Some people have asked why TLS 1.3 isn’t available yet. This might help; it’s
a draft of a posting for my company’s blog.
Can I Haz TLS 1.3 ?
Everybody wants to be able to use TLS 1.3. Among the reasons are:
It’s faster – being able to reconnect to a server you’ve
previously used, and saving a full round-trip latency is impressive.
It’s more reliable – the protocol has been cleaned up and
simplified. For example, the related concepts of sessions, tickets, and
pre-shared keys are merged and treated consistently. To a protocol designer, it
is much more elegant, and therefore much easier to implement
It’s more secure – Many world-class cryptographers have been
involved in the protocol design, analyzed it, and tried to break it.
TLS has been in the “last call” for several weeks now. What does that mean,
and what’s holding it up?
The IETF is the organization that defines most of the standards that define how
the Internet works. They cover everything from naming (DNS) to routing around
firewalls, up to and including HTTP. The documents, known as RFCs, are created
by working groups, passed to a steering committee for review, and then
published as “Internet Standards.”
Participation in a working group (WG) is, by design, very easy and not a lot of
overhead. You just have to join a mailing list. Every WG has a mailing list
and there are currently more than 110 working groups hosted at the IETF. Each
one has a status page, that shows their charter (what they are working on), the
current sent of documents, and pointers to the mailing lists. For the TLS
working group, that page is at https://datatracker.ietf.org/wg/tls/documents/.
Future RFC’s start as Internet-Drafts. Each draft usually goes through multiple
revisions, as the working group members comment on it, other feedback is
addressed, and so on. At some point, the authors or editors will post a new
draft. By convention, every working group draft is named
“draft-ietf-{WGNAME}-{subject}-{nn}” where {WGNAME} is the name of the working
group, {subject} is the name of the document, and {nn} is the revision number.
For example, “draft-ietf-tls-tls13-21” is the 21st draft of the TLS 1.3
specification from the TLS working group.
When the working group thinks a document is done, it enters WGLC, working group
last call. This period, usually lasting a couple of weeks, is the last chance
to make editorial or serious factual fixes. Since most people are
deadline-driven, this is usually when many on the WG wake up and read the
drafts. After WGLC, it goes to the IESG (technical leadership basically) for
review. As I said, TLS 1.3 has been in WGLC for weeks. So why can’t we use it
yet?
First, the different drafts don’t interoperate. Each represents a different
milestone on the way to the full specification, and a flag in the header
identifies which draft is being used. OpenSSL, used by most of the servers on
the Internet, is currently at draft-21. Chrome and Firefox, two of the most
popular browsers on the Internet, are staying at draft-18; they don’t want to
upgrade until we have the final version. (I think that’s silly, but I don’t
work for either browser.)
Tests run by various companies, including Google, Mozilla, and Facebook,
indicate that the “failure rate” of TLS 1.3 is disturbingly high. It appears
that network hardware such as routers, gateways, load balancers and the like,
are blocking TLS 1.3 packets because they don’t recognize the protocol. They
are doing “fail closed” and block the connections because they don’t understand
it, rather than assuming it’s safe to forward. The IETF often uses the term
“middlebox” to describe such hardware that operates between endpoints, and this
type of behavior that blocks new protocols as “ossificiation.” The various
companies, and no doubt others, are trying experiments to tweak the protocol to
lower the failure rate. For example, in some circumstances it might be
acceptable to make a TLS 1.3 message look like a TLS 1.2 message (after you’ve
already committed to doing TLS 1.3).
So far nobody has released any details. When it happens, it will be on the
TLS-WG mailing list, which you can find at the page I referenced above. Until
then, because of the draft differences, it’s impractical to run even limited
deployment tests unless you’re willing to work with bleeding edge releases and
undocumented flags. That’s unfortunate, and we all hope that the situation will
be improved by the next IETF meeting in November. Until then, we just have to
sit tight and wait.
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