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90 lines
3.3 KiB
Markdown
90 lines
3.3 KiB
Markdown
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---
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id: version-0.5.0-secp256k1
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title: Secp256k1
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original_id: secp256k1
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---
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[Libsecp256k1](https://github.com/bitcoin-core/secp256k1) is used to preform cryptographic operations on the secp256k1 curve.
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This is the curve that bitcoin uses. There is a _signficant_ speedup when using this library compared to java crypto libraries
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like bouncy castle.
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In bitcoin-s, we support native binaries for libsecp256k1
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1. [linux 32 bit](../../secp256k1jni/natives/linux_32)
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2. [linux 64 bit](../../secp256k1jni/natives/linux_64)
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3. [mac osx 64 bit](../../secp256k1jni/natives/osx_64)
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4. [windows 64 bit](../../secp256k1jni/natives/windows_64)
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Bitcoin-s uses a zero dependency library called [`native-lib-loader`](https://github.com/scijava/native-lib-loader).
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That does the appropriate loading of the library onto your classpath to be accessed.
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### Using libsecp256k1
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To tell if you have access to libsecp256k1 you can do the following
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```scala
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val isEnabled = org.bitcoin.Secp256k1Context.isEnabled()
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println(s"Secp256k1Context.isEnabled=${isEnabled}")
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```
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If libsecp256k1 is enabled, you can use [NativeSecp256k1](/api/org/bitcoin/NativeSecp256k1)
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with static method defined in the class.
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```scala
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val privKey = ECPrivateKey.freshPrivateKey
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val pubKey = privKey.publicKey
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val dataToSign = DoubleSha256Digest.empty
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val signature = NativeSecp256k1.sign(dataToSign.bytes.toArray, privKey.bytes.toArray)
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val verify = NativeSecp256k1.verify(dataToSign.bytes.toArray, signature, pubKey.bytes.toArray)
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println(s"Verified with NativeSecp256k1 signature=${verify}")
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//you can also just directly sign with the ECKey interface:
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val signature2 = privKey.sign(dataToSign)
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val verified2 = pubKey.verify(dataToSign, signature2)
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println(s"Verified with NativeSecp256k1 again=${verified2}")
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```
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### When libsecp256k1 isn't available, or you want to turn it off
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There are two reasons you wouldn't want to use libsecp256k1
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1. You don't trust the pre-compiled binaries we are using
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2. Your OS/arch is not supported
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There are two ways you can circumvent libsecp256k1
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1. Set `DISABLE_SECP256K1=true` in your environment variables. This will force `CryptoContext.default` to return false which will make Bitcoin-S act like `Secp256k1Context.isEnabled()` has returned false.
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2. Call Bouncy castle methods in `ECKey`.
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Here is an example of calling bouncy castle methods in `ECKey`
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```scala
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val privKey = ECPrivateKey.freshPrivateKey
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// privKey: ECPrivateKey = Masked(ECPrivateKeyImpl)
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val publicKey = privKey.publicKeyWithBouncyCastle
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// publicKey: ECPublicKey = ECPublicKey(02b967793f6d2af1a140d09a50da7bc79eab92302c6bc6726e3a35b6aa99abc8b2)
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val dataToSign = DoubleSha256Digest.empty
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// dataToSign: DoubleSha256Digest = DoubleSha256Digest(0000000000000000000000000000000000000000000000000000000000000000)
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val signature = privKey.signWithBouncyCastle(dataToSign.bytes)
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// signature: ECDigitalSignature = ECDigitalSignature(3044022010e33d10f53d6359662468321879d745940981648c252c6f862621087c7441b7022029c40ee3bad3116bb1a9027fd871df4247ef5b28007cda88eaf0535e66681676)
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val verified = publicKey.verifyWithBouncyCastle(dataToSign.bytes, signature)
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// verified: Boolean = true
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println(s"Verified with bouncy castle=${verified}")
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// Verified with bouncy castle=true
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```
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### Building libsecp256k1
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[See instructions here](add-to-jni.md#adding-to-bitcoin-s)
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