Electronic signature addition method, electronic signature verification method, and system and computer program product using these methods

• US 5,915,024 A
• Filed: 06/17/1997
• Issued: 06/22/1999
• Est. Priority Date: 06/18/1996
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Kitaori, Shoji, Koganezawa, Yuichi
• Primary Examiner(s): Swann, Tod R.
• Assistant Examiner(s): Callahan, Paul E.
• Application Number:
  US08/877,555
• Time in Patent Office: 735 Days
• Field of Search: 380/25, 380/24, 380/23, 380/3, 380/4, 380/30, 380/21, 380/33, 380/43-46, 380/49, 380/50, 380/52, 364/130, 364/136, 364/153, 364/184, 364/140.06, 364/140.09, 364/186, 364/222.5, 364/225.2, 364/200, 707/204, 707/101-104, 707/512, 707/515, 707/537, 707/540, 707/539, 395/182.04, 395/204, 395/600, 395/180, 395/370, 395/386-384, 395/390-392, 395/561, 395/733, 395/670, 395/182.01, 711/111, 711/162, 382/115-119, 382/124, 382/125, 382/175, 382/176, 382/181, 382/190, 382/209, 382/217, 382/232-235, 382/292, 382/243-244, 382/248, 382/251, 382/312, 382/305 , 382/306, 235/380, 235/381, 235/382.5
• US Class Current: 713/176
• CPC Class Codes: H04L 9/3247 involving digital signatures
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface

Abstract

An apparatus for adding an electronic signature to document data includes a delimiter character detector for dividing the input document data into a plurality of divided document data by using as a delimiter a predetermined character appearing in a document represented by the document data, a digest generator and an encrypter for generating an electronic signature based on the divided document data for each divided document data, and a signature-added message generator for generating the divided document data, the electronic signature based on the divided document data, and information for associating the divided document data with the electronic signature.

Claims

1. A method of adding an electronic signature to document data, comprising the steps of:

dividing the document data into a plurality of divided document data using as a delimiter a predetermined character appearing in a document represented by the document data;

generating an electronic signature for each of the divided document data on the basis of the divided document data; and

storing the divided document data, the electronic signature based on the divided document data, and information for associating the divided document data with the electronic signature.

2. A method according to claim 1, wherein the information for associating the divided document data with the electronic signature contains:

information about division of document data contained in the divided document data; and

non-encrypted information about division of document data contained in the electronic signature.

3. A method according to claim 1, further comprising the step of excluding from the document data an unprintable character appearing in the document data and storing the excluded unprintable character.

4. A method of verifying the electronic signature generated by the method of claim 1, comprising the step of, when the divided document data added with the electronic signature is contained in the received document data, determining the validity of the document for each divided document data on the basis of information for associating the divided document data with the electronic signature.

14. An apparatus for verifying the electronic signature generated by the apparatus of claim 1, comprising means for, when the divided document data added with the electronic signature is contained in the received document data, determining the validity of the document for each divided document data on the basis of information for associating the divided document data with the electronic signature.

5. A method of adding an electronic signature to document data, comprising the steps of:

storing the document data upon excluding a predetermined character appearing in a document represented by the document data;

generating an electronic signature on the basis of the document data from which the predetermined character is excluded; and

storing the document data from which the predetermined character is not excluded, the electronic signature, and information for associating the electronic signature with the document data from which the predetermined character is not excluded.

6. A method according to claim 5, wherein the predetermined character is an unprintable character.

7. A method according to claim 5, wherein the information for associating the electronic signature with the document data contains information associated with exclusion of the predetermined character.

8. A method of verifying the electronic signature generated by the method of claim 5, comprising the step of excluding the predetermined character from the document data on the basis of information for associating the electronic signature with the document data and determining the validity of the document data on the basis of the electronic signature and data from which the predetermined character is excluded.

9. A method of evaluating reliability associated with alteration of document data with an electronic signature, comprising the steps of:

obtaining a total number of printable characters in the document data and a total number of unprintable characters in the document data; and

evaluating reliability on the basis of the total numbers of printable and unprintable characters.

10. A method according to claim 9, wherein the step of evaluating reliability comprises

calculating a reliability value T by:

space="preserve" listing-type="equation">T=(p k)×

(m+1)×

(m+2)×

. . . ×

(m+k)/(2

     1)

where p is the number of types of unprintable characters, m is the number of document characters, k is the number of printable characters, and L is the bit length of a message digest, and

evaluating reliability of the signature information by comparing the obtained reliability value T and a predetermined threshold value.

11. An apparatus for adding an electronic signature to document data, comprising:

input means for the document data;

means for dividing the input document data into a plurality of divided document data using as a delimiter a predetermined character appearing in a document represented by the document data;

means for generating an electronic signature based on the divided document data for each divided document data; and

means for outputting the divided document data, the electronic signature based on the divided document data, and information for associating the divided document data with the electronic signature.

12. An apparatus according to claim 11, further comprising means for making the information for associating the divided document data with the electronic signature contain information about division of document data contained in the divided document data, and non-encrypted information about division of document data contained in the electronic signature.

