Cryptology ePrint Archive: Report 2020/784

CRAFT: Composable Randomness and Almost Fairness from Time

Carsten Baum and Bernardo David and Rafael Dowsley and Jesper Buus Nielsen and Sabine Oechsner

Abstract: Cryptographic protocols often need to encompass time, e.g. for time outs. Modeling time formally is therefore crucial, as security of protocols can then be proven under more realistic assumptions. This is particularly important when considering composition, as protocols are rarely used in a stand-alone setting. This work extends the recent TARDIS model of abstract composable time (ACT) to the case of multiparty functionalities encompassing communication, publicly verifiable time-based primitives and secure computation. We model delayed multiparty communication through an ACT treatment of broadcast channels and public ledgers. Next, we introduce a publicly verifiable time-lock puzzle (TLP) functionality which we realize by showing that the TLP construction from TARDIS is publicly verifiable. Finally, we show that these new primitives can be used as building blocks for obtaining highly efficient composable randomness beacons and MPC with output independent abort and financial fairness.

Category / Keywords: cryptographic protocols / Universal Composability, Time Lock Puzzle, Output Independent Abort, Multiparty Computation, Randomness Beacons, Public Verifiability

Date: received 24 Jun 2020

Contact author: cbaum at cs au dk,bernardo@bmdavid com,rafael@dowsley net,jbn@cs au dk,oechsner@cs au dk

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Version: 20200627:184740 (All versions of this report)

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