Electronic document management program, electronic document management system and electronic document management method

An electronic document management apparatus comprising:

• a document managing section that encrypts information of a non-disclosure part coupled with a random number for the non-disclosure part of original information which is divided into a plurality of parts, by using an encryption key, and generates partial encrypted original information where information of the non-disclosure part is replaced with encrypted information;
• a partial signature information generation section that performs a process of generating hash information corresponding to information for each of the plurality of parts by using a one-way hash function for information of the plurality of parts coupled with a random number, so as to generate first signature information corresponding to the original information, and a process of generating hash information corresponding to the encrypted information by using a one-way hash function for the encrypted information of the non-disclosure part coupled with a random number which is different from the random number used for the encrypted information so as to generate second signature information corresponding to the partial encrypted original information where only the information of the non-disclosure part for the first signature information is replaced with the hash information corresponding to the encrypted information;
• a partial signature verification section that performs a process of proving that the partial encrypted original information is not altered except for the non-disclosure part by comparing the first signature information with the second signature information and a process of decrypting the encrypted information of the non-disclosure part included in the partial encrypted original information by using a decryption key corresponding to the encryption key, generating hash information by using a one-way hash function for decrypted information which is coupled with the random number, and comparing generated hash information with the hash information corresponding to the non-disclosure part included in the first signature information so as to prove that the information of the non-disclosure part is not altered.

An electronic document management method comprising:

• dividing original information into a plurality of parts;
• generating hash information corresponding to information of a part for each of the plurality of parts by using a one-way hash function for the information of the part coupled with a random number, so as to generate first signature information corresponding to the original information;
• encrypting the information coupled with the random number for information of a non-disclosure part of the original information by using an encryption key, and generating partial encrypted original information where the information of the non-disclosure part of the original information is replaced with encrypted information;
• generating hash information corresponding to the encrypted information by using a one-way hash function for the encrypted information of the non-disclosure part coupled with a random number which is different from the random number used for the encrypted information so as to generate second signature information corresponding to the partial encrypted original information where only the information of the non-disclosure part for the first signature information is replaced with the hash information corresponding to the encrypted information;
• proving that the partial encrypted original information is not altered except for the non-disclosure part by comparing the first signature information with the second signature information;
• and
• decrypting the encrypted information of the non-disclosure part included in the partial encrypted original information by using a decryption key corresponding to the encryption key, generating hash information by using a one-way hash function for decrypted information which is coupled with the random number, and comparing generated hash information with the hash information corresponding to the non-disclosure part included in the first signature information so as to prove that the information of the non-disclosure part is not altered.