Subject: [TLS] rfc6066 ->Server Name extension sending issue from server

From: Sajeev S <[email-masked]>
Date: Sat, 22 Jan 2022 10:23:37 +0530

Hi All,

In this below RFC->RFC 6066 - Transport Layer Security (TLS) Extensions:
Extension Definitions (ietf.org)
<https://datatracker.ietf.org/doc/html/rfc6066>

3 <https://datatracker.ietf.org/doc/html/rfc6066#section-3>.  Server
Name Indication

A server that receives a client hello containing the "server_name"
   extension MAY use the information contained in the extension to guide
   its selection of an appropriate certificate to return to the client,
   and/or other aspects of security policy.  In this event, the server
   SHALL include an extension of type "server_name" in the (extended)
   server hello.  The "extension_data" field of this extension SHALL be
   empty.

Some of the implementations are not sending this ->the server

   SHALL include an extension of type "server_name" in the (extended)
   server hello.

And this is causing the Reuse session to fail with those Servers
because the client will not know whether the Server is using SNI or
not.

i.e whether to resume the session with SNI or not.

"When the server is deciding whether or not to accept a request to
   resume a session, the contents of a server_name extension MAY be used
   in the lookup of the session in the session cache.  The client SHOULD
   include the same server_name extension in the session resumption
   request as it did in the full handshake that established the session."

Regards,

Sajeev