JPS6346028A - Cryptographic key distribution system - Google Patents

Abstract

PURPOSE:To safely describute a key for cryptographic communication to the person concerned of communication, by constituting the titled system so that a cryptographic key peculiar to a user station is sent to a toll center, the toll center generates its cryptographic key, executes cryptographing by using it and distributes it to the user station, and the user station decoding it by using a decoding key of its own station. CONSTITUTION:When user stations A, B have come to necessitate a cryptographic key for communication with regard to communication which is started newly or is executed already, said user stations A, B generate a cryptographing key and a decoding key for distributing the communication use cryptographic key, and send its distribution use cryptographing key to a toll center 1. The toll center 1 cryptographs the communication use cryptographic key allocated to communication of the user stations A, B, by using the distribution use cryptographing key and sends it to the user stations A, B. The user stations A, B obtain the communication use cryptographic key by decoding a signal from the toll center 1 by a distribution use decoding key. In such a way, no restriction is applied to both the communication use key and the distribution use key used for distributing the key, and also, according to such a system, it is unnecessary to manage concentrically these keys, and the safety is high.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a cryptographic key distribution method that is effective for safely distributing a key for cryptographic communication to parties to the communication in a communication system that performs cryptographic communication.

(Prior Art) In current communication formats, it is often possible for third parties to intercept communications. Under these circumstances, encryption technology becomes important as a means of safely transmitting information.

The basic encryption technology performs encryption and decryption using keys determined by the sending and receiving sides. Therefore, if the key used for the communication becomes known to a third party, the entire contents of the communication will become known, and encryption becomes meaningless. Furthermore, if one key is used for a long time, the risk of the key itself being decrypted increases.

From the above, when transmitting information safely,
For example, the security of encryption can be strengthened by determining the encryption key to be used for communication at the time a call occurs. From this point of view, multiple stations (
In a communication system consisting of user stations, at least one of the user stations or separately from the user stations generates an encryption key to be used for each communication between user stations, and transmits this to the user station. There is an encrypted communication system that has a central station (centralized station) that distributes information to the public. In such a system,
Although it is possible to change the encryption key as appropriate, leading to stronger communication security, a new issue is how to maintain the confidentiality of the encryption key assuming that the encryption key is distributed from the central station to the user station. .

Conventionally, the following three main methods have been proposed as methods for distributing encryption keys from a central station to user stations.

Method (1): The key generated at the central station is sent as is to the user station by some communication means.

Method (2): A unique key (master key) is prepared for each user station, and the central station encrypts the communication key with the master key of each user station and sends it to the user station. Decrypt with the master key to obtain the communication key.

Method (3): For each user station, apply the public key distribution method with the central station to create a common key for the user station and the central station, and use this as the master key as in method (2). A key for communication between user stations is distributed using the method described in the following.

Note that the public key distribution method described in method (3) means that when two stations want to possess a common key, each station independently generates a random number, uses it as a private key, and uses it as its own private key. At the same time, the result of a one-way transformation (a transformation that is difficult to reverse) is sent to the other station as a public key, and the secret key stored in one's own station and the result sent from the other station are sent to the other station. This method creates a key common to both parties from a public key. This method is described in the literature (W, Diffie and M, E, Hel.
lman, -New Directions in
Cryptography'', IEEE Trans
AC-tions on Information
Theory, Vol, IT-22, No, 6゜pp,
644-854. Nov, 197B).

In addition, method (3) is a demand allocation TD! using the communications equipment ECOME 1! It has been adopted in the IIA communication system, and has been adopted in the literature (J, C, Bic, J, C, Bousqu).
et and M, 0bera, ”Pr1vacy o
ver 5atellite Links”.

International Conference
on Digital 5atellite(:om
mumucation 1981. pp, 243-24
9) is explained in detail.

(Problems to be Solved by the Invention) The methods (1) to (3) described above each have the following problems.

Method (1) is the simplest method, but since the key is transmitted as is, if it is intercepted, the key cannot be easily known, so it is not very practical from a security standpoint.

In method (2), since the security of the communication key depends on the security of the master key, problems arise in how to set the master key and how to safely manage the master key at the central station.

In method (3), the master key can be set safely, but as with method (2), it is necessary to sufficiently protect the central station. Furthermore, since the master key is set using the public key distribution method, the key generated using the public key distribution method must be converted into a key for the encryption method applied to the actual key distribution method.

