fix bug for Python3

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/trunk@1388 b32b6428-25c9-4566-ad07-03861ab6144f

xaal-lib/src/xAAL/message.py

@@ -91,7 +91,7 @@ class MessageFactory():
 
         # Payload Ciphering: ciph
         # Additionnal Data == json serialization of the targets array
-        ad = json.dumps(msg.get_targets())
+        ad = json.dumps(msg.get_targets()).encode("utf8")  # Additional Data
         nonce = build_nonce(msg.get_timestamp())
         key = self.get_cipher_key()
         ciph = pysodium.crypto_aead_chacha20poly1305_encrypt(