Adaptor Signature

An adaptor signature is a cryptographic construction that ties the publication of a valid signature to the revelation of a hidden secret. Informally, it is a "promise" that the moment a complete signature appears on-chain, anyone watching can extract a specific secret value from it. This links a payment to a piece of knowledge, enabling powerful contracts that look like ordinary transactions.

Scriptless scripts

Adaptor signatures are the foundational building block of "scriptless scripts," an approach that enforces contract conditions through the algebraic properties of signatures rather than through explicit Bitcoin Script opcodes. Because the contract logic lives in the signature math, an outside observer sees only a normal-looking single-signature spend. This improves privacy, since complex conditions are indistinguishable from routine activity, and reduces on-chain weight.

Atomic swaps and Lightning

The canonical application is the atomic swap: two parties on two chains construct adaptor signatures so that completing the swap on one chain unavoidably reveals the secret needed to complete it on the other, making the trade all-or-nothing without a trusted intermediary. The same mechanism yields a "point time-locked contract" (PTLC) variant of Lightning's HTLCs, replacing hash preimages with secrets revealed via signatures for better privacy and resistance to certain attacks. Adaptor signatures pair naturally with Schnorr signatures and complement multi-party schemes like FROST.

For self-sovereign users, adaptor signatures represent a path to more private, more efficient cross-chain and Layer 2 settlement, with the cryptography rather than the blockchain doing the enforcement.