1. Outsourced Computation Verification
Roy Luo, UC Berkeley
Under the mentorship of
Graham Cormode, AT&T Labs
DIMACS REU 2010

2. The Background Streaming Model Large amounts of data, limited memory
E.g. Router observing network traffic
Answer questions about data after only one pass
E.g. what was the kth element? Most frequent element?
One solution: outsource problem to a 3rd party with more computing power (cloud computing)

3. The Model You(verifier) and a 3rd party (helper)
Both agents process entire data stream
After seeing all the data, helper responds to verifier with answer to query
Data Stream
“Answer” V H

4. The Problem If we fully trust 3rd party, we’re done
But: helper may have made an error or may be outright deceptive
Require helper to prove correctness
Need a “proof” that can be verified in limited space
One-round model: H sends V one message containing the answer and a proof
Multi-round model: H and V exchange messages until V is satisfied that H gave the right answer

5. An Example The INDEX problem:
Without a helper, takes (N) space for N items (even probabilistically)
Using one-round protocol, INDEX has solution with HV = O(Nlog(N)), H = length of helper’s message, V = space used by verifier
E.g. H = O(√N), V = O(√N*log(N))
Using multi-round protocol, INDEX has a solution that uses V = O(log(N)) and H = O(log(N))

6. Directions for Research
Are existing protocols practical for real-world use?
What other problems require protocols?
What class of problems can be solved in this model?