JPH11187008A - Delivering method for cryptographic key - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a delivering method for cryptographic key improved in versatility or convenience by safely and easily delivering a cryptographic key for cryptographic communication to the user of a cryptographic communication system by communication through an internet while securing its secrecy. SOLUTION: Communication is enabled though an internet 3 between terminal equipment 1 of a key issue station and terminal equipment 2 of the user while using a hyper text transfer protocol(HTTP), a disclosed key based on an Elgamal code is transmitted from the terminal equipment 1 through the internet 3 to the terminal equipment 2. Next, random number data generated by the terminal equipment 2 are enciphered by the disclosed key, transmitted to the terminal equipment 1 and deciphered by the terminal equipment 2 so that common random number data are shared between both the terminal equipment 1 and 2. Next, these random number data are used as the key of a common key system, the cryptographic key for user generated by the terminal equipment 1 is enciphered and transmitted to the terminal equipment 2 and that key is deciphered while using the random number data held at the terminal equipment 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for distributing an encryption key used for performing cryptographic communication between users of a cryptographic communication system to each user.

[0002]

2. Description of the Related Art Public key systems and common key systems are known as methods for performing encrypted communication between users of a cryptographic communication system. Among them, the public key system is used for encrypting data by each user. Public key as a public key, and possesses a key for decryption in secret as a secret key. The so-called RSA encryption and Elgamal encryption belong to the category of this method. is there. In this case, a public key and a secret key for each user are generated by a key issuing station of the cryptographic communication system, and the key issuing station manages a public key for each user and distributes a secret key to each user. Then, in the encrypted communication between the users, the transmitting user encrypts the data using the public key of the receiving user and transmits the data, and the receiving user decrypts the data using his / her private key. .

[0003] In the common key method, users performing cryptographic communication share a common key for encryption and decryption. In this method, for example, a paper "NO
N-PUBLIC KEY DISTRIBUTION / Advance in Cryptology:
Proceedings of CRYPTO '82 / Plenum Press 1983, pp.23
1-236 ", also published by Rolf Blom," An OptimalCla
ss of Symmetric Key Generation Systems / Advances
in Cryptology: EUROCRYPT '84 / Springer LNCS 209, 19
85, pp. 335-338 ", or Japanese Patent Publication No. 5-48980 or U.S. Pat. No. 5,016,276, by applying an identifier such as the name of a communication partner to make a common key with the communication partner. Is generated by a key issuing authority for each user as a secret key unique to each user, and the algorithm is delivered from the key issuing authority to each user. In this system, when performing cryptographic communication between users, each user generates a common key with the user of the communication partner by applying the identifier of the communication partner to its own secret key at its own terminal device. And encrypts / decrypts the data using the common key to perform encrypted communication.

In this type of cryptographic communication system, an encryption key such as a secret key in the above-described public key system and a secret key in the common key system requires extremely high confidentiality. It must be delivered to the user from the key issuing authority. Therefore, it is an important issue how to securely distribute an encryption key requiring high confidentiality to each user as described above.

On the other hand, in the field of information communication in recent years, the use of the Internet has rapidly spread, and in such a situation, considering the versatility or convenience of the cryptographic communication system, the encryption key as described above is used. It is desired that delivery be performed by communication via the Internet.

However, since the Internet can be freely used by anyone, it is difficult to secure confidentiality by delivering an encryption key requiring high confidentiality via the Internet as described above. Is believed to be.

For this reason, conventionally, the above-described distribution of the encryption key is generally performed by distributing a physical recording medium such as a floppy disk storing the data of the encryption key to each user. .

However, such an encryption key distribution method is disadvantageous in terms of cost. In addition, after a user applies for a subscription to the encryption communication system, the user receives the encryption key and actually uses the encryption communication system. It took a long time to be able to do so, which was inconvenient.

When an encryption key is delivered from one party to another, a secret word and the like are agreed upon in advance between the two parties and shared, and the sender and the receiver of the encryption key start with the secret word and the like shared by each other. DES (Data E
In addition to generating a key of the encryption standard), the sender encrypts the encryption key to be delivered using the above-mentioned DES key and gives it to the receiver.
By decrypting using the ES key, the encryption key can be safely delivered to RSA Laboratories (RSA Laboratories).
Research Institute A has a homepage on the Internet (http: // w
ww.rsa.com/rsalab) (title: “PKCS
# 5 / Password-Based Encryption Standard / An RSA Lab
oratories Technical Note ／ Version 1.5 ／ Revised No
vember 1,1993 "). In this method, since the encryption key is encrypted and distributed, at first glance, it seems that the key can be safely distributed by communication such as the Internet. However, in this method, in order to ensure the security of the distribution of the encryption key, the password and the like must be negotiated safely (not to be understood by a third party) between the sender and the receiver of the encryption key. Must. Therefore, there is a problem how to securely exchange the password and the like between the two, and if the exchange is performed on a physical recording medium such as a floppy disk, the same inconvenience as described above occurs. Would.

[0010]

SUMMARY OF THE INVENTION In view of this background, the present invention distributes an encryption key for encrypted communication to a user of an encrypted communication system safely and easily by communication via the Internet while securing the confidentiality. It is an object of the present invention to provide an encryption key distribution method which is excellent in versatility and convenience.

[0011]

According to a first aspect of the present invention, there is provided a method for distributing an encryption key, comprising: A method of distributing a key from a key issuing station of the cryptographic communication system to each user, the method comprising: transmitting to a terminal device owned by each user and the key issuing station in advance an unspecified communication on the Internet for each communication of data. Prepare Internet communication means to communicate via the route,
When the user requests the terminal device of the key issuing authority to deliver the encryption key from the terminal device, a public key for encryption for encryption communication by a public key method and a decryption Generating and holding a secret key of the public key and the secret key, and transmitting the public key from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means; and In the terminal device of the user receiving the, after the user performs a predetermined operation of the terminal device to generate and hold random number data unique to the user, encrypts the random number data with the public key, Transmitting the encrypted random number data from the terminal device of the user to the terminal device of the key issuing station via the Internet communication means; and transmitting the encrypted random number data to the key issuing station receiving the encrypted random number data. Decrypting the encrypted random number data with the secret key and holding the encrypted random number data, and generating the encryption key of the user in the terminal device of the key issuing authority holding the decrypted random number data. ,
The encryption key is encrypted using the random number data as a key for encrypted communication by a common key method, and the encrypted encryption key is transmitted from the terminal of the key issuing authority to the terminal of the user via the Internet communication means. And decrypting the encrypted encryption key using the random number data held in the terminal device as a key according to the common key method in a user terminal device that has received the encrypted encryption key. And holding it.

According to the present invention, when the user accesses the terminal device of the key issuing station from the terminal device and requests the delivery of the encryption key, the terminal device of the key management station:
A public key for encryption and a secret key for decryption by the public key system are generated, and among these public keys and private keys, the public key transmits Internet communication means from the terminal device of the key management station to the terminal device of the user. Given through. Then, in the terminal device of the user who has received the public key, random number data unique to the user generated and held by the user by a predetermined operation of the terminal device is encrypted by the public key,
The encrypted random number data is transmitted from the user terminal device to the key management station terminal device via the Internet communication means. The terminal device of the key issuing station that has received the random number data encrypted as described above decrypts the random number data with the secret key and generates a random number common to the random number data held by the terminal device on the user side. Get the data. As a result, the user and the key issuing station share the random number data that can be used as a key for the common key cryptographic communication.

At this time, since the public key and the random number data encrypted with the public key are individually communicated via Internet communication means, their communication paths on the Internet are unspecified and generally Do not follow the same communication path. For this reason, even if a third party individually obtains the public key and the random number data encrypted thereby, it is extremely difficult to obtain them collectively. Therefore, for example, even if a third party obtains the encrypted random number data, it is not known what encryption method has been used. Further, since the random number data is unique to the user generated by operating the user's own terminal device, it is originally difficult for a third party to predict and the cryptographic data is encrypted by the public key. And sent. This makes it difficult for a third party to decrypt the random number data encrypted with the public key, and the random number data is safely passed from the user to the key issuing authority.

Next, the terminal device of the key issuing authority, which has obtained the decrypted random number data as described above, generates the encryption key to be delivered to the user, and then replaces the encrypted key with the decrypted random number data. Is used as a key for encryption communication by the common key method, and the encrypted encryption key is transmitted from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means. Then, the terminal device of the user who has received the encrypted encryption key decrypts the encrypted encryption key using the random number data held in the terminal device as a key of a common key system, and To obtain a desired encryption key.

