Encryption/decryption method for data limited in value range, apparatus and program therefor

• US 20040170277A1
• Filed: 01/09/2004
• Published: 09/02/2004
• Est. Priority Date: 01/14/2003
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Iwamura, Keiichi, Suga, Yuji
• Granted Patent: US 7,512,811 B2
• Time in Patent Office: Days
• US Class Current: 380/217
• CPC Class Codes: H04L 9/36 with means for detecting characters not meant for transmission

Abstract

On an encrypted object code obtained by encrypting an object code, there is discriminated whether an inhibited code defined in data format is present in a code concerning such encrypted object code, and, in case such inhibited code is judged absent, the encrypted object code is determined as an encryption result of the object code.

Claims

1. An encryption method comprising:

an encryption step of encrypting a code;

an encryption result judgment step of judging whether a code, concerning an encrypted object code obtained by encrypting an object code by said encryption step, generates a code of a value within a predetermined range; and

an encryption result determination step which, in case said encryption result judgment step identifies that a code of a value within the predetermined range is not generated, determines said encrypted object code as an encryption result of said object code.

2. An encryption method according to claim 1, further comprising a re-encryption step which, in case said encryption result judgment step identifies that a code of a value within the predetermined range is generated, re-encrypts said encrypted object code.

3. An encryption method according to claim 1, wherein said judgment step includes:

a first encryption result judgment step of judging whether said encrypted object code is a code of a value within a predetermined range; and

a second encryption result judgment step of judging whether a concatenated result of an encrypted code immediately preceding said encrypted object code and said encrypted object code generates a code of a value within said predetermined range.

4. An encryption method according to claim 1, wherein said encryption step executes an encryption for every predetermined number of codes.

5. An encryption method according to claim 1, wherein, in case said encryption result judgment step identifies that a code of a value within said predetermined range is generated, said encryption result determination step determines said object code itself as an encryption result of said object code.

6. An encryption method according to claim 1, wherein said encryption result judgment step includes:

a third encryption result judgment step of judging whether said encrypted object code is a code of a value within a predetermined range;

a fourth encryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of said encrypted object code and symbols of a predetermined number from the beginning of a code immediately after said object code is a code of a value within a predetermined range; and

a fifth encryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of a code immediately in front of said object code and symbols of a predetermined number from the beginning of said encrypted object code is a code of a value within a predetermined range.

7. An encryption method according to claim 6, wherein said encryption result judgment step further includes:

a sixth encryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of said object code and symbols of a predetermined number from the beginning of a code obtained by encrypting a code immediate after said object code is a code of a value within a predetermined range.

8. An encryption method according to claim 1, wherein said encryption step executes encryption by a common key cipher method.

9. An encryption method according to claim 1, wherein the code of a value of said predetermined range includes a part of marker codes in JPEG 2000.

10. An encryption method according to claim 1, wherein said encryption step executes encryption by determining an exclusive logic sum of the object code and pseudo random number data.

11. An encryption method according to claim 10, wherein said encryption step executes an encryption process, for every 8 bits, on a bit train excluding a top bit.

12. An encryption method according to claim 11, wherein said encryption step applies an exclusive logic sum calculation on every two portions from 2nd to 4th bits and from 5th to 8th bits counted from the beginning.

13. An encryption method according to claim 1, further comprising:

a conversion step which, in case said encryption result judgment step identifies that a code of a value of a predetermined range is generated, converts the code of the value of such predetermined range into another code of a value of the predetermined range; and

a second encryption step of encrypting another code converted by said conversion step.

14. A decryption method comprising:

a decryption step for decrypting an encrypted code;

a decryption result judgment step of discriminating whether a code, concerning a decrypted object code obtained by decrypting an object code by said decryption step, generates a code of a value within a predetermined range; and

a decryption result determination step which, in case said decryption result discriminating step identifies that a code of a value within the predetermined range is not generated, determines said decrypted object code as a decryption result of said object code.