(Means for Solving the Problems) The present invention has been made in view of the drawbacks of the above-mentioned conventional techniques.
Regarding the distribution of communication keys from the central station to user stations, no restrictions are placed on either the communication keys or the distribution keys used for key distribution, and there is no need to centrally manage these keys. The purpose is to provide a highly secure cryptographic key distribution method. The feature is that when a user station needs a communication encryption key for a new communication or an existing communication, the user station can use the encryption key for distributing the communication encryption key and the decryption key. generates a lock, sends the distribution encryption key to the central station, and the central station uses the distribution encryption key sent from the user station to assign the communication encryption key to the communication of the user station. It is characterized in that the signal is encrypted and sent to the user station, and the user station obtains the encryption key for communication by decoding the signal from the central station using the decryption lock for distribution.

(Structure and operation of the invention) The present invention will be explained in detail below.

FIG. 1 shows the basic configuration of a communication system envisaged in the present invention, which is composed of one central station 1 and a plurality of user stations A to E. Communication lines are set up between the user stations A to E at any time, and messages can be sent and received between the central station and the user stations as necessary. Now, taking the example of trying to set up a communication line between user stations A and B, each of user stations A and B generates a set of an encryption key and a decryption wave, and sends the encryption key as a message. Central station 1
send to Centralized station 1 randomly generates an encryption key for communication between user stations A and B, encrypts it with the encryption key in the message sent from user stations A and B, and responds in the form of a message. Send to user stations A and B. User stations A and B decrypt the communication encryption key in the sent message using the decryption waves that each station owns to obtain a communication encryption key.

Here, the above-mentioned encryption method in which the encryption key and the decryption wave are different from each other is called an asymmetric encryption method, and among these, R5A
The Rivest-5hamir-Adleman method is widely known and is described in the literature (R, L.).

Rivest, A., Shamir and L.
1man, A Method for Obtain
ing Digital Signatures an
dPublic-Key Cryptosystems
”, Communications of the
A.C.M.

Vol, 21. No, 2. pp, 120-126. Fe
Bruary 1978).

In the above explanation, the case where a new communication line is set up between user stations A and B is taken as an example, but the encryption key used for the encrypted communication in the communication line that has already been set up between the user stations. The same procedure can be applied when changing.

The security of the communication encryption key in the configuration according to the present invention described above will be described.

First, the centralized station 1 generates a communication encryption key based on a request from one of the user stations, but if it is discarded after being distributed to the user station, it will not be possible to manage it for a long time. This is not necessary and will improve safety.

Furthermore, since the user station manages the encryption key for distribution, there is no need for management at the central station.

Next, regarding the security of the communication encryption key during the distribution process, if the aforementioned asymmetric encryption method is used as the encryption method for the distribution means, the encryption key will be known to the outside while being sent from the user station to the central station 1. Even if the encrypted signal from the central station 1 to the user station is decrypted, the encrypted signal from the central station 1 to the user station will not be decoded because the decrypted wave forming the pair will not be known. therefore,
The security of the communication encryption key is maintained even during the distribution process.

From the above, the security of the communication encryption key according to the present invention depends on the management of the decrypted wave at the user station. However, in this respect as well, security can be improved if keys are strictly managed at the user station. Furthermore, if the decrypted wave used - times is immediately discarded, there is no need to manage it, further increasing security. Note that in the present invention, the same key can be used any number of times as the distribution encryption key. Through this repeated use, even if the decryption wave were to become known to the outside world, a new key would be generated at the user station.
If this key is used from now on, the security of subsequent communications will be restored. Additionally, the generation of keys at the user station can be performed using a computer, etc., thereby increasing confidentiality through the hardware configuration.

As described above, according to the configuration of the present invention, it is possible to safely distribute a communication encryption key, and the confidentiality of encrypted communication using this key is greatly improved.

Here, a brief description will be given of the encryption method for communication between user stations. There have been various proposals for this type of encryption, but for example, the DES (Data Encryption Standard) established by the U.S. Department of Commerce is the standard for encryption for data transmission.
Cryption 5 standard). In this method, a data series is divided into blocks, and data symbols are exchanged within the block, or a specific pattern is exchanged with another pattern.

In this case, the encryption key is a data symbol permutation rule, a specific pattern, or another pattern. In such an encryption system, if the present invention is applied to change the encryption key every short period of time, even if the signal of the communication between user stations is intercepted, there is almost no possibility that the contents of the communication will be decrypted.

(Example) An example of the present invention is shown in FIG. 2, and will be described in detail below. Note that, in the description, an example will be taken in which encrypted communication is performed between user stations A and B, as in the previous section. Further, it is assumed that DES is used as the encryption method for communication, and the R5A method among the asymmetric encryption methods is used as the encryption method used for distributing the encryption key for communication.

