JP2002185443A - Secret key managing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is necessary in the conventional technique that the same number of secret keys as the number of the other parties are reserved so as not to be known by a third party, when secret communication is performed with a plurality of the other parties, in public key ciphering. SOLUTION: Personal information input 101 and a master key storing part 103 are prepared. From personal information of the other party of transmission and a master key, a secret key provided with the personal information is formed (104) by using a unidirectional hash function, and reserved in a temporary storage 108 of the secret key. When the secret key is once erased after it is used, its formation is enabled again. As a result, reservation of the secret key is not necessary but the master key only is reserved so as not to be known by a third party.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the generation of a secret key of a cryptographic technique, and more particularly to a secret key generation method suitable for handling many secret keys regardless of a public key method or a common key method.

[0002]

2. Description of the Related Art Conventionally, when secret communication is performed with a plurality of parties using common key cryptography, it is necessary to store a number of secret keys equal to the number of communicating parties. Conventional key management for secret communication is based on encryption and information security (Shokodo 1990
March 29), page 58.

[0003]

In the prior art, when performing secret communication with a plurality of partners, it is necessary to store a plurality of secret keys.

An object of the present invention is to reduce the number of secret keys to be stored.

[0005]

According to the present invention, a master key, which is the only information that must be secretly managed, is generated, and a secret key is generated as necessary from the master key and information that can be disclosed. I do. Since this secret key is recoverable, it can be deleted after use, and there is no need to manage it secretly.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a secret document transmission device according to the present invention. The ciphertext creation device 105 includes a personal information input unit 101 for inputting personal information of a person to whom the ciphertext is to be sent, a plaintext input unit 102 for inputting a document (plaintext) to be secretly transmitted, and a ciphertext created by the ciphertext creation device. Device 109 for transmitting a sentence, and a secret key transmission device with personal information for transmitting a secret key with personal information generated by the ciphertext creation device
110 and a ciphertext decryption device 111 for decrypting the received ciphertext are connected. The ciphertext creation device includes a master key generation unit 103 that generates a key (master key) that must be secretly stored by the person who transmits the ciphertext, and a master key storage unit that is a medium for storing the generated master key. Ten
7. Private key with personal information generation unit 104 for generating a key (private key with personal information) used for encryption from master key and personal information, personal information for temporarily storing the generated private key with personal information A secret key temporary storage unit 108 and a plaintext encryption unit 106 for creating a ciphertext from the input plaintext and the secret key with personal information are provided. The ciphertext decryption device includes a ciphertext decryption unit 112 for decrypting a received ciphertext, and a private key with private information storage unit 113 for storing the received private key with private information.

FIGS. 2 and 3 show examples of the flow of a secret document transmission process according to the present invention.

First, a plain text to be transmitted is input (step 201), and personal information such as a user ID of a transmission partner is input (step 202). Then, it is determined whether or not the master key already exists in the master key storage device (step 203). If the master key does not exist, a new master key is generated (step 204), and the generated master key is stored. (Step 205). Next, the stored master key is read (step 206), and a private key with personal information is generated from the master key and personal information (step 20).
Perform 7). The plaintext is encrypted using the private key with personal information (step 208), and the encrypted text is transmitted (step 209). Then, it is determined whether the transmission partner is a partner who has transmitted the private key with personal information in the past (step 210). If the transmission partner is a partner who has not transmitted the secret key with personal information in the past, A private key with personal information is transmitted (step 211). Thereafter, the secret key with personal information is deleted (step 212). The ciphertext decryption device that has received the ciphertext determines whether the private key with personal information has been transmitted (step 213), and if so, stores it in the private key with private information storage unit. (Step 214). Thereafter, the private key with personal information stored in the private key with private information storage unit is read (step 215), and the ciphertext is decrypted using this key (step 216).

In step 202, the user ID of the transmission destination
Is input, but other publicly available information that can identify the key to be generated, such as a public key encryption public information, a simple numerical value, or a symbol, may be used.

FIG. 4 is a flowchart showing the process of generating a new master key (step 204) in FIG.

First, a random number is generated (step 301), and a new master key is generated by treating the random number as binary data (step 302).

FIG. 5 is a flowchart showing the process of generating a private key with personal information (step 207) in FIG.

First, the master key is represented by binary data, and this is substituted for a variable X (step 401). Also, the personal information of the destination is expressed in binary data, and this is
Substitute Y (step 402). Next, the counter and the variable k are initialized (step 403), and the binary expression of the counter is substituted for the variable C (step 404). Variable X, variable Y and variable
The combination of C is substituted for the variable Z (step 406). And
A hash value is obtained by the one-way hash function of the variable Z, and this is combined with the variable k (step 407). The bit length of the variable k is compared with the bit length of the private key with personal information (step 408). If the bit length of the variable k is smaller than the bit length of the private key with personal information, the counter is increased by 1 (step 408).
405) Returning to step 404, when the bit length of the variable k is larger than the bit length of the private key with personal information, the bit length of the private key with personal information from the beginning of the variable k is output as a key (step 409). .

In step 406, the variables X, Y, and C are combined, but relational operations such as sum, difference, and exclusive OR may be used.

FIG. 6 shows an example of data in the flowchart of FIG.

Reference numeral 501 denotes a data example of a master key, personal information, and a counter. Reference numeral 502 denotes data examples of variables X, Y, and C.
Reference numeral 503 denotes a data example of the combination of the variables X, Y, and C. 504 is the variable Z
5 is an example of hash value data. Reference numeral 505 denotes a data example of the variable k.

FIG. 7 shows an example of secret key management using the present invention, in which a user X (601) has a user A (602) and a user B (6).
03) and secret communication with the user C (604). The user X secretly manages only the master key K and generates a private key with personal information as needed. User A secretly manages secret key KA used for secret communication with X. A user
B secretly manages a secret key KB used for secret communication with X.
User A secretly manages secret key KC used for secret communication with X.

[0019]

As described above, according to the present invention,
In a system requiring a plurality of secret keys, the number of stored secret keys can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a secret document transmission device according to the present invention.

FIG. 2 is a diagram showing an example of a flow of a secret document transmission process according to the present invention.

FIG. 3 is a diagram showing an example of a flow of a secret document transmission process according to the present invention.

FIG. 4 is a diagram illustrating an example of a flow of a new master key generation process.

FIG. 5 is a diagram illustrating an example of a flow of a process of generating a private key with personal information.

FIG. 6 is a diagram illustrating an example of data of a process of generating a private key with personal information.

FIG. 7 is a diagram showing an example of secret key management according to the present invention.

[Explanation of symbols]

101 ... Personal information input unit, 103 ... Master key generation unit, 104 ...
Private key generation unit with personal information.

Claims (1)

[Claims] 1. A secret key management method for generating a secret key with personal information from a master key and personal information using a one-way hash function.