What Is BLS Signature?
Also known as: BLS Signatures, Boneh-Lynn-Shacham Signature, BLS
In short
A BLS signature is a digital signature scheme developed by Dan Boneh, Ben Lynn and Hovav Shacham that allows many signatures to be combined into a single short signature. It is used by Ethereum's Proof of Stake validators.
BLS signatures are based on a mathematical operation called pairing, defined over elliptic curves. Its most important feature is aggregation: many signatures produced by different people for the same or different messages can be combined into a single signature, and this combined signature can be verified in one step with the signers' public keys. Signatures are also deterministic; the same key and message always produce the same signature.
In Ethereum's Proof of Stake architecture, a large number of validators publish votes (attestations) that confirm blocks. Transmitting and verifying these votes one by one would put a heavy load on the network. Thanks to BLS signatures on the BLS12-381 curve, the signatures of validators confirming the same block are combined and the amount of data carried is greatly reduced. Projects such as Chia, Filecoin and Dfinity also make use of BLS signatures; the scheme can also be used in threshold signature systems.
Verifying BLS signatures requires more computation than the ECDSA or Schnorr signatures used by Bitcoin. In aggregation, additional measures such as proving ownership of public keys are needed to prevent rogue key attacks. For this reason, BLS is preferred in systems where the gain from combining many signatures outweighs this cost.
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