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49 lines
2.0 KiB
Markdown
49 lines
2.0 KiB
Markdown
---
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id: adaptor-signatures
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title: Adaptor Signatures
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---
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Bitcoin-S now has support for [ECDSA Adaptor Signatures](https://github.com/discreetlogcontracts/dlcspecs/blob/03bf7095c2016e1ce9c9fb612920872d4456f179/ECDSA-adaptor.md).
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There are four relevant functions to adaptor signatures:
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* `sign` (aka encrypt)
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* This function belongs to `ECPrivateKey` and creates an adaptor signature given a message (`ByteVector`) and an adaptor point (`ECPublicKey`).
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* `verify`
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* Verifies an adaptor signature given the signing public key, the message and the adaptor point.
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* `complete` (aka decrypt)
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* This function belongs to `ECPrivateKey` and computes a valid ECDSA signature given a valid adaptor signature whose adaptor point is this private key's public key.
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* `extract` (aka recover)
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* This function belongs to `ECPublicKey` and computes the adaptor secret (private key to this public key) given a valid adaptor signature for this adaptor point, and the valid ECDSA signature computed using `complete`.
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The following code shows each function to do with adaptor signature usage:
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```scala mdoc:invisible
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import org.bitcoins.crypto.ECPrivateKey
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val privKey = ECPrivateKey.freshPrivateKey
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val pubKey = privKey.publicKey
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val adaptorSecret = ECPrivateKey.freshPrivateKey
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val adaptorPoint = adaptorSecret.publicKey
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val msg = scodec.bits.ByteVector.fromValidHex("010101010101")
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```
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```scala mdoc:compile-only
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// Alice generates an adaptor signature using her private key and the adaptor point
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val adaptorSig = privKey.adaptorSign(adaptorPoint, msg)
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// Bob verifies this adaptor signature using Alice's public key and the adaptor point
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require(pubKey.adaptorVerify(msg, adaptorPoint, adaptorSig))
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// Bob computes a valid ECDSA signature using the adaptorSignature, which he knows
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val sig = adaptorSecret.completeAdaptorSignature(adaptorSig)
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// Anyone can validate this signature
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require(pubKey.verify(msg, sig))
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// Alice can compute the adaptor secret from the signatures
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val secret = adaptorPoint.extractAdaptorSecret(adaptorSig, sig)
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require(secret == adaptorSecret)
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```
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