On Statistical Security in Two-Party Computation

There has been a large body of work characterizing the round complexity of general-purpose maliciously secure two-party computation (2PC) against probabilistic polynomial time adversaries. This is particularly true for zero-knowledge, which is a special case of 2PC. In fact, in the special case of zero knowledge, optimal protocols with unconditional security against one of the two players have also been meticulously studied and constructed. On the other hand, general-purpose maliciously secure 2PC with statistical or unconditional security against one of the two participants has remained largely unexplored so far. In this work, we initiate the study of such protocols, which we refer to as 2PC with one-sided statistical security. We settle the round complexity of 2PC with one-sided statistical security with respect to black-box simulation by obtaining the following tight results: In a setting where only one party obtains an output, we design 2PC in $4$ rounds with statistical security against receivers and computational security against senders. In a setting where both parties obtain outputs, we design 2PC in $5$ rounds with computational security against the party that obtains output first and statistical security against the party that obtains output last. Katz and Ostrovsky (CRYPTO 2004) showed that 2PC with black-box simulation requires at least $4$ rounds when one party obtains an output and $5$ rounds when both parties obtain outputs, even when only computational security is desired against both parties. Thus in these settings, not only are our results tight, but they also show that statistical security is achievable at no extra cost to round complexity. This still leaves open the question of whether 2PC can be achieved with black-box simulation in $4$ rounds with statistical security against senders and computational security against receivers. Based on a lower bound on computational zero-knowledge proofs due to Katz (TCC 2008), we observe that the answer is negative unless the polynomial hierarchy collapses

Acaricidal activities of whole cell suspension, cell-free supernatant, and crude cell extract of Xenorhabdus stokiae against mushroom mite (Luciaphorus sp.)*

Xenorhabdus bacterium has been used as a biological control agent against Luciaphorus sp., a mushroom mite endemic in Thailand. To develop an effective formulation of Xenorhabdus stokiae, treatments using different parts of X. stokiae isolate PB09 culture, including whole cell suspension, cell-free supernatant, and crude cell extract, were performed. The results show that different parts of X. stokiae isolate PB09 culture could induce variable effects on mite mortality and fecundity. Application with cell-free supernatant of X. stokiae culture resulted in both the highest mite mortality rate [(89.00±3.60)%] and the lowest mite fecundity [(41.33±23.69) eggs/gravid female]. Whole cell suspension of X. stokiae isolate PB09 culture was found to be slightly less effective than its cell-free supernatant, suggesting that X. stokiae was more likely to release its metabolites with acaricidal activities to the surrounding culture media. Crude cell extract of X. stokiae was not effective against mites. Cell-free supernatant of X. stokiae isolate PB09 was the most effective biological control agent and it could be conveniently used in future formulations instead of live bacteria