Bolton Bailey

New fascinating work by @or_sattath and Bolton Bailey exhibits a new quantum attack on Bitcoin (and PoW in general), that only requires a single "relatively small" quantum computer. The gist of that attack is that the attacker cultivates a side chain where they *increase* the difficulty by a factor of X, increasing the weight of their blocks by X while only increasing the work they put into each block by sqrt(X), allowing them to create a heavier chain despite being computationally inferior. This attack does not contradict previous results showing quantum miners only have quadratic advantage, since these works assume constant difficulty whereas the new attack abuses difficulty adjustment. The paper leaves mitigating the attack (by means better than repeated hashing) an open problem. More details here: arxiv.org/abs/2403.08023