Polkadot-Kusama APK Bridge PoC

[k-gunjan]

Project Abstract

We are developing a Proof-of-Concept for a next-generation bridge between Polkadot and other ecosystems that leverages Aggregated Public Key (APK) proofs to enable trustless, cost-efficient cross-chain communication. Unlike traditional bridge architectures that require expensive verification of hundreds of individual validator signatures, our APK-based approach aggregates these signatures into a single cryptographic proof—dramatically reducing on-chain verification costs while maintaining the same security guarantees. This innovation addresses one of the most critical challenges in blockchain interoperability: making cross-chain operations economically viable at scale and promoting cross-chain dApps with Ethereum and other ecosystems.

The bridge utilizes advanced pairing-friendly elliptic curves (BLS12-377/381 paired with BW6-761/767) to generate succinct proofs that are both computationally efficient and cryptographically secure. BLS12-381 is particularly interesting for bridging with EVM chains. By demonstrating this technology between Polkadot and Kusama, we're not only strengthening the core relay chain ecosystem but also establishing a replicable framework for secure interoperability with external networks like Ethereum. This proof-of-concept represents a significant step toward realizing the vision of a truly interconnected multi-chain future, where assets and data can flow seamlessly across independent consensus systems without compromising security or incurring prohibitive costs.

Application Checklist

• The application template has been copied and aptly renamed (project_name.md).
• I have read and followed the program guidelines.
• I am aware that, in order to receive a grant, I (and the entity I represent) have to successfully complete a KYC/KYB check.
• The software delivered for this grant will be released under an open-source license specified in the application.

[keeganquigley]

Hi @k-gunjan thanks for the application. This is interesting, but when it comes to trustless bridging I'm not entirely sure yet if the bounty is the right mechanism to fund it. Have you already talked to the other bridge teams to determine the feasibility of this approach? I see that Snowbridge had already investigated possibilities back in 2022. Do you know if they are planning any upgrades?

That being said, my research shows that EIP-2537 was successfully included in May's Ethereum Pectra fork, which adds native precompiles for BLS12-381. So this is likely good timing, but I think we will want to have some input from both the Snowfork team and W3F researchers. Perhaps you could create a forum post to gauge interest on a next-gen bridge.

[drskalman]

Hello @keeganquigley, this grant has the backing of the research (including @AlistairStewart's and Fatemeh). It helps us to demonstrate the power of APK Proof in practice, and the smart contract, being in Solidity, could be used by other solidity-compatible ecosystems who wishes to bridge to Polkadot. This is not however won't be immediately deploy-able on Ethereum, because the verification is carried out on BW6-767 (not BLS12-381) as there is no precompile for it there, but it could be used on other chain without prohibitively expensive computation cost.

I was not aware that Snowbridge runs a Polkadot->Kusama bridge, but if they do and they are interested to upgrade to an APK-proof based BLS bridge, they could readily use the result of @k-gunjan work for that.

Nonetheless, if you think that there is a more appropriate track to which @k-gunjan can to apply to, please point them to. 🙏

[semuelle]

Thanks for the review, @drskalman. Happy to support this. Just a minor issue below.

[k-gunjan]

Thanks @semuelle for the corrections and the support. I have applied the changes.

[k-gunjan]

Hi @keeganquigley , thank you for the review. I appreciate @drskalman 's clarification on the research backing and the technical deployment paths. I'm eager to collaborate with the broader ecosystem with the result of this work. Looking forward to your continued support and feedback!

[semuelle]

Thanks, LGTM.

wrong account

[ditavia-br]

@k-gunjan Thanks for the application. We are nearing the end of our runway, so we’ll need to wait for clarity on the budget before moving forward with any remaining applications. We’ll get in touch as soon as we have an update.

[k-gunjan]

@ditavia-br Thank you for the transparency and the update. While awaiting clarity on the budget, I'm ready to provide any additional information as needed. Looking forward to hearing from you!