At this time, even if a third party individually obtains the encrypted encryption key transmitted from the terminal of the key issuing authority to the terminal of the user, the encryption key of the encryption key may be obtained. The random number data used as the key is originally difficult to be predicted by a third party, and the cryptographic communication using the random number data as a key is performed by transmitting the cryptographic key from the terminal device of the key issuing authority to the terminal device of the user. Therefore, it is extremely difficult for a third party who has acquired the encryption key to decrypt the encrypted encryption key using the random number data as a key. Moreover, the encryption communication of the random number data by the public key method performed prior to the encryption communication of the encryption key from the key issuing station to the user, and the encryption communication of the encryption key by the common key method using the random number data as a key. Is performed via an unspecified communication path on the Internet, and it is difficult for a third party to collectively collect the encrypted random number data and the encrypted encryption key. Therefore, even if a third party obtains and decrypts the random number data encrypted with the public key, it is difficult to obtain the encryption key encrypted using the random number data as a key.

Thus, the encryption key is safely delivered to each user via the Internet. Further, since the communication of the encryption key is performed by the encryption communication using the common key system, the encryption and decryption of the encryption key can be performed quickly and efficiently.

Therefore, according to the present invention, an encryption key for encrypted communication can be safely and easily delivered to a user of an encrypted communication system through communication via the Internet while securing the confidentiality of the encryption key. It is possible to provide an encryption key distribution method that is excellent in convenience and convenience.

In a second more specific aspect of the present invention, an encryption key used by each user when performing cryptographic communication between users of the cryptographic communication system is transmitted from a key issuing station of the cryptographic communication system to each user. Is delivered to a terminal device owned by each user and the key issuing authority in advance.
Internet communication means for performing communication through an unspecified communication path of the Internet for each data communication is prepared, and a user joins the terminal device of the key issuing authority from the terminal device to the cryptographic communication system. At the terminal of the key issuing authority, generates and holds an encryption public key and a decryption private key for cryptographic communication by the public key method, and stores the public key and the secret key among the public key and the secret key. Transmitting the public key from the terminal of the key issuing authority to the terminal of the user via the Internet communication means; and in the terminal of the user receiving the public key, By performing the operation, random number data unique to the user is generated and held, and the key issuing authority inputs personal information of the user for identifying the user to the terminal device. Encrypting the random number data and the personal information with the public key, and transmitting the encrypted random number data and the personal information from the terminal device of the user to the terminal device of the key issuing station via the Internet communication means. Receiving the encrypted random number data and personal information in a terminal device of a key issuing authority, decrypting the encrypted random number data and personal information with the secret key, and holding the decrypted random number data and personal information; After generating the encryption key of the user related to the personal information in the terminal device of the key issuing authority holding the data and the personal information, the terminal encrypts the encryption key using the decrypted random number data as a key according to the common key method. Transmitting the encrypted encryption key from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means. Decrypting the encrypted encryption key by using the random number data held in the terminal device as a key according to the common key method in a terminal device of the user that has received the encrypted key, and holding the decrypted encryption key. It is characterized by the following.

According to the present invention, when the user accesses the terminal device of the key issuing authority from the terminal device and applies for the key issuing authority to join the cryptographic communication system, the first aspect of the present invention described above. After the public key is passed from the terminal device of the key issuing authority to the terminal device of the user in the same manner as described above, random number data unique to the user generated by the user through a predetermined operation of the terminal device, The input personal information of the user is encrypted by the public key in the terminal device of the user, and the encrypted random number data and the personal information are transmitted from the terminal device of the user to the terminal device of the key issuing authority through the Internet communication. Transmitted via the means. Then, the terminal device of the key issuing authority that has received the encrypted random number data and the personal information decrypts the random number data and the personal information using the secret key and holds the data. This allows the key issuing authority to provide the user who subscribes to the cryptographic communication system with random number data used as a key for delivering the cryptographic key by cryptographic communication using the common key method, and the user's personal information for identifying the user. Information can be obtained.

At this time, as in the case of the first aspect described above, the communication of the public key and the communication of the random number data and personal information encrypted with the public key are transmitted over the Internet by the Internet communication means. Is performed individually via an unspecified communication path, and random number data and personal information are encrypted and communicated with a public key, so it is difficult for a third party to decrypt the random number data and personal information . Therefore, the transfer of the random number data and the personal information from the user to the key issuing station is performed safely. In addition, since the personal information is encrypted and decrypted by the common key method, the encryption and decryption are performed quickly.

