Sync Committee
A small, randomly selected, periodically rotating group of Ethereum validators whose signatures let light clients efficiently verify the chain without downloading and checking every block.
A sync committee is a small, randomly chosen subset of Ethereum's full validator set, rotated periodically, whose members sign off on recent blocks specifically to support efficient light client (see Kaavon's "Light Client" glossary definition) verification. Rather than requiring a light client to track the entire, much larger validator set and its votes directly, it only needs to verify the much smaller sync committee's signatures and periodically verify the committee's own rotation from one period to the next.
This dramatically reduces the computational and bandwidth burden for light clients, such as wallets or mobile devices, that want cryptographic assurance about the chain's state without running a full node (see Kaavon's "Full Node" glossary definition) themselves. The tradeoff is that light clients relying on sync committee signatures are trusting that mechanism's own security assumptions — namely, that an adversary can't control enough of a given sync committee to produce a false signed attestation about the chain's state.
Examples
- A mobile Ethereum wallet acting as a light client can verify recent chain state by checking the current sync committee's signatures, without downloading and verifying every historical block.
- Sync committees rotate periodically specifically to limit how long any single set of validators has concentrated influence over light client verification.