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65 lines
3 KiB
Markdown
65 lines
3 KiB
Markdown
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---
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id: version-v0.4-sign
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title: Sign API
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original_id: sign
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---
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### The [`Sign` API](/api/org/bitcoins/crypto/Sign)
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This is the API we define to sign things with. It takes in an arbitrary byte vector and returns a `Future[ECDigitalSignature]`. The reason we incorporate `Future`s here is for extensibility of this API. We would like to provide implementations of this API for hardware devices, which need to be asynchrnous since they may require user input.
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From [Sign.scala](/api/org/bitcoins/crypto/Sign):
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```scala
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import scodec.bits._
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import org.bitcoins.crypto._
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import scala.concurrent._
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import scala.concurrent.duration._
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trait Sign {
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def signFunction: ByteVector => Future[ECDigitalSignature]
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def signFuture(bytes: ByteVector): Future[ECDigitalSignature] =
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signFunction(bytes)
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def sign(bytes: ByteVector): ECDigitalSignature = {
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Await.result(signFuture(bytes), 30.seconds)
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}
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def publicKey: ECPublicKey
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}
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```
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The `ByteVector` that is input to the `signFunction` should be the hash that is output from [`TransactionSignatureSerializer`](/api/org/bitcoins/core/crypto/TransactionSignatureSerializer)'s `hashForSignature` method. Our in-memory [`ECKey`](/api/org/bitcoins/crypto/ECKey) types implement the `Sign` API.
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If you wanted to implement a new `Sign` api for a hardware wallet, you can easily pass it into the `TxBuilder`/`Signer` classes to allow for you to use those devices to sign with Bitcoin-S.
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This API is currently used to sign ordinary transactions with our [`Signer`](/api/org/bitcoins/core/wallet/signer/Signer)s. The `Signer` subtypes (i.e. `P2PKHSigner`) implement the specific functionality needed to produce a valid digital signature for their corresponding script type.
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### The [`ExtSign`](/api/org/bitcoins/crypto/Sign) API.
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An [ExtKey](/api/org/bitcoins/core/crypto/ExtKey) is a data structure that can be used to generate more keys from a parent key. For more information look at [hd-keys.md](../core/hd-keys.md)
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You can sign with `ExtPrivateKey` the same way you could with a normal `ECPrivateKey`.
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```scala
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import org.bitcoins.core.hd._
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import org.bitcoins.core.crypto._
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val extPrivKey = ExtPrivateKey(ExtKeyVersion.SegWitMainNetPriv)
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// extPrivKey: ExtPrivateKey = Masked(ExtPrivateKeyImpl)
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extPrivKey.sign(DoubleSha256Digest.empty.bytes)
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// res0: ECDigitalSignature = ECDigitalSignature(3044022034008a40435a0bd15cf4b54630188d677bfb81283e704364c6fcb55addfcd6e4022026abe200f4d890ff4e9957764d0e267cad8622283e145a2a899bf29605b35e2c)
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val path = BIP32Path(Vector(BIP32Node(0,false)))
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// path: BIP32Path = m/0
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extPrivKey.sign(DoubleSha256Digest.empty.bytes,path)
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// res1: ECDigitalSignature = ECDigitalSignature(3044022006846c117ab4911901e370e5e7e308dd6dd4701e6f73d7a6188716132a0690e302206bb4cd3245c4cfbd157b9cb8ed0f89ff1a8768bb092014f363b77746bc80db60)
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```
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With `ExtSign`, you can use `ExtPrivateKey` to sign transactions inside of `TxBuilder` since `UTXOSpendingInfo` takes in `Sign` as a parameter.
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You can also provide a `path` to use to derive a child `ExtPrivateKey`, and then sign with that child private key
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