Added secure random implementation for Android (hyperledger-web3j#146).

core/src/main/java/org/web3j/crypto/Keys.java

@@ -6,7 +6,6 @@
 import java.security.KeyPairGenerator;
 import java.security.NoSuchAlgorithmException;
 import java.security.NoSuchProviderException;
-import java.security.SecureRandom;
 import java.security.Security;
 import java.security.spec.ECGenParameterSpec;
 import java.util.Arrays;
@@ -16,6 +15,8 @@
 import org.web3j.utils.Numeric;
 import org.web3j.utils.Strings;
 
+import static org.web3j.crypto.SecureRandomUtils.secureRandom;
+
 
 /**
  * Crypto key utilities.
@@ -47,7 +48,7 @@ static KeyPair createSecp256k1KeyPair() throws NoSuchProviderException,
 
         KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("ECDSA", "BC");
         ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec("secp256k1");
-        keyPairGenerator.initialize(ecGenParameterSpec, new SecureRandom());
+        keyPairGenerator.initialize(ecGenParameterSpec, secureRandom());
         return keyPairGenerator.generateKeyPair();
     }
 

core/src/main/java/org/web3j/crypto/LinuxSecureRandom.java

@@ -0,0 +1,104 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * 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.web3j.crypto;
+
+import java.io.DataInputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.security.Provider;
+import java.security.SecureRandomSpi;
+import java.security.Security;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * Implementation from
+ * <a href="https://github.com/bitcoinj/bitcoinj/blob/master/core/src/main/java/org/bitcoinj/crypto/LinuxSecureRandom.java">BitcoinJ implementation</a>
+ *
+ * A SecureRandom implementation that is able to override the standard JVM provided implementation, and which simply
+ * serves random numbers by reading /dev/urandom. That is, it delegates to the kernel on UNIX systems and is unusable on
+ * other platforms. Attempts to manually set the seed are ignored. There is no difference between seed bytes and
+ * non-seed bytes, they are all from the same source.
+ */
+public class LinuxSecureRandom extends SecureRandomSpi {
+    private static final FileInputStream urandom;
+
+    private static class LinuxSecureRandomProvider extends Provider {
+        public LinuxSecureRandomProvider() {
+            super("LinuxSecureRandom", 1.0, "A Linux specific random number provider that uses /dev/urandom");
+            put("SecureRandom.LinuxSecureRandom", LinuxSecureRandom.class.getName());
+        }
+    }
+
+    private static final Logger log = LoggerFactory.getLogger(LinuxSecureRandom.class);
+
+    static {
+        try {
+            File file = new File("/dev/urandom");
+            // This stream is deliberately leaked.
+            urandom = new FileInputStream(file);
+            if (urandom.read() == -1)
+                throw new RuntimeException("/dev/urandom not readable?");
+            // Now override the default SecureRandom implementation with this one.
+            int position = Security.insertProviderAt(new LinuxSecureRandomProvider(), 1);
+
+            if (position != -1)
+                log.info("Secure randomness will be read from {} only.", file);
+            else
+                log.info("Randomness is already secure.");
+        } catch (FileNotFoundException e) {
+            // Should never happen.
+            log.error("/dev/urandom does not appear to exist or is not openable");
+            throw new RuntimeException(e);
+        } catch (IOException e) {
+            log.error("/dev/urandom does not appear to be readable");
+            throw new RuntimeException(e);
+        }
+    }
+
+    private final DataInputStream dis;
+
+    public LinuxSecureRandom() {
+        // DataInputStream is not thread safe, so each random object has its own.
+        dis = new DataInputStream(urandom);
+    }
+
+    @Override
+    protected void engineSetSeed(byte[] bytes) {
+        // Ignore.
+    }
+
+    @Override
+    protected void engineNextBytes(byte[] bytes) {
+        try {
+            dis.readFully(bytes); // This will block until all the bytes can be read.
+        } catch (IOException e) {
+            throw new RuntimeException(e); // Fatal error. Do not attempt to recover from this.
+        }
+    }
+
+    @Override
+    protected byte[] engineGenerateSeed(int i) {
+        byte[] bits = new byte[i];
+        engineNextBytes(bits);
+        return bits;
+    }
+}

core/src/main/java/org/web3j/crypto/SecureRandomUtils.java

@@ -0,0 +1,38 @@
+package org.web3j.crypto;
+
+import java.security.SecureRandom;
+
+/**
+ * Utility class for working with SecureRandom implementation.
+ *
+ * This is to address issues with SecureRandom on Android. For more information, refer to the
+ * following <a href="https://github.com/web3j/web3j/issues/146">issue</a>.
+ */
+final class SecureRandomUtils {
+
+    private static final SecureRandom SECURE_RANDOM;
+
+    static {
+        if (isAndroidRuntime()) {
+            new LinuxSecureRandom();
+        }
+        SECURE_RANDOM = new java.security.SecureRandom();
+    }
+
+    static java.security.SecureRandom secureRandom() {
+        return SECURE_RANDOM;
+    }
+
+    // Taken from BitcoinJ implementation
+    // https://github.com/bitcoinj/bitcoinj/blob/3cb1f6c6c589f84fe6e1fb56bf26d94cccc85429/core/src/main/java/org/bitcoinj/core/Utils.java#L573
+    private static int isAndroid = -1;
+    static boolean isAndroidRuntime() {
+        if (isAndroid == -1) {
+            final String runtime = System.getProperty("java.runtime.name");
+            isAndroid = (runtime != null && runtime.equals("Android Runtime")) ? 1 : 0;
+        }
+        return isAndroid == 1;
+    }
+
+    private SecureRandomUtils() { }
+}

core/src/main/java/org/web3j/crypto/Wallet.java

@@ -3,7 +3,6 @@
 import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
-import java.security.SecureRandom;
 import java.util.Arrays;
 import java.util.UUID;
 import javax.crypto.BadPaddingException;
@@ -21,6 +20,7 @@
 import org.web3j.utils.Numeric;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.web3j.crypto.SecureRandomUtils.secureRandom;
 
 /**
  * <p>Ethereum wallet file management. For reference, refer to
@@ -47,8 +47,6 @@
  */
 public class Wallet {
 
-    private static SecureRandom SECURE_RANDOM = new SecureRandom();
-
     private static final int N_LIGHT = 1 << 12;
     private static final int P_LIGHT = 6;
 
@@ -239,7 +237,7 @@ static void validate(WalletFile walletFile) throws CipherException {
 
     static byte[] generateRandomBytes(int size) {
         byte[] bytes = new byte[size];
-        SECURE_RANDOM.nextBytes(bytes);
+        secureRandom().nextBytes(bytes);
         return bytes;
     }
 }

core/src/test/java/org/web3j/crypto/SecureRandomUtilsTest.java

@@ -0,0 +1,20 @@
+package org.web3j.crypto;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.web3j.crypto.SecureRandomUtils.isAndroidRuntime;
+import static org.web3j.crypto.SecureRandomUtils.secureRandom;
+
+public class SecureRandomUtilsTest {
+
+    @Test
+    public void testSecureRandom() {
+        secureRandom().nextInt();
+    }
+
+    @Test
+    public void testIsNotAndroidRuntime() {
+        assertFalse(isAndroidRuntime());
+    }
+}