After the key issuing authority has obtained the random number data and the personal information unique to the user in this way, the terminal device of the key issuing authority generates the encryption key of the user relating to the personal information, This encryption key is transmitted from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means by a common key cryptographic communication using the random number data as a key in exactly the same manner as in the first aspect. You. Then, the user's terminal device obtains the required encryption by decrypting the encrypted encryption key using the random number data stored therein as a key.

At this time, as described in the first aspect, the encryption key is safely delivered to each user via the Internet. Further, since the communication of the encryption key is performed by the encryption communication using the common key system, the encryption and decryption of the encryption key can be performed quickly and efficiently.

According to the second aspect of the present invention,
The cryptographic key for the cryptographic communication can be safely and easily delivered to the user of the cryptographic communication system by communication via the Internet while ensuring the confidentiality of the key, as in the first aspect. The key issuing authority can safely and efficiently receive the user's personal information for identifying the user on the side, so that the procedure for the user to join the cryptographic communication system can be performed safely including the distribution of the cryptographic key. In addition, the versatility and convenience of the cryptographic communication system can be improved.

The second aspect of the present invention is particularly effective when the encryption key is generated at the terminal of the key issuing authority based on the personal information of the user. That is, in this case, since the personal information of the user required to generate the encryption key is safely and efficiently passed from the user to the key issuing authority as described above, the encryption key based on the personal information is also used. It can be generated safely and efficiently on the key management station side.

Further, in the first or second aspect of the present invention as described above, it is preferable that the cipher communication by the public key method uses Elgamal encryption. That is, the ElGamal encryption requires a relatively short time for data encryption and decryption processing compared to the RSA encryption or the like, and therefore, the random number data can be efficiently encrypted and decrypted. it can. In this case, although the El Gamar encryption is said to be weaker in security than the RSA encryption, it is less resistant to attacks such as collection of a large number of encrypted data.
In the present invention, the encryption communication using the Elgar cipher is used only when transmitting the random number data from the user terminal device to the key issuing authority terminal device, so that sufficient security can be ensured.

In particular, when the public key and the secret key according to the public key system are generated each time the public key is transmitted from the terminal of the key issuing authority to the terminal of the user, the Elgammal encryption is used. In the communication of the random number data, basically, the encryption and decryption of the random number data are performed using a different key each time the communication is performed, so that the strength of security can be further increased. . In this case, the strength of security can be higher than that of ordinary RSA encryption.

In the first or second aspect of the present invention,
It is preferable that the random number data is generated in the terminal device of the user based on a timing of a predetermined input operation by the user. By generating such random number data, it is possible to generate random number data unique to the user with poor reproducibility and hard to predict, and the encryption key using the random number data as a key in a common key system. Security of the encrypted communication can be further improved.

In the present invention, the encryption key comprises an algorithm for generating a common key for encrypted communication with the user at the communication partner by applying an identifier of the user at the communication partner to the encryption key. In this case, when the users communicate with each other after the encryption key is delivered, each user simply applies the identifier of the user on the communication partner side to his or her own encryption key. Since a common key with the user on the side can be obtained, encrypted communication using the common key can be easily performed.

[0029]

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

FIG. 1 shows the overall configuration of an encryption communication system to which the encryption key distribution method of the present embodiment is applied.
The terminal device 1 provided in the key issuing authority and the terminal device 2 owned by each user are connected to each other so as to be able to communicate via the Internet 3. A gateway of a provider, a public line network, or the like may be interposed between each of the terminal devices 1 and 2 and the Internet 3.

Each of the terminal devices 1 and 2 is constituted by a computer such as a personal computer (including a communication device such as a modem, a display, a keyboard, and the like). The terminal device 1 of the key issuing authority is a server, and the terminal device 2 of a user. In order to carry out communication between the terminal devices 1 and 2 via the Internet 3 as a client, the terminal device 1 of the key issuing authority includes a well-known TCP.
/ IP (Transmission Control Protocol / Internet P
rotocol), HTTP (Hyper-Text Transfer Protocol)
Protocols such as l) are incorporated as the Internet communication means 1a, and a homepage for applying for subscription to the cryptographic communication system is incorporated.

The user terminal 2 has a TCP /
A browser including IP and HTTP is incorporated as the Internet communication means 2a.

Here, the HTTP included in the Internet communication means 1a, 2a of each of the terminal devices 1, 2 is set such that each time one communication of data is completed (every communication of one packet),
It has a function of communicating the data via an unspecified communication path of the Internet 3.

