I think that it could be acceptable to "reuse" an old validation provided WHOIS 
is checked right?
Eg, if a hash is made of all the WHOIS data, and all the WHOIS data stays 
identical from last validation, then theres proof that control of domain has 
not shifted in the meantime, which is the main reason to implement random 
challenge checks.

Because if you sell, transfer, change owner, renew, change DNS server, the 
domain is disabled, or if domain expires, then some data in the WHOIS will 
change.
Especially the "last update" date.
And same also applies to the DNS servers and/or DNSSEC keys.

So combining a static entry with a WHOIS hash check, would propably suffice, 
but the static entry must be randomly generated AND contain a key, to prevent 
"preloading" malicious software with challenges.
Of course, for the scheme to be secure, there must be something that enforces 
the challenge is passed in a short time, for example 24 hours, but once 
challenge is passed, it will stay valid until WHOIS changes.

Of course, such a check could only be accepted for base level domains, where 
the person validating the domain effectively is the person who paid for the 
domain aswell, NOT subdomains, as subdomains can be part of "free webhosting 
services" which will stay static for a very long period.

-----Ursprungligt meddelande-----
Från: Acme [mailto:[email protected]] För Tim Hollebeek
Skickat: den 23 januari 2018 17:38
Till: Jacob Hoffman-Andrews <[email protected]>; [email protected]
Ämne: [invalid signature!]

> This challenge has the big advantage that subscribers only need to do a one-
> time CNAME setup, and renewals can be reliably automated without requiring
> that renewing systems have permission to update DNS. In effect, the CNAME
> record would act like a long-term delegation permitting the CA to issue
> continuously for the base domain.

Yes, not having to validate domains saves customers a lot of time and effort!
See BR validation methods #1 and #5 for more information!! 😊

Your proposed method defeats one of the goals of the BR domain control 
validation requirements, which is to demonstrate control at time of validation, 
not just as some previous time in the past.  That's why the existing, approved
validation methods require random numbers to guarantee the validation is
fresh and not based on some previous validation.

If control at some time in the past is sufficient, you can just re-use the 
previous 
validation, which is allowed in some circumstances (see the BRs).

-Tim



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