International Association for Cryptologic Research (IACR)
Abstract
A Hashed Time Lock Contract (HTLC) is a central concept in cryptocurrencies where some value can be spent either with the preimage of a public hash by one party (Bob) or after a timelock expires by another party (Alice). We present a bribery attack on HTLC\u27s where Bob\u27s hash-protected transaction is censored by Alice\u27s timelocked transaction. Alice incentivizes miners to censor Bob\u27s transaction by leaving almost all her value to miners in general. Miners follow (or refuse) this bribe if their expected payoff is better (or worse). We explore conditions under which this attack is possible, and how HTLC participants can protect themselves against the attack. Applications like Lightning Network payment channels and Cross-Chain Atomic Swaps use HTLC\u27s as building blocks and are vulnerable to this attack. Our proposed solution uses the hashpower share of the weakest known miner to derive parameters that make these applications robust against this bribing attack