In FIG. 2, the central station 1 includes a DES communication encryption key generation unit 11 used for communication between user stations A and B, and a DE
an R5A encrypting unit 12 that encrypts the key of S using the R5A method;
Sending/receiving unit 1 that sends and receives messages to and from user station A
3a and user station B for sending and receiving messages.
It is composed of a receiving section 13b. User station A includes an R5A method key generation unit 21a, R used for encryption/decryption of communication keys.
A memory 22a that stores a decryption lock based on the 5A method, and an R5A method decryption unit 2 that decrypts a communication key encrypted using the R5A method.
3a, a transmitting/receiving unit 24a for transmitting and receiving messages with the central station 1, and a memory 25a for storing a DES key for communication.
, a DES encryption/decryption section 26a, and a transmission/reception section 27a that transmits and receives data to and from user station B. User station B has a similar configuration to user station A.

When starting a new encrypted communication from user station A to user station B, user station A uses R5A method key generation unit 2.
A set of an encryption key and a decryption lock for the R5A method is generated using 1a. The decryption lock is stored in the memory 22a, and the encryption key is passed to the transmitting/receiving section 24a. The transmitting/receiving unit 24a creates a communication key distribution request message 31 containing the passed encryption key and sends it to the central station 1 according to the procedure shown in FIG. In the central station 1, when the transmitting/receiving section 13a receives the message 31 from the user station A, it creates an encryption key request message 32 for key distribution according to the procedure shown in FIG. Send it out. In user station B, when the sending/receiving unit 24b receives the message 32, the R5A method key generation unit 21b generates a set of an R5A encryption key and a decryption lock, and the decryption lock is stored in the memory 22b. The encryption key is passed to the sending/receiving section 24b. Send/
The receiving unit 24b creates a message 33 containing the encryption key and sends it to the central station 1.

At the central station, when the transmitting/receiving section 13b receives the message 233 from the user station B, the communication encryption key generating section 11 generates a DES encryption key 111 for communication between user stations, and the transmitting/receiving section 13a generates a DES encryption key 111 for communication between the user stations. R5A using user station A's key distribution encryption key 121a retrieved from message 31.
The cryptographic key 111 is encrypted into a code 122a in the cryptographic division section 12, and is passed to the transmitting/receiving section 13a. At the same time, the encryption key 111 is encrypted to 112b in the R5A encrypting unit 12 using the user station B's key distribution encryption key 121b extracted from the message 33 by the transmitting/receiving unit 14a. The sending/receiving unit 13a sends the encrypted key 122a to the message 3.
4 and transmits from user station A. Further, the sending/receiving unit 13b sends the encrypted key 122b to the user station B by putting it in the message 35. When the user station A receives the message 34 from the central station in the transmitting/receiving unit 24a, it takes out the communication key encrypted using the R5A method and uses the R5A method to encrypt the communication key.
The data is passed to the 5A method decoding unit 23a. The R5A method decryption unit 23a decrypts the communication DES key using the decryption lock stored in the memory 22a, and stores the decrypted key in the memory 25a. User station B also executes the same procedure for the message 35 and stores it in the memory 25a of user station A.
The same key stored in 25b is stored in 25b. As a result, user station A and user station B can encrypt and decrypt data using the same key, and can communicate with each other using encryption.

As mentioned above, not only when starting a new encrypted communication, but also when changing the key of the currently ongoing encrypted communication, by adding information on the timing of changing the key to the message 34.35, it is possible to do the same. You can change the communication encryption key using the steps below.

Although FIG. 2 shows a configuration in which there are three user stations, A and B, encryption keys can be distributed using a substantially similar configuration even when there are a large number of user stations.

(Effects of the Invention) As described above in detail, according to the present invention, a highly secure communication encryption key distribution system is realized, and encrypted communication with extremely high secrecy compared to conventional encrypted communication is guaranteed.

[Brief explanation of drawings]

FIG. 1 is a configuration example of a communication system to which the present invention is applied, FIG. 2 is a block diagram of the present invention, and FIG. 3 is a diagram showing the operation of the present invention. 1: Centralized stations A, B, C, D, E, user stations

Claims (1)

[Claims] In a communication system consisting of at least one central station that distributes encryption keys and a plurality of user stations that perform encrypted communications using the keys distributed from the central station, an encryption key is required. The user station that has become the user station sends an encryption key unique to the user station to the central station, and the central station generates an encryption key for communication for the user station and transfers the encryption key to the user station. It is encrypted using the encryption key sent from the station and distributed to the user station, and the user station obtains the encryption key for the communication by decrypting it using the decryption key it owns. An encryption key distribution method characterized by: