Merge pull request #1354 from bob-beck/main

Forbid the sender from sending duplicate supported groups entries.

draft-ietf-tls-rfc8446bis.md

@@ -2246,7 +2246,9 @@ Finite Field Groups (DHE):
 {:br }
 
 Items in "named_group_list" are ordered according to the sender's
-preferences (most preferred choice first).
+preferences (most preferred choice first). The "named_group_list"
+MUST NOT contain any duplicate entries.  A recipient MAY abort a connection
+with a fatal illegal_parameter alert if it detects a duplicate entry.
 
 As of TLS 1.3, servers are permitted to send the "supported_groups"
 extension to the client. Clients MUST NOT act upon any information