code: /*
   * Copyright 2013 Google Inc.
   * Copyright 2014-2016 the libsecp256k1 contributors
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.bitcoin;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  import java.math.BigInteger;
  import com.google.common.base.Preconditions;
  import java.util.concurrent.locks.Lock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  import static org.bitcoin.NativeSecp256k1Util.*;
  
  /**
   * <p>This class holds native methods to handle ECDSA verification.</p>
   *
   * <p>You can find an example library that can be used for this at https://github.com/bitcoin/secp256k1</p>
   *
   * <p>To build secp256k1 for use with bitcoinj, run
   * `./configure --enable-jni --enable-experimental --enable-module-ecdh`
   * and `make` then copy `.libs/libsecp256k1.so` to your system library path
   * or point the JVM to the folder containing it with -Djava.library.path
   * </p>
   */
  public class NativeSecp256k1 {
  
      private static final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
      private static final Lock r = rwl.readLock();
      private static final Lock w = rwl.writeLock();
      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) throws AssertFailException{
          Preconditions.checkArgument(data.length == 32 && signature.length <= 520 && pub.length <= 520);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < 520) {
              byteBuff = ByteBuffer.allocateDirect(520);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(data);
          byteBuff.put(signature);
          byteBuff.put(pub);
  
          byte[][] retByteArray;
  
          r.lock();
          try {
            return secp256k1_ecdsa_verify(byteBuff, Secp256k1Context.getContext(), signature.length, pub.length) == 1;
          } finally {
            r.unlock();
          }
      }
  
      /**
       * libsecp256k1 Create an ECDSA signature.
       *
       * @param data Message hash, 32 bytes
       * @param key Secret key, 32 bytes
       *
       * Return values
       * @param sig byte array of signature
       */
      public static byte[] sign(byte[] data, byte[] sec) throws AssertFailException{
          Preconditions.checkArgument(data.length == 32 && sec.length <= 32);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < 32 + 32) {
              byteBuff = ByteBuffer.allocateDirect(32 + 32);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(data);
          byteBuff.put(sec);
  
          byte[][] retByteArray;
  
          r.lock();
          try {
            retByteArray = secp256k1_ecdsa_sign(byteBuff, Secp256k1Context.getContext());
          } finally {
            r.unlock();
          }
  
          byte[] sigArr = retByteArray[0];
          int sigLen = new BigInteger(new byte[] { retByteArray[1][0] }).intValue();
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(sigArr.length, sigLen, "Got bad signature length.");
  
          return retVal == 0 ? new byte[0] : sigArr;
      }
  
      /**
       * libsecp256k1 Seckey Verify - returns 1 if valid, 0 if invalid
       *
       * @param seckey ECDSA Secret key, 32 bytes
       */
      public static boolean secKeyVerify(byte[] seckey) {
          Preconditions.checkArgument(seckey.length == 32);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < seckey.length) {
              byteBuff = ByteBuffer.allocateDirect(seckey.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(seckey);
  
          r.lock();
          try {
            return secp256k1_ec_seckey_verify(byteBuff,Secp256k1Context.getContext()) == 1;
          } finally {
            r.unlock();
          }
      }
  
  
      /**
       * libsecp256k1 Compute Pubkey - computes public key from secret key
       *
       * @param seckey ECDSA Secret key, 32 bytes
       *
       * Return values
       * @param pubkey ECDSA Public key, 33 or 65 bytes
       */
      //TODO add a 'compressed' arg
      public static byte[] computePubkey(byte[] seckey) throws AssertFailException{
          Preconditions.checkArgument(seckey.length == 32);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < seckey.length) {
              byteBuff = ByteBuffer.allocateDirect(seckey.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(seckey);
  
          byte[][] retByteArray;
  
          r.lock();
          try {
            retByteArray = secp256k1_ec_pubkey_create(byteBuff, Secp256k1Context.getContext());
          } finally {
            r.unlock();
          }
  
          byte[] pubArr = retByteArray[0];
          int pubLen = new BigInteger(new byte[] { retByteArray[1][0] }).intValue();
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(pubArr.length, pubLen, "Got bad pubkey length.");
  
          return retVal == 0 ? new byte[0]: pubArr;
      }
  
      /**
       * libsecp256k1 Cleanup - This destroys the secp256k1 context object
       * This should be called at the end of the program for proper cleanup of the context.
       */
      public static synchronized void cleanup() {
          w.lock();
          try {
            secp256k1_destroy_context(Secp256k1Context.getContext());
          } finally {
            w.unlock();
          }
      }
  
      public static long cloneContext() {
         r.lock();
         try {
          return secp256k1_ctx_clone(Secp256k1Context.getContext());
         } finally { r.unlock(); }
      }
  
