We describe efficient constructions for two oblivious twoparty computation problems: l-out-of-N Oblivious Transfer &d 'Oblivious Poly&nial Evaluation.The oblivious polynomial evaluation protocol is based on a new intractability assumption which is closely related to noisy polynomial re construction.A direct corollary of the l-out-of-N OT protccol is an efficient transformation of any Private Information Retrieval (PIR) protocol to a Symmetric PIR (SPIR) prc-tow1 without increasing the number of databases.The new construction for l-out-of-N OT is highly efficient -it requires only log N executions of a l-out-of-2 OT protocol.We also present a construction for k-out-of-N OT which is more efficient than k repetitions of l-out-of-N OT.The efficiency of the new OT protocols makes them useful for a variety of applications.These include oblivious sampling which can be used to securely compare the sizes of web search engines, protocols for privately solving the list intersection problem and for mutually authenticated key exchange based on (possibly weak) passwords, and protocols for anonymity preserving web usage metering.
In this paper, we show that the special case of strong conditional oblivious transfer from
S to
R can be obtained from only one instance of itself from
R to
S .Our reduction protocol Is simple and efficient, and preserves the security of the inversion.