Pseudonymous Secure Computation from Time-Lock Puzzles

In standard models of secure computation, point-to-point channels between parties are assumed to be authenticated by some pre-existing means. In other cases, even stronger pre-existing setup—e.g., a public-key infrastructure (PKI)—is assumed. These assumptions are too strong for open, peer-to-peer networks, where parties do not necessarily have any prior relationships and can come and go as they please. Nevertheless, these assumptions are made due to the prevailing belief that nothing “interesting” can be achieved without them. Taking inspiration from Bitcoin, we show that precise bounds on computational power can be used in place of pre-existing setup to achieve weaker (but nontrivial) notions of security. Specifically, under the assumptions that digital signatures exist and each party can solve cryptographic “time-lock” puzzles only at a bounded rate, we show that without prior setup and with no bound on the number of corruptions, a group of parties can agree on a PKI with which they can then realize pseudonymous notions of authenticated communication, broadcast, and secure computation. Roughly, “pseudonymous” here means that inputs/outputs are (effectively) bound to pseudonyms rather than parties’ true identities.