Blockstream CTO Greg Maxwell Provides an Update on Bitcoin Sidechains


The concept of sidechains was first brought to the public in the 99th episode of Let’s Talk Bitcoin back in April of 2014. While plenty of progress has been made since that first, conceptual announcement of the idea, the first true, decentralized sidechains are still not available on Bitcoin’s mainnet.

CoinJournal reached out to Blockstream CTO Greg Maxwell to get an update on the current status of sidechains, and he provided some insight into what can be expected over the next few months and what will eventually be made possible with this innovation.

Sidechains Today and What’s Next

As many bitcoiners know, there is currently a sidechains test network available in the form of Blockstream’s Elements Alpha project; however, this testnet is not the final vision of the sidechains concept. Maxwell noted, “[It] uses the full sidechains mechanism in one of the two peg directions, though not with compact SPV proofs.”

Maxwell also added, “We have a new version of the construction under development which should be released soon (e.g. two months or so).”

There is also still work to be done on the optimal design parameters for compact SPV proofs, which were outlined in the sidechains white paper. Maxwell claimed, “After [work is completed on compact SPV proofs], we would then look to release a BIP with reference code for community feedback to start the open design and review process.”

The Blockstream CTO also pointed out that a recent paper from National and Kapodistrian University of Athens has confirmed the company’s work in this area.

Blockstream Not the Only Team Working on Sidechains

Although sidechains are Blockstream’s pet project, there are also many other companies and individuals working on this concept. Bitcoin Hivemind’s Paul Sztorc recently wrote about his concept of a drivechain, and Rootstock blogged about their own drivechain-sidechain hybrid model. To this point, Greg Maxwell stated

“The technical community has been supportive of the concept of sidechains as a framework for independent development of interoperable bitcoin denominated chains.”

Although a representative from Blockstream claimed it was too early to comment on the drivechain idea, Maxwell did state that he is looking forward to a possible zerocash sidechain and other innovations. A non-Bitcoin version of zerocash, Zcash, is expected to be released this summer.

The Coming Experimentation Made Possible By Sidechains

The main value of sidechains has been most-properly explained as a way to allow for more experimentation in the Bitcoin development process. For example, the upcoming Segregated Witness improvement came out of the Elements Alpha sidechain. In his comments to CoinJournal, Greg Maxwell revealed that he recently proposed a signature aggregation scheme that would reduce transaction sizes by 30 percent, which is another improvement that could be prototyped on a sidechain.

Some of the other sidechain-related projects to think about for now are Bitcoin Hivemind, Rootstock, a zerocash sidechain, and a sidechain for testing Confidential Transactions (another possible privacy improvement for Bitcoin).