The document discusses secure multi-owner data sharing for dynamic groups in clouds. It outlines Mona, a scheme that uses dynamic broadcast encryption for access control and group signatures for authentication. Mona allows efficient revocation without updating other users' keys and supports anonymity and traceability. The document compares Mona to other schemes and finds Mona addresses issues around identity privacy and revocation more effectively. Future work aims to make Mona more reliable and scalable by handling failures of the group manager.

1. 1
SFS: Secure File Sharing Scheme
For Cloud Groups
Shruthi Suresh
M-tech CSE

2. 2
OUTLINE
• Objective
• Introduction
• Literature Survey
• Performance Comparison
• Conclusion
• Future Work
• References

3. OBJECTIVE
To implement an effective mechanism for sharing of data in a
multi-owner manner in dynamic groups in an untrusted cloud
while preserving data and identity privacy.
3

4. INTRODUCTION
• Data storage is one of the primal services offered by cloud
computing.
• Data storage and sharing in cloud possess substantial risk to
confidentiality.
• Challenging issues in multi-owner data sharing in dynamic
groups are :
– Identity privacy
– Implementation of multiple-owner manner
– Effect of dynamic groups
• Basic solution for preservation of data is to encrypt it [2].
[2] S. Kamara and K. Lauter, “Cryptographic Cloud Storage,” Proc. Int’l Conf. Financial Cryptography and Data
Security (FC), pp. 136- 149, Jan. 2010.
4

5. IDENTITY PRIVACY
• One of the major issue in data sharing
• If privacy is not assured, users will be doubtful to join the
cloud
• Another issue is unconditional identity privacy
– If a member of the group deceives others, this leads to the
abuse of privacy
– Real user identity of betrayal should be traceable
5

6. MULTIPLE-OWNER MANNER
• Every member should be able to alter their own data part
• More flexible than single-owner manner.
• Single-owner manner allows only the group manager to alter
data [3]
– Members can only read data
[3] S. Yu, C. Wang, K. Ren, and W. Lou, “Achieving Secure, Scalable, and Fine-Grained Data Access Control in
Cloud Computing,” Proc. IEEE INFOCOM, pp. 534-542, 2010.
6

7. DYNAMIC GROUPS
• The number of users keep changing
• Data security is very difficult
• Two major issues to be addressed are :
– Newly approved users must be able to get all the files
shared prior to their joining without contacting data owners
– After each revocation , keys of remaining members in the
group need not be updated
7

8. RELATED WORKS
1. Plutus: Scalable Secure File Sharing On Untrusted Storage
2. Sirius: Securing Remote Untrusted Storage
3. Improved Proxy Re-encryption Schemes With Applications To
Secure
4. Achieving Secure, Scalable, And Fine-grained Data Access
Control In Cloud Computing
5. Secure Provenance: The Essential Of Bread And Butter Of
Data Forensics In Cloud Computing
6. Mona: Secure Multi-owner Data Sharing For Dynamic Groups
In The Cloud
8

9. PLUTUS: SCALABLE SECURE FILE SHARING ON
UNTRUSTED STORAGE [4]
• Facilitates secure file sharing on untrusted servers.
• Protects network integrity with file-sign/file-verify keys .
• Files are divided into filegroups and each group is encrypted
with an exclusive fileblock key
Disadvantages
- Heavy key distribution
- After each user revocation the file-block key needs to be
updated and distributed again.
[4] M. Kallahalla, E. Riedel, R. Swaminathan, Q. Wang, and K. Fu, “Plutus: Scalable Secure File Sharing on
Untrusted Storage,” Proc. USENIX Conf. File and Storage Technologies, pp. 29-42, 2003.
9

10. SIRIUS: SECURING REMOTE UNTRUSTED
STORAGE [5]
• Handle multi-user file systems
• All users maintain two keys :
– MEK
– MSK
Disadvantages
- File metadata needs to be updated after each revocation
[5] E. Goh, H. Shacham, N. Modadugu, and D. Boneh, “Sirius: Securing Remote Untrusted Storage,” Proc.
Network and Distributed Systems Security Symp. (NDSS), pp. 131-145, 2003. 10

