Digital signature method and information communication system and apparatus using such method

A digital signature method including a public information generating step of generating public information specific to each user in accordance with a public parameter which satisfies a predetermined condition and is common to each user, and secret information specific to each user, a first signature generating step of generating a signature of digital information by converting the digital information by using the secret information and the public parameter, and a first signature discrimination step of verifying whether a relation between the digital information and the signature is correct, by using the public parameter and the public information, the digital signature method comprising:

• a user information generating step of generating new secret information specific to the user, a new parameter, and new public information by using the public information;
• a confirmation step of confirming whether or not the new secret information, the new parameter, and the new public information generated by said user information generating step satisfy a predetermined relation;
• and
• a second signature generating step of generating a signature of digital information by using the new parameter and the new public information confirmed by said confirmation step.

A digital signature method including a public information generating step of generating public information of each user, the public information being a result of an exponent calculation using a base value which satisfies a predetermined condition and is common to a plurality of users, and secret information of each user as an exponent value, the method comprising:

• a secret information generating step of generating new secret information of a user in accordance with a signature of a plain text generated by using the public information of the user as a common base value and the secret information of the user;
• a parameter generating step of generating a new parameter corresponding to the new secret information generated by said secret information generating step;
• a public information generating step of generating new public information of the user in accordance with the signature, the public information of the user, the common base value, and the plain text;
• and
• a cryptogram execution step of executing a public key cryptogram by using the new secret information generated at said secret information generating step, the new parameter generated at said parameter generating step, and the new public information generated by said public information generating step.

A communication apparatus for executing a digital signature method, comprising:

• public information generating means for generating public information specific to each user in accordance with a public parameter which satisfies a predetermined condition and is common to each user, and secret information specific to each user;
• signature discriminating means for verifying whether a relation between received digital information and a signature of the received digital information is correct, by using the public parameter and the public information;
• user information generating means for generating new secret information specific to the user, a new parameter, and new public information by using the public information;
• confirming means for confirming whether or not the new secret information, the new parameter, and the new public information generated by said user information generating means satisfy a predetermined relation;
• and
• enciphering means for enciphering digital information by using the new parameter and the new public information confirmed by said confirming means.

A communication apparatus for executing a digital signature method, comprising:

• public information generating means for generating public information of each user, the public information being a result of an exponent calculation using a base value which satisfies a predetermined condition and is common to a plurality of users, and secret information of each user as an exponent value;
• secret information generating means for generating new secret information of a user in accordance with a signature of digital information generated by using the public information of the user as a common base value and the secret information of the user;
• parameter generating means for generating a new parameter corresponding to the new secret information generated by said secret information generating means;
• public information generating means for generating new public information in accordance with the signature, the public information, the common base value, and the digital information;
• and
• cryptogram executing means for executing a public key cryptogram by using the new secret information generated by said secret information generating means, the new parameter generated by said parameter generating means, and the new public information generated by said public information generating means.

A digital signature method comprising:

• a public information generating step of generating public information specific to each user in accordance with a public parameter which satisfies a predetermined condition and is common to each user, and secret information specific to each user;
• a member information generating step of generating member information by an authority of a group in accordance with the public information specific to each user belonging to the group, the member information including new secret information, a new parameter, and new public information;
• a secrecy communication step of transmitting in secret the member information generated at said member information generating step to a user belonging to the group;
• a member information confirmation step of confirming whether or not the member information generated at said member information generating step satisfies a predetermined relation;
• a signature generating step of generating a signature corresponding to digital information by using the member information confirmed by said member information confirmation step;
• a signature confirmation step of confirming whether or not the member information confirmed at said member information confirmation step and the signature generated at said signature generating step are valid, by using the public information generated by the authority;
• and
• a signed user identifying step of identifying a user that made the signature in accordance with a random number used when the signature is generated at said signature generating step.

A communication apparatus for communications between authority communication means of an arbitrary group and communication means of another user by using a digital signature method, the apparatus comprising:

• public information generating means for generating specific public information which satisfies a predetermined condition in accordance with a common public parameter and specific secret information;
• member information confirming means for confirming whether or not member information satisfies a predetermined relation, the member information being generated by said authority communication means in accordance with the public information, transmitted therefrom in secret, and including new secret information, a new parameter, and new public information;
• signature generating means for generating a signature corresponding to digital information by using the member information confirmed by said member information confirming means;
• transmitting means for transmitting the signature generated by said signature generating means to another user;
• and
• signature verifying means for verifying a signature of the other user by using the public information of the authority.

A communication apparatus for an authority of an arbitrary group for communicating with user communication means of a user at least belonging to the group by using a digital signature method, the communication apparatus comprising:

• public information generating means for generating specific public information in accordance with a common public parameter which satisfies a predetermined condition, and specific secret information;
• member information generating means for generating new secret information, a new parameter, and new public information in accordance with the public information specific to a user belonging to the group;
• secrecy communication means for transmitting in secret the member information generated by said member information generating means to said user communication means of a user belonging to the group;
• and
• signed user identifying means for identifying a user that made a signature corresponding to digital information in accordance with a random number used for the signature generated by using the member information, if said user communication means of the user belonging to the group confirms that the member information generated by said member information generating means satisfies a predetermined relation.