treat omemo keys >= 32 bytes as containing auth tag. add config flag to put auth tag in key

3 files changed, 52 insertions, 23 deletions

diff --git a/src/main/java/de/pixart/messenger/Config.java b/src/main/java/de/pixart/messenger/Config.java
index cd708213d..9141f3944 100644
--- a/src/main/java/de/pixart/messenger/Config.java
+++ b/src/main/java/de/pixart/messenger/Config.java
@@ -93,6 +93,7 @@ public final class Config {
     public static final long OMEMO_AUTO_EXPIRY = 7 * MILLISECONDS_IN_DAY; // delete old OMEMO devices after 7 days od inactivity
     public static final boolean REMOVE_BROKEN_DEVICES = false;
     public static final boolean OMEMO_PADDING = false;
+    public static boolean PUT_AUTH_TAG_INTO_KEY = false;
 
     public static final int MAX_DISPLAY_MESSAGE_CHARS = 4096;
 
diff --git a/src/main/java/de/pixart/messenger/crypto/axolotl/AxolotlService.java b/src/main/java/de/pixart/messenger/crypto/axolotl/AxolotlService.java
index 16a4919fc..11f51eaa2 100644
--- a/src/main/java/de/pixart/messenger/crypto/axolotl/AxolotlService.java
+++ b/src/main/java/de/pixart/messenger/crypto/axolotl/AxolotlService.java
@@ -1003,14 +1003,12 @@ public class AxolotlService implements OnAdvancedStreamFeaturesLoaded {
     }
 
     @Nullable
-    private XmppAxolotlMessage buildHeader(Conversation conversation) {
-        final XmppAxolotlMessage axolotlMessage = new XmppAxolotlMessage(
-                account.getJid().toBareJid(), getOwnDeviceId());
+    private boolean buildHeader(XmppAxolotlMessage axolotlMessage, Conversation conversation) {
 
         Set<XmppAxolotlSession> remoteSessions = findSessionsForConversation(conversation);
         Collection<XmppAxolotlSession> ownSessions = findOwnSessions();
         if (remoteSessions.isEmpty()) {
-            return null;
+            return false;
         }
         for (XmppAxolotlSession session : remoteSessions) {
             axolotlMessage.addDevice(session);
@@ -1019,26 +1017,26 @@ public class AxolotlService implements OnAdvancedStreamFeaturesLoaded {
             axolotlMessage.addDevice(session);
         }
 
-        return axolotlMessage;
+        return true;
     }
 
     @Nullable
     public XmppAxolotlMessage encrypt(Message message) {
-        XmppAxolotlMessage axolotlMessage = buildHeader(message.getConversation());
-
-        if (axolotlMessage != null) {
-            final String content;
-            if (message.hasFileOnRemoteHost()) {
-                content = message.getFileParams().url.toString();
-            } else {
-                content = message.getBody();
-            }
-            try {
-                axolotlMessage.encrypt(content);
-            } catch (CryptoFailedException e) {
-                Log.w(Config.LOGTAG, getLogprefix(account) + "Failed to encrypt message: " + e.getMessage());
-                return null;
-            }
+        final XmppAxolotlMessage axolotlMessage = new XmppAxolotlMessage(account.getJid().toBareJid(), getOwnDeviceId());
+        final String content;
+        if (message.hasFileOnRemoteHost()) {
+            content = message.getFileParams().url.toString();
+        } else {
+            content = message.getBody();
+        }
+        try {
+            axolotlMessage.encrypt(content);
+        } catch (CryptoFailedException e) {
+            Log.w(Config.LOGTAG, getLogprefix(account) + "Failed to encrypt message: " + e.getMessage());
+            return null;
+        }
+        if (!buildHeader(axolotlMessage, message.getConversation())) {
+            return null;
         }
 
