Re: [Acme] Short term certificates - two options

[Chris Drake <[e-mail]>]

Hi Yaron,

The premise seems wrong:
> These certificates allow the domain owner to terminate the TLS server's authorization when necessary, 

What that is technically true, it does not facilitate the *purpose* of the termination (which would be to prevent continued CDN content distribution) - clients can simply ignore the "expired certificate" problem and still get the content.

Trying to build a kludge to use certificates where session keys should be used instead seems a bad-idea(tm) to me.

Kind Regards,
Chris Drake


Thursday, July 21, 2016, 5:53:37 PM, you wrote:

YS> Hi Chris,

YS> The LURK CDN use case is described here: 
YS> https://tools.ietf.org/html/draft-mglt-lurk-tls-use-cases-02#section-5.3

YS> Personally I care more about the case of the TLS server being part of 
YS> the cloud infrastructure (e.g. Amazon ELB or even an on-premise F5 box),
YS> and talking to enterprise-based servers that hold the long-term credentials.

YS> Thanks,
YS>         Yaron

YS> On 20/07/16 23:32, Chris Drake wrote:
>> Hi Yaron,
>>
>> What is the use case for these?
>>
>> Kind Regards,
>> Chris Drake
>>
>>
>> Wednesday, July 20, 2016, 7:51:57 PM, you wrote:
>>
>> YS> Hi,
>>
>> YS> At the LURK BoF this week there was some interest in having a solution
>> YS> where a domain owner can delegate to some other entity (which we will
>> YS> call "the TLS server") the authority to terminate TLS connections on its
>> YS> behalf, using short-term certificates. These certificates allow the
>> YS> domain owner to terminate the TLS server's authorization when necessary,
>> YS> without requiring certificate revocation - which we know doesn't work
>> YS> reliably. The certificates' validity is measured in days, e.g. 3 days.
>>
>> YS> First, I would like to request the working group to adopt short-term
>> YS> certificates as a charter item.
>>
>> YS> Second, I would like the group's advice in choosing between two very
>> YS> different approaches to this problem.
>>
>>
>> YS> Option 1: Certificate Pull
>>
>> YS> This option is documented in the LURK draft [1], which will be modified
>> YS> to include feedback received this week, specifically to use more
>> YS> traditional certification request (CSR) flows. But the basic idea is
>> YS> very simple:
>>
>> YS> 1. TLS server generates a CSR once every 3 days for www.example.com,
>> YS> sends it to the domain owner using an authenticated REST API.
>>
>> YS> 2. Domain owner validates the CSR, forwards it to ACME server, gets back
>> YS> a short-term cert.
>>
>> YS> 3. Domain owner returns the cert to the TLS server.
>>
>> YS> If something bad happens, the domain owner simply stops forwarding
>> YS> requests from this particular TLS server.
>>
>>
>> YS> Option 2: Certificate Delegation
>>
>> YS> This option moves more of the responsibility to the ACME server.
>>
>> YS> 1. Domain owner contacts the ACME server and obtains a "delegation
>> YS> ticket" which is specific to the TLS server. The ticket is good for a
>> YS> long period, e.g. 1 year.
>>
>> YS> 2. TLS server regularly contacts the ACME server, proves ownership of
>> YS> the delegation ticket, and receives a short-term certificate.
>>
>> YS> If something bad happens, the domain owner contacts the ACME server and
>> YS> revokes the delegation ticket.
>>
>>
>> YS> Comparison:
>>
>> YS> 1. Option 2 is clearly more complicated to specify and to implement.
>>
>> YS> 2. Option 2 extends the ACME protocol. Many clients can ignore it, but
>> YS> servers will need to implement it.
>>
>> YS> 3. Option 1 requires the domain owner to have a server available
>> YS> regularly, even if it is only a short REST interaction once every few
>> YS> days. Option 2 doesn't require any such server.
>>
>> YS> 4. Option 1 looks to the ACME server as a normal cert request, and
>> YS> therefore will swamp the CT logs with lots of short-term certs. With
>> YS> Option 2, we can log to CT the issuance of the delegation ticket instead
>> YS> of the actual certificates.
>>
>>
>> YS> I would appreciate your input!
>>
>> YS> Thanks,
>>
>> YS>       Yaron
>>
>>
>> YS> [1] https://tools.ietf.org/html/draft-sheffer-lurk-cert-delegation-00
>>
>>
>>
>>