to be the input of the data decryption component from the plaintext MD, Is the gist.

Unlike the conventional method, the encryption key is selected based on the MD of the plaintext data instead of based on the ID of the decryption side. The key can be used, and the fact that the encryption device cooperates with the existing signature device to eliminate the need for ID notification of the key used for encryption (the plaintext MD is encrypted via the electronic signature). Utilizes that it is shared between the decryption side and the encryption side). Action On the encryption side, the plaintext data MD is extracted from the signature generation device. On the decryption side, the plaintext data MD is taken out from the signature verification device. That is, the MD of plaintext data can be taken out from both the signature generation device and the signature verification device before encryption and decryption. Therefore,
If the key is selected based on the MD of the plaintext data, it is not necessary for the encryption side to explicitly notify the decryption side of the key ID.

On the other hand, a set of keys (metakeys) to which sequence numbers are given is input to the encryption device and the decryption device,
Further, the MD of the plaintext data extracted from the signature generation device and the signature verification device can be regarded as an integer. Therefore, by selecting a key with a remainder obtained by dividing MD of plaintext data by the number of elements of the meta key, a different key can be selected for each plaintext data.

As described above, the objects of the present invention, that is, the same encryption key is not used for various kinds of data, and that there is no need to explicitly notify the decryption side of the key ID, are solved. It is possible to realize an encryption / decryption device for data to be processed.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment FIG. 1 is a diagram for explaining a first embodiment of the present invention and shows a functional configuration of an encryption device and a processing procedure at the time of encryption. 1. The plaintext data input to the encryption device is input to the signature generation device 11 and the data encryption component 12. 2. The plaintext data input to the signature generation device 11 becomes an input to the MD generation component 13 in the same device, and M of the plaintext data is input.
Generate D. 3. MD of plaintext data output from the MD generation component 13
Is an input to both the MD encryption component 14 and the key selector 15 in the signature generation device. MD generation component 13 is MD
It is realized by a hash function such as 4, MD5. 4. The MD encryption component 14 uses the given secret key for signature M
D is encrypted and an electronic signature is output as the output of the encryption device. The MD encryption component 14 is realized by an asymmetric key encryption algorithm such as RSA. 5. The key selector 15 selects a common key to be input to the data encryption component 12 from the meta key storage unit 16 according to the algorithm shown in FIG. 4 and outputs it. 6. The data encryption component 12 encrypts the plaintext data with the common key and outputs the result as the output of the encryption device. This component is realized by a symmetric key encryption algorithm such as DES and IDEA. Second Embodiment FIG. 2 is a diagram for explaining a second embodiment of the present invention, showing a functional configuration and a flow at the time of decoding. 1. The ciphertext data and the electronic signature input to the decryption device are the data decryption component 21 and the signature verification device 2, respectively.
It becomes the input of 2. 2. The electronic signature input to the signature verification device 22 is input to the MD decryption component 23 in the device, and the MD decryption component 23 decrypts the electronic signature with the given public key for signature. The obtained plaintext data MD is input to both the MD verification component 24 and the key selector 25 in the signature verification device 22. The MD decryption component 23 is realized by an asymmetric key encryption algorithm such as RSA. 3. The key selector 25 selects the common key to be input to the data decryption component 21 from the meta key storage unit 26 according to the algorithm shown in FIG. 4 and outputs it. 4. The data decryption component 21 decrypts plaintext data with a common key. The obtained result becomes the output of the decoding device and the input to the MD verification component 24. This part 21
Is realized by a symmetric key cryptographic algorithm such as DES or IDEA. 5. The MD collation component 24 uses MD4, M
The result obtained by applying a hash function such as D5 is compared with the other input MD, and the result (OK / NG) is output as the output of the decoding device.

FIG. 3 shows an example of the structure of the meta key. A key identifier field that stores information that identifies the meta key, and the number of keys included in the meta key (the number of entries in the individual key part below)
There is an encryption key number field in which is stored, a field in which a key sequence number assigned from 0 to "the number of keys included" -1 is stored, and a field in which key data is stored. The key data includes the length of the key used by the encryption / decryption algorithm (key length) and the substance of the key that is input to the encryption / decryption device. The key selector 15/25 selects a key having the same key sequence number as the remainder when the hash value of plaintext data is divided by the number of encryption keys.

