Jyh-haw Yeh Dept. of Computer Science Boise State University

1. A PASS Scheme in Clouding Computing - Protecting Data Privacy by Authentication and Secret Sharing Jyh-haw Yeh Dept. of Computer Science Boise State University

2. Cloud Computing Introduction • Cloud provides services – software,, platform, Infrastructure. • Clients are charged by per-use basis. • Capital Expenditure (CapExp) -> Operational Expenditure (OpExp) • Multi-tenancy: better resource utilization • Reliability: redundant sites • Security: better protection from outside attacks. • Security: big ? from malicious cloud employees.

3. The Problem to solve • Protecting clients’ data privacy from cloud employee. • Perfect solution: fully homomophic encryption algorithm (FHEA). No practical algorithm available. • Without FHEA, 100% data privacy may not be possible.

4. PASS Scheme • Protect data Privacy by Authentication and Secret Sharing (PASS). • Objective: minimize the risk of leaking private data. • Approach: • Encrypt data by a key shared with the client. • Do not store the key anywhere in the cloud. • Use secret sharing to authenticate users and recover the shared key.

5. PASS Scheme • 5 security components: • Public key cryptosystem (PKC): published by cloud. • Key agreement (KA): agree on a shared key and two secret shares at registration. • Key management (KM): keep a profile for each client. • Authentication(AUTH): • client’s counter <-> server’s counter; • Computed hashed key from client’s request<-> stored hashed key • Access control (ACL): second defense for a time frame that the secret key is in use for processing a query.

6. PASS Scheme • Design guideline: • Ensure secret isolation (secret compartment). • Security with a higher priority than efficiency. • Choose a design choice that would benefit multiple security components.

7. PASS Scheme - PKC • PASS chooses ECC over RSA. • ECC: a curve is chosen over a prime p. A base point G with an order n. • Cloud provider publishes the ECC domain parameter <p, a, b, G, n>. • Each cloud entity (server, clients) sets up his own public-private key pair. • Server: public , private , where • Client i: public , private , where

8. PASS Scheme – Key Agreement • Each client iand the cloud server s agree on a data encryption key and two secret shares (known to the client) and (known to the server). • The secret shares are used to recover the encryption key.

9. PASS Scheme – Key Agreement • Encryption key agreement: • Client i chooses a random number and then sends to the server s • Server s chooses a random number and then sends to the client i • Both compute a point • Agree on an encryption key : the x-coordinate of

10. PASS Scheme – Key Agreement • Secret shares agreement: • Both computes a point and let be the x-coordinate of the point • Both construct a same poly • With both secret shares, the poly and then the secret key can be recovered

11. PASS Scheme – Key Management • The cloud keeps a profile for each client i • Hashed key and server request counter for authentication • Security label for access control

12. PASS Scheme – Client Authentication • Client keeps his own request counter • Client  Server: • Server decrypt and get both and • Client authentication succeeds if both • the stored hashed key matches the hashed key derived from secret shares • The server and client request counters are matched

13. PASS Scheme – Access Control • Security label: (security level, {categories}) • Security level: secret, non-secret • Each client iis a category • All query servers/processes are in category “query-system”  {all } • Security label for client i’s profile: (secret, { })

14. PASS Scheme – Integrating five Components • Step1 - 4 for initial client registration: key agreement and data encryption • Step 5-12 for a query processing • Diagram in the following link shows these steps. • http://cs.boisestate.edu/~jhyeh/pass_diagram.pdf