We continue the line of work initiated by Katz (Eurocrypt 2007) on using
for universally composable secure computation. As our main result, we show an efficient oblivious-transfer (OT) protocol in which two parties each create and exchange a single, stateless token and can then run an unbounded number of OTs. Our result yields what we believe is the most
known approach for oblivious transfer based on tamper-proof tokens, and implies that the parties can perform (repeated) secure computation of arbitrary functions without exchanging additional tokens.
Motivated by this result, we investigate the minimal number of stateless tokens needed for universally composable OT/secure computation. We prove that our protocol is
in this regard for constructions making
use of the tokens (in a sense we define). We also show that nonblack-box techniques can be used to obtain a construction using only a single stateless token.