The US Patent and Trademark Office (USTPO) has published a patent application submitted by bitcoin startup Blockstream related to its work on sidechains.

The application, submitted on 9th May and published earlier this week, outlines “systems and methods…for transferring an asset from a parent chain to a sidechain”. It names Blockstream CEO Adam Back and Blockstream CTO Greg Maxwell (who is also a Core contributor) as inventors. Sidechains are envisioned as a way to allow the movement of digital assets from one blockchain to another, opening the door to new kinds of applications and experiments using the tech.

The application’s release comes months after the startup announced a patent pledge, saying at the time that it would make its patents and applications available under the Defensive Patent License. The application outlines how assets could be exchange between a primary blockchain and a sidechain to which it is connected, explaining:

“A simplified payment verification (SPV) proof associated with the parent chain asset may be generated. The SPV proof may include a threshold level of work. The SPV proof associated with the parent chain asset may be validated, and a sidechain asset corresponding to the parent chain asset may be generated. If no reorganization proof is detected, the sidechain asset is released.”

Blockstream released its first open-source code for sidechains last summer, later moving to debut a sidechains projects dubbed Liquid aimed at bitcoin exchanges.

The startup raised $55m in a Series A funding round in February, and in July acquired bitcoin wallet startup GreenAddress in a bid to boost its development of sidechains.

Disclosure: CoinDesk is a subsidiary of Digital Currency Group, which has an ownership stake in Blockstream.

Correction: A previous version of this article incorrectly reported that Adam Back was a contributor to the Bitcoin Core development team. The article has been updated to remove this inaccuracy.

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