1 files changed, 95 insertions, 0 deletions
diff --git a/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/prng/ThreadedSeedGenerator.java b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/prng/ThreadedSeedGenerator.java
new file mode 100644
index 000000000..fc1035423
--- /dev/null
+++ b/libraries/spongycastle/core/src/main/java/org/spongycastle/crypto/prng/ThreadedSeedGenerator.java
@@ -0,0 +1,95 @@
+package org.spongycastle.crypto.prng;
+
+/**
+ * A thread based seed generator - one source of randomness.
+ * <p>
+ * Based on an idea from Marcus Lippert.
+ * </p>
+ */
+public class ThreadedSeedGenerator
+{
+    private class SeedGenerator
+        implements Runnable
+    {
+        private volatile int counter = 0;
+        private volatile boolean stop = false;
+
+        public void run()
+        {
+            while (!this.stop)
+            {
+                this.counter++;
+            }
+
+        }
+
+        public byte[] generateSeed(
+            int numbytes,
+            boolean fast)
+        {
+            Thread t = new Thread(this);
+            byte[] result = new byte[numbytes];
+            this.counter = 0;
+            this.stop = false;
+            int last = 0;
+            int end;
+
+            t.start();
+            if(fast)
+            {
+                end = numbytes;
+            }
+            else
+            {
+                end = numbytes * 8;
+            }
+            for (int i = 0; i < end; i++)
+            {
+                while (this.counter == last)
+                {
+                    try
+                    {
+                        Thread.sleep(1);
+                    }
+                    catch (InterruptedException e)
+                    {
+                        // ignore
+                    }
+                }
+                last = this.counter;
+                if (fast)
+                {
+                    result[i] = (byte) (last & 0xff);
+                }
+                else
+                {
+                    int bytepos = i/8;
+                    result[bytepos] = (byte) ((result[bytepos] << 1) | (last & 1));
+                }
+
+            }
+            stop = true;
+            return result;
+        }
+    }
+
+    /**
+     * Generate seed bytes. Set fast to false for best quality.
+     * <p>
+     * If fast is set to true, the code should be round about 8 times faster when
+     * generating a long sequence of random bytes. 20 bytes of random values using
+     * the fast mode take less than half a second on a Nokia e70. If fast is set to false,
+     * it takes round about 2500 ms.
+     * </p>
+     * @param numBytes the number of bytes to generate
+     * @param fast true if fast mode should be used
+     */
+    public byte[] generateSeed(
+        int numBytes,
+        boolean fast)
+    {
+        SeedGenerator gen = new SeedGenerator();
+
+        return gen.generateSeed(numBytes, fast);
+    }
+}