11. IMPROVED PROXY RE-ENCRYPTION SCHEMES
WITH APPLICATIONS TO SECURE [6]
• Strengthens the distributed storage.
• The data encryption is a two-step procedure.
– encryption is done using exclusive and symmetric content
keys.
– data is encrypted with a master public key.
• Proxy cryptography is used by the server to re-encrypt the
particular content key(s) from the master public key
Disadvantages
- Collusion attack may occur
[6] G. Ateniese, K. Fu, M. Green, and S. Hohenberger, “Improved Proxy Re-Encryption Schemes with
Applications to Secure Distributed Storage,” Proc. Network and Distributed Systems Security Symp. (NDSS),
pp. 29-43, 2005. 11

12. ACHIEVING SECURE, SCALABLE, AND FINE-GRAINED DATA
ACCESS CONTROL IN CLOUD COMPUTING [3]
• Scalable and fine-grained data access control scheme
• KP-ABE technique is used [9]
• An access structure and the corresponding secret key are
assigned to authorized users by data manager
Disadvantages
- Single-owner manner makes it less flexible
- User keys needed to be updated after each revocation
[3] S. Yu, C. Wang, K. Ren, and W. Lou, “Achieving Secure, Scalable, and Fine-Grained Data Access Control in
Cloud Computing,” Proc. IEEE INFOCOM, pp. 534-542, 2010. 12

13. SECURE PROVENANCE: THE ESSENTIAL OF BREAD AND
BUTTER OF DATA FORENSICS IN CLOUD COMPUTING [7]
• Group signatures are used
• Encryption is done by ciphertext-policy attribute-based
encryption technique
• Each user will have 2 keys
– Group signature key
– Attribute key
Disadvantages
- User revocation is not supported
[7] R. Lu, X. Lin, X. Liang, and X. Shen, “Secure Provenance: The Essential of Bread and Butter of Data Forensics in
Cloud Computing,” Proc. ACM Symp. Information, Computer and Comm. Security, pp. 282-292, 2010. 13

14. MONA: SECURE MULTI-OWNER DATA SHARING
FOR DYNAMIC GROUPS IN THE CLOUD [1]
• A secure data sharing model for dynamic groups in a remote
storage
• Dynamic broadcast encryption is used
• Authentication is done by Group signatures
• Supports effective user repudiation and new user registration
• Revocation can be attained without updating the private keys of
other users
[1] Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and Jingbo Yan Xuefeng Liu, Yuqing Zhang, Member,
IEEE, Boyang Wang, and Jingbo Yan, “Mona: Secure Multi- Owner Data Sharing For Dynamic Groups In The Cloud”,
Ieee transactions on parallel and distributed systems, vol. 24, no. 6, june 2013. 14

15. MONA: SECURE MULTI-OWNER DATA SHARING
FOR DYNAMIC GROUPS IN THE CLOUD [1]
Design Goals
 Access control
 Data confidentiality
 Anonymity and traceability
 Efficiency
15
[1] Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and Jingbo Yan Xuefeng Liu, Yuqing Zhang, Member,
IEEE, Boyang Wang, and Jingbo Yan, “Mona: Secure Multi- Owner Data Sharing For Dynamic Groups In The Cloud”,
Ieee transactions on parallel and distributed systems, vol. 24, no. 6, june 2013.

16. MONA: SECURE MULTI-OWNER DATA SHARING
FOR DYNAMIC GROUPS IN THE CLOUD [1]
16
System model
[1] Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and Jingbo Yan Xuefeng Liu, Yuqing Zhang, Member,
IEEE, Boyang Wang, and Jingbo Yan, “Mona: Secure Multi- Owner Data Sharing For Dynamic Groups In The Cloud”,
Ieee transactions on parallel and distributed systems, vol. 24, no. 6, june 2013.

17. MONA: SECURE MULTI-OWNER DATA SHARING
FOR DYNAMIC GROUPS IN THE CLOUD [1]
Cloud
 Operated by CSPs
 Not fully trusted
 Assume cloud to be honest but curious
Group manager
 Parameters generation
 User registration
 User revocation
 Tracing real identity of a dispute data owner 17

18. MONA: SECURE MULTI-OWNER DATA SHARING
FOR DYNAMIC GROUPS IN THE CLOUD [1]
Group members
 A set of registered users
 Group memberships keeps on changing
Disadvantage
• Lacks reliability and scalability
18
[1] Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and Jingbo Yan Xuefeng Liu, Yuqing Zhang, Member,
IEEE, Boyang Wang, and Jingbo Yan, “Mona: Secure Multi- Owner Data Sharing For Dynamic Groups In The Cloud”,
Ieee transactions on parallel and distributed systems, vol. 24, no. 6, june 2013.

