New quadratic delays in Bitcoin scripts

I have a fixation with algorithm complexity. When I was young I was an early optimizer, and, I must admit, that didn’t help me much in dates. Today I occasionally code a sub-optimized algorithm when there is no need for high performance, but it stills bothers me when I do. When I review code, it […]


The relation between Segwit and AsicBoost, covert and overt

I will try to explain the relation between Segwit and AsicBoost, in both the covert and overt forms, in certain detail. I will also try to explain why a method was recently proposed to reduce the interference between covert-AsicBoost and some protocol improvements, by reducing the incentives for covert AsicBoost. The proposal makes covert AsicBoost more expensive, […]


A Bitcoin transaction that takes 5 hours to verify

In 2013 I found a Bitcoin transaction that takes 3 minutes to verify (CVE-2013-2292) related to O(N^2) hashing in signatures. Since then, the O(N^2) argument has popped up in many contexts, mainly in discussions about a block size increase. Now the problem is partially solved by Segwit. During January 2016 I tried to beat the […]

, ,

1 Comment

Drivechains vs Sidechains

As segwit has been merged by Bitcoin Core, and the block size increase seems it will never be merged, I perceive waters are calmer. Not because there is consensus, but because it feels there will never be. But ScalingBitcoin Milan conference is close, tomorrow precisely. So let’s work on other ways to expand Bitcoin without […]


Uncle Mining, an Ethereum Consensus Protocol Flaw

A year ago I was hired by Eth Dev Ltd through Coinspect to perform a security audit on the Ethereum design. One of our findings was that the uncle reward strategy in Ethereum was weird, and could lead to miners abusing the uncle rewards to almost triple the money supply. We discovered this problem because […]


“SPV mining” is the solution, not the problem

Is was Wednesday, March 26, 2014. It was a cold winter outside, but not inside an old building of the Princeton university campus. The room, full of people, was warm. I was standing in front of some of the brightest minds in Bitcoin: Andresen, Bonneau, Eyal, Maxwell, Miller, Gün Sirer, Szabo, Todd and Zooko, to name only a few. My talk was about “SPV Mining”, […]


Proof of unique blockchain storage revised

In this post I describe a new way to for a node in the Bitcoin blockchain to prove to its peers that it is storing a copy of the blockchain. The core primitive that enables this protocol this is the Asymmetric-Time Function (ATF). You won’t get much info by googling ATF since I coined that term […]