Bram Cohen has already made an enormous contribution to the decentralized web. As the creator of the BitTorrent protocol, he brought about the golden era of peer-to-peer file-sharing in the early 2000s. Within a year of starting the project in 2003, files shared on BitTorrent made up more than a third of all traffic on the internet.

When a figure of this pedigree announces a move into cryptocurrency, people take notice. Driven by his love for solving hard problems, and affronted by bitcoin’s enormous energy usage, Cohen decided to work on designing a cryptocurrency that would maintain the decentralized properties of bitcoin without requiring the power input of a small nation.

The result was Chia. Based on proof-of-space rather than proof-of-work, the network uses hard disk space rather than computing power for the mining process (dubbed “farming”), making use of a resource that is already widely available instead of voraciously drawing power. This has another built-in consequence: flattening the incentives that lead bitcoin miners to continually expand their equipment racks.

“The idea is that you’re leveraging this resource of storage capacity, and people already have ludicrous amounts of excess storage on their laptops, and other places, which is just not being utilized,” says Cohen in a call with BREAKER. “There is so much of that already that it should eventually reach the point where if you were buying new hard drives for the purpose of farming, it would lose you money.”

Security = space x time

Cohen has also made the claim that Chia is more secure than bitcoin—something that seems like an overstatement, considering that there has never been a successful attack against the bitcoin network.

But as he points out, there have been times when a single mining pool has controlled the majority of the network hash power. In fact, as recently as June this year, a group of mining pools controlled by Bitmain controlled 42 percent of bitcoin hash power even with some of its resources focused on mining other coins.

“If someone wanted to buy up resources just for the purpose of attacking bitcoin, it would be expensive but do-able, especially for variants like Bitcoin Cash and SV which have less hash power,” he says. “To attack Chia you’d have to get access to more resources than the network as a whole, which will be a huge amount of resources once everyone has signed up. The cost of acquiring them upfront would be huge, higher than the cost of the ASICs you’d need to attack bitcoin, so to overwhelm the system would be much more difficult.”

Proof-of-space could be more secure in theory, but there are also drawbacks—notably that low cost (or zero cost) mining means that certain forms of attack can essentially be run for free.

The major attack in question is known as a “re-mining from genesis” attack, in which an attacker with a large proportion of the network resources creates an entirely new blockchain from scratch, eventually switching it for the historical blockchain when it becomes longer. If executed correctly, an attacker would be able to get the new chain accepted by a majority of nodes while transferring ownership of any number of coins into their possession and/or undoing past transactions.

"The attacker can rewrite the last few years of work, but it’s going to take them several real calendar years to pull it off."

This means that for a network maintained by proof-of-space to be secure, it’s also necessary to have a proof-of-time. This involves a non-parallelizable computing process, i.e. something that takes the same length of time regardless of how much processing power is applied.

“By throwing in proofs-of-time you stop that attack, because the attacker can rewrite the last few years of work, but it’s going to take them several real calendar years to pull it off,” Cohen says.

Recently, Chia announced the launch of a competition to optimize the proof-of-time protocol, with $100,000 in prize money split among the winners in two separate categories. By broadening the field of submissions beyond himself and the Chia team, Cohen hopes to find the best possible way to implement the algorithms that will keep the platform secure. Entries have already started to roll in, he says—but “more is always better.”

Not just green, but practical

Ultimately, Cohen says, he’d like to see people abandon bitcoin entirely in favor of Chia, and he has a pragmatic view of the kind of features that will be needed to make that a reality.

“To some degree people will switch over to something just because it’s greener, but it’s not a big enough thing on its own,” he says. “Being more distributed should make for a better system, and also we’re working on Chiascript, which is going to be a better platform for the kind of smart transactions people actually want to use.”

Chiascript will be inspired by bitcoin’s Script, but is based on the Lisp programming language instead of Forth. For Cohen and his team, this means that none of the existing bitcoin codebase can be directly reused, creating a lot more work on the development side.

As for the kind of features people want, he mentions velocity control, where users can set a maximum rate at which wallet funds can be withdrawn as a safety precaution, and private payment channels, as implemented in bitcoin’s Lightning Network.

Chia’s launch was supposed to be scheduled for the end of 2018, but has been pushed back “because you know…software.”



Cohen and his team have solved many of the fundamental math problems associated with Chia’s development, but he still needs to build out the rest of the code. He expects a public launch sometime in 2019. If Chia succeeds, one of the biggest criticisms made of cryptocurrency today—that it’s environmentally harmful—could eventually become outdated.