Comparing ALPS and Half-RTT Data
draft-davidben-tls-alps-half-rtt-00

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TLS                                                          D. Benjamin
Internet-Draft                                                Google LLC
Intended status: Informational                           3 December 2020
Expires: 6 June 2021

                    Comparing ALPS and Half-RTT Data
                  draft-davidben-tls-alps-half-rtt-00

Abstract

   This document compares the Application Layer Protocols Settings
   extension with the half-RTT feature in TLS 1.3.

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   This Internet-Draft will expire on 6 June 2021.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Using Half-RTT Data . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Half-RTT Delimiter  . . . . . . . . . . . . . . . . . . .   3
     2.2.  Non-Integer HTTP Settings . . . . . . . . . . . . . . . .   4
     2.3.  Early Data and Session Tickets  . . . . . . . . . . . . .   4
     2.4.  Client Certificates . . . . . . . . . . . . . . . . . . .   5
     2.5.  TLS Terminators . . . . . . . . . . . . . . . . . . . . .   6
     2.6.  TCP Flow Control  . . . . . . . . . . . . . . . . . . . .   7
   3.  Using ALPS  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Half-RTT Delimiter  . . . . . . . . . . . . . . . . . . .   8
     3.2.  Non-Integer HTTP Settings . . . . . . . . . . . . . . . .   8
     3.3.  Early Data and Session Tickets  . . . . . . . . . . . . .   8
     3.4.  Client Certificates . . . . . . . . . . . . . . . . . . .   8
     3.5.  TLS Terminators . . . . . . . . . . . . . . . . . . . . .   8
     3.6.  TCP Flow Control  . . . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   An application-layer protocol often starts with both parties
   negotiating parameters under which the protocol operates; for
   instance, HTTP/2 [RFC7540] and HTTP/3 [I-D.ietf-quic-http] use a
   SETTINGS frame to exchange the list of protocol parameters supported
   by each endpoint.  This can achieved by waiting for TLS handshake
   [RFC8446] to complete and then performing the application-layer
   handshake within the application protocol itself.

   This approach, however, means application protocols must wait for a
   secondary negotiation to complete, often incurring network round-
   trip.  HTTP/2 and HTTP/3 mitigate this with a best-effort negotiation
   scheme: clients do not wait for server SETTINGS before sending a
   request.  But then, by the time the client applies the setting, it
   has already sent the first request based on the default values.  This
   limits the kinds of extensions possible.  For example, the SETTINGS
   frame cannot support negotiate header compression [QUIC-3622] or a
   different static table [HTTP2-788] without changing the protocol to
   disable compression by default and switch partway through.

   Protocol selection is another example of application-level
   negotiation with these trade-offs.  The Application Layer Protocol
   Negotiation (ALPN) extension [RFC7301] adds protocol selection into
   the TLS handshake.  ALPN is instead consistently ordered before all

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