diff -r 000000000000 -r 6474c204b198 mobile/android/base/browserid/SigningPrivateKey.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/browserid/SigningPrivateKey.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,41 @@
+/* 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.browserid;
+
+import java.security.GeneralSecurityException;
+
+import org.mozilla.gecko.sync.ExtendedJSONObject;
+
+public interface SigningPrivateKey {
+  /**
+   * Return the JSON Web Token "alg" header corresponding to this private key.
+   * <p>
+   * The header is used when formatting web tokens, and generally denotes the
+   * algorithm and an ad-hoc encoding of the key size.
+   *
+   * @return header.
+   */
+  public String getAlgorithm();
+
+  /**
+   * Generate a JSON representation of a private key.
+   * <p>
+   * <b>This should only be used for debugging. No private keys should go over
+   * the wire at any time.</b>
+   *
+   * @param privateKey
+   *          to represent.
+   * @return JSON representation.
+   */
+  public ExtendedJSONObject toJSONObject();
+
+  /**
+   * Sign a message.
+   * @param message to sign.
+   * @return signature.
+   * @throws GeneralSecurityException
+   */
+  public byte[] signMessage(byte[] message) throws GeneralSecurityException;
+}