JP2002359615A - Private key control method for public key encryption system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the confidentiality and the guaranty principal performance in an electronic signature/authentication system. SOLUTION: Mr.A encrypts a plaintext M1 by using a public key PKbc to produce an encrypted text M2 and transmits it to both or either of Messrs B and C via the Internet. Mr.B or C receiving this encrypted text M2 uses both private keys SKb, SKc of the both in common to decode the encrypted text M2 and to obtain the original plaintext M1 because the decoding of the encrypted text M2 is impossible by using only the private key SKb or SKc. In this case, even if the private key of Mr.B or C is stolen, a 3rd party cannot interpret the encrypted text M2 by using the stolen key.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a secret key management method of a public key cryptosystem.

[0002]

2. Description of the Related Art With the spread of the Internet in recent years, electronic commerce has rapidly spread, and more recently, the digital signature law has come into effect, and electronic signature and authentication systems have received much attention. In this electronic signature / authentication system, the security of transactions is ensured by using encryption technology. There are two main types of information encryption schemes: a “common key scheme” and a “public key encryption scheme”. In the common key method, the sender and the receiver of information have a common key, and use this common key to encrypt and decrypt information. However, the sender and the receiver use the same key. Has the disadvantage that it is difficult to ensure the confidentiality of the information because it owns the information, and it is not possible to identify on which side the created ciphertext was created . For this reason, in the current electronic signature / authentication system, a public key cryptosystem is often used. This public key cryptosystem is further classified into several systems, and a system called an RSA system is a representative system, and is the system most frequently employed.

[0003] The public key cryptosystem will be briefly described. In this system, information is exchanged between two parties using a pair of a "public key" and a "private key". For example, a case where a contract is sent from Mr. A to Mr. B on the Internet, and Mr. B signs this contract will be described. In this case, it is assumed that Mr. B has previously applied to a public certification organization and has received a public key, and Mr. A has obtained the data of Mr. B's public key from the certification organization.

[0004] Mr. A first encrypts the plaintext contract written in ordinary text by multiplying it by the public key of Mr. B, and transmits the encrypted contract to Mr. B on the Internet. I do. Mr. B decrypts the encrypted contract using his private key, and restores the original text. Here, a sentence encrypted using Mr. B's public key cannot be decrypted without using Mr. B's private key. Therefore, Mr. B needs to strictly manage his private key data so that it cannot be stolen by others.

[0005] Mr. B creates a document signed by agreeing to this contract, and encrypts the document by multiplying it with his / her private key, and sends it to Mr. A. Mr. A decrypts the cipher text sent from Mr. B using his public key. Here, the text encrypted using Mr. B's private key cannot be decrypted without using Mr. B's public key. Therefore, if Mr. A can decrypt the encrypted document sent using Mr. B's public key, the document is definitely proved to be an encrypted document created by Mr. B himself. It was done. In other words, it is proved that Mr. B himself has signed the contract.

In the above public key cryptosystem, the cipher text sent from Mr. A to Mr. B can decrypt the contents of the cipher text to others as long as Mr. B securely manages his / her private key. It will not be done. Also, if Mr. A can decrypt using Mr. B's public key, he can confirm that the signature sent from Mr. B is definitely Mr. B himself. As described above, in the public key cryptosystem, the confidentiality of information can be easily secured by using a pair of a public key and a secret key, and the identity of the signature can be easily proved. As such, it has been commonly used in electronic signature and certification systems.

[0007]

As described above, in the public key cryptosystem, as long as the owner of the secret key manages the secret key securely, the confidentiality and the identity of the signature are secured. Proof will be guaranteed. However, if the secret key (data) is stolen by another person, the confidentiality and identity of the user are immediately lost, and there is a possibility that a person who conducts e-commerce will be greatly damaged. .

At present, it is said that it is practically impossible to determine the secret key data from the public key data if the number of bits of the key data is set to a certain value or more. However, it cannot always be said that it is absolutely safe, depending on the level of increase in the level of information processing technology on the intruder side.

The present invention has been made in view of the above circumstances, and provides a private key management method of a public key cryptosystem capable of improving confidentiality and personality in an electronic signature / authentication system by a simple device. It is intended to be.

[0010]

Means for Solving the Problems As means for solving the above-mentioned problems, the invention according to claim 1 is a method in which a public key previously disclosed to a third party is paired with the public key. Two keys, a secret key kept secret from the
A public key cryptosystem that enables a ciphertext to be created from a plaintext by using one of these two keys as an encryption key and returns the ciphertext to a plaintext by using the other key as a decryption key. The method is characterized in that the secret key is divided into a plurality of pieces and managed.

According to a second aspect of the present invention, in the first aspect of the present invention, when the secret key is divided into a plurality of keys, the ratio of parameters constituting each divided key is set irregularly. Features.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory diagram of a method according to this embodiment. According to the present invention, the secret key used in the public key cryptosystem is divided into a plurality of pieces and managed. The example of FIG. 1 shows an example in which the secret key is divided into two pieces.

In this example, Mr. A sends a confidential document in which a certain message is written to Mr. B and Mr. C. Mr. B and Mr. C work together. The public key PKbc and the private keys SKb and SKc are issued by the certification body. Mr. B owns the secret key SKb, and Mr. C owns the secret key SKc.
A description will be given of the case in which

Mr. A prepares a plaintext M1 containing a message to be sent to Mr. B and Mr. C.
Obtain the public keys PKbc of Mr. and Mr. C, and
The plaintext M1 is encrypted by bc to create a ciphertext M2. Then, the created ciphertext is transmitted to both or one of Mr. B and C via the Internet. Since Mr. B or Mr. C who received this ciphertext M2 cannot decrypt with only his / her own secret key SKb or SKc, he / she uses this secret key SKb and SKc jointly, By decrypting the sentence M2, the original plaintext M1 can be obtained.

