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Cloud Cryptography Seny Kamara Cryptography Group Microsoft Research Outline Cloud Architecture What is cloud computing? o Cloud Ecosystem Who provides and who consumes cloud services? o Cloud Cryptography What are the security

  1. Cloud Cryptography Seny Kamara Cryptography Group Microsoft Research

  2. Outline • Cloud Architecture What is cloud computing? o • Cloud Ecosystem Who provides and who consumes cloud services? o • Cloud Cryptography What are the security concerns & how can cryptography help? o 2/24/11 2

  3. Computing as a Service • Computing is a vital resource Enterprises, governments, scientists, consumers, … o • Computing is manageable at small scales… e.g., PCs, laptops, smart phones o • …but becomes hard to manage at large scales build and manage infrastructure, schedule backups, hardware o maintenance, software maintenance, security, trained workforce, … • Why not outsource it? 2/24/11 3

  4. Computing Architecture Email, WWW, DBs,… Applications Windows, Linux, MacOSX ,… Platform memory, disk, network, Infrastructure 2/24/11 4

  5. Cloud Services • Infrastructure as a service Service: customer can store data in the cloud o Customer: enterprise, developers o e.g., MS Azure storage, Amazon S3 o • Platform as a service Service: customer can run its apps in the cloud o Customer: developers o e.g., MS Azure, Amazon EC2, Google AppEngine, o • Software as a service Service: customer makes use of app in the cloud o Customer: consumers & enterprise o e.g., web-based email, Flickr, delicious, Facebook, Office Web, Google o Docs, … 2/24/11 5

  6. Cloud Deployment Models Public Private 2/24/11 6

  7. The Cloud Ecosystem 2/24/11 7

  8. Who Provides Cloud Services? 2/24/11 8

  9. Cloud Infrastructure Providers • Provide access to infrastructure e.g., Amazon, Microsoft, Google, IBM, EMC, Equinix, AT&T, Verizon o • Characteristics Requires very large investments o • build data centers • acquire expertise • provide physical security • energy consumption • … Large (often) publicly traded companies o Have a reputation to uphold o 2/24/11 9

  10. Cloud Service Companies • Provide cloud-based applications e.g., Salesforce, GoGrid, NetSuite o • Characteristics Requires small investment o • developers • Platform/infrastructure services from larger cloud providers Startups (often) privately held o 2/24/11 10

  11. Who Consumes Cloud Services? • Consumers e.g., Facebook (500+ M), Web-based email (840 M), Flickr, Dropbox , … o • Enterprise E.g., Amazon EC2/S3, MS Azure, Google AppEngine, Google Apps o • Governments 120,000 US Dept. of Agriculture employees will move to MS cloud services o 17,000 Gen. Serv. Admin. Employees will move to Google cloud services o • Local Governments 100,000 NYC emplyees will move to MS cloud services o 34,000 L.A. emplyees will move to Google cloud services o 2/24/11 11

  12. Cloud Cryptography 2/24/11 12

  13. Concerns • Outsider security Can other tenants, hackers, competitors access my data? o • Insider security Can the cloud operator (and its employees) access my data? o • Intellectual property Can outsiders or insiders see my code and algorithms? o • Compliance Can I remain compliant if I move to the cloud? o • Availability Can I access my data or service at all times? o 2/24/11 13

  14. Modern Cryptography • Primitives e.g., encryption, digital signatures, hash functions, pseudo-random o generators, … • Protocols e.g., key agreement, zero-knowledge proofs, multi-party computation o • Security definitions Formal definition of what it means to be secure o • “Proofs” of security Proof that primitive/protocol meets security definition o Unconditional security (e.g., one-time pad) o Conditional security (e.g., RSA, El Gamal ,…) o • Leads to very strong security guarantees e.g., digital signatures are widely accepted in court o SHA-2, AES, ECC are certified for government use by NIST & NSA o 2/24/11 14

  15. Modern Cryptography Encryption Signatures No! EncK ( ) Secure Comp. $5B $45B   2/24/11 15

  16. Cloud Cryptography • Current crypto tools are inappropriate for the cloud Due to assumptions about how tools will be used o Results in efficiency loss & insecurity o • New tools Homomorphic encryption o Searchable/Structured encryption o Proofs of storage o Server-aided secure computation o 2/24/11 16

  17. [ …, G09,… ] Homomorphic Encryption • Encryption that supports comp. on encrypted data Fully homomorphic [G09, DGHV10] o Partially homomorphic [SYY99, BGN05, IP07,GHV10a,GHV10b,KR11] o • Guarantees that Cloud never sees plaintext/message o • Pros FHE is general-purpose o Partial & parallel HE can be efficient o • Cons FHE is inefficient (but improvements are being made rapidly) o 2/24/11 17

