Fix backup MAC checking.

if(MessageDigest.isEqual(ourMac, theirMac) was always returning false
since ourMac was of length 32 and theirMac was of length 10.

src/org/thoughtcrime/securesms/backup/FullBackupImporter.java

@@ -283,7 +283,7 @@ public class FullBackupImporter extends FullBackupBase {
 
         out.close();
 
-        byte[] ourMac   = mac.doFinal();
+        byte[] ourMac   = ByteUtil.trim(mac.doFinal(), 10);
         byte[] theirMac = new byte[10];
 
         try {
@@ -293,7 +293,7 @@ public class FullBackupImporter extends FullBackupBase {
           throw new IOException(e);
         }
 
-        if (MessageDigest.isEqual(ourMac, theirMac)) {
+        if (!MessageDigest.isEqual(ourMac, theirMac)) {
           //destination.delete();
           throw new IOException("Bad MAC");
         }
@@ -314,9 +314,9 @@ public class FullBackupImporter extends FullBackupBase {
         System.arraycopy(frame, frame.length - 10, theirMac, 0, theirMac.length);
 
         mac.update(frame, 0, frame.length - 10);
-        byte[] ourMac = mac.doFinal();
+        byte[] ourMac = ByteUtil.trim(mac.doFinal(), 10);
 
-        if (MessageDigest.isEqual(ourMac, theirMac)) {
+        if (!MessageDigest.isEqual(ourMac, theirMac)) {
           throw new IOException("Bad MAC");
         }