We show how to realize this strong notion of secure encryption by making the additional, very realistic assumption that intermediate results of an iterative, public, large-scale computation --- like the computations performed by users of the popular cryptocurrency Bitcoin --- are publicly available. We use these computations as a "computational reference clock", which mimics a physical clock in a computational setting, and show how the computations performed by the reference clock can be "reused" to build secure time-lock encryption. A nice feature of this approach is that it can be based on a public computation which is performed "anyway" and independent of the time-lock encryption scheme.
We provide the first formal definitions of computational reference clocks and time-lock encryption, and give a proof-of-concept construction which combines a computational reference clock with witness encryption (Garg et al., STOC 2013). We also explain how to construct a computational reference clock based on Bitcoins.Category / Keywords: foundations / Time-lock encryption, timed-release encryption, Bitcoins, witness encryption, time-lock puzzles, timed commitments Date: received 19 May 2015, last revised 21 Sep 2015 Contact author: tibor jager at rub de Available format(s): PDF | BibTeX Citation Version: 20150921:115232 (All versions of this report) Short URL: ia.cr/2015/478 Discussion forum: Show discussion | Start new discussion