Next, in this cryptographic communication system, the operation when the cryptographic key necessary for the users to perform the cryptographic communication with each other from the key issuing authority to each user will be described with reference to the flowcharts of FIGS. explain.

First, a user who intends to join the cryptographic communication system obtains a password distributed by a key issuing authority (or a system administrator) in advance (STEP 1).
-1, 2-1). This password is for, for example, excluding users outside the region that the cryptographic communication system of the present embodiment intends to support. The distribution of the password to each user is performed off-line through mail or the like.

Next, when the user joins the cryptographic communication system, the user accesses the terminal 1 (server) of the key issuing authority from his own terminal 2 via the Internet 3 by the Internet communication means 2a (STEP 1).
2).

At this time, in the terminal device 1 of the key issuing station, when the above access is made (STEP 2-2), the terminal device 1 performs the cryptographic communication by the public key method using Elgamal cipher (Elgamal) described below. A public key and a secret key are generated and stored (STEP 2-3).

In the above-mentioned El Gamal encryption, p: prime number, k:
an integer that is relatively prime to p-1, g: an integer that satisfies g <p,
When x: an integer satisfying x <p, y: y = g ^x mod p, the communication data M (plaintext) is encrypted by the following equation (1).

B = y ^k M modp (1) Here, b indicates an encrypted communication data M.

When the communication data M is encrypted as described above, if a: a = g ^k mod p, the communication data M is decrypted by the following equation (2).

[0041] ^{M = b / a x mod p} ...... (2) Therefore, in the present embodiment, the terminal device 1 of the key issuing station,
In STEP 2-3, the prime number p and the integers k, g, and x defined as described above are generated, and the y (= g ^x
mod p) and a (= g ^k mod p) are calculated. And
Among these, y, k, and p are held as public keys for encrypting the communication data M, and a and x are held as secret keys for decryption together with the prime number p.

In this case, in STEP 2-3, the prime number p and the integers k, g, x that define the public key and the secret key are randomly generated. More specifically, a plurality of prime number p candidates are prepared in advance, and when generating a public key and a secret key in STEP 2-3, one prime number p is randomly selected from the prepared plurality of prime numbers. . Then, for the selected prime number p, integers k, g, and x are randomly generated so as to satisfy the above-described definition conditions.
At this time, the integers k, g, and x are determined to be finite for each prime number p.
May be stored in advance and integers k, g, and x may be randomly selected one by one from them.

When the size of the communication data M to be encrypted by the above equation (1) is, for example, 1 byte ( ²⁸ bits), the prime number p is 2 ⁸ −1 = 255 or more. Is preferred.

After generating and holding the public key and the private key by the El Gamal encryption as described above, the terminal device 1 (server) of the key issuing authority transmits the encrypted data to the user terminal device 2 (client). A home page for applying for a subscription to the communication system is transmitted to the user terminal device 2 via the Internet 3 by the Internet communication means 1a (STEP 2-4).

When the user receives the homepage on the terminal device 2 in this manner (STEP 1-3), the user checks the contents described on the homepage and the like, and then checks the public key and the later-described information. A download request for receiving communication processing software required for processing to the terminal device 2 of the user is transmitted from the terminal device 2 to the terminal device 1 of the key issuing authority via the Internet communication means 2a (STEP 1). 4).

At this time, when the terminal device 1 of the key issuing station receives the download request (STEP 2-5),
The public key (y, y,
k, p) and communication processing software stored and held in advance are transmitted to the user terminal device 2 via the Internet communication means 1a (STEP 2-6).

Here, the communication processing software includes processing software for generating random number data, processing software for encrypted communication, processing software for inputting personal information of a user, and the like. ing.

In this way, the user can use the terminal device 2
When the above public key and communication processing software are received (STE
P1-5) Then, in the terminal device 2 of the user, the communication processing software is activated (STEP 1-6).

At this time, the communication processing software first enters a mode for generating random number data to be used as a session key for cryptographic communication using the common key method described later. Data is generated and stored (STEP 1-7).

That is, the communication processing software instructs the user to input, for example, a predetermined word or sentence in the terminal device 2. At this time, when the user inputs a predetermined word or sentence in accordance with the instruction, the communication processing software measures the time difference between inputs of each word of the word or sentence, and uses the time difference as a seed to generate random number data (session key). Generate and save. In this case, since the time difference as a seed of the random number data is due to an artificial operation of the user, the time difference generally differs for each user, and thus the generated random number data is unique to the user. Further, since it is difficult for each user to accurately control the timing of the input operation of the word or the sentence, random data that is difficult to predict only this time is generated.