      /**
       * libsecp256k1 PrivKey Tweak-Mul - Tweak privkey by multiplying to it
       *
       * @param tweak some bytes to tweak with
       * @param seckey 32-byte seckey
       */
      public static byte[] privKeyTweakMul(byte[] privkey, byte[] tweak) throws AssertFailException{
          Preconditions.checkArgument(privkey.length == 32);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < privkey.length + tweak.length) {
              byteBuff = ByteBuffer.allocateDirect(privkey.length + tweak.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(privkey);
          byteBuff.put(tweak);
  
          byte[][] retByteArray;
          r.lock();
          try {
            retByteArray = secp256k1_privkey_tweak_mul(byteBuff,Secp256k1Context.getContext());
          } finally {
            r.unlock();
          }
  
          byte[] privArr = retByteArray[0];
  
          int privLen = (byte) new BigInteger(new byte[] { retByteArray[1][0] }).intValue() & 0xFF;
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(privArr.length, privLen, "Got bad pubkey length.");
  
          assertEquals(retVal, 1, "Failed return value check.");
  
          return privArr;
      }
  
      /**
       * libsecp256k1 PrivKey Tweak-Add - Tweak privkey by adding to it
       *
       * @param tweak some bytes to tweak with
       * @param seckey 32-byte seckey
       */
      public static byte[] privKeyTweakAdd(byte[] privkey, byte[] tweak) throws AssertFailException{
          Preconditions.checkArgument(privkey.length == 32);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < privkey.length + tweak.length) {
              byteBuff = ByteBuffer.allocateDirect(privkey.length + tweak.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(privkey);
          byteBuff.put(tweak);
  
          byte[][] retByteArray;
          r.lock();
          try {
            retByteArray = secp256k1_privkey_tweak_add(byteBuff,Secp256k1Context.getContext());
          } finally {
            r.unlock();
          }
  
          byte[] privArr = retByteArray[0];
  
          int privLen = (byte) new BigInteger(new byte[] { retByteArray[1][0] }).intValue() & 0xFF;
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(privArr.length, privLen, "Got bad pubkey length.");
  
          assertEquals(retVal, 1, "Failed return value check.");
  
          return privArr;
      }
  
      /**
       * libsecp256k1 PubKey Tweak-Add - Tweak pubkey by adding to it
       *
       * @param tweak some bytes to tweak with
       * @param pubkey 32-byte seckey
       */
      public static byte[] pubKeyTweakAdd(byte[] pubkey, byte[] tweak) throws AssertFailException{
          Preconditions.checkArgument(pubkey.length == 33 || pubkey.length == 65);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < pubkey.length + tweak.length) {
              byteBuff = ByteBuffer.allocateDirect(pubkey.length + tweak.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(pubkey);
          byteBuff.put(tweak);
  
          byte[][] retByteArray;
          r.lock();
          try {
            retByteArray = secp256k1_pubkey_tweak_add(byteBuff,Secp256k1Context.getContext(), pubkey.length);
          } finally {
            r.unlock();
          }
  
          byte[] pubArr = retByteArray[0];
  
          int pubLen = (byte) new BigInteger(new byte[] { retByteArray[1][0] }).intValue() & 0xFF;
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(pubArr.length, pubLen, "Got bad pubkey length.");
  
          assertEquals(retVal, 1, "Failed return value check.");
  
          return pubArr;
      }
  
      /**
       * libsecp256k1 PubKey Tweak-Mul - Tweak pubkey by multiplying to it
       *
       * @param tweak some bytes to tweak with
       * @param pubkey 32-byte seckey
       */
      public static byte[] pubKeyTweakMul(byte[] pubkey, byte[] tweak) throws AssertFailException{
          Preconditions.checkArgument(pubkey.length == 33 || pubkey.length == 65);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < pubkey.length + tweak.length) {
              byteBuff = ByteBuffer.allocateDirect(pubkey.length + tweak.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(pubkey);
          byteBuff.put(tweak);
  