19. PERFORMANCE COMPARISON
19
Parameters PLUTUS SIRIUS IMPROVED
PROXY
ENCRYPTION
SECURE
SCALABLE DATA
ACCESS SCHEME
MONA
Encryption
technique
File -block
key &
lockbox-key
Public key
cryptography
Proxy
cryptography
KP-ABE
technique
Broadcast
encryption
Identity
privacy
Satisfactory Satisfactory Less Less High
Revocation
mechanism
Inefficient Inefficient Inefficient Inefficient Efficient
Key
Distribution
Heavy Heavy Medium Independent of
number of
revoked users
Independent
of number of
revoked users

20. CONCLUSION
• Several techniques have been proposed to address multi-owner data sharing
in dynamic clouds
• Identity privacy and user revocation mechanisms are to be efficiently
addressed
• An efficient method is Mona which includes solution for the above
mentioned issues
20

21. FUTURE WORK
• Aims at achieving reliable and scalable framework of MONA
• Problems to be handled are
– Failure of group manager
– Hanging of group manager
21

22. REFERENCES
22
[1] Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and Jingbo
Yan Xuefeng Liu, Yuqing Zhang, Member, IEEE, Boyang Wang, and
Jingbo Yan, “Mona: Secure Multi- Owner Data Sharing For Dynamic
Groups In The Cloud”, Ieee transactions on parallel and distributed
systems, vol. 24, no. 6, june 2013.
[2] S. Kamara and K. Lauter, “Cryptographic Cloud Storage,” Proc. Int’l Conf.
Financial Cryptography and Data Security (FC), pp. 136- 149, Jan. 2010.
[3] S. Yu, C. Wang, K. Ren, and W. Lou, “Achieving Secure, Scalable, and
Fine-Grained Data Access Control in Cloud Computing”, Proc. IEEE
INFOCOM, pp. 534-542, 2010.
[4] M. Kallahalla, E. Riedel, R. Swaminathan, Q. Wang, and K. Fu, “Plutus:
Scalable Secure File Sharing on Untrusted Storage,” Proc.USENIX Conf.
File and Storage Technologies, pp. 29-42, 2003.

23. REFERENCES
23
[5] E. Goh, H. Shacham, N. Modadugu, and D. Boneh, “Sirius: Securing Remote
Untrusted Storage,” Proc. Network and Distributed Systems Security Symp.
(NDSS), pp. 131-145, 2003.
[6] G. Ateniese, K. Fu, M. Green, and S. Hohenberger, “Improved Proxy Re-
Encryption Schemes with Applications to Secure Distributed Storage,” Proc.
Network and Distributed Systems Security Symp. (NDSS), pp. 29-43, 2005.
[7] R. Lu, X. Lin, X. Liang, and X. Shen, “Secure Provenance: The Essential of
Bread and Butter of Data Forensics in Cloud Computing,” Proc. ACM Symp.
Information, Computer and Comm. Security, pp. 282-292, 2010.
[8] B. Waters, “Ciphertext-Policy Attribute-Based Encryption: An Expressive,
Efficient, and Provably Secure Realization,” Proc. Int’l Conf. Practice and
Theory in Public Key Cryptography Conf. Public Key Cryptography,
http://eprint.iacr.org/2008/290.pdf, 2008.

24. REFERENCES
[9] V. Goyal, O. Pandey, A. Sahai, and B. Waters, “Attribute-Based Encryption
for Fine- Grained Access Control of Encrypted Data,” Proc. ACM Conf.
Computer and Comm. Security (CCS), pp. 89-98, 2006.
[10] D. Naor, M. Naor, and J.B. Lotspiech, “Revocation and Tracing Schemes
for Stateless Receivers,” Proc. Ann. Int’l Cryptology Conf. Advances in
Cryptology (CRYPTO), pp. 41-62, 2001.
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