After generating the random number data in this manner,
The communication processing software enters a mode in which the user's personal information and password are input to the terminal device 2 of the user.
The password acquired in advance in 1-1 is input to the terminal device 2 (STEP 1-8). Here, the personal information of the user to be input includes the address, name, telephone number,
An e-mail address or the like.

When the user's personal information and password are input in this manner, the communication processing software
Random number data (session key) generated in TEP1-7
Then, the personal information and the password of the user input in STEP 1-8 are encrypted by the above formula (1) using the public key downloaded to the terminal device 2 in STEP 1-5 (STEP 1-9). Then, the communication processing software transmits the random number data (session key), personal information and password thus encrypted to the terminal device 1 of the key issuing authority via the Internet communication means 2a of the terminal device 2 (STEP 1-10). ).

On the other hand, when the terminal device 1 of the key issuing station receives the random number data, personal information, and password encrypted by the public key as described above (STEP 2-7), the terminal device 1 generates the random number data as described above in STEP 2-3. Using the secret key (a, x, p) held as described above, the above-described encrypted data is decrypted according to the equation (2), thereby obtaining random number data, personal information, and a password (STEP 2-8). At this time, both the user's terminal device 2 and the terminal device 1 of the key issuing authority hold the random number data as a common session key for encrypted communication by a common key method described later.

Next, in the terminal device 1 of the key issuing authority, the user information obtained from the user side when the password is distributed to the user in the above-mentioned STEP2-1,
Step 8 checks the personal information obtained in step 8
Confirm the password obtained in 2-8 (STEP 2-
9) If the password is correct, the personal information acquired in STEP 2-8 is registered in the database of the terminal device 1 (STEP 2-10). If the password is not correct, the flow returns to the processing from STEP 2-3 to newly generate a public key and a secret key again, and transmits the home page to the user terminal device 2. In this case, the terminal device 1 of the key issuing authority sends a message indicating that the password is incorrect or a message requesting that the user perform the above-described procedure again together with the homepage. Send to 2.

After the user's personal information is registered as described above, the terminal device 1 of the key issuing authority issues a personal key (encryption key) for later performing encrypted communication with another user. ) Is generated (STEP 2-11).

Here, in the cryptographic communication system of the present embodiment, a common key method is adopted as a method of cryptographic communication between users, and the personal key generated in STEP 2-11 performs cryptographic communication between users. In this case, the algorithm is configured by an algorithm for generating a common key shared by the users. More specifically, this algorithm is such that, when performing cryptographic communication between users, each user inputs an identifier such as the name of the communication partner to the algorithm at the terminal device 2 of the user itself, and the user of the communication partner This generates a common key for encrypted communication with the server. Then, the terminal device 1 of the key issuing station generates such a personal key (algorithm) based on the personal information and random number data obtained in STEP 2-8.

Since a more specific method for generating such a private key has been described in detail by the present applicant in, for example, Japanese Patent Application No. 9-23745, further description will be omitted here.

After generating the personal key (encryption key) of the user as described above, the terminal device 1 of the key issuing authority executes STEP 2-8.
The random number data obtained in the above is used as a session key for the distribution of a personal key by cryptographic communication using the common key method (note that this is different from the common key for performing cryptographic communication between users)
Is used to encrypt the personal key generated in STEP 2-11 (STEP 2-12). In this case, this encryption is performed, for example, in a three-stage DES (Data Encryption Standa
rd).

Then, the terminal device 1 of the key issuing station transmits the personal key thus encrypted to the user terminal device 2 via the Internet communication means 1a (STEP 2-1).
3).

On the other hand, the personal key encrypted as described above is received by the user terminal device 2 (STEP 2).
1-11). In the terminal device 2 of the user who has received the encrypted personal key, the communication processing software
The personal key is decrypted using the random number data generated and held in STEP 1-7 as a session key and stored in the terminal device 2 (STEP 1-12).

Thus, the delivery of the private key (encryption key) from the key issuing station to the user is completed. Thereafter, the user who has received this personal key, when performing cryptographic communication with another user, adds the identifier (name, etc.) of the user on the communication partner side to the personal key stored in his / her own terminal device 2. By acting on the above, a common key with the communication partner user is generated. Then, encrypted communication between users is performed using the common key.

