1 files changed, 54 insertions, 0 deletions
diff --git a/java/src/main/java/org/whispersystems/libaxolotl/ratchet/RootKey.java b/java/src/main/java/org/whispersystems/libaxolotl/ratchet/RootKey.java
new file mode 100644
index 00000000..39f3a831
--- /dev/null
+++ b/java/src/main/java/org/whispersystems/libaxolotl/ratchet/RootKey.java
@@ -0,0 +1,54 @@
+/**
+ * Copyright (C) 2014 Open Whisper Systems
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+package org.whispersystems.libaxolotl.ratchet;
+
+import org.whispersystems.libaxolotl.InvalidKeyException;
+import org.whispersystems.libaxolotl.ecc.Curve;
+import org.whispersystems.libaxolotl.ecc.ECKeyPair;
+import org.whispersystems.libaxolotl.ecc.ECPublicKey;
+import org.whispersystems.libaxolotl.kdf.DerivedRootSecrets;
+import org.whispersystems.libaxolotl.kdf.HKDF;
+import org.whispersystems.libaxolotl.util.ByteUtil;
+import org.whispersystems.libaxolotl.util.Pair;
+
+public class RootKey {
+
+  private final HKDF   kdf;
+  private final byte[] key;
+
+  public RootKey(HKDF kdf, byte[] key) {
+    this.kdf = kdf;
+    this.key = key;
+  }
+
+  public byte[] getKeyBytes() {
+    return key;
+  }
+
+  public Pair<RootKey, ChainKey> createChain(ECPublicKey theirRatchetKey, ECKeyPair ourRatchetKey)
+      throws InvalidKeyException
+  {
+    byte[]             sharedSecret       = Curve.calculateAgreement(theirRatchetKey, ourRatchetKey.getPrivateKey());
+    byte[]             derivedSecretBytes = kdf.deriveSecrets(sharedSecret, key, "WhisperRatchet".getBytes(), DerivedRootSecrets.SIZE);
+    DerivedRootSecrets derivedSecrets     = new DerivedRootSecrets(derivedSecretBytes);
+
+    RootKey  newRootKey  = new RootKey(kdf, derivedSecrets.getRootKey());
+    ChainKey newChainKey = new ChainKey(kdf, derivedSecrets.getChainKey(), 0);
+
+    return new Pair<>(newRootKey, newChainKey);
+  }
+}