1 files changed, 146 insertions, 0 deletions
diff --git a/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupCipher.java b/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupCipher.java
new file mode 100644
index 00000000..43dac752
--- /dev/null
+++ b/java/src/main/java/org/whispersystems/libaxolotl/groups/GroupCipher.java
@@ -0,0 +1,146 @@
+package org.whispersystems.libaxolotl.groups;
+
+import org.whispersystems.libaxolotl.DuplicateMessageException;
+import org.whispersystems.libaxolotl.InvalidKeyIdException;
+import org.whispersystems.libaxolotl.InvalidMessageException;
+import org.whispersystems.libaxolotl.LegacyMessageException;
+import org.whispersystems.libaxolotl.NoSessionException;
+import org.whispersystems.libaxolotl.groups.ratchet.SenderChainKey;
+import org.whispersystems.libaxolotl.groups.ratchet.SenderMessageKey;
+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.SenderKeyMessage;
+
+import java.security.InvalidAlgorithmParameterException;
+import java.security.NoSuchAlgorithmException;
+
+import javax.crypto.BadPaddingException;
+import javax.crypto.Cipher;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.NoSuchPaddingException;
+import javax.crypto.spec.IvParameterSpec;
+import javax.crypto.spec.SecretKeySpec;
+
+public class GroupCipher {
+
+  static final Object LOCK = new Object();
+
+  private final SenderKeyStore senderKeyStore;
+  private final String         senderKeyId;
+
+  public GroupCipher(SenderKeyStore senderKeyStore, String senderKeyId) {
+    this.senderKeyStore = senderKeyStore;
+    this.senderKeyId    = senderKeyId;
+  }
+
+  public byte[] encrypt(byte[] paddedPlaintext) throws NoSessionException {
+    synchronized (LOCK) {
+      try {
+        SenderKeyRecord  record         = senderKeyStore.loadSenderKey(senderKeyId);
+        SenderKeyState   senderKeyState = record.getSenderKeyState();
+        SenderMessageKey senderKey      = senderKeyState.getSenderChainKey().getSenderMessageKey();
+        byte[]           ciphertext     = getCipherText(senderKey.getIv(), senderKey.getCipherKey(), paddedPlaintext);
+
+        SenderKeyMessage senderKeyMessage = new SenderKeyMessage(senderKeyState.getKeyId(),
+                                                                 senderKey.getIteration(),
+                                                                 ciphertext,
+                                                                 senderKeyState.getSigningKeyPrivate());
+
+        senderKeyState.setSenderChainKey(senderKeyState.getSenderChainKey().getNext());
+
+        senderKeyStore.storeSenderKey(senderKeyId, record);
+
+        return senderKeyMessage.serialize();
+      } catch (InvalidKeyIdException e) {
+        throw new NoSessionException(e);
+      }
+    }
+  }
+
+  public byte[] decrypt(byte[] senderKeyMessageBytes)
+      throws LegacyMessageException, InvalidMessageException, DuplicateMessageException
+  {
+    synchronized (LOCK) {
+      try {
+        SenderKeyRecord  record           = senderKeyStore.loadSenderKey(senderKeyId);
+        SenderKeyMessage senderKeyMessage = new SenderKeyMessage(senderKeyMessageBytes);
+        SenderKeyState   senderKeyState   = record.getSenderKeyState(senderKeyMessage.getKeyId());
+
+        senderKeyMessage.verifySignature(senderKeyState.getSigningKeyPublic());
+
+        SenderMessageKey senderKey = getSenderKey(senderKeyState, senderKeyMessage.getIteration());
+
+        byte[] plaintext = getPlainText(senderKey.getIv(), senderKey.getCipherKey(), senderKeyMessage.getCipherText());
+
+        senderKeyStore.storeSenderKey(senderKeyId, record);
+
+        return plaintext;
+      } catch (org.whispersystems.libaxolotl.InvalidKeyException | InvalidKeyIdException e) {
+        throw new InvalidMessageException(e);
+      }
+    }
+  }
+
+  private SenderMessageKey getSenderKey(SenderKeyState senderKeyState, int iteration)
+      throws DuplicateMessageException, InvalidMessageException
+  {
+    SenderChainKey senderChainKey = senderKeyState.getSenderChainKey();
+
+    if (senderChainKey.getIteration() > iteration) {
+      if (senderKeyState.hasSenderMessageKey(iteration)) {
+        return senderKeyState.removeSenderMessageKey(iteration);
+      } else {
+        throw new DuplicateMessageException("Received message with old counter: " +
+                                            senderChainKey.getIteration() + " , " + iteration);
+      }
+    }
+
+    if (senderChainKey.getIteration() - iteration > 2000) {
+      throw new InvalidMessageException("Over 2000 messages into the future!");
+    }
+
+    while (senderChainKey.getIteration() < iteration) {
+      senderKeyState.addSenderMessageKey(senderChainKey.getSenderMessageKey());
+      senderChainKey = senderChainKey.getNext();
+    }
+
+    senderKeyState.setSenderChainKey(senderChainKey.getNext());
+    return senderChainKey.getSenderMessageKey();
+  }
+
+  private byte[] getPlainText(byte[] iv, byte[] key, byte[] ciphertext)
+      throws InvalidMessageException
+  {
+    try {
+      IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
+      Cipher          cipher          = Cipher.getInstance("AES/CBC/PKCS5Padding");
+
+      cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"), ivParameterSpec);
+
+      return cipher.doFinal(ciphertext);
+    } catch (NoSuchAlgorithmException | NoSuchPaddingException | java.security.InvalidKeyException |
+             InvalidAlgorithmParameterException e)
+    {
+      throw new AssertionError(e);
+    } catch (IllegalBlockSizeException | BadPaddingException e) {
+      throw new InvalidMessageException(e);
+    }
+  }
+
+  private byte[] getCipherText(byte[] iv, byte[] key, byte[] plaintext) {
+    try {
+      IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);
+      Cipher          cipher          = Cipher.getInstance("AES/CBC/PKCS5Padding");
+
+      cipher.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"), ivParameterSpec);
+
+      return cipher.doFinal(plaintext);
+    } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidAlgorithmParameterException |
+             IllegalBlockSizeException | BadPaddingException | java.security.InvalidKeyException e)
+    {
+      throw new AssertionError(e);
+    }
+  }
+
+}