According to the method of delivering a personal key (encryption key) to each user in this embodiment, as described above, first, a public key by the ElGamal encryption is transmitted from the terminal 1 of the key issuing authority to the terminal 2 of the user. After being given via the Internet 3 and random number data generated by the terminal device 2 on the user side, personal information of the user, and the like are encrypted by the public key, the terminal device 2 of the user issues a terminal 1 of the key issuing authority. Given to. Then, the encrypted random number data and the personal information of the user are decrypted by the terminal device 1 of the key issuing authority using the secret key corresponding to the public key, so that the key issuing authority side obtains the random number data possessed by the user side. While sharing the same random number data, the personal information of the user is acquired. In such communication, communication of a public key from the key issuing authority side to the user side, and communication from the user side to the key issuing authority side of the random number data, personal information, and the like encrypted with the public key are as described in the above H.
Since the communication is performed via the Internet communication means 1a and 1b having TTP, the communication is generally performed via different communication paths on the Internet 3. For this reason, even if a third party individually obtains the public key, the random number data encrypted with the public key, personal information, and the like, it is difficult to obtain them in association with one another. In addition, the public key and the secret key are not used repeatedly, but are generated randomly each time the public key is transmitted, and basically different ones are generated each time. The random number data and personal information passed from the user to the key issuing station are encrypted with such a public key.

Therefore, when the random number data and personal information are transferred from the user side to the key issuing authority side via the Internet 3, even if a third party obtains the encrypted random number data or personal information, Decoding data and personal information is difficult. In particular, the random number data used as the session key when the personal key is finally delivered from the key issuing authority side to the user side is originally the artificial terminal device 2 of the user.
Since it is difficult to make a prediction generated based on the input operation described above, it becomes difficult to decode the random number data.

In this case, the ElGamal cipher, which is the basis of the cryptographic communication of the random number data and personal information, is said to have lower security strength than RSA belonging to the same category of the public key system. For the reasons described above, sufficient security can be ensured. Further, the ElGamal encryption used in the present embodiment is simpler in processing for encryption and decryption than RSA, and the processing can be performed efficiently and in a short time.

As described above, in this embodiment, before the private key is distributed from the key issuing authority to the user, the communication of the random number data and the personal information performed from the user to the key issuing authority can be performed safely and securely. It can be performed efficiently, and in particular, the random number data used as the session key when the private key is delivered by encrypted communication is securely shared between the user and the key issuing authority without being decrypted by a third party can do.

Further, according to the method of delivering a personal key (encryption key) to each user according to the present embodiment, after the random number data is shared between the user side and the key issuing authority side as described above, A private key (encryption key) generated by the key issuing authority using the data as a session key (common key) using the common key method
Is provided to the user via the Internet 3. Then, on the user side, the encrypted personal key is obtained by decrypting using the random number data as a session key.

At this time, the communication of the private key encrypted by the random number data (session key) has the HTTP as in the case of the communication of the public key and the random number data encrypted thereby. Since the communication is performed via the Internet communication means 1a and 1b, it is difficult for a third party to collectively obtain the communication data. In addition, the encryption communication using the common key method using the random number data as a session key is a key communication. This is only once when the private key is delivered from the issuing authority to the user. Further, the random number data which is the session key of the encrypted communication is hard to predict as described above.

Accordingly, when a final private key (encryption key) is transferred from the key issuing authority side to the user side via the Internet 3, even if a third party obtains the encrypted personal key, Decrypting a private key is extremely difficult.

Since the final private key distribution is a common key system in which encryption and decryption processes are easier than the public key system, the private key can be distributed quickly and efficiently. it can.

As described above, the private key (encryption key) of the present embodiment
According to the delivery method, the private key necessary for the encrypted communication between the users can be transferred to each user from the key issuing station safely and easily and in a short time by communication using the Internet 3. Thus, it is possible to construct a cryptographic communication system having excellent versatility and convenience.

In this embodiment, the Elgamal encryption is used for the encryption communication of the random number data (session key) by the public key method. However, the RSA encryption may be used. However, as mentioned above, even if the El Gamar code is used, sufficient security can be ensured,
In addition, since ElGamal encryption can perform encryption and decryption processing more efficiently and in a shorter time than RSA encryption, the use of ElGamal encryption is faster and simpler in system processing. It is advantageous.

In this embodiment, the personal key (encryption key)
In this embodiment, the personal information of the user is exchanged with the distribution process of the user. However, the exchange of the personal information of the user is separately performed in advance, and only the distribution process of the personal key (encryption key) is performed. May be performed in the same manner as described above.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of an encryption communication system to which an encryption key distribution method according to an embodiment of the present invention is applied.

