From 525ad3504d6751aa9d61075fefd1e0f478ce9ac8 Mon Sep 17 00:00:00 2001
From: Andreas Schildbach <andreas@schildbach.de>
Date: Mon, 8 Dec 2014 22:29:21 +0100
Subject: [PATCH] Move LinuxSecureRandom from Bitcoin Wallet to bitcoinj. This
 class is in use since August 2013 without any signs of RNG issues.

---
 .../bitcoinj/crypto/LinuxSecureRandom.java    | 88 +++++++++++++++++++
 1 file changed, 88 insertions(+)
 create mode 100644 core/src/main/java/org/bitcoinj/crypto/LinuxSecureRandom.java

diff --git a/core/src/main/java/org/bitcoinj/crypto/LinuxSecureRandom.java b/core/src/main/java/org/bitcoinj/crypto/LinuxSecureRandom.java
new file mode 100644
index 00000000..57919ef3
--- /dev/null
+++ b/core/src/main/java/org/bitcoinj/crypto/LinuxSecureRandom.java
@@ -0,0 +1,88 @@
+/*
+ * 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.bitcoinj.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;
+
+/**
+ * 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());
+        }
+    }
+
+    static {
+        try {
+            File file = new File("/dev/urandom");
+            if (file.exists()) {
+                // This stream is deliberately leaked.
+                urandom = new FileInputStream(file);
+                // Now override the default SecureRandom implementation with this one.
+                Security.insertProviderAt(new LinuxSecureRandomProvider(), 1);
+            } else {
+                urandom = null;
+            }
+        } catch (FileNotFoundException e) {
+            // Should never happen.
+            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;
+    }
+}