JPH1020779A - Key changing method in open key cipher system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change a key without inconvenience by decoding encoded data and electronic signed data smoothly with a past key so as to be able to obtain transmitter authorization after the key change of an open key cipher system. SOLUTION: This key changing method is provided with a table 201 holding past secret keys, a table 211 holding past open keys, and a table 221 holding transmitted side data before the change of keys. An old open key is transmitted to the transmitted side to which data was actually sent before the change of the key, and the data before the change of the secret key and open key is decoded on the transmitted side to confirm a signature. In decoding processing on the receiving side, whether the received data can be decoded with a present secret key or not is judged, and in the negative case, the old secret key is retrieved from the secret key table 201 to decode the data with the retrieved old secret key.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for changing an encryption key when performing cryptographic data communication between computer systems using a public key cryptosystem, and more particularly, to cryptographic communication with an unspecified majority in a wide area network environment. At times, it relates to a key change method in public key cryptography suitable for data encryption and sender authentication.

[0002]

2. Description of the Related Art Conventionally, there are a "secret key method" and a "public key method" as encryption methods for protecting communication contents. Of these, the "secret key method" is a method in which the sender and the receiver hold the same encryption key information so that the communication contents can be encrypted or decrypted, and the information for encryption and decryption is between the parties. Since only the information is known, the confidentiality of the information is high, but on the other hand, it is unsuitable when communicating with an unspecified number of people (broadcast or broadcast communication). On the other hand, the "public key method" is suitable for communicating with an unspecified number of parties, and has attracted attention, for example, as a technology for supporting commercial transactions on the Internet. In the public key method, only decryption information for decrypting encrypted communication contents is kept private as a private key, and encryption information for encryption is made public as a public key. Conventional literatures on the secret key method and the public key method include, for example, "Implementation and Examples of Encrypted E-mail PEM", IPSJ 46th Annual Convention (by Kikuchi and Morishita), and "Encryption E-mail Mechanism and FJPEM" Open Experiment ”May 31, 1994 (Kuroda,
Kikuchi, Yamaguchi).

FIG. 9 is an explanatory view showing a general public key encryption / decryption method. In FIG. 9, the sender A encrypts the plaintext using the B public key published by the recipient B, creates an encrypted text, and transmits the encrypted text to the recipient B. On the other hand, the receiver B decrypts the received ciphertext using the B secret key held only by the receiver B, and restores the original plaintext. FIG. 10 is a configuration diagram when the public key method is used in a computer network system. Here, a case is shown in which the public key method is used in a computer network system represented by the Internet. As shown in FIG.
The public key for encryption is registered in the server computer and can be referenced and used by anyone. On the other hand, a secret key for decrypting the received cipher text is secretly held and managed by each computer. Further, the public key cryptosystem is a cryptographic system suitable for authentication on the transmission side. That is, the transmitting side encrypts the authentication message with its own secret key and transmits it to the receiving side, so that the receiving side decrypts and authenticates the received authentication message with the transmitting side public key. In this case, the private and public keys in a computer system are mathematically paired.

[0004]

However, each of the secret key and public key cryptosystems has the following problems. First, the public key cryptosystem presupposes that the secret key is kept secret in each computer system, so if this premise breaks down, the sender encrypts with the receiver's public key. The ciphertext has a problem that it can be decrypted by anyone who holds the secret key on the receiving side. In addition, even if the sender encrypts the authentication message with its own secret key and sends it to the receiver, the receiver can decrypt the authentication message with the sender's public key, even if the sender can decrypt the authentication message. There is also a problem that can not be. In such a case, a method for changing the secret key and the public key of the computer system is required. Conventionally, due to the above-described problems, when a public key cryptosystem is used for an unspecified number of cryptographic communications in a wide area network environment, it has been impossible to quickly change the key. In general, in the case of one-to-many cryptographic communication, since it is practically equivalent to one-to-one cryptographic communication, it is easy to synchronize between computer systems in advance, and thus it is necessary to change keys quickly. Is easily conceived. However, in a wide area network environment, it is extremely difficult to synchronize changes and updates of private keys and public keys among an unspecified number of computer systems, and thus it is not possible to easily change keys. Also, if the key is changed after a certain point in time, the ciphertext received before that one point cannot be decrypted with the new private key, and the authentication message received before one point in time will In such a case, there arises a problem that authentication cannot be performed. Therefore, an object of the present invention is to solve these conventional problems, to smoothly decrypt the data encrypted by the past key and the digitally signed data after the key is changed and to perform sender authentication, and to quickly release the public key and the public key. An object of the present invention is to provide a key changing method in a public key cryptosystem in which a secret key can be changed and a key can be changed without any inconvenience.

