Adaptor Signature
A cryptographic technique that links the validity of a digital signature to a separate secret value, letting two actions be coupled together without revealing that link on-chain.
An adaptor signature is a cryptographic construction, built on Schnorr signatures (see Kaavon's "Schnorr Signature" glossary definition), that produces a signature which only becomes fully valid once a specific secret value is also revealed — and critically, revealing a completed adaptor signature simultaneously reveals that secret value to anyone who sees it. This lets two separate actions be cryptographically linked together — one party only gets paid if and when they complete a signature that necessarily exposes information the other party needed — without that link ever being visible on-chain as a distinguishable, special transaction type.
Adaptor signatures underpin more efficient, more private alternatives to traditional hash-based constructions like a Hashed Timelock Contract (see Kaavon's "Hashed Timelock Contract (HTLC)" glossary definition), most notably forming the basis of a Point Time-Locked Contract (see Kaavon's "Point Time-Locked Contract (PTLC)" glossary definition). Because adaptor-signature-based transactions look like ordinary, simple signatures on-chain rather than revealing a distinctive hash-locked script structure, they improve both privacy and the amount of on-chain data needed compared to the equivalent HTLC-based construction.
Examples
- An adaptor signature can link a Lightning Network payment to a secret value, such that completing the payment's signature necessarily reveals that secret to the other party.
- Unlike a traditional HTLC, a completed adaptor-signature-based transaction looks like an ordinary signature on-chain, without revealing a distinctive hash-locked script structure.