We're getting there. :-) See below.
On 7/19/22 9:14 AM, Rob Wilton (rwilton) wrote:
Hi Peter,
More inline ...
-----Original Message-----
From: Peter Saint-Andre <[email protected]>
Sent: 19 July 2022 14:59
To: Rob Wilton (rwilton) <[email protected]>; The IESG <[email protected]>
Cc: [email protected]; [email protected]; [email protected];
[email protected]
Subject: Re: Robert Wilton's Discuss on draft-ietf-uta-rfc7525bis-09: (with
DISCUSS and COMMENT)
Hi Rob, more follow-up inline.
On 7/19/22 3:42 AM, Rob Wilton (rwilton) wrote:
Hi Peter,
Thanks for the further information. I'm not sure whether we have quite
met in the middle yet, some further comments below.
-----Original Message-----
From: Peter Saint-Andre <[email protected]>
Sent: 18 July 2022 18:56
To: Rob Wilton (rwilton) <[email protected]>; The IESG <[email protected]>
Cc: [email protected]; [email protected]; [email protected];
[email protected]
Subject: Re: Robert Wilton's Discuss on draft-ietf-uta-rfc7525bis-09: (with
DISCUSS and COMMENT)
Hi Rob, I'm circling back to an earlier point in the thread to cover all
of the issues. (Thomas and I just discussed these topics, but Yaron was
not able to join our call because of illness.)
On 7/14/22 9:06 AM, Peter Saint-Andre wrote:
Hi Robert, thanks for the review. Comments inline.
On 7/14/22 3:37 AM, Robert Wilton via Datatracker wrote:
Robert Wilton has entered the following ballot position for
draft-ietf-uta-rfc7525bis-09: Discuss
<snip/>
(2)
* New protocol designs that embed TLS mechanisms SHOULD
use only TLS
1.3 and SHOULD NOT use TLS 1.2; for instance, QUIC
[RFC9001]) took
this approach. As a result, implementations of such
newly-
developed protocols SHOULD support TLS 1.3 only with no
negotiation of earlier versions.
Why is this only a SHOULD and not a MUST? If a new protocol (rather
than an
updated version of an existing protocol) was being designed why would
it be
reasonable to design it to support TLS 1.2? If you want to keep these
as
SHOULD rather than MUSTs then please can the document specify
under
what
circumstances it would be reasonable for a new protocol design to use
TLS 1.2.
Although personally I'm open to MUST here, I'd like to discuss that with
my co-authors (one of whom is offline this week).
Unfortunately Yaron was not able to join our call, but Thomas and I
discussed it and we think there could be two different cases:
(a) new security-focused protocols such as QUIC
(b) new application protocols (say, for real-time collaboration)
For (a), it definitely makes sense to use TLS 1.3 only (as noted in the
current text, QUIC uses the TLS handshake protocol with a different
record layer).
Okay. But I still note that the text for this is still only SHOULD rather than
MUST. I can live with this, even though I still believe that MUST would be
better.
The confusion arises from the fact that this bit of text is making
recommendations for two kinds of protocols: secure transport protocols
like QUIC and application protocols like IMAP. Their layering with TLS
is quite different. I think we probably want to say MUST 1.3 for the
former and SHOULD 1.3 for the latter, which would clear up your next
point...
Okay. I'll leave it to the authors discretion, but I would suggest that it may
be worth adding a sentence to indicate under what circumstances the SHOULD
applies here. I.e., you could add a sentence to your rationale to help justify
when a new protocol might choose to use TLS 1.2 rather than TLS 1.3.
Here is the provisional text I just checked into GitHub, see
https://github.com/yaronf/I-D/pull/464/files
###
* New transport protocols that integrate the TLS/DTLS handshake protocol
and/or record layer MUST use only TLS/DTLS 1.3 (for instance, QUIC
{{RFC9001}}) took this approach) and new application protocols that
employ TLS/DTLS for channel or session encryption MUST use TLS/DTLS 1.2
and/or 1.3. Implementations would then adhere to the TLS/DTLS version
used by the relevant protocol.
Rationale: Although secure deployment of TLS 1.3 is easier and less
error-prone than TLS 1.2 because of the need to follow the
recommendations provided in this document for secure deployment of TLS
1.2, development of new transport protocols is significantly more
complex than simply re-using the existing support for TLS/DTLS in
underlying libraries or operating systems as is usually done in
application protocols.
###
For (b), we see reasons why it might make sense to build on top of both
TLS 1.2 and TLS 1.3 at the present time: for instance, implementations
might want to "cast a wide net" in terms of underlying library or
operating support and thus avoid the significant effort involved in
building a secure transport protocol such as QUIC. Naturally, this
advice will probably change in 7525ter a few years from now.
Yes, I can see why it *might* make sense and implementations *might*
want to cast a wide net, which is why I think that SHOULD is better than
MUST. I.e., SHOULD means that implementations must support TLS 1.2
unless they have a good reason not to, whereas MUST means that they are
required to deploy TLS 1.2 even in scenarios where they know that all clients
support TLS 1.3, and don't want to pay the additional administration
overhead of safely deploying and maintaining TLS 1.2 ...
