diff -r 000000000000 -r 6474c204b198 mobile/android/base/sync/jpake/BigIntegerHelper.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/sync/jpake/BigIntegerHelper.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.sync.jpake;
+
+import java.math.BigInteger;
+
+public class BigIntegerHelper {
+
+  public static byte[] BigIntegerToByteArrayWithoutSign(BigInteger value) {
+    byte[] bytes = value.toByteArray();
+    if (bytes[0] == (byte) 0) {
+      bytes = copyArray(bytes, 1, bytes.length - 1);
+    }
+    return bytes;
+  }
+
+  private static byte[] copyArray(byte[] original, int start, int length) {
+    byte[] copy = new byte[length];
+    System.arraycopy(original, start, copy, 0,
+        Math.min(original.length - start, length));
+    return copy;
+  }
+
+  /**
+   * Convert an array of bytes to a non-negative big integer.
+   */
+  public static BigInteger ByteArrayToBigIntegerWithoutSign(byte[] array) {
+    return new BigInteger(1, array);
+  }
+
+  /**
+   * Convert a big integer into hex string. If the length is not even, add an
+   * '0' character in the beginning to make it even.
+   */
+  public static String toEvenLengthHex(BigInteger value) {
+    String result = value.toString(16);
+    if (result.length() % 2 != 0) {
+      result = "0" + result;
+    }
+    return result;
+  }
+}