Research ·
Shorter proofs for light clients
Our fellows cut proof size by a third without a new trusted setup.
Kenji Arai
Research, council · 6 min read
A light-client proof on Oriel is now a third smaller, 9.4 KB instead of 14.1 KB, and it needs no new trusted setup. Lucie Moreau, a 2026 cryptography fellow, did most of the work, and we published the paper and its code on 1 Oct 2026 under an open licence.
What a light client checks
A light client is the part of a wallet or a bridge that checks the chain without storing it. It asks a full node for a block header and a proof that enough validators signed that block. The signature itself is small. Most of the proof is the record of which validators signed and which validator set they belonged to at the time.
Where the third went
The old format repeated the full validator set in every proof, even though the set changes only a few times a month. The new one sends the set only when it changes, and in between it sends a short reference to the last set the client has already checked. The list of who signed is also packed into a bitmap instead of a list of keys.
Both changes use the curves and parameters the chain already runs on. That is why no setup ceremony was needed, and why existing nodes can serve the new proofs after a routine upgrade.
What it changes
For a phone wallet, smaller proofs mean less data on a slow connection and a faster check before a payment shows as final. For the bridge, the contract that verifies Oriel proofs on the other chain does about a third less work per transfer, which lowers the cost of every crossing.
We stopped sending the client things it already knew. Most of the saving came from that one idea.
What comes next
- The new format ships in the light-client library from version 2.4, behind a flag.
- Wallet teams can test against a public endpoint until 30 Nov 2026.
- The bridge moves to the new verifier only after the second audit has reviewed it.
Tessel has started testing the new format in its wallet. If you build a light client of your own, the paper has a section on migrating, and Lucie answers questions on the research forum every Tuesday.
