600.412.Lecture08

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CS 600.412 Security and Privacy in Cloud Computing

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600.412.Lecture08

  1. 1. Security and Privacy in Cloud Computing<br />Ragib HasanJohns Hopkins Universityen.600.412 Spring 2010<br />Lecture 8<br />04/05/2010<br />
  2. 2. The Data Outsourcing Problem<br />Clients store data on untrusted remote servers<br />Clients need guarantees about their data integrity<br />Clients may not have computational resources or time to verify integrity<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />2<br />
  3. 3. Different approaches<br />PDP<br />Proof of data possession<br />PoR<br />Proof of data possession + retrievability<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />3<br />
  4. 4. Limitations of PDF/PoR models<br />Lack of dynamic update<br />Using the index of blocks in tag generation<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />4<br />
  5. 5. This paper<br />Goals<br />Public verification<br />Dynamic modification support<br />Blockless verification<br />Stateless verification<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />5<br />Enabling Public Verifiability and Data Dynamics for Storage Security in Cloud Computing<br />Wang et al., ESORICS 2009<br />
  6. 6. Model<br />Clients: Store data on cloud; don’t have resources to audit <br />Cloud service provider: Untrusted data store <br />Third Party auditor: Can audit data without any knowledge of data<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />6<br />
  7. 7. Discussion<br />Looking at the big picture:<br />Is third party auditability / pubic auditability a practical idea?<br />Should cloud data be publicly verifiable?<br />Can we use a delegation scheme for non-public but third party verification?<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />7<br />
  8. 8. Key idea<br />Client and cloud provider use a Merkle Hash Tree for the file blocks, the root is signed by client<br />A challenge is given to the cloud provider<br />To compute a response, cloud provider needs to have the original blocks<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />8<br />
  9. 9. Merkle hash tree<br />Client signs only top hash<br />To prove the server holds a data block 000, server needs to provide Hash 0-1, Hash 1, and hash of datablock 000 to client.<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />9<br />
  10. 10. Client/provider interaction<br />Setup: Client precomputes the homomorphic tags for file F<br />KeyGen: Client prepares the keypairs<br />SigGen: <br />Client prepares signatures for each block, <br />Then creates a Merkle hash tree<br />Finally signs root hash<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />10<br />
  11. 11. Auditor/ Cloud Provider interaction<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />11<br />
  12. 12. Dynamic updates<br />Modification/insertion/deletions supported by update of the Merkle tree<br />Idea: Client sends update to server, server returns sibling hashes of the updated node, also new root hash<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />12<br />
  13. 13. Update<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />13<br />
  14. 14. Deletion<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />14<br />Modification<br />
  15. 15. Experiments<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />15<br />
  16. 16. Discussion<br />Threat model<br />Is it realistic to trust the third party auditor?<br />Efficiency<br />How efficient/practical is this scheme?<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />16<br />
  17. 17. Discussion<br />Experiments<br />Were the experiments well designed / comprehensive?<br />Should they have used multiple file sizes<br />What is missing from the experiments?<br />4/05/2010<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />17<br />
  18. 18. 4/05/2010<br />18<br />en.600.412 Spring 2010 Lecture 8 | JHU | Ragib Hasan<br />Further Reading<br />PoR paper from RSA Labs http://www.rsa.com/rsalabs/hail/POR.pdf<br />

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