bitcoin-s/docs/secp256k1/secp256k1.md

---
id: secp256k1
title: Secp256k1
---

[Libsecp256k1](https://github.com/bitcoin-core/secp256k1) is used to preform cryptographic operations on the secp256k1 curve.
This is the curve that bitcoin uses. There is a _signficant_ speedup when using this library compared to java crypto libraries
like bouncy castle.

In bitcoin-s, we support native binaries for libsecp256k1

1. [linux 32 bit](../../secp256k1jni/natives/linux_32)
2. [linux 64 bit](../../secp256k1jni/natives/linux_64)
3. [mac osx 64 bit](../../secp256k1jni/natives/osx_64)
4. [windows 64 bit](../../secp256k1jni/natives/windows_64)

Bitcoin-s uses a zero dependency library called [`native-lib-loader`](https://github.com/scijava/native-lib-loader). 
That does the appropriate loading of the library onto your classpath to be accessed.

### Using libsecp256k1

To tell if you have access to libsecp256k1 you can do the following

```scala mdoc:invisible
import org.bitcoin._
import org.bitcoins.crypto._

```

```scala mdoc:compile-only
val isEnabled = org.bitcoin.Secp256k1Context.isEnabled()

println(s"Secp256k1Context.isEnabled=${isEnabled}")
```

If libsecp256k1 is enabled, you can use [NativeSecp256k1](/api/org/bitcoin/NativeSecp256k1)
with static method defined in the class.


```scala mdoc:compile-only
val privKey = ECPrivateKey.freshPrivateKey
val pubKey = privKey.publicKey
val dataToSign = DoubleSha256Digest.empty

val signature = NativeSecp256k1.sign(dataToSign.bytes.toArray, privKey.bytes.toArray)
    
val verify = NativeSecp256k1.verify(dataToSign.bytes.toArray, signature, pubKey.bytes.toArray)

println(s"Verified with NativeSecp256k1 signature=${verify}")

//you can also just directly sign with the ECKey interface:
val signature2 = privKey.sign(dataToSign)

val verified2 = pubKey.verify(dataToSign, signature2)

println(s"Verified with NativeSecp256k1 again=${verified2}")

```

### When libsecp256k1 isn't available, or you want to turn it off

There are two reasons you wouldn't want to use libsecp256k1 

1. You don't trust the pre-compiled binaries we are using
2. Your OS/arch is not supported

There are two ways you can circumvent libsecp256k1

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.
2. Call Bouncy castle methods in `ECKey`. 

Here is an example of calling bouncy castle methods in `ECKey`

```scala mdoc:to-string

val privKey = ECPrivateKey.freshPrivateKey
// calls bouncy castle indirectly via CryptoContext
val publicKey = privKey.publicKey
val dataToSign = DoubleSha256Digest.empty

// calls bouncy castle indirectly via CryptoContext
val signature = privKey.sign(dataToSign.bytes)

// calls bouncy castle indirectly via CryptoContext
val verified = publicKey.verify(dataToSign.bytes, signature)

println(s"Verified with bouncy castle=${verified}")

```

### Building libsecp256k1

[See instructions here](add-to-jni.md#adding-to-bitcoin-s)