[0005]

In order to achieve the above object, a key changing method in a public key cryptosystem according to the present invention comprises:
In each computer system, a table (private key table) holding past private keys and their attributes, a table (public key table) holding past public keys and their attributes,
A transmission result table before the key change final point and a data (transmission result table) holding data on its attributes are provided.
When the encryption key is changed, the old public key is transmitted from the transmitting computer system to the destination already transmitted before the last key change based on the transmission result table, and the receiving computer system transmits the old public key according to the attribute of the received old public key. Then, the necessity or unnecessary of the old public key is determined, the accumulation or destruction of the old public key is determined, and when the old public key is accumulated, the old public key and the attribute thereof are stored in a table (public key table). And
By retrieving the old secret key corresponding to the stored public key from the secret key table, data can be decrypted with the retrieved old secret key. The above-mentioned public key table is referred to when the necessity of the old public key is determined. This makes it possible to decrypt the data before changing the secret key and the public key and confirm the signature. Further, even when the public key is held locally, it is possible to automatically notify the timing of the change.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of a computer system to which a public key cryptosystem according to an embodiment of the present invention is applied. In FIG. 1, reference numeral 101 denotes a transmitting computer A that transmits data, and 111 denotes a receiving computer B that receives data. Also, 102 and 112 are key management files storing tables used in a system to be described later (see FIG. 2), 103 and 113 are data storage files storing data received from other computer systems, and 104 and 114. Is an encryption program that operates on the computer A or B, and 105 and 115 are key management programs that use the tables of the key management files 102 and 112 to perform processing when managing and changing private keys and public keys. Each of the computers 101 and 111 on the transmission side and the reception side holds the past secret key and the destination data before the key change in the table, so that the computer 101 and 111 refer to this table to change the encryption key. The old public key is transmitted to a transmission destination having a record of transmitting data before the key change, and the receiving computer 111 stores the received old public key in the data storage file 113 and the key management file 112. Referring to each table, the data before the secret key and the public key are changed is decrypted and the signature is confirmed. As a result, the data encrypted with the past key and the data with the digital signature can be smoothly decrypted after the key is changed, and the sender can be authenticated.

FIG. 2 is a format diagram of each table constituting the key management file according to the present invention. In FIG. 2, reference numeral 201 denotes a secret key table that stores a past secret key in the computer A in the contents of the key management file, and 202 denotes a period of use of the corresponding secret key in year / month / day / minute / second. Indicates the data of the secret key. Reference numeral 211 denotes a public key table for storing past public keys received from another computer system in the contents of the key management file. Reference numeral 212 denotes an ID of a computer that owns the public key. Indicates the use period of the public key in year, month, day, minute, and second, and 214 indicates the data of the public key. Reference numeral 221 denotes a transmission result table storing destination attributes before the last key change in the contents of the key management file. Reference numeral 222 denotes a destination computer ID as the destination attribute. Here, the ID of the computer 101 is A, and the computer 11 is
The ID of 1 is B.