The key identifier and the number of encryption keys are commonly provided at the beginning of the meta key as a common part, and for each key sequence number, the number and key data (key length, key substance) are in the individual key part,
There are as many encryption / decryption keys as there are repetitions. Only one entry is shown in FIG. The selection algorithm of the key selector 15/25 is shown in FIG. First, MD is divided by the number of encryption keys to obtain the remainder r (S1), and the pointer pointing inside the meta key is initialized to the head of the 0th individual key partial entry (S2). It is checked whether the key sequence number of the entry matches r (S3). If they do not match, the pointer is moved to the beginning of the next entry and the process returns to step S3 (S4). If a match is obtained in step S3, the substance of the key corresponding to the key sequence number of the entry is extracted and output (S5). Third Embodiment FIG. 5 shows an encryption device according to a third embodiment of the present invention.
The same symbols are attached to the portions corresponding to. In this embodiment, the key version is added as an input to FIG. 1, and this becomes the input of the MD generation component 13 instead of the plaintext data.
It is subject to electronic signatures as necessary. The key version may be any data, for example, in the case of date data, the key version is updated every day, but the data having the same key version number is used for one day, and the same key is used. A new key is automatically used when the key version number is updated. In the case of the date data, on the next day, the key version number is updated and a new key is used. By enclosing the meta key in an IC card or the like in advance, the key can be updated by rewriting the key version while maintaining the key identity. The update of the key version may be performed simultaneously from the center to a plurality of encryption devices, for example. Even if the key versions are the same between the encryption devices, the meta keys may be different from each other. On the contrary, even if the meta keys are the same, the key versions may be different from each other. Fourth Embodiment FIG. 6 shows a decoding device according to a fourth embodiment of the present invention, and FIG.
The same symbols are attached to the portions corresponding to. This decryption device corresponds to the encryption device shown in FIG.
The electronic signature of the key version is input to the signature verification device 22. Unlike FIG. 2, the MD matching component 24 is omitted. In other words, signature verification is not performed on plaintext data.

In the embodiment shown in FIG. 5, the MD encryption component 14 may be omitted and the key version of the MD may be sent to the decryption device. In this case, in the decoding device of FIG.
The MD decryption part 23 is omitted, and the MD of the received key version is input to the key selector 25. In the above description, the present invention is applied to the symmetric key cryptosystem. Therefore, the same set of common keys is stored in the meta key storage units 16 and 26. The present invention can be applied to an asymmetric key cryptosystem. In this case, a set of public keys is stored in the encryption-side meta key storage unit 16, a set of private keys is stored in the decryption-side meta key storage unit 26, and these public keys and secret keys are respectively stored. A number is given, and a public key and a secret key having the same number are used for encryption and decryption.

[0017]

As described above, according to the present invention, a plaintext M shared by an encryption side and a decryption side from a set of keys to which an input sequence number is added is shared via an electronic signature.
Since the key used for encryption / decryption is automatically selected by the key selector based on D or the MD of the key version, the key is not changed for each data or the key version is updated without explicit delivery of the key ID. Is automatically changed. Therefore, it is possible to provide a general-purpose key ID notification method in which the risk of attacking the ciphertext is reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a functional configuration of an embodiment of an encryption device of the present invention.

FIG. 2 is a diagram showing a functional configuration of an embodiment of a decoding device of the present invention.

FIG. 3 is a diagram showing a configuration example of a meta key.

FIG. 4 is a flowchart showing an example of a key selector selection algorithm.

FIG. 5 is a diagram showing a functional configuration of another embodiment of the encryption device of the present invention.

FIG. 6 is a diagram showing the functional configuration of another embodiment of the decoding device of the present invention.

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Claims (12)