         return axolotlMessage;
@@ -1065,8 +1063,12 @@ public class AxolotlService implements OnAdvancedStreamFeaturesLoaded {
         executor.execute(new Runnable() {
             @Override
             public void run() {
-                XmppAxolotlMessage axolotlMessage = buildHeader(conversation);
-                onMessageCreatedCallback.run(axolotlMessage);
+                final XmppAxolotlMessage axolotlMessage = new XmppAxolotlMessage(account.getJid().toBareJid(), getOwnDeviceId());
+                if (buildHeader(axolotlMessage, conversation)) {
+                    onMessageCreatedCallback.run(axolotlMessage);
+                } else {
+                    onMessageCreatedCallback.run(null);
+                }
             }
         });
     }
diff --git a/src/main/java/de/pixart/messenger/crypto/axolotl/XmppAxolotlMessage.java b/src/main/java/de/pixart/messenger/crypto/axolotl/XmppAxolotlMessage.java
index 94064a661..fa91ee122 100644
--- a/src/main/java/de/pixart/messenger/crypto/axolotl/XmppAxolotlMessage.java
+++ b/src/main/java/de/pixart/messenger/crypto/axolotl/XmppAxolotlMessage.java
@@ -40,6 +40,7 @@ public class XmppAxolotlMessage {
 
     private byte[] innerKey;
     private byte[] ciphertext = null;
+    private byte[] authtagPlusInnerKey = null;
     private byte[] iv = null;
     private final Map<Integer, XmppAxolotlSession.AxolotlKey> keys;
     private final Jid from;
@@ -164,6 +165,14 @@ public class XmppAxolotlMessage {
             Cipher cipher = Cipher.getInstance(CIPHERMODE, PROVIDER);
             cipher.init(Cipher.ENCRYPT_MODE, secretKey, ivSpec);
             this.ciphertext = cipher.doFinal(Config.OMEMO_PADDING ? getPaddedBytes(plaintext) : plaintext.getBytes());
+            if (Config.PUT_AUTH_TAG_INTO_KEY && this.ciphertext != null) {
+                this.authtagPlusInnerKey = new byte[16 + 16];
+                byte[] ciphertext = new byte[this.ciphertext.length - 16];
+                System.arraycopy(this.ciphertext, 0, ciphertext, 0, ciphertext.length);
+                System.arraycopy(this.ciphertext, ciphertext.length, authtagPlusInnerKey, 16, 16);
+                System.arraycopy(this.innerKey, 0, authtagPlusInnerKey, 0, this.innerKey.length);
+                this.ciphertext = ciphertext;
+            }
         } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException
                 | IllegalBlockSizeException | BadPaddingException | NoSuchProviderException
                 | InvalidAlgorithmParameterException e) {
@@ -200,7 +209,12 @@ public class XmppAxolotlMessage {
     }
 
     public void addDevice(XmppAxolotlSession session) {
-        XmppAxolotlSession.AxolotlKey key = session.processSending(innerKey);
+        XmppAxolotlSession.AxolotlKey key;
+        if (authtagPlusInnerKey != null) {
+            key = session.processSending(authtagPlusInnerKey);
+        } else {
+            key = session.processSending(innerKey);
+        }
         if (key != null) {
             keys.put(session.getRemoteAddress().getDeviceId(), key);
         }
@@ -252,6 +266,18 @@ public class XmppAxolotlMessage {
         byte[] key = unpackKey(session, sourceDeviceId);
         if (key != null) {
             try {
+                if (key.length >= 32) {
+                    int authtaglength = key.length - 16;
+                    Log.d(Config.LOGTAG, "found auth tag as part of omemo key");
+                    byte[] newCipherText = new byte[key.length - 16 + ciphertext.length];
+                    byte[] newKey = new byte[16];
+                    System.arraycopy(ciphertext, 0, newCipherText, 0, ciphertext.length);
+                    System.arraycopy(key, 16, newCipherText, ciphertext.length, authtaglength);
+                    System.arraycopy(key, 0, newKey, 0, newKey.length);
+                    ciphertext = newCipherText;
+                    key = newKey;
+                }
+
                 Cipher cipher = Cipher.getInstance(CIPHERMODE, PROVIDER);
                 SecretKeySpec keySpec = new SecretKeySpec(key, KEYTYPE);
                 IvParameterSpec ivSpec = new IvParameterSpec(iv);