diff --git a/Group-chat-feature-(design-draft).md b/Group-chat-feature-(design-draft).md
index 393a12d3ff83e958f6c1b18e446c2456893a3faf..bee2f27274b968195fbb66f1cbd81328a632c877 100644
--- a/Group-chat-feature-(design-draft).md
+++ b/Group-chat-feature-(design-draft).md
@@ -11,6 +11,8 @@ So, the *swarm* is defined by:
 4. Non-repudiation. Devices must be able to verify old messages validity and to replay the whole history.
 5. PFS on the transport. Storage is managed by the device.
 
+Main idea is to get a synchronized merkle tree with the participants.
+
 # Scenarios
 
 ## Create a Swarm