FIG. 2 is a flowchart for explaining an encryption key distribution method in the system of FIG. 1;

FIG. 3 is a flowchart for explaining an encryption key distribution method in the system of FIG. 1;

[Explanation of symbols]

1: Terminal device of key issuing authority, 2: Terminal device of user, 1:
a, 2a: Internet communication means, 3: Internet.

Claims (7)

[Claims] 1. A method for delivering an encryption key used by each user when performing cryptographic communication between users of a cryptographic communication system from a key issuing station of the cryptographic communication system to each user. Each terminal device owned by the issuing authority prepares Internet communication means for performing communication through an unspecified communication path of the Internet for each data communication, and a user issues a key issuing authority from the terminal device. When requesting the terminal device to deliver the encryption key, the terminal device of the key issuing station generates and holds a public key for encryption and a secret key for decryption for encryption communication by a public key method, Transmitting the public key from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means, among the public key and the secret key; In the terminal device, after the user performs a predetermined operation of the terminal device to generate and hold random number data unique to the user, the random number data is encrypted with the public key, and the encrypted random number data is encrypted. Transmitting from the terminal device of the user to the terminal device of the key issuing authority via the Internet communication means, and the terminal device of the key issuing authority receiving the encrypted random number data, Decrypting the data with the secret key, and holding the decrypted random number data; and generating the encryption key of the user in the terminal device of the key issuing authority holding the decrypted random number data, and encrypting the random number data by a common key method. The encryption key is encrypted by using the key as a key for communication, and the encrypted encryption key is transmitted from the terminal of the key issuing authority to the terminal of the user via the Internet. Transmitting via a communication means, and in the terminal device of the user who has received the encrypted encryption key, the encrypted data is encrypted using the random number data held in the terminal device as a key according to the common key method. Decrypting and holding the encryption key. 2. A method for delivering an encryption key used by each user when performing cryptographic communication between users of a cryptographic communication system from a key issuing station of the cryptographic communication system to each user, the method comprising: Each terminal device owned by the issuing authority prepares Internet communication means for performing communication through an unspecified communication path of the Internet for each data communication, and a user issues a key issuing authority from the terminal device. When an application to join the cryptographic communication system is made to a terminal device, a public key for encryption and a private key for decryption are generated and held in the terminal device of the key issuing authority for cryptographic communication by the public key system. Transmitting the public key from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means, among the public key and the secret key; In the terminal device of the user who has received the information, the user performs a predetermined operation on the terminal device to generate and hold random number data unique to the user, and the user for the key issuing authority to identify the user. After the personal information of the user is input to the terminal device, the random number data and the personal information are encrypted with the public key, and the encrypted random number data and the personal information are transmitted from the terminal device of the user to the terminal device of the key issuing station. Transmitting the data via the Internet communication means, and at the terminal device of the key issuing authority receiving the encrypted random number data and the personal information, decrypting the encrypted random number data and the personal information with the secret key. Holding the decrypted random number data and personal information in a terminal device of a key issuing authority, wherein the encryption key of a user related to the personal information is stored. Is generated, the encryption key is encrypted using the decrypted random number data as a key according to a common key method,
Transmitting the encrypted encryption key from the terminal device of the key issuing authority to the terminal device of the user via the Internet communication means; and the terminal device of the user receiving the encrypted encryption key. Decrypting the encrypted encryption key using the random number data stored in the common key system as a key according to the common key method, and storing the decrypted encryption key. 3. The encryption key distribution method according to claim 2, wherein the encryption key is generated in a terminal device of the key issuing authority based on personal information of the user. 4. The method according to claim 1, wherein said public key cryptographic communication uses Elgamal encryption.
4. The encryption key distribution method according to any one of claims 1 to 3. 5. The cipher according to claim 4, wherein the public key and the secret key according to the public key method are generated each time the public key is transmitted from the terminal of the key issuing authority to the terminal of the user. Key distribution method. 6. The method according to claim 1, wherein the generation of the random number data in the terminal device of the user is performed based on a timing of a predetermined input operation by the user.
The encryption key distribution method according to any of the above. 7. The communication device according to claim 1, wherein the encryption key is formed by an algorithm for generating a common key for encrypted communication with the communication partner user by applying an identifier of the communication partner user to the encryption key. Item 7. The encryption key distribution method according to any one of Items 1 to 6.