          byte[][] retByteArray;
          r.lock();
          try {
            retByteArray = secp256k1_pubkey_tweak_mul(byteBuff,Secp256k1Context.getContext(), pubkey.length);
          } finally {
            r.unlock();
          }
  
          byte[] pubArr = retByteArray[0];
  
          int pubLen = (byte) new BigInteger(new byte[] { retByteArray[1][0] }).intValue() & 0xFF;
          int retVal = new BigInteger(new byte[] { retByteArray[1][1] }).intValue();
  
          assertEquals(pubArr.length, pubLen, "Got bad pubkey length.");
  
          assertEquals(retVal, 1, "Failed return value check.");
  
          return pubArr;
      }
  
      /**
       * libsecp256k1 create ECDH secret - constant time ECDH calculation
       *
       * @param seckey byte array of secret key used in exponentiaion
       * @param pubkey byte array of public key used in exponentiaion
       */
      public static byte[] createECDHSecret(byte[] seckey, byte[] pubkey) throws AssertFailException{
          Preconditions.checkArgument(seckey.length <= 32 && pubkey.length <= 65);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < 32 + pubkey.length) {
              byteBuff = ByteBuffer.allocateDirect(32 + pubkey.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(seckey);
          byteBuff.put(pubkey);
  
          byte[][] retByteArray;
          r.lock();
          try {
            retByteArray = secp256k1_ecdh(byteBuff, Secp256k1Context.getContext(), pubkey.length);
          } finally {
            r.unlock();
          }
  
          byte[] resArr = retByteArray[0];
          int retVal = new BigInteger(new byte[] { retByteArray[1][0] }).intValue();
  
          assertEquals(resArr.length, 32, "Got bad result length.");
          assertEquals(retVal, 1, "Failed return value check.");
  
          return resArr;
      }
  
      /**
       * libsecp256k1 randomize - updates the context randomization
       *
       * @param seed 32-byte random seed
       */
      public static synchronized boolean randomize(byte[] seed) throws AssertFailException{
          Preconditions.checkArgument(seed.length == 32 || seed == null);
  
          ByteBuffer byteBuff = nativeECDSABuffer.get();
          if (byteBuff == null || byteBuff.capacity() < seed.length) {
              byteBuff = ByteBuffer.allocateDirect(seed.length);
              byteBuff.order(ByteOrder.nativeOrder());
              nativeECDSABuffer.set(byteBuff);
          }
          byteBuff.rewind();
          byteBuff.put(seed);
  
          w.lock();
          try {
            return secp256k1_context_randomize(byteBuff, Secp256k1Context.getContext()) == 1;
          } finally {
            w.unlock();
          }
      }
  
      private static native long secp256k1_ctx_clone(long context);
  
      private static native int secp256k1_context_randomize(ByteBuffer byteBuff, long context);
  
      private static native byte[][] secp256k1_privkey_tweak_add(ByteBuffer byteBuff, long context);
  
      private static native byte[][] secp256k1_privkey_tweak_mul(ByteBuffer byteBuff, long context);
  
      private static native byte[][] secp256k1_pubkey_tweak_add(ByteBuffer byteBuff, long context, int pubLen);
  
      private static native byte[][] secp256k1_pubkey_tweak_mul(ByteBuffer byteBuff, long context, int pubLen);
  
      private static native void secp256k1_destroy_context(long context);
  
      private static native int secp256k1_ecdsa_verify(ByteBuffer byteBuff, long context, int sigLen, int pubLen);
  
      private static native byte[][] secp256k1_ecdsa_sign(ByteBuffer byteBuff, long context);
  
      private static native int secp256k1_ec_seckey_verify(ByteBuffer byteBuff, long context);
  
      private static native byte[][] secp256k1_ec_pubkey_create(ByteBuffer byteBuff, long context);
  
      private static native byte[][] secp256k1_ec_pubkey_parse(ByteBuffer byteBuff, long context, int inputLen);
  
      private static native byte[][] secp256k1_ecdh(ByteBuffer byteBuff, long context, int inputLen);
  
  }
  