- From: Mike Bishop <mbishop@evequefou.be>
- Date: Wed, 15 Nov 2017 10:04:45 +0000
- To: Kazuho Oku <kazuhooku@gmail.com>
- CC: Nick Sullivan <nicholas.sullivan@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>
- Message-ID: <MWHPR08MB2432902018DECDF6CDBD95A2DA290@MWHPR08MB2432.namprd08.prod.outlook.com>
I’ve put together a PR with a first pass at implementing your suggestion. Give it a look before I merge? Feedback from anyone else is welcome as well.
https://github.com/MikeBishop/http2-certs/pull/17
From: Kazuho Oku [mailto:kazuhooku@gmail.com]
Sent: Wednesday, November 15, 2017 12:21 AM
To: Mike Bishop <mbishop@evequefou.be>
Cc: Nick Sullivan <nicholas.sullivan@gmail.com>; HTTP Working Group <ietf-http-wg@w3.org>
Subject: Re: FW: New Version Notification for draft-bishop-httpbis-http2-additional-certs-05.txt
Hi Mike,
2017-11-14 23:16 GMT+08:00 Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>:
What the draft currently says about that is:
Client implementations need to carefully consider the impact of setting the AUTOMATIC_USE flag. This flag is a performance optimization, permitting the client to avoid a round-trip on each request where the server checks for certificate authentication. However, once this flag has been sent, the client has zero knowledge about whether the server will use the referenced cert for any future request, or even for an existing request which has not yet completed. Clients MUST NOT set this flag on any certificate which is not appropriate for currently-in-flight requests, and MUST NOT make any future requests on the same connection which they are not willing to have associated with the provided certificate.
So basically, if a client provides a certificate to example.com<http://example.com> with AUTOMATIC_USE set, then later decides that it doesn’t want to use that certificate with example.org<http://example.org>, then it MUST NOT send example.org<http://example.org> requests on that connection and would need to start a fresh one.
Thank you for pointing that out. I remember reading the section, but it's obvious I missed the intent of the text.
I think that you’re right that negotiation isn’t needed if the client is allowed to preemptively send USE_CERTIFICATE with every request. That introduces a race condition where confusion could ensue about whether the USE_CERTIFICATE was preemptive or in response to a CERTIFICATE_NEEDED. However, that seems solvable if we specify timing rules. A strawman:
* Eliminate AUTOMATIC_USE – the semantics are always true for servers and never true for clients
* Clients which have previously been challenged for and provided a certificate MAY send USE_CERTIFICATE as part of their subsequent or still-open requests
* Servers MUST NOT send CERTIFICATE_REQUIRED before seeing a complete request
* If the request included a USE_CERTIFICATE frame, the server MUST NOT send CERTIFICATE_REQUIRED, but MAY reset the stream with a NOT_WHAT_I_WANTED error code (better name TBD).
* Upon receipt of a NOT_WHAT_I_WANTED error, clients SHOULD resend the request without a USE_CERTIFICATE frame and expect a CERTIFICATE_REQUIRED frame
* If not, it MAY send a CERTIFICATE_REQUIRED if a certificate is required.
The strawman looks good to me. Thank you for writing them down. I like the fact that the approach is simpler than the current one, and that the round-trips required to perform the requests have been minimized in all cases.
I have only one comment.
You might want to adjust the timing so that we could cap the amount of memory need to buffer a pending request (note that in case of CGI, properties of the client certificate needs to be sent to the application before the request body. Also I would assume that such requirement exists for other gateway protocols).
One way to implement such cap would be to change the timing requirement as follows:
* a client that associates a client certificate to a request MUST send USE_CERTIFICATE frame prior to sending a DATA frame
* otherwise, a client should send the USE_CERTIFICATE frame only in response to a CERTIFICATE_REQUIRED frame
Something else that should have occurred to me long ago, but hit me while writing the above: USE_CERTIFICATE will necessarily be sendable on a half-closed stream. That’s possible in HTTP/2, but problematic in HTTP/QUIC. We’ll have to think about that.
-----Original Message-----
From: Kazuho Oku [mailto:kazuhooku@gmail.com<mailto:kazuhooku@gmail.com>]
Sent: Tuesday, November 14, 2017 2:24 PM
To: Nick Sullivan <nicholas.sullivan@gmail.com<mailto:nicholas.sullivan@gmail.com>>
Cc: Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>; HTTP Working Group <ietf-http-wg@w3.org<mailto:ietf-http-wg@w3.org>>
Subject: Re: FW: New Version Notification for draft-bishop-httpbis-http2-additional-certs-05.txt
Hi Nick, Ilari, Mike,
Thank you for your responses.
