1 files changed, 72 insertions, 11 deletions

diff --git a/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupSessionBuilder.java b/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupSessionBuilder.java
index 8b73484b..ee02fffd 100644
--- a/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupSessionBuilder.java
+++ b/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupSessionBuilder.java
@@ -1,9 +1,44 @@
+/**
+ * Copyright (C) 2014-2015 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.groups;
 
-import org.whispersystems.libaxolotl.ecc.ECKeyPair;
+import org.whispersystems.libaxolotl.InvalidKeyException;
+import org.whispersystems.libaxolotl.InvalidKeyIdException;
 import org.whispersystems.libaxolotl.groups.state.SenderKeyRecord;
+import org.whispersystems.libaxolotl.groups.state.SenderKeyState;
 import org.whispersystems.libaxolotl.groups.state.SenderKeyStore;
 import org.whispersystems.libaxolotl.protocol.SenderKeyDistributionMessage;
+import org.whispersystems.libaxolotl.util.KeyHelper;
+
+/**
+ * GroupSessionBuilder is responsible for setting up group SenderKey encrypted sessions.
+ *
+ * Once a session has been established, {@link org.whispersystems.libaxolotl.groups.GroupCipher}
+ * can be used to encrypt/decrypt messages in that session.
+ * <p>
+ * The built sessions are unidirectional: they can be used either for sending or for receiving,
+ * but not both.
+ *
+ * Sessions are constructed per (groupId + senderId + deviceId) tuple.  Remote logical users
+ * are identified by their senderId, and each logical recipientId can have multiple physical
+ * devices.
+ *
+ * @author Moxie Marlinspike
+ */
 
 public class GroupSessionBuilder {
 
@@ -13,26 +48,52 @@ public class GroupSessionBuilder {
     this.senderKeyStore = senderKeyStore;
   }
 
-  public void process(String sender, SenderKeyDistributionMessage senderKeyDistributionMessage) {
+  /**
+   * Construct a group session for receiving messages from senderKeyName.
+   *
+   * @param senderKeyName The (groupId, senderId, deviceId) tuple associated with the SenderKeyDistributionMessage.
+   * @param senderKeyDistributionMessage A received SenderKeyDistributionMessage.
+   */
+  public void process(SenderKeyName senderKeyName, SenderKeyDistributionMessage senderKeyDistributionMessage) {
     synchronized (GroupCipher.LOCK) {
-      SenderKeyRecord senderKeyRecord = senderKeyStore.loadSenderKey(sender);
+      SenderKeyRecord senderKeyRecord = senderKeyStore.loadSenderKey(senderKeyName);
       senderKeyRecord.addSenderKeyState(senderKeyDistributionMessage.getId(),
                                         senderKeyDistributionMessage.getIteration(),
                                         senderKeyDistributionMessage.getChainKey(),
                                         senderKeyDistributionMessage.getSignatureKey());
-      senderKeyStore.storeSenderKey(sender, senderKeyRecord);
+      senderKeyStore.storeSenderKey(senderKeyName, senderKeyRecord);
     }
   }
 
-  public SenderKeyDistributionMessage process(String groupId, int keyId, int iteration,
-                                              byte[] chainKey, ECKeyPair signatureKey)
-  {
+  /**
+   * Construct a group session for sending messages.
+   *
+   * @param senderKeyName The (groupId, senderId, deviceId) tuple.  In this case, 'senderId' should be the caller.
+   * @return A SenderKeyDistributionMessage that is individually distributed to each member of the group.
+   */
+  public SenderKeyDistributionMessage create(SenderKeyName senderKeyName) {
     synchronized (GroupCipher.LOCK) {
-      SenderKeyRecord senderKeyRecord = senderKeyStore.loadSenderKey(groupId);
-      senderKeyRecord.setSenderKeyState(keyId, iteration, chainKey, signatureKey);
-      senderKeyStore.storeSenderKey(groupId, senderKeyRecord);
+      try {
+        SenderKeyRecord senderKeyRecord = senderKeyStore.loadSenderKey(senderKeyName);
+
+        if (senderKeyRecord.isEmpty()) {
+          senderKeyRecord.setSenderKeyState(KeyHelper.generateSenderKeyId(),
+                                            0,
+                                            KeyHelper.generateSenderKey(),
+                                            KeyHelper.generateSenderSigningKey());
+          senderKeyStore.storeSenderKey(senderKeyName, senderKeyRecord);
+        }
+
+        SenderKeyState state = senderKeyRecord.getSenderKeyState();
+
+        return new SenderKeyDistributionMessage(state.getKeyId(),
+                                                state.getSenderChainKey().getIteration(),
+                                                state.getSenderChainKey().getSeed(),
+                                                state.getSigningKeyPublic());
 
-      return new SenderKeyDistributionMessage(keyId, iteration, chainKey, signatureKey.getPublicKey());
+      } catch (InvalidKeyIdException | InvalidKeyException e) {
+        throw new AssertionError(e);
+      }
     }
   }
 }