bitcoin-s/secp256k1jni/README.md

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## Secp256k1jni


This project gives people a convenient way to use [libsecp256k1](https://github.com/bitcoin-core/secp256k1) on the JVM without compiling natives themselves. 

Currently we have support for natives on

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


This uses a zero depdency library called [`native-lib-loader`](https://github.com/scijava/native-lib-loader). The does the appropriate loading of the library onto your classpath to be accessed. To tell if you have access to libsecp256k1 you can do the following

```scala
sbt:root> project secp256k1jni
[info] Set current project to bitcoin-s-secp256k1jni (in build file:/home/chris/dev/bitcoin-s-core/)
sbt:bitcoin-s-secp256k1jni> console
[info] Starting scala interpreter...
Welcome to Scala 2.12.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_191).
Type in expressions for evaluation. Or try :help.

scala> import org.bitcoin.Secp256k1Context;

scala> Secp256k1Context.isEnabled()
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
res0: Boolean = true
```

## Adding secp256k1jni to your project

To add `bitcoin-s-secp256k1jni` to your project you add it like this 

```
"org.bitcoins" % "bitcoin-s-secp256k1jni" % "0.0.1"
```

or with maven

```
<dependency>
  <groupId>org.bitcoins</groupId>
  <artifactId>bitcoin-s-secp256k1jni</artifactId>
  <version>0.0.1</version>
</dependency>
```

## Using secp256k1

The file [NativeSecp256k1.java](src/main/java/org/bitcoin/NativeSecp256k1.java) contains basic functionality for 

1. Verifying digital signatures
2. Producing digital signatures
3. Computing a public key from a private key
4. tweaking keys
5. Checking public key validity

## Binaries

The binaries provided here are PGP signed, to give at least some assurances that
nothing funny has happened to them.

### macOS 64 bit

```bash
bitcoin-s/secp256k1jni/natives/osx_64 $ find -type f -exec sha256sum {} \; | \
        sort -k 2 | sha256sum | cut --fields 1 --delimiter=" " | \
        gpg --clearsign --output hashed-dir.sig --detach-sig

bitcoin-s/secp256k1jni/natives/osx_64 $ cat hashed-dir.sig
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

341d768b915d989db82c1fb94b29faec9509ad45e30a27c217feb121747789ce
-----BEGIN PGP SIGNATURE-----

iQEzBAEBCgAdFiEEcQE9FyWyvvLjrwybHk0b2DvgrM0FAlxPHuQACgkQHk0b2Dvg
rM07EwgApXWPlVKMDP7Z8RQhhDmlnycTJxFaw315TH2IKDMEtCA0mBGY8UOy7jis
ZtQEyUQdspBnLW6RHeEBhkDlQzjMS3G4K2T2D1r2eL4vXf7dnZ2CUSy7N9Gd8Lsy
Tcdi9a/GSyFu1RCtmklCZ75/oECPlmNctdOY30+5FDIfWIcTHqKebfDstTqeYGbd
0+U5N2xDI/07g5jCF1EsgiqvFkXZEjI/44xlxWon6GtbiYR/n+MHzgwBi5XqNs2p
0t3Tvx5NbJiVVn7K2ThQFaW4ap/bqggZh1ddT/v2Wq0BH+UX6b6Abrq0tD5+ZPst
5+tz19oEa9XK+X/DDkFrT4WEMDpyIw==
=CauS
-----END PGP SIGNATURE-----

bitcoin-s/secp256k1jni/natives/osx_64 $ gpg --verify hashed-dir.sig
gpg: Signature made Mon 28 Jan 2019 04:25:24 PM CET
gpg:                using RSA key 71013D1725B2BEF2E3AF0C9B1E4D1BD83BE0ACCD
gpg: Good signature from "Torkel Rogstad <torkel@suredbits.com>" [ultimate]

```


### Linux 32 bit

TODO

### Linux 64 bit

TODO


### Windows 64 bit

To build binaries for windows, you need to cross compile them from a linux machine. This can be done with the following commands. The origin of these commands [comes from ACINQ](https://github.com/ACINQ/bitcoin-lib/blob/bf115a442e17e1522eba98a362473fddd9b1ffe6/BUILDING.md#for-windows-64-bits)


```
$ sudo apt install g++-mingw-w64-x86-64
$ sudo update-alternatives --config x86_64-w64-mingw32-g++ # Set the default mingw32 g++ compiler option to posix.
```

```
# this is needed to compile shared libraries, otherwise you'll get:
# libtool: warning: undefined symbols not allowed in x86_64-w64-mingw32 shared libraries; building static only
$ echo "LDFLAGS = -no-undefined" >> Makefile.am
$ ./configure --host=x86_64-w64-mingw32 --enable-experimental --enable-module_ecdh --enable-jni && make clean && make CFLAGS="-std=c99"
cp ./.libs/libsecp256k1-0.dll ../src/main/resources/fr/acinq/native/Windows/x86_64/secp256k1.dll
```


#### Windows 64 bit signature

```
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

510f864a2d5d5ec238aa8e3653d01e3c027caef810797c494fc22e8f6fd8fe84  libsecp256k1-0.dll
-----BEGIN PGP SIGNATURE-----
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=2mZ8
-----END PGP SIGNATURE-----
```