First, let me argue that there is no need to negotiate AUTOMATIC_USE.
Current draft permits the server to let the client choose a certificate even in case AUTOMATIC_USE is being used. So it is possible to cover the CGI use case under the current draft, though the need to spend 2 RTT makes me bit sad (especially since I do not understand the benefit of letting the server choose the certificate).
That said, let me elaborate about another issue related to AUTOMATIC_USE; a potential privacy concern.
Consider the case of a CDN terminating example.com<http://example.com> and example.org<http://example.org>.
Both of the hosts require authentication using client certificates issued by the same CA.
At first, a client connects to the CDN sending a request to example.com<http://example.com>, and sends its client certificate with AUTOMATIC_USE flag set.
Then, using the same connection, a client sends a request to example.org<http://example.org>. At this point, is the CDN allowed to present the certificate that was sent for example.com<http://example.com> to example.org<http://example.org>? My understanding is that in HTTP/1, a user has the total control of choosing the certificate the person wants to send to each domain.
So to me, it seems that we would be required to standardize when a certificate sent with AUTOMATIC_USE flag set can be reused across the authorities that are coalesced into a single connection, if we are to enable automatic reuse (please let me know if that’s already specified; I may have missed that).
One way to avoid the issue is to drop AUTOMATIC_USE from the specification, and require the client to specify the certificate that is associated to every request.
If we take that route, we would no longer be required to seek an agreement and document when an intermediary can reuse a client certificate across authorities. Elimination of AUTOMATIC_USE would give the clients total control on how certificates are associated to the requests they send, and the added bonus would be that the behavior could be verified by consulting the client behavior.
2017-11-13 17:29 GMT+08:00 Nick Sullivan <nicholas.sullivan@gmail.com<mailto:nicholas.sullivan@gmail.com>>:
> Hi Kazuho,
>
> Thanks for this. I think you found an issue that we did not consider:
> the fact that server support for setting AUTOMATIC_USE in client
> certificates may not be desirable for all servers. The CGI case you
> describe would work find as long as the client doesn't use AUTOMATIC_USE.
>
> Here's a possible solution to this:
> Let the server advertise support for AUTOMATIC_USE in the
> CERTIFICATE_REQUEST message as a flag. If the client receives a
> CERTIFICATE_REQUEST without AUTOMATIC_USE set, then it should not be
> able to reply with a CERTIFICATE with AUTOMATIC_USE set.
>
> Nick
>
> On Mon, Nov 13, 2017 at 3:18 PM Kazuho Oku <kazuhooku@gmail.com<mailto:kazuhooku@gmail.com>> wrote:
>>
>> Hi, Mike, Nick, Martin,
>>
>> I have briefly asked this in the IETF meeting, but let me question if
>> it sounds logical to adjust the approach so that the client will be
>> required to proactively specify the certificate that is associated to
>> each HTTP request.
>>
>> I ask this due to the following reason.
>>
>> In HTTP/1, it was always clear from the server’s viewpoint which
>> certificate is associated to a HTTP request. This is because the
>> underlying connection allowed only one client certificate at maximum
>> to be used. CGI is designed after that model. A CGI gateway is
>> expected to designate _at most one_ certificate that has been
>> associated to the request by using a set of environment variables
>> (e.g., `SSL_CLIENT_S_DN` [1]). I would assume that it is the same for
>> other de-facto standards that have evolved from CGI (e.g., FastCGI,
>> Rack).
>>
>> The secondary certificates draft changes the model. Under the model
>> proposed by the draft, the server is expected to choose from one of
>> the certificates that it has received with AUTOMATIC_USE flag set, or
>> to request the client to send a new certificate.
>>
>> However, to me (as a HTTP server developer that acts as a CGI
>> gateway) it is unclear how a server can make such choice.
>> Applications that are run using the CGI protocol _might_ have
>> sufficient information to make such choice, but that is not the case for a CGI gateway.
>>
>> That means that unless the draft (in the following revisions) specify
>> the guess logic that I should implement, I would be forced into
>> sending CERTIFICATE_NEEDED for every HTTP request I receive. Doing so
>> would introduce one extra roundtrip.
>>
>> Considering that, I wonder if you could adjust the approach proposed
>> in the draft to require the client to proactively clarify the
>> certificate that is associated to each HTTP request.
>>
>> For example, I believe that the draft could specify that:
>> * If the client does not specify a certificate that is associated to
>> a request, a server MAY request the client to specify the certificate.
>> * The client can specify the certificate that is associated to a
>> request proactively, instead of sending USE_CERTIFICATE frame in
>> response to a CERTIFICATE_NEEDED frame.