15. A decryption method according to claim 14, further comprising a re-decryption step which, in case said decryption result discriminating step identifies that a code of a value within the predetermined range is generated, re-decrypts said decrypted object code.

16. A decryption method according to claim 14, wherein said decryption result judgment step includes:

a first decryption result judgment step of judging whether said decrypted object code is a code of a value within a predetermined range; and

a second decryption result judgment step of judging whether a concatenated result of a decrypted code immediately preceding said decrypted object code and said decrypted object code generates a code of a value within said predetermined range.

17. A decryption method according to claim 14, wherein said decryption step executes a decryption for every predetermined number of codes.

18. A decryption method according to claim 14, wherein, in case said decryption result judgment step identifies that a code of a value within said predetermined range is generated, said decryption result determination step determines said object code itself as a decryption result of said object code.

19. A decryption method according to claim 14, wherein said decryption result judgment step includes:

a third decryption result judgment step of judging whether said encrypted object code is a code of a value within a predetermined range;

a fourth decryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of said encrypted object code and symbols of a predetermined number from the beginning of a code immediately after said object code is a code of a value within a predetermined range; and

a fifth decryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of a code immediately in front of said object code and symbols of a predetermined number from the beginning of said encrypted object code is a code of a value within a predetermined range.

20. A decryption method according to claim 19, wherein said decryption result judgment step further includes:

a sixth decryption result judgment step of judging whether a combination of symbols of a predetermined number from the end of said object code and symbols of a predetermined number from the beginning of a code obtained by encrypting a code immediate after said object code is a code of a value within a predetermined range.

21. A decryption method according to claim 14, wherein said decryption step executes decryption by a common key cipher method.

22. A decryption method according to claim 14, wherein the code of a value of said predetermined range includes a part of marker codes in JPEG 2000.

23. A decryption method according to claim 14, wherein said decryption step executes decryption by determining an exclusive logic sum of the object code and pseudo random number data.

24. A decryption method according to claim 23, wherein said decryption step executes a decryption process, for every 8 bits, on a bit train excluding a top bit.

25. A decryption method according to claim 24, wherein said decryption step applies an exclusive logic sum calculation on every two portions from 2nd to 4th bits and from 5th to 8th bits counted from the beginning.

26. A decryption method according to claim 14, further comprising:

a conversion step which, in case said judgment step identifies that a code of a value of a predetermined range is generated, converts the code of the value of such predetermined range into another code of a value of the predetermined range; and

a second decryption step of decrypting another code converted by said conversion step.

27. An encryption apparatus comprising:

encryption means which encrypts a code;

encryption result judgment means which judges whether a code, concerning an encrypted object code obtained by encrypting an object code by said encryption means, generates a code of a value within a predetermined range; and

encryption result determination means which, in case said encryption result judgment means identifies that a code of a value within the predetermined range is not generated, determines said encrypted object code as an encryption result of said object code.

28. A decryption apparatus comprising:

decryption means which decrypts a code;

decryption result judgment means which judges whether a code, concerning a decrypted object code obtained by decrypting an object code by said decryption means, generates a code of a value within a predetermined range; and

decryption result determination means which, in case said decryption result judgment means identifies that a code of a value within the predetermined range is not generated, determines said decrypted object code as a decryption result of said object code.

29. A computer readable program for encryption comprising:

an encryption step for encrypting a code;

an encryption result judgment step of judging whether a code, concerning an encrypted object code obtained by encrypting an object code by said encryption step, generates a code of a value within a predetermined range; and

an encryption result determination step which, in case said encryption result judgment step identifies that a code of a value within the predetermined range is not generated, determines said encrypted object code as an encryption result of said object code.

30. A computer readable program for decryption comprising:

a decryption step of decrypting a code;

a decryption result judgment step of judging whether a code, concerning a decrypted object code obtained by decrypting an object code by said decryption step, generates a code of a value within a predetermined range; and

a decryption result determination step which, in case said decryption result judgment step identifies that a code of a value within the predetermined range is not generated, determines said decrypted object code as a decryption result of said object code.