FIG. 3 is a diagram showing a format of an old public key and a format of received data. Here, the format 311 of the old public key transmitted by the computer A
And the received data format 301 stored in the received data storage file of the computer B. In the received data format of (a), 302
Is the ID of the destination computer, 303 is the date and time of transmission, and 30
Reference numeral 4 denotes received data. Also, in the old public key format of (b), 312 is the ID of the computer that has made the public, 313 is the period during which this public key was used, 3
14 is old public key data. When the old public key is transmitted from the transmitting computer system A at the time of key change, the receiving computer system B transmits the received usage period of the old public key format of (b) and transmission of the received data storage file format of (a). The date and time are compared to determine whether there is a match, and if so, the old public key is stored in the public key table.

Next, the operation of the key change process of the key management program and the process of receiving the old public key will be described. FIG.
5 is an operation flowchart of a key change process of the key management program operating on the computer A, and FIG. 5 is an operation flowchart of an old public key reception process of the key management program operating on the computer B. As shown in FIG. 4, when the key is changed in the computer A, the old secret key is added to the secret key table 201 of the computer A and stored in step 401, and the transmission result table 22 is stored in step 402.
1, the old public key is transmitted to the computer (identified by the ID 222), which is the data transmission destination before the last time of the key change (here, transmitted to the computer B).
Next, as shown in FIG. 5, in step 501, the old public key 3
In step 502, the computer B that has received the “11” receives the I of the transmitting computer in the reception data format 301 stored in the reception data storage file 113.
D302 and transmission date 303, the received old public key transmission computer ID 312 and usage period 31
Then, it is determined whether or not there is one that matches 3 and if it exists, it is added to the public key table 211 of the computer B in step 503 and stored. An old secret key corresponding to the added and stored old public key can be searched from the secret key table 201, and data can be decrypted with the searched old secret key. If there is no match, the old public key received immediately is discarded in step 504.

Next, each processing of encryption and decryption in the present invention will be described in detail. FIG. 6 is an operation flowchart of the encryption program operating on the computer A,
FIG. 7 is an operation flowchart of the decryption process operating on the computer B, and FIG. 8 is an operation flowchart of the sender authentication process in FIG. When transmitting encrypted data from computer A to computer B,
As shown in FIG. 6, an encryption process is performed using a current public key in step 601, and an electronic signature process is performed using a current private key in step 602. Further, step 603
The ID of the computer A and the transmission date are added in the same format as the data storage file 301,
In step 604, a transmission process is performed to the destination. Next, when the computer B decodes the received data from the computer A, as shown in FIG. 7, the corresponding data is referred to from the received data storage file 113 in step 701, and the secret key table 201 in the computer B is read in step 702. From the use period 202 of the private key at the present time and the data format 30 stored in the received data storage file 113 in the computer B.
The data is compared with the transmission date and time 303 of the corresponding data of No. 1 and if the use start date and time of the secret key is later than the transmission date and time of the received data, it cannot be decrypted with this secret key. Therefore, in this case, in step 703, the secret key data 203 whose transmission date and time of the received data is included in the use period 202 in the secret key table 201 in the computer B is searched.
This is decrypted in step 704 with reference to the data. Further, in step 705, a sender authentication process is performed by decrypting the authentication message with the current public key.

The details of the sender authentication process are shown in FIG. In step 801 of FIG. 8, the current public key of the computer A is obtained from the public key table 211. In step 802, the use start date and time of the public key of the computer A at present and the received data storage file 113 in the computer B are stored. The transmission date and time 303 of the corresponding data format 301 are compared with each other, and when the use start date and time of the public key is later than the transmission date and time of the data, sender authentication cannot be performed with this public key. Therefore, step 80
In 3, the computer ID of the computer B in the public key table 211 in the computer B is computer A, the public key data 214 included in the usage period 213 is searched, and the search is performed in step 805 using the searched public key. Perform user authentication processing. However, if there is no data whose sender public key usage period matches the transmission date and time in the data that can be authenticated by the sender, that is, the received data, is not in the stored data of the received data storage file 113 (step 80).
4) In step 806, the public key in the public key table 211 is immediately discarded. If it is determined in step 802 that the received data can be checked for a signature with the current public key, a sender authentication process is performed in step 805 using the current public key.