>>
>> By changing the approach as such, the only case in which two
>> roundtrips are required for processing a request could become when
>> the client is required to send a new certificate. Also, AUTOMATIC_USE
>> flag becomes unnecessary.
>>
>> One downside caused by such change is that the bandwidth slightly
>> increases due to the fact that the client would be required to
>> specify the certificate that is associated to every HTTP request.
>> However that is just sending Cert-ID per every HTTP request; I
>> believe that the increase of bandwidth is negligible.
>>
>> To summarize, I am suggesting to push the responsibility of choosing
>> the certificate back to the client. Note that in the current draft
>> the client is still required to make such choice if the server sends
>> a CERTIFICATE_NEEDED frame; so I think requiring the client to
>> _always_ make the choice does not increase the complexity on the client side.
>>
>> [1] https://httpd.apache.org/docs/2.4/mod/mod_ssl.html
>>
>> 2017-10-31 8:14 GMT+08:00 Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>:
>> > In preparation for Singapore, we've updated the Additional Certs
>> > draft to track changes in TLS 1.3 and the Exported Authenticators TLS draft.
>> > There's been substantial interest here, and we'll be discussing the
>> > draft during the WG meeting.
>> >
>> > -----Original Message-----
>> > From: internet-drafts@ietf.org<mailto:internet-drafts@ietf.org> [mailto:internet-drafts@ietf.org]
>> > Sent: Monday, October 30, 2017 2:40 PM
>> > To: Martin Thomson <martin.thomson@gmail.com<mailto:martin.thomson@gmail.com>>; Mike Bishop
>> > <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>; Nick Sullivan <nick@cloudflare.com<mailto:nick@cloudflare.com>>
>> > Subject: New Version Notification for
>> > draft-bishop-httpbis-http2-additional-certs-05.txt
>> >
>> >
>> > A new version of I-D,
>> > draft-bishop-httpbis-http2-additional-certs-05.txt
>> > has been successfully submitted by Mike Bishop and posted to the
>> > IETF repository.
>> >
>> > Name: draft-bishop-httpbis-http2-additional-certs
>> > Revision: 05
>> > Title: Secondary Certificate Authentication in HTTP/2
>> > Document date: 2017-10-30
>> > Group: Individual Submission
>> > Pages: 21
>> > URL:
>> > https://www.ietf.org/internet-drafts/draft-bishop-httpbis-http2-add
>> > itional-certs-05.txt
>> > Status:
>> > https://datatracker.ietf.org/doc/draft-bishop-httpbis-http2-additio
>> > nal-certs/
>> > Htmlized:
>> > https://tools.ietf.org/html/draft-bishop-httpbis-http2-additional-c
>> > erts-05
>> > Htmlized:
>> > https://datatracker.ietf.org/doc/html/draft-bishop-httpbis-http2-ad
>> > ditional-certs-05
>> > Diff:
>> > https://www.ietf.org/rfcdiff?url2=draft-bishop-httpbis-http2-additi
>> > onal-certs-05
>> >
>> > Abstract:
>> > TLS provides fundamental mutual authentication services for HTTP,
>> > supporting up to one server certificate and up to one client
>> > certificate associated to the session to prove client and server
>> > identities as necessary. This draft provides mechanisms for
>> > providing additional such certificates at the HTTP layer when these
>> > constraints are not sufficient.
>> >
>> > Many HTTP servers host content from several origins. HTTP/2
>> > [RFC7540] permits clients to reuse an existing HTTP connection to a
>> > server provided that the secondary origin is also in the certificate
>> > provided during the TLS [I-D.ietf-tls-tls13] handshake.
>> >
>> > In many cases, servers will wish to maintain separate certificates
>> > for different origins but still desire the benefits of a shared HTTP
>> > connection. Similarly, servers may require clients to present
>> > authentication, but have different requirements based on the content
>> > the client is attempting to access.
>> >
>> > This document describes how TLS exported authenticators
>> > [I-D.ietf-tls-exported-authenticator] can be used to provide proof of
>> > ownership of additional certificates to the HTTP layer to support
>> > both scenarios.
>> >
>> >
>> >
>> >
>> > Please note that it may take a couple of minutes from the time of
>> > submission until the htmlized version and diff are available at
>> > tools.ietf.org<http://tools.ietf.org>.
>> >
>> > The IETF Secretariat
>> >
>> >
>>
>>
>>
>> --
>> Kazuho Oku
>>
>
--
Kazuho Oku
--
Kazuho Oku
Received on Wednesday, 15 November 2017 10:05:13 UTC