ELECTRONIC SIGNATURE METHOD, APPARATUS, AND RECORDING MEDIUM HAVING ELECTRONIC SIGNATURE PROGRAM RECORDED THEREON

• US 20090193256A1
• Filed: 01/21/2009
• Published: 07/30/2009
• Est. Priority Date: 01/21/2008
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: TAKENAKA, Masahiko, Izu, Tetsuya
• Granted Patent: US 8,433,910 B2
• Time in Patent Office: Days
• US Class Current: 713/176
• CPC Class Codes: H04L 9/302 involving the integer factorization problem, e.g. RSA or quadratic sieve [QS] schemes
• CPC Class Codes: H04L 9/3249 using RSA or related signature schemes, e.g. Rabin scheme

Abstract

A computer divides a target electronic document into a plurality of document segments. Then, the computer generates a signature (s, t) that includes a set of two values having a signature value s forming a signature on the electronic document and a deletion signature value t used for deletion, the signature value s which serves as a body of the signature being formed by a superposition of signature information on the individual document segments. Then, in a case where one of the plurality of document segments obtained by the division is to be extracted, the computer superimposes deletion information of a document segment to be deleted on the deletion signature value t to generate a new signature value t′, and produces an updated signature (s, t′).

Claims

1. An electronic signature method executed by a computer, the computer executing the steps of:

dividing a target electronic document into a plurality of document segments;

generating a signature (s, t) that includes a set of two values having a signature value s forming a signature on the electronic document and a deletion signature value t used for deletion, the signature value s, which serves as a body of the signature, being formed by a superposition of signature information on the individual document segments; and

superimposing, in a case where one of the plurality of document segments obtained by the division is to be extracted, deletion information of a document segment to be deleted on the deletion signature value t to generate a new signature value t′

, and producing an updated signature (s, t′

).

2. The electronic signature method according to claim 1, further comprising the step of:

performing signature verification based on a hash value of the extracted document segment and the updated signature (s, t′

).

3. The electronic signature method according to claim 1, further comprising:

generating the signature value s serving as a body of the signature of the electronic document using two values having a signature value r used as a document identifier and a signature value s1 serving as a body of the signature;

dividing a target electronic document into a plurality of document segments;

generating set of signatures (r, s, t) including a set of three values having the signature value r used as a document identifier, the signature value s1 serving as a body of the signature, and the deletion signature value t, the signature value s serving as a main portion of the signature being formed of a superposition of signature information about the individual document segments; and

superimposing, in a case where one of the plurality of document segments obtained by the division is to be extracted, deletion information about a document segment to be deleted on the deletion signature value t to generate a new signature value t′

, and producing an updated signature (r, s, t′

).

4. The electronic signature method according to claim 3, further comprising:

performing signature verification based on a hash value of the extracted document segment and the updated signature (r, s, t′

).

5. The electronic signature method according to claim 3, further comprising:

calculating the signature value r used as a document identifier from a public key of a signing process and a secret key of the signing process.

6. The electronic signature method according to claim 3, further comprising:

generating a secret key from a random number k generated by the signing process.

7. The electronic signature method according to claim 6, further comprising:

calculating the signature value r=g^k mod N, where N is a product of two prime numbers p and q, and g is a generator relatively prime to N, N and g being public keys of the signing process and the random number k being the secret key, the random number k being less than an order φ

of the generator g, where φ

=LCM(p−

1)(q−

1).

8. The electronic signature method according to claim 7, further comprising:

performing signature verification by comparing a value of a right-hand side calculated from the signature value t′

, the public key N, and a hash value hi of an extracted identifier-added document segment, the right-hand side being given by t′

<sup>Π

hi</sup> r mod N, with a value of a left-hand side calculated from the signature value and the public keys g and N, the left-hand side being given by g^s mod N.

9. The electronic signature method according to claim 8, further comprising:

outputting a result indicating that the signature is valid when the value of the right-hand side and the value of the left-hand side coincide with each other, and a result indicating that the signature is invalid when the value of the right-hand side and the value of the left-hand side do not coincide with each other.

10. The electronic signature method according to claim 1, further comprising:

calculating the signature value s serving as a body of the signature using a mask value z generated by using a random number to realize a deletable signature.

11. The electronic signature method according to claim 1, further comprising:

publishing a hash value of the document segment to be deleted, instead of superimposing the deletion information of the document segment to be deleted during extraction of a document segment on the deletion signature value t, to realize a sanitizable signature.

12. A recording medium having an electronic signature program recorded thereon, the electronic signature program causing a computer to execute an electronic signature process comprising:

dividing a target electronic document into a plurality of document segments;

generating a signature (s, t) that includes a set of two values having a signature value s forming a signature on the electronic document and a deletion signature value t used for deletion, the signature value s which serves as a body of the signature being formed by a superposition of signature information on the individual document segments; and

superimposing, in a case where one of the plurality of document segments obtained by the division is to be extracted, deletion information of a document segment to be deleted on the deletion signature value t to generate a new signature value t′

, and producing an updated signature (s, t′

).

13. An electronic signature device comprising:

dividing process for dividing a target electronic document into a plurality of document segments;

generating process for generating a signature (s, t) that includes a set of two values having a signature value s forming a signature on the electronic document and a deletion signature value t used for deletion, the signature value which serves as a body of the signature being formed by a superposition of signature information on the individual document segments; and

updating process for, in a case where one of the plurality of document segments obtained by the division is to be extracted, superimposing deletion information of a document segment to be deleted on the deletion signature value t to generate a new signature value t′

, and producing an updated signature (s, t′

).

14. The electronic signature device according to claim 13, further comprising:

signature verifying process for performing signature verification based on a hash value of the extracted document segment and the updated signature (s, t′

).