As described above, according to the present invention, each of the computer systems on the transmitting side and the receiving side is provided with a table for storing the past secret key and a table for storing the transmission destination data before the key change, and the transmitting side computer has the key. At the time of change, the old public key is sent to the destination that has sent data before the key change based on these tables, and the data before the private key and public key are changed is decrypted and the signature is confirmed. I do. Thus, in public key cryptography,
The data encrypted with the past key and the data signed with the electronic signature can be smoothly decrypted and the sender authenticated after the key is changed. As a result, the key can be changed without any inconvenience.

[0013]

As described above, according to the present invention,
Since the data encrypted with the past key and the digitally signed data are smoothly decrypted and the sender is authenticated after the key is changed, the public key and the private key can be changed quickly, and changing the key is inconvenient. It is possible to do without.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a computer system to which a public key cryptosystem according to an embodiment of the present invention is applied.

FIG. 2 is a table format diagram stored in a key management file in FIG. 1;

FIG. 3 is a diagram showing a format of a received data stored in a data storage file in FIG. 1 and a format of an old public key transmitted by a computer whose key has been changed.

FIG. 4 is an operation flowchart of a key change process of a key management program in FIG. 1;

FIG. 5 is an operation flowchart of an old public key reception process of the key management program in FIG. 1;

FIG. 6 is an operation flowchart of the encryption program in FIG. 1;

FIG. 7 is an operation flowchart of a decoding process according to the present invention.

FIG. 8 is an operation flowchart of a sender authentication process in FIG. 7;

FIG. 9 is an overall configuration diagram showing a conventional public key cryptosystem encryption and decryption processing method.

FIG. 10 is a functional block diagram when a conventional public key cryptosystem is used in a computer network system.

[Explanation of symbols]

101: Data transmitting computer A, 111: Data receiving computer B, 102, 112: Key management file, 103, 113: Data storage file, 104, 114: Encryption program, 105, 115: Key management program, 201: Private key table, 202: Private key usage period, 203: Private key data, 211: Public key table, 212: Computer I
D, 213: public key usage period, 214: public key data, 221: transmission result table, 222: destination computer ID, 301: received data format, 31
1: Old public key format.

Claims (3)

[Claims] In a key changing method for performing cryptographic data communication between an unspecified number of computer systems using a public key cryptosystem, both the transmitting and receiving computer systems are
A secret key table that holds a history of past private keys, a public key table that holds a history of received past public keys, and a transmission result table that holds a destination ID of data transmitted before the change of the encryption key. At the time of the key change, the old public key is transmitted from the transmission-side computer system to the transmission destination that has transmitted the data before the encryption key change, based on the transmission destination ID of the transmission result table, and the reception-side computer system receives the old public key. A key change method in a public key cryptosystem, wherein data before the change of the encryption key is decrypted using the old public key and the contents of each of the tables, and the signature of the sender is confirmed. 2. The receiving computer system receiving the old public key includes a data storage file for storing all data received from another computer system, and the ID and transmission of the transmitting computer system of the data storage file. By referring to the date, if there is any one that matches the ID and the use period of the received old public key transmission computer system, the public key is stored in the public key table, and 2. The key changing method according to claim 1, wherein the received old public key is discarded when the key does not exist. 3. The transmission-side computer system performs data encryption processing with a current public key and signature processing with a current private key, adds a date to the data, and transmits the data to a destination. When decrypting the received data, comparing the use start date and time of the secret key at the present time with the transmission date and time of the received data from the use period of the secret key table, If it is after the transmission date and time, the transmission date and time of the received data is searched for the secret key data included in the use period in the secret key table, and the received data is decrypted using the searched secret key data. When the sender authentication is performed, the current public key is obtained from the public key table, the use start date and time of the public key is compared with the transmission date and time of the received data, and the public key If the use start date and time is later than the transmission date and time of the data, search for public key data whose transmission date and time is included in the usage period in the public key table, and perform sender authentication using the searched public key. 2. The key changing method in the public key cryptosystem according to claim 1, wherein