  18. Homomorphic Encryption K EncK , F EncK F 2/24/11 18

  19. [ SWP01 ] Searchable Encryption • Encryption that supports search on encrypted text Symmetric key [SWP01,Goh03,CM05,CGKO06] o Public key [BDOP06, BKOS07,…] o • Guarantees that Cloud never sees documents o Cloud never sees search keywords o • Pros Symmetric variant is very efficient! o • Cons Reveals access and search patterns o [GO96] shows how to hide this but it is expensive o 2/24/11 19

  20. Searchable (Symm.) Encryption EncK K t w EncK EncK 2/24/11 20

  21. [ CK10 ] Structured Encryption • Encryption that supports queries on encrypted data Query over encrypted graphs [CK10] o Query over encrypted web graphs [CK10] o • Guarantees that Cloud never sees data o Cloud never sees queries o • Pros Symmetric variant is very efficient! o • Cons Reveals access and search patterns o 2/24/11 21

  22. Structured Encryption EncK K t EncK EncK 2/24/11 22

  23. [ JK07, ABC+07 ] Proofs of Storage • Tamper detection without knowing original file Symmetric-key [JK07, SW08, DVW10] o Public-key [ABC+07, SW08, AKK10] o • Guarantees that Cloud will be caught if it tampers with data o • Pros Symmetric variant is efficient! o Verification does not require copy of original data o • Cons -- o 2/24/11 23

  24. Proofs of Storage Petabytes K ? proof O(1) ≈ 200 bits 2/24/11 24

  25. [ KMR11 ] Server-Aided Secure Comp. • Joint computation w/o revealing inputs (plain) secure computation [Yao82,GMW87,…] o • Guarantees that Parties will not learn each other’s inputs o Cloud will not learn parties’ inputs o • Pros General- purpose (e.g., data mining, voting, negotiations,…) o Efficient o • Cons -- o 2/24/11 25

  26. Server-Aided Secure Comp. x y f(x,y) 2/24/11 26

  27. Questions? 2/24/11 27

  28. References [MG09] • The NIST Definition of Cloud Computing o http://csrc.nist.gov/groups/SNS/cloud-computing/cloud-def-v15.doc o [G09] • Craig Gentry o Fully Homomorphic Encryption from Ideal Lattices. o ACM Symposium on Theory of Computing, 2009. o [DGHV10] • Martin van Dijk, Craig Gentry, Shai Halevi and Vinod Vaikuntanathan o Fully Homomorphic Encryption Over the Integers o [SYY99] • Tomas Sanders, Adam Young and Moti Yung o Non-interactive Cryptocomputing for NC1 o IEEE Symposium on the Foundations of Computer Science, 1999 o 2/24/11 28

  29. References [BGN05] • Dan Boneh, Eu-Jin Goh and Kobi Nissim o Evaluating 2-DNF Formulas on Ciphertexts o Theory of Cryptography Conference, 2005 o [IP07] • Yuval Ishai and Anat Paskin o Evaluating branching programs on encrypted data o Theory of Cryptography Conference, 2007 o [GHV10a] • Craig Gentry, Shai Halevi and Vinod Vaikuntanathan o A Simple BGN-style Encryption Scheme from LWE o Advances in Cryptology – Eurocrypt, 2010 o 2/24/11 29

  30. References [GHV10b] • Craig Gentry, Shai Halevi and Vinod Vaikuntanathan o i-hop Homomorphic Encryption Schemes o Advances in Cryptology – CRYPYO, 2010 o [KR11] • Seny Kamara and Mariana Raykova o Parallel Homomorphic Encryption o Under submission o [SWP01] • Dawn Song, David Wagner and Adrian Perrig o Practical Techniques for Searches on Encrypted Data o IEEE Security and Privacy Symposium, 2000 o 2/24/11 30

  31. References [Goh03] • Eu-Jin Goh o Secure Indexes o http://eprint.iacr.org/2003/216 o [CM05] • Yang-Chen Chang and Michael Mitzenmacher o Privacy preserving keyword searches on remote encrypted data o Conference on Applied Cryptography and Network Security, 2005 o [CGKO06] • Reza Curtmola, Juan Garay, Seny Kamara and Rafail Ostrovsky o Symmetric Searchable Encryption: Improved Definitions and Efficient o Constructions. ACM Conference on Computer & Communication Security, 2006 o 2/24/11 31

  32. References [BDOP04] • Dan Boneh, Giovanni di Crescenzo, Rafail Ostrovsky and Giuseppe o Persiano Public-Key Encryption with Keyword Search o Advances in Cryptology – Eurocrypt, 2004 o [BKOS07] • Dan Boneh, Eyal Kushilevitz, Rafail Ostrovsky, William E. Skeith III o Public Key Encryption That Allows PIR Queries o Advances in Cryptology – CRYPTO, 2007 o [CK10] • Melissa Chase and Seny Kamara o Structured Encryption and Controlled Disclosure o Advances in Cryptology – Asiacrypt, 2010 o 2/24/11 32

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