## Cryptology ePrint Archive: Report 2016/991

Bootstrapping the Blockchain, with Applications to Consensus and Fast PKI Setup

Juan A. Garay and Aggelos Kiayias and Nikos Leonardos and Giorgos Panagiotakos

Abstract: The Bitcoin backbone protocol [Eurocrypt 2015] extracts basic properties of Bitcoin's underlying {\em blockchain} data structure, such as common prefix'' and chain quality,'' and shows how fundamental applications including consensus and a robust public transaction ledger can be built on top of them. The underlying assumptions are proofs of work'' (POWs), adversarial hashing power strictly less than $1/2$ {\em and} no adversarial pre-computation---or, alternatively, the existence of an unpredictable genesis'' block.

In this paper we first show how to remove the latter assumption, presenting a bootstrapped'' Bitcoin-like blockchain protocol relying on POWs that builds genesis blocks from scratch'' in the presence of adversarial pre-computation. Importantly, the round complexity of the genesis block generation process is \emph{independent} of the number of participants.

Next, we consider applications of our construction, including a PKI generation protocol and a consensus protocol without trusted setup assuming an honest majority (in terms of computational power). Previous results in the same setting (unauthenticated parties, no trusted setup, POWs) required a round complexity linear in the number of participants.

Category / Keywords: cryptographic protocols / Bitcoin, bootstrapping, unlinkability

Original Publication (with minor differences): IACR-PKC-2018

Date: received 13 Oct 2016, last revised 23 Mar 2018

Contact author: pagio91i at gmail com

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2016/991

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