JPH10111653A - Digital signature method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which enables the signature satisfying the same requirements as those for the digital signature of a public key cipher by using the technique of a secret key cipher. SOLUTION: At the time a transmitting person A sends a transmission message M, the person ciphers the message by capturing the characteristics intrinsic to the transmission message M by the secret key Ks possessed by the transmitting person A and not possessed by a receiving person B, adds the characteristics to the transmission message M and sends the message. The effectiveness of the signature may be authenticated by previously commissioning the secret key Ks to a third warrantee organization J, such as public organization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signature method in a data communication system corresponding to a signature or a seal for authenticating the validity of a document such as a contract.

[0002]

2. Description of the Related Art Conventionally, there is a technique called a digital signature in which a sender signs a sentence. The signature requirements are three that cannot be forged by a third party, cannot be forged by the recipient, and that the sender cannot later deny the fact of transmission. Conventionally, this digital signature can be performed only by encryption called public key encryption, and it has been quite difficult for secret key encryption to satisfy all three requirements.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method using a technique of secret key cryptography, which enables a signature to meet the same requirements as a digital signature of public key cryptography.

[0004]

In order to enable a digital signature, a private key that only the sender has when sending a message but not the receiver has to be unique to the message. Is captured, encrypted, and transmitted along with the transmission text. The validity of the signature can be assured, when needed, by depositing the private key with a third-party assurance body such as a public institution.

[0005]

FIG. 1 is a diagram showing an embodiment of the present invention, and shows an example in which data communication is performed between a sender A and a receiver B.

[0006] A description will be given of a method of signing a message M sent from the sender A. Note that the transmission text M may be transmitted as plain text or encrypted.

This signature is valid only for the transmission message M to which the signature has been applied, and is not valid for other texts. The signature is held only by the sender, and the receiver encrypts information unique to the sentence M, that is, a sentence that is meaningful only for the sentence M, using a secret key Ks that the receiver does not own. It is added to the sentence M.

[0008] The information that is used only for the sentence that is significant for the signature includes information such as the reference number of the sentence, the total number of characters of the sentence, the total number of lines of the sentence, or the number of lines. Part or all of the text of the eyes,
Alternatively, it is made by combining the number of the character on each line or one or more of the characters unique to the sentence.

By designating these unique information, the sender A
Is encrypted using the secret key Ks held by the user and added to the transmission message M as a signature message S. It is preferable that what is to be the signature text S is determined in advance and incorporated in the software so that when the transmission text M is transmitted, it is automatically selected and encrypted so as to become a signature.

The signature created in this way can be made only by those who know the contents of the sent message, and is encrypted with the secret key Ks possessed only by the sender, ie, the signer A. The three parties cannot forge the signature, and the signer A cannot later deny the fact of the signature.

[0011] Since the receiver B does not have the key Ks, the signature cannot be decrypted and the meaning of the signature cannot be understood. Nor can you forge a signature for the same reason. This signature is effective only when it is paired with a transmission message. Even if this signature alone is removed and attached to another transmission message, the signature has no effect. Therefore, there is no worry that the signature will be misused.

The secret key Ks is deposited (registered) with a third party assurance organization J such as a public organization. The guarantor J can decrypt this signature and authenticate its validity when requested by a party for a dispute or for any other reason.

[0013] Recipient B only needs to be able to finally obtain plaintext regardless of whether it is encrypted or not.
Identification by signature is not always necessary, but if it is not necessary for the sender A to deny the transmission later, it is preferable to request a signed transmission so that such a denial cannot be made. Then, as shown in FIG. 1, the fact of the transmission can be authenticated by an authoritative third party assurance organization J. On the other hand, the sender A can have a sense of security that the forgery by the receiver B can be prevented by the signature.

As the encryption used for encrypting the signature sentence S, DES (data encryption standard) encryption of secret key encryption or other general secret key encryption may be used. Private key K for signing
When s is deposited with the third party assurance organization J, the type of encryption used for signature is also deposited.

When the transmission message M is encrypted and sent, the transmission message M
It is reasonable to encrypt the signature using the same encryption as the encryption used for the encryption.

[0016]

As noted above, the signature of the present invention is a requirement of a digital signature: the signature cannot be forged by a third party, cannot be forged by the recipient, and the sender cannot deny the fact of transmission later. Meets three requirements,
The present invention can be applied to a data communication system to increase the reliability of personal authentication.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention.

[Explanation of symbols]

 A Sender B Recipient J Third-party assurance institution M Sent message S Signature statement Ks Private key

Claims (2)

[Claims] In a data communication system, information unique to a transmitted message is encrypted with a secret key held by a sender but not held by a receiver, and added as a signature to the transmitted message and transmitted. Characteristic digital signature method. 2. The private key according to claim 1, which is deposited with a third party assurance institution, and the third party assurance institution converts the signature statement into the secret in response to a request from the sender or the receiver. A digital signature method characterized by decrypting with a key and performing authentication.