(57) [Claims] 1. An MD generation component that inputs plaintext data and outputs a message digest (hereinafter referred to as MD), and an MD encryption component that inputs MD of the plaintext data and a signature private key and outputs an electronic signature. And a plaintext data described above, and a common key for encryption (hereinafter referred to as a common key) shared in advance by the encryption side and the decryption side, as input, and the ciphertext data is output. In a symmetric key encryption device having a data encryption component, a set of common keys is stored as one key (meta key), and the common key that is an element of the meta key has the same sequence number as the decryption side. The meta key storage unit to which is added, the meta key, and the MD of the plain text data are input, and the MD of the plain text data is divided by the number of common keys included in the meta key to obtain an order equal to the remainder. Corresponds to the number And a key selector for inputting a common key to the data encryption component. 2. An MD generation component that inputs plaintext data and outputs a message digest (hereinafter referred to as MD), and an MD encryption component that inputs the MD of the plaintext data and a signature secret key and outputs an electronic signature. And a plaintext data and the public key for encryption that forms a pair with the private key of the decryption side (hereinafter referred to as the public key), and the data encryption that outputs the ciphertext data. In the asymmetric key encryption device having a component, a set of public keys is stored as one key (meta key), and the public key that is an element of the meta key has the same secret key as the pair on the decryption side. The meta key storage unit to which the sequence number is assigned, the meta key, and the MD of the plain text data are input, and the MD of the plain text data is divided by the number of public keys included in the meta key to obtain the remainder. Corresponds to a sequence number equal to And a key selector for inputting a public key to the data encryption component. 3. A symmetric key encryption device that receives plaintext data and a common key for encryption (hereinafter referred to as a common key) as input, and outputs the ciphertext data from a data encryption component. The meta key is stored as a key (meta key), and the common key, which is an element of the meta key, is given a meta key storage section to which the same sequence number as that on the decryption side is given, and a message version (hereinafter MD An MD generation component for outputting the above), the meta key and the MD of the key version described above are input, and the MD of the key version is divided by the number of common keys included in the meta key in an order equal to the remainder. An encryption device, comprising: a key selector for inputting a common key corresponding to a number to the data encryption component. 4. The plaintext data and an encryption public key (hereinafter referred to as a public key) paired with a private key on the decryption side are input,
In an asymmetric key encryption device that outputs ciphertext data from a data encryption component, a set of public keys is stored as one key (meta key), and the public key that is an element of that meta key contains the decryption side A meta key storage unit to which the same sequence number as the secret key to be paired is added, an MD generation component that inputs a key version and outputs a message digest (hereinafter referred to as MD), the meta key and the key version MD and MD as input, and a key selector for inputting a public key corresponding to a sequence number equal to the remainder when the MD of the key version is divided by the number of public keys included in the meta key to the data encryption component. An encryption device provided with. 5. The encryption device according to claim 3, further comprising an MD of the key version and an MD encryption component that inputs a private key for signature and outputs an electronic signature. 6. An MD decoding component which inputs a digital signature and a public key for signature verification and outputs a message digest (hereinafter referred to as MD) of plaintext data, and a MD verification component which inputs MD and plaintext of the plaintext data as input. MD that outputs the result
In a symmetric key decryption device that has a signature verification device consisting of a verification component, and a data decryption component that inputs ciphertext data and a common key and outputs plaintext data, a set of common keys is one key. A meta key storage unit that is stored as a (meta key) and has the same sequence number as the encryption side in the common key that is an element of the meta key, the meta key, and the MD of the plaintext data. And a key selector for inputting a common key corresponding to an order number equal to a remainder when the MD of the plaintext data is divided by the number of common keys included in the meta key to the data decryption component. Decoding device. 7. An MD decoding component that inputs a digital signature and a public key for signature verification and outputs a message digest of plaintext data (hereinafter referred to as MD), and a MD verification component that inputs MD and plaintext of the plaintext data as an input. MD that outputs the result
An asymmetric key decryption device including a signature verification device including a verification component, and a data decryption component that inputs ciphertext data and a decryption secret key (hereinafter referred to as a secret key) and outputs plaintext data as an output. In, the set of secret keys is stored as one key (meta key), and the secret key, which is an element of the meta key, is assigned the same sequence number as the public key of the encryption side. The key storage unit, the meta key, and the MD of the plaintext data are input, and the secret key corresponding to the sequence number equal to the remainder when the MD of the plaintext data is divided by the number of secret keys included in the meta key. And a key selector for inputting to the data decryption component. 8. In a decryption device which inputs ciphertext data and a decryption common key (hereinafter referred to as a common key) and outputs plaintext data from a data decryption component, a set of common keys is one key ( Meta key), and a common key that is an element of the meta key has a meta key storage unit to which the same sequence number as the encryption side is added, and a message digest of the meta key and the key version (hereinafter referred to as MD). And a key selector that inputs a common key corresponding to a sequence number equal to a remainder when the MD of the key version is divided by the number of common keys included in the meta key to the data decryption component. And a decoding device. 9. Decryption in which ciphertext data and a decryption secret key (hereinafter referred to as a secret key) paired with an encryption public key on the encryption side are input, and plaintext data is output from a data decryption component. In the encryption device, a set of secret keys is stored as a single key (meta key), and the secret key that is an element of the meta key has a meta key storage unit that has the same sequence number as the encryption side. , The meta key and the message digest of the key version (hereinafter referred to as MD) are input, and the MD of the key version corresponds to a sequence number equal to the remainder when divided by the number of secret keys included in the meta key. And a key selector for inputting a secret key to the data decryption component. 10. The apparatus according to claim 8 or 9, further comprising: an MD decryption component that inputs the electronic signature of the key version and the public key for signature verification, and outputs the MD of the key version. Decoding device. 11. A computer-readable recording medium recording a program for causing a computer to function as the encryption device according to claim 1 . 12. The method according to any one of claims 6 to 10.
Flop <br/> computer-readable recording medium recording a program for causing a computer to function as the decrypted apparatus.