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Core Developer Jonas Schnelli: Segregated Witness Improves and Optimizes Bitcoin Protocol

In part six of this series, Bitcoin Wallet developer and bitcoinj maintainer Andreas Schildbach talks about SegWit's future
Op-ed - Core Developer Jonas Schnelli: Segregated Witness Improves and Optimizes Bitcoin Protocol

The long-lasting block size dispute has catapulted into the center of attention again. One of the most talked-about developments is Segregated Witness, of which a public testnet iteration was launched last week. The innovation as recently proposed by Blockstream co-founder and Bitcoin Core developer Dr. Pieter Wuille is a centerpiece of a scalability “roadmap” set out by Bitcoin Core.

To find out where the broader development community stands on Segregated Witness, Bitcoin Magazine reached out to library and wallet developers; those who will need to do the heavy lifting in order to utilize the innovation once rolled out.

In part 6 of this series: Bitcoin Core and Bitcoin C library developer Jonas Schnelli.

Less Than a Week of Work

Jonas Schnelli is an independent Bitcoin Core developer who also develops the libbtc library that runs on iOS, Android, Mac, PC, Linux and MCUs. Schnelli additionally founded, which is in the process of creating a simple and secure hardware wallet.

Like many other wallet and library developers, Schnelli believes the integration of Segregated Witness would significantly benefit the Bitcoin protocol.


“I have read the relevant Bitcoin Improvement Proposals in detail, and have started experimenting with Segregated Witness to get a better feeling for how it works and how long it might take to adapt it for my projects. I think from the wallet perspective – SPV, hardware-wallet, wallet-libraries – integration is pretty simple. Probably less then one week of work, including testing and deploying. This is also evident from looking at the basic Bitcoin Core wallet changes; it’s just a couple of lines of code.”

Schnelli agrees that a roll-out of Segregated Witness is the best first step toward broader Bitcoin scalability.

“I completely agree the added effort for wallet and library developers is worth it, considering the risks of hard forking,” Schnelli explained. “People are often favoring simple infrastructure improvements rather then going into optimizing the software itself. But that’s a common mistake we have seen in the IT industries in the past decades. It’s short-term thinking and will very likely cause bigger problems in the future.”

Soft Fork: Chance for a Better Protocol

Roll-out of Segregated Witness on the Bitcoin network is currently scheduled for April of this year. Once a super-majority of miners agrees on the solution, Segregated Witness will be activated, and can be utilized by wallet software.

The most notable difference between Bitcoin Core and its recently launched competitor Bitcoin Classic is that the former plans to roll out Segregated Witness through a soft fork, while the latter wants to deploy a block-size increase through a hard fork, meaning all full nodes on the network need to switch.

Schnelli considers the choice an obvious one: a Segregated Witness soft fork is preferable for now.

“A 2-megabyte hard fork does not improve the protocol itself, not a tiny bit,” Schnelli said. “With Segregated Witness, we have a chance to get a ‘better,’ more optimized protocol, and reach almost the same amount of transactions per block. And, extremely important, Segregated Witness has almost full consensus.”

He continued:

“I personally cannot understand why some developers are still thinking that a 2- megabyte hard fork is preferable. The main risks of a hard fork are not technical, but there are huge risks of disrupting the whole Bitcoin economy. The Bitcoin market is extremely fragile, and it fully trusts in developer consensus. Bitcoin is still very young. If we start fighting and disagree on the very deepest technical layer, we hurt Bitcoin in its core and will lose irreplaceable trust from the markets.”

Schnelli noted, however, that he has no fundamental problems with alternative Bitcoin implementations, including Bitcoin Classic. It’s mostly the proposed block size increase prior to consensus that he condemns.

“I’m still hoping there could be a full agreement between Classic and Core on the consensus layer. Code forks are healthy – chain forks not,” he said. “If we go down the road of a ‘Let’s see who will make the race; Classic or Core’ there will only be one winner in the end: other cryptocurrency protocols like Ethereum and Ripple.”

For more information on Segregated Witness, see Bitcoin Magazine’s three-partseries on the subject, or part 1, part 2, part 3, part 4 and part 5 of this development series.