13. An apparatus according to claim 11, further comprising means for excluding from the document data an unprintable character appearing in the document data and storing the excluded unprintable character.

15. An apparatus for adding an electronic signature to document data, comprising:

input means for the document data;

means for storing the document data upon excluding a predetermined character appearing in a document represented by the document data;

means for generating an electronic signature on the basis of the document data from which the predetermined character is excluded; and

means for storing the document data from which the predetermined character is not excluded, the electronic signature, and information for associating the electronic signature with the document data from which the predetermined character is not excluded.

16. An apparatus according to claim 15, wherein the predetermined character is an unprintable character.

17. An apparatus according to claim 15, further comprising means for making the information for associating the electronic signature with the document data contain information about exclusion of the predetermined character.

18. An apparatus for verifying the electronic signature generated by the apparatus of claim 15, comprising means for excluding the predetermined character from the document data on the basis of the information for associating the electronic signature with the document data and determining the validity of the document data on the basis of the electronic signature and data from which the predetermined character is excluded.

19. An apparatus for evaluating reliability associated with alteration of document data with an electronic signature, comprising:

means for obtaining a total number of printable characters in the document data and a total number of unprintable characters in the document data; and

means for evaluating reliability on the basis of the total numbers of printable and unprintable characters.

20. An apparatus according to claim 19, wherein said means for evaluating reliability

calculates a reliability value T by:

space="preserve" listing-type="equation">T=(p k)×

(m+1)×

(m+2)×

. . . ×

(m+k)/(2

     1)

where p is the number of types of unprintable characters, m is the number of document characters, k is the number of printable characters, and L is the bit length of a message digest, and

evaluates reliability of the signature information by comparing the obtained reliability value T and a predetermined threshold value.

21. A computer program product for causing a computer system to execute processing for adding an electronic signature to document data, comprising:

a recording medium;

means for supplying to said computer system an instruction recorded on said recording medium to divide the document data into a plurality of divided document data by using as a delimiter a predetermined character appearing in a document represented by the document data;

means for supplying to said computer system an instruction recorded on said recording medium to generate an electronic signature based on the divided document data for each divided document data; and

means for supplying to said computer system an instruction recorded on said recording medium to store the divided document data, the electronic signature based on the divided document data, and information for associating the divided document data with the electronic signature.

22. A product according to claim 21, wherein the information for associating the divided document data with the electronic signature contains:

information about division of document data contained in the divided document data; and

non-encrypted information about division of document data contained in the electronic signature.

23. A product according to claim 21, further comprising means for supplying to said computer system an instruction recorded on said recording medium to exclude an unprintable character appearing in the document data and storing the unprintable character.

24. A computer program product for causing a computer system to verify the electronic signature generated in claim 21, comprising:

a recording medium; and

means for, when the divided document data added with the electronic signature is contained in the received document data, supplying to said computer system an instruction recorded on said recording medium to determine the validity of the document for each divided document data on the basis of information for associating the divided document data with the electronic signature.

25. A computer program product for causing a computer system to execute processing for adding an electronic signature to document data, comprising:

a recording medium;

means for supplying to said computer system an instruction recorded on said recording medium to exclude a predetermined character appearing in a document represented by the document data and store the excluded predetermined character;

means for supplying to said computer system an instruction recorded on said recording medium to generate an electronic signature on the basis of the document data from which the predetermined character is excluded; and

means for supplying to said computer system an instruction recorded on said recording medium to store the document data from which the predetermined character is not excluded, the electronic signature, and information for associating the electronic signature with the document data from which the predetermined character is not excluded.

26. A product according to claim 25, wherein the predetermined character is an unprintable character.

27. A product according to claim 25, wherein the information for associating the electronic signature with the document data contains information about exclusion of the predetermined character.

28. A computer program product for causing a computer system to verify the electronic signature generated by the product of claim 25, comprising:

a recording medium; and

means for supplying to said computer system an instruction recorded on said recording medium to exclude a predetermined character from the document data on the basis of the information for associating the electronic signature with the document data and determine the validity of the document on the basis of the electronic signature and data from which the predetermined character is excluded.

29. A computer program product for causing a computer system to evaluate reliability associated with alteration of document data added with an electronic signature, comprising:

a recording medium;

means for supplying to said computer system an instruction recorded on said recording medium to obtain a total number of printable characters in the document data and a total number of unprintable characters in the document data; and

means for supplying to said computer system an instruction recorded on said recording medium to evaluate reliability on the basis of the total numbers of printable and unprintable characters.

30. A product according to claim 29, wherein said means for evaluating reliability causes said computer system to perform processing for

calculating a reliability value T by:

space="preserve" listing-type="equation">T=(p k)×

(m+1)×

(m+2)×

. . . ×

(m+k)/(2

     1)

where p is the number of types of unprintable characters, m is the number of document characters, k is the number of printable characters, and L is the bit length of a message digest, and

evaluating reliability of the signature information by comparing the obtained reliability value T and a predetermined threshold value.