However, I think that I've stated my opinion, and if you want to keep it as a
MUST, I will acquiesce and remove my blocking discuss on this point.
Would the change suggested above address your concerns?
Not sure. Although the placing of my comment above wasn't particularly clear, it was
intended to be related to the "Implementations MUST support TLS 1.2" statement.
So, consider NETCONF, a network management protocols for configuring network devices and
retrieving operational data, there is a new draft to allow NETCONF to run over TLS 1.3.
NETCONF effectively runs in a closed management domain where a single entity (the
operator) has control over all NETCONF servers (i.e., network devices) and all management
clients and controllers. In this scenario, if all clients and devices support TLS 1.3
then I would think that it is easier/simpler for them to just deploy TLS 1.3, but that
would seem to conflict with the "Implementations must support TLS 1.2"
statement.
But it is possible that I'm misunderstanding this section/text. Perhaps the disagreement
(or my confusion) is that I interpret "Implementations MUST support TLS 1.2" to
mean that deployments MUST allow clients to use TLS 1.2 (e.g., if I setup an IMAP server,
I have to allow TLS 1.2 clients), whereas the constraint is only mean to be on the
software itself. I.e., my IMAP server code must be capable of supporting TLS 1.2, but it
can be deployed to only negotiate TLS 1.3?
Well, implementation != deployment and we've tried to be careful about
that distinction in the document. Administrators who deploy live
services using a software or hardware implementation are of course free
to (and often encouraged to) do so in the most secure manner possible
for feasible for them. Thus a service isn't forced to offer TLS 1.2 if
they want to offer 1.3 only, but we're saying that the implementation
needs to support both of these recommended versions.
(3)
When TLS-only
communication is available for a certain protocol, it MUST be used
by implementations and MUST be configured by
administrators. When
a protocol only supports dynamic upgrade, implementations MUST
provide a strict local policy (a policy that forbids use of
plaintext in the absence of a negotiated TLS channel) and
administrators MUST use this policy.
The MUSTs feel too strong here, since there are surely deployments
and
streams
of data where encryption, whilst beneficial, isn't an absolute
requirement?
In addition "MUST be used by implementations and MUST be
configured
by
administrators" also seem to conflict, i.e., if the implementation
must use it
then why would an administrator have to enable it?
I believe this is a duplicate of an issue that other folks have already
raised:
https://github.com/yaronf/I-D/issues/437
At https://github.com/yaronf/I-D/pull/461 I'm proposing the following
text:
###
When TLS-only communication is available for a certain protocol, it MUST
be supported by implementations and MUST be configured by
administrators
in preference to a dynamic upgrade method. When a protocol only
supports
dynamic upgrade, implementations MUST provide a way for
administrators
to set a strict local policy that forbids use of plaintext in the
absence of a negotiated TLS channel, and administrators MUST use this
policy.
I appreciate that the context of this text is the upgrade case (which makes
sense), but I'm still able to read this text as casting a wider net than
hopefully
intended. I.e., I'm still concerned that someone could quote this text to say
that unencrypted comms is strictly not allowed anywhere, whenever a TLS
version of the protocol exists, and whilst I entirely agree that using TLS is
appropriate in the vast majority of places, I'm not convinced that is
everywhere.
If people want to run unencrypted communications, that's their business,
but this document is about how best to use TLS once you've chosen to do
so, not about whether to use TLS in the first place.
Okay.
Hence, I wonder whether we could restructure the first sentence to ensure
that it's scope if focused purely on the upgrade scenario. I.e., I suggest
something like the following for the first sentence:
"When a protocol defines both a dynamic upgrade method and a separate
TLS-only channel, then the separate TLS-only channel MUST be supported by
implementations and MUST be configured by administrators to be used in
preference to the dynamic upgrade method."
That's what we were trying to say, so your phrasing seems fine to me.
However, I feel that "channel" could be confusing and would prefer
"method" in both cases.
Sure.
Great. Updated text at https://github.com/yaronf/I-D/pull/461/files as
follows:
###
* Many existing application protocols were designed before the use of
TLS became common. These protocols typically support TLS in one of two
ways: either via a separate port for TLS-only communication (e.g., port
443 for HTTPS) or via a method for dynamically upgrading a channel from
unencrypted to TLS-protected (e.g., STARTTLS, which is used in protocols
such as IMAP and XMPP). Regardless of the mechanism for protecting the
communication channel (TLS-only port or dynamic upgrade), what matters
is the end state of the channel. When a protocol defines both a dynamic
upgrade method and a separate TLS-only method, then the separate
TLS-only method MUST be supported by implementations and MUST be
configured by administrators to be used in preference to the dynamic
upgrade method. When a protocol supports only a dynamic upgrade,
implementations MUST provide a way for administrators to set a strict
local policy that forbids use of plaintext in the absence of a
negotiated TLS channel, and administrators MUST use this policy.
###
Peter
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