Contrary to the case shown in FIG. 1, when the plaintext M1 created jointly by Mr. B and Mr. C is sent to Mr. A, Mr. B and Mr. C have secret keys SKb, SKc. Is used to encrypt the plaintext M1 to create a ciphertext M2, which is transmitted to Mr. A via the Internet. Mr. A can decrypt the sent ciphertext M2 using the public key PKbc to obtain the original plaintext M1. In this case, if Mr. A knows that there are two secret keys of Mr. B and Mr. C, the ciphertext M2 sent can be decrypted into the plaintext M1 with the public key PKbc. It can be confirmed that the plain text M1 is not a document created by either one of Mr. B or Mr. C without permission of the other, but a document created jointly by both parties and reflecting the intentions of both parties.

As described above, the secret keys of Mr. B and Mr. C are 1
Instead, it is divided into two secret keys SKb and SKc, so that the inconvenience of not functioning as a key unless both keys are used arises. it can. That is, even if either of Mr. B and Mr. C stolen the private key, the created ciphertext will not be read by a third party by itself, and the signed document of both parties may be forged. Nor.

In the above example, a case has been described in which two divided private keys are owned by two persons, respectively. However, it is needless to say that two divided private keys are owned by one person. It is also possible. Also, the number of divisions is not limited to two, and can be set to an arbitrary number of three or more. And if there is more than one owner of the private key, confidential information related to itself will not be disclosed without the approval of all owners.
If at least each owner strictly manages the secret key, he or she can obtain a sense of security because there is almost no risk of leakage of confidential information.

The method of dividing and managing a secret key into a plurality of pieces as described above is an extremely effective method that can enhance confidentiality with a simple configuration. That is, usually
Developers and designers of public key cryptosystems tend to consider means for improving confidentiality from a purely technical point of view, such as by improving software. However, the inventor of the present invention simply conceived of a configuration in which a secret key is divided into a plurality of pieces based on a free idea without being bound by the stereotype that it is natural that the key is one. is there.

Next, a method of creating a secret key will be described. In the public key cryptosystem, a public key and a secret key are simultaneously created as a pair of key pairs. In this case, a key pair is created by giving an encryption algorithm, a key length, a seed (random number), and the like to electronic information (plaintext). . Further, the secret key is usually stored in a medium that is inaccessible to anyone other than the person, such as an IC card, and measures are usually taken to require a password even when access is made.

When the secret key is divided into a plurality of pieces as in the present invention, it is necessary to provide a secret key division number and a secret key division parameter SKp (division ratio). Irregularities need to be provided to make it difficult for a person to make illegal decisions. Various methods are conceivable for giving irregularities.

FIG. 2 is an explanatory diagram of a method of determining a division ratio of a secret key based on a date and time, for example. In this example, the secret key division number is "5" and the date and time when the division was attempted happened at 15:39:49 on September 22, so the bit length of the secret key (for example, 1024 bits or 2048 bits) as "9: 22: 15: 3".
9:49 ", irregularities in the value of the division ratio are ensured.

FIG. 3 is an explanatory diagram of a method of determining a division ratio from a cursor movement position on a personal computer screen, for example. Since almost the same movement trajectory of the cursor of the personal computer does not occur, irregularities can be given to the division ratio using this property. The example shown is 6
This shows the coordinate positions of five points P1 to P5 at which the cursor has temporarily stopped on a screen of 40 × 400 pixels. Then, the sum of the x-coordinate value and the y-coordinate value of each of these five points is directly used as the division ratio “400: 300: 55”.
0: 700: 650 ".

The method of dividing and managing a secret key as in the present invention is suitable in the following case, that is, when information must not be disclosed unless all the owners of the secret key reach an agreement. It is believed that there is.

(1) A case where group companies exchange data requiring high confidentiality on the extranet.

(2) A case where a specific confidential information is held by a plurality of parties in a project employing the third sector system or the like. For example, when exchanging highly confidential data between the national government, local governments, and private companies via the Internet, or when using SI (System Integrated)
This is a case where highly confidential data is exchanged between companies including vendors.

(3) A case where highly confidential data is transferred between departments in a general company using an intranet.

(4) A case where a public institution (for example, a hospital or a school) holds information for which privacy is required. In this case, if the divided private key is owned by the person and a public organization, it is possible to prevent personal information from leaking outside without the person's knowledge.

[0028]

As described above, according to the present invention, since the secret key is divided into a plurality of parts and managed, the confidentiality and personality in the electronic signature / authentication system can be improved. Become.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a method of determining a division ratio of a secret key based on a date and time when a secret key is created.

FIG. 3 is an explanatory diagram of a method of determining a division ratio from a cursor movement position on a personal computer screen when creating a secret key.

[Explanation of symbols]

 PKbc B and C's public key SKb B's secret key SKc C's secret key M1 plaintext M2 ciphertext PK secret key SK1 to SK5 secret key P1 to P5 Cursor moving point

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J104 AA16 EA04 EA13 EA16 JA21 PA07 PA10

Claims (2)

[Claims] A public key previously disclosed to a third party;
Two keys, a public key and a secret key that is kept secret from a third party, are used. By using one of these two keys as an encryption key, a ciphertext can be converted from a plaintext. A public key cryptosystem that creates and uses the other key as a decryption key to convert the ciphertext back to plaintext, wherein the private key is divided into a plurality of pieces and managed. A secret key management method for key encryption. 2. The secret of the public key cryptosystem according to claim 1, wherein when the secret key is divided into a plurality of parts, a ratio of parameters constituting each divided key is set irregularly. Key management method.