Aggregate Signature

Overview

An aggregate signature combines several valid signatures into a smaller representation that can be checked against the corresponding public keys and messages. BLS signatures are widely associated with this property because independently produced signatures can be aggregated without interactive coordination. Some systems aggregate signatures over one common message, while others support different messages. The verifier must know which mode applies and which signer set is claimed.

Aggregation improves scalability when many validators or participants sign similar data. Instead of transmitting and storing one full signature per participant, a protocol can carry one aggregate plus a bitmap, committee list, or other signer metadata. This can make consensus votes and light-client proofs more compact. It does not remove the need to validate membership, voting weight, message domain, and the relevant Consensus Quorum.

Security details are critical. A naive aggregation design can permit a rogue participant to choose a public key that cancels or impersonates another signer. Protocols address this through proof of possession, distinct-message rules, authenticated key registration, or scheme-specific verification. Implementations must also prevent duplicate signers, mismatched message ordering, invalid subgroup elements, and acceptance of malformed encodings. A single failed component can invalidate the aggregate.

Operationally, systems should preserve the aggregate signature together with the signer set, public keys, message root, domain, and protocol version. A successful aggregate verification proves that the required cryptographic relationship holds, but business authorization still depends on current roles and thresholds. For example, an aggregate may authenticate many Consensus Vote messages while the application separately checks whether their combined voting power is sufficient to commit or finalize a block.