Using TLS 1.3 with HTTP/2
Google LLC
davidben@google.com
Applications and Real-Time
HTTP
HTTP
renegotiation
post-handshake client authentication
This document updates RFC 7540 by forbidding TLS 1.3 post-handshake
authentication, as an analog to the existing TLS 1.2 renegotiation restriction.
Introduction
TLS 1.2 and earlier
versions of TLS support renegotiation, a mechanism for changing
parameters and keys partway through a connection. This was sometimes
used to implement reactive client authentication in HTTP/1.1 , where the server decides whether or
not to request a client certificate based on the HTTP request.
HTTP/2 multiplexes multiple
HTTP requests over a single connection, which is incompatible with the
mechanism above. Clients cannot correlate the certificate request with
the HTTP request that triggered it. Thus, forbids renegotiation.
TLS 1.3 removes
renegotiation and replaces it with separate post-handshake
authentication and key update mechanisms. Post-handshake authentication
has the same problems with multiplexed protocols as TLS 1.2
renegotiation, but the prohibition in only applies to renegotiation.
This document updates HTTP/2 to similarly forbid TLS 1.3 post-handshake
authentication.
Requirements Language
The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are
to be interpreted as described in BCP 14
when, and only when, they appear in all capitals,
as shown here.
Post-Handshake Authentication in HTTP/2
HTTP/2 servers MUST NOT send post-handshake TLS 1.3 CertificateRequest messages.
HTTP/2 clients MUST treat such messages as connection errors (see ) of type PROTOCOL_ERROR.
permitted renegotiation before the HTTP/2 connection preface to
provide confidentiality of the client certificate. TLS 1.3 encrypts the client
certificate in the initial handshake, so this is no longer necessary. HTTP/2
servers MUST NOT send post-handshake TLS 1.3 CertificateRequest messages before
the connection preface.
The above applies even if the client offered the
post_handshake_auth TLS extension. This extension is advertised
independently of the selected Application-Layer Protocol Negotiation
(ALPN) protocol , so it is not
sufficient to resolve the conflict with HTTP/2. HTTP/2 clients that also
offer other ALPN protocols, notably HTTP/1.1, in a TLS ClientHello
MAY include the post_handshake_auth extension to
support those other protocols. This does not indicate support in
HTTP/2.
Other Post-Handshake TLS Messages in HTTP/2
defines two other messages that are exchanged after the handshake is
complete: KeyUpdate and NewSessionTicket.
KeyUpdate messages only affect TLS itself and do not require any interaction
with the application protocol. HTTP/2 implementations MUST support key updates
when TLS 1.3 is negotiated.
NewSessionTicket messages are also permitted. Though these interact
with HTTP when early data is enabled, these interactions are defined in
and are allowed for in the
design of HTTP/2.
Unless the use of a new type of TLS message depends on an interaction
with the application-layer protocol, that TLS message can be sent after
the handshake completes.
Security Considerations
This document resolves a compatibility concern between HTTP/2 and TLS 1.3 when
supporting post-handshake authentication with HTTP/1.1. This lowers the barrier
for deploying TLS 1.3, a major security improvement over TLS 1.2.
IANA Considerations
This document has no IANA actions.
References
Normative References
Informative References