Add JNI wrapper for org.bitcoin.NativeSecp256k1 (bitcoinj)

This isnt as optimal as it could be, but its also a very simple API
which is nice.

Makefile

@@ -6,6 +6,7 @@ FLAGS_TEST:=-DVERIFY -ggdb3 -O2 -march=native
 SECP256K1_FILES := src/num.h   src/field.h   src/field_5x52.h   src/group.h   src/ecmult.h   src/ecdsa.h   \
                    src/num.cpp src/field.cpp src/field_5x52.cpp src/group.cpp src/ecmult.cpp src/ecdsa.cpp
 
+JAVA_FILES := src/java/org_bitcoin_NativeSecp256k1.h src/java/org_bitcoin_NativeSecp256k1.c
 
 ifndef CONF
 CONF := gmp
@@ -56,7 +57,7 @@ tests-any: tests-$(CONF)
 all-$(CONF): bench-$(CONF) tests-$(CONF) libsecp256k1-$(CONF).a
 
 clean-$(CONF):
-	rm -f bench-$(CONF) tests-$(CONF) libsecp256k1-$(CONF).a obj/*
+	rm -f bench-$(CONF) tests-$(CONF) libsecp256k1-$(CONF).a libjavasecp256k1-$(CONF).so obj/*
 
 obj/secp256k1-$(CONF).o: $(SECP256K1_FILES) src/secp256k1.cpp include/secp256k1.h
 	$(CXX) $(FLAGS_COMMON) $(FLAGS_PROD) $(FLAGS_CONF) src/secp256k1.cpp -c -o obj/secp256k1-$(CONF).o
@@ -69,3 +70,8 @@ tests-$(CONF): $(OBJS) src/tests.cpp
 
 libsecp256k1-$(CONF).a: $(OBJS)
 	$(AR) -rs $@ $(OBJS)
+
+libjavasecp256k1-$(CONF).so: $(OBJS) $(JAVA_FILES)
+	$(CXX) $(FLAGS_COMMON) $(FLAGS_PROD) $(FLAGS_CONF) -I. src/java/org_bitcoin_NativeSecp256k1.c $(LIBS) $(OBJS) -shared -o libjavasecp256k1-$(CONF).so
+
+java: libjavasecp256k1-$(CONF).so

src/java/org/bitcoin/NativeSecp256k1.java

@@ -0,0 +1,60 @@
+package org.bitcoin;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+import com.google.common.base.Preconditions;
+
+
+/**
+ * This class holds native methods to handle ECDSA verification.
+ * You can find an example library that can be used for this at
+ * https://github.com/sipa/secp256k1
+ */
+public class NativeSecp256k1 {
+    public static final boolean enabled;
+    static {
+        boolean isEnabled = true;
+        try {
+            System.loadLibrary("javasecp256k1");
+        } catch (UnsatisfiedLinkError e) {
+            isEnabled = false;
+        }
+        enabled = isEnabled;
+    }
+    
+    private static ThreadLocal<ByteBuffer> nativeECDSABuffer = new ThreadLocal<ByteBuffer>();
+    /**
+     * Verifies the given secp256k1 signature in native code.
+     * Calling when enabled == false is undefined (probably library not loaded)
+     * 
+     * @param data The data which was signed, must be exactly 32 bytes
+     * @param signature The signature
+     * @param pub The public key which did the signing
+     */
+    public static boolean verify(byte[] data, byte[] signature, byte[] pub) {
+        Preconditions.checkArgument(data.length == 32 && signature.length <= 520 && pub.length <= 520);
+
+        ByteBuffer byteBuff = nativeECDSABuffer.get();
+        if (byteBuff == null) {
+            byteBuff = ByteBuffer.allocateDirect(32 + 8 + 520 + 520);
+            byteBuff.order(ByteOrder.nativeOrder());
+            nativeECDSABuffer.set(byteBuff);
+        }
+        byteBuff.rewind();
+        byteBuff.put(data);
+        byteBuff.putInt(signature.length);
+        byteBuff.putInt(pub.length);
+        byteBuff.put(signature);
+        byteBuff.put(pub);
+        return secp256k1_ecdsa_verify(byteBuff) == 1;
+    }
+
+    /**
+     * @param byteBuff signature format is byte[32] data,
+     *        native-endian int signatureLength, native-endian int pubkeyLength,
+     *        byte[signatureLength] signature, byte[pubkeyLength] pub
+     * @returns 1 for valid signature, anything else for invalid
+     */
+    private static native int secp256k1_ecdsa_verify(ByteBuffer byteBuff);
+}

src/java/org_bitcoin_NativeSecp256k1.c

@@ -0,0 +1,23 @@
+#include "org_bitcoin_NativeSecp256k1.h"
+#include "include/secp256k1.h"
+
+JNIEXPORT jint JNICALL Java_org_bitcoin_NativeSecp256k1_secp256k1_1ecdsa_1verify
+  (JNIEnv* env, jclass classObject, jobject byteBufferObject)
+{
+	unsigned char* data = (unsigned char*) env->GetDirectBufferAddress(byteBufferObject);
+	int sigLen = *((int*)(data + 32));
+	int pubLen = *((int*)(data + 32 + 4));
+
+	return secp256k1_ecdsa_verify(data, 32, data+32+8, sigLen, data+32+8+sigLen, pubLen);
+}
+
+static void __javasecp256k1_attach(void) __attribute__((constructor));
+static void __javasecp256k1_detach(void) __attribute__((destructor));
+
+static void __javasecp256k1_attach(void) {
+	secp256k1_start();
+}
+
+static void __javasecp256k1_detach(void) {
+	secp256k1_stop();
+}

src/java/org_bitcoin_NativeSecp256k1.h

@@ -0,0 +1,21 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class org_bitcoin_NativeSecp256k1 */
+
+#ifndef _Included_org_bitcoin_NativeSecp256k1
+#define _Included_org_bitcoin_NativeSecp256k1
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     org_bitcoin_NativeSecp256k1
+ * Method:    secp256k1_ecdsa_verify
+ * Signature: (Ljava/nio/ByteBuffer;)I
+ */
+JNIEXPORT jint JNICALL Java_org_bitcoin_NativeSecp256k1_secp256k1_1ecdsa_1verify
+  (JNIEnv *, jclass, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif