1 files changed, 75 insertions, 0 deletions
diff --git a/src/main/java/org/whispersystems/libaxolotl/ratchet/ChainKey.java b/src/main/java/org/whispersystems/libaxolotl/ratchet/ChainKey.java
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+++ b/src/main/java/org/whispersystems/libaxolotl/ratchet/ChainKey.java
@@ -0,0 +1,75 @@
+/**
+ * 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.kdf.DerivedMessageSecrets;
+import org.whispersystems.libaxolotl.kdf.HKDF;
+
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+
+public class ChainKey {
+
+  private static final byte[] MESSAGE_KEY_SEED = {0x01};
+  private static final byte[] CHAIN_KEY_SEED   = {0x02};
+
+  private final HKDF   kdf;
+  private final byte[] key;
+  private final int    index;
+
+  public ChainKey(HKDF kdf, byte[] key, int index) {
+    this.kdf   = kdf;
+    this.key   = key;
+    this.index = index;
+  }
+
+  public byte[] getKey() {
+    return key;
+  }
+
+  public int getIndex() {
+    return index;
+  }
+
+  public ChainKey getNextChainKey() {
+    byte[] nextKey = getBaseMaterial(CHAIN_KEY_SEED);
+    return new ChainKey(kdf, nextKey, index + 1);
+  }
+
+  public MessageKeys getMessageKeys() {
+    byte[]                inputKeyMaterial = getBaseMaterial(MESSAGE_KEY_SEED);
+    byte[]                keyMaterialBytes = kdf.deriveSecrets(inputKeyMaterial, "WhisperMessageKeys".getBytes(), DerivedMessageSecrets.SIZE);
+    DerivedMessageSecrets keyMaterial      = new DerivedMessageSecrets(keyMaterialBytes);
+
+    return new MessageKeys(keyMaterial.getCipherKey(), keyMaterial.getMacKey(), keyMaterial.getIv(), index);
+  }
+
+  private byte[] getBaseMaterial(byte[] seed) {
+    try {
+      Mac mac = Mac.getInstance("HmacSHA256");
+      mac.init(new SecretKeySpec(key, "HmacSHA256"));
+
+      return mac.doFinal(seed);
+    } catch (NoSuchAlgorithmException | InvalidKeyException e) {
+      throw new AssertionError(e);
+    }
+  }
+}