1. 1 Digitally Signed Document Sanitizing Scheme Based on Bilinear Maps Kunihiko Miyazaki, Goichiro Hanaoka, Hideki Imai ASIACCS’06, March 21–24, 2006, Taipei, Taiwan Adviser: 鄭錦楸, 郭文中 教授 Reporter: 林彥宏

2. 2 Outline Introduction Preliminaries Digitally signed Document Sanitizing Scheme Based on Bilinear Maps Modifications and Extensions Conclusions

3. 3 Introduction protect documents from alteration by malicious attackers digital document sanitizing problem current digital signature schemes cannot assure both the confidentiality and integrity of a document

4. 4 Introduction Content extraction signature R. Steinfeld, L. Bull, and Y. Zheng. ; ICISC 2001, volume 2288 of LNCS extracted signature on selected portions extracted from the original documents Sanitizable signature G. Ateniese, D. H. Chou, B. de Medeiros, and G. Tsudik ;ESORICS 2005, volume 3679 of LNCS uses the chameleon hash function instead of an usual hash function

5. 5 Introduction Digitally Signed Document Sanitizing Scheme with Disclosure Condition Control K. Miyazaki, M. Iwamura, T. Matsumoto, R. Sasaki, H. Yoshiura, S. Tezuka, and H. Imai ; IEICE Fundamentals, Vol. E88-A, No.1, 2005 SUMI-5, that protects documents from additional sanitizing three disclosure conditions: 1.Sanitized 2.disclosed and additional sanitizing is allowed 3.disclosed and additional sanitizing is prohibited

6. 6 Motivation of Work sanitizing should be invisible no one should be able to determine whether or not the disclosed document has been sanitized

7. 7 Our Contribution propose a digitally signed document invisible sanitizing scheme with disclosure condition control SUMI-5, disclosure condition: Sanitized: sanitized document that consists of only the legitimate mask data disclosed and additional sanitizing is allowed: both the original document and the legitimate mask data disclosed and additional sanitizing is prohibited: only the original document

8. 8 Our Contribution legitimate mask data can be used to count up how many masks appear in a sanitized document Aggregate and Verifiably Encrypted Signatures from Bilinear Maps D. Boneh, C. Gentry, B. Lynn, and H. Shacham ; In Eurocrypt 2003, volume 2656 of LNCS allow to aggregate all of the individual signatures into one aggregate signature helpful to hide the number of sanitized portion of the document

9. 9 Preliminaries Security Definition: proposed scheme has the following three properties Privacy: verifier is difficult to retrieve sanitized information about subdocuments of the document Unforgeability: It is difficult for everyone to generate a signed and sanitized document that has not been signed before Invisibility: verifier is difficult to know how many and whether the document has been sanitized

10. 10 Aggregate Signature scheme based on bilinear maps

11. 11 Aggregate Signature Key Generation: Signing: Verification:

12. 12 Aggregate Signature Aggregation: Aggregate Verification:

13. 13 Digitally signed Document Sanitizing Scheme Based on Bilinear Maps (SANI) (DASP) (DASA)

14. 14 Detailed Description of Scheme Key Generation: Signing:

15. 15 Detailed Description of Scheme Sanitizing:

16. 16 Detailed Description of Scheme Verification:

17. 17 Security Analysis Indistinguishable: no information about sanitized portions of the document remains in the sanitized document Unforgeable: attacker cannot forge a signature for a document M that has not been signed before Perfectly Invisible: attacker cannot distinguish the input document is signed and sanitized

18. 18 Modifications and Extensions Binding Subdocuments: ensure a subsequent sanitizer cannot sanitize two individually but can both be sanitized together assign another condition “bound” to any two subdocument Multiple Signers: sanitizer can merge documents signed by different signers into a document

19. 19 Modifications and Extensions

20. 20 Conclusions Sanitizer can hide the number of sanitized portions. Assign a different disclosure condition for each portion of the document. Their scheme is suitable for application for log files archiving.