Hello,
Am 14.11.18 um 11:09 schrieb Werner Koch:
On Tue, 13 Nov 2018 22:37,
bartbutler=40protonmail(_dot_)com(_at_)dmarc(_dot_)ietf(_dot_)org
said:
"The key MUST carry a User ID packet ([RFC4880]) containing the email
address to which mail sent to the queried email address will be routed."
You are talking about how mail is routed, the spec is about discovering
the one and only key to be used for a given mail address. And by key I
mean the OpenPGP keyblock, that is the public key plus one user ID (or
several if they have the same addrspec part).
A mail address is here considered as an identifier for an entity and not
as an addressing scheme for mails. An entity may have several
identifiers like Werner.Koch@foo, Werner_Koch@foo, wernerkoch@foo,
wk@foo, koch@foo. That is a pretty normal but there is no way a sender
can decide whether they are all the same; for example the last two of
the list could also identify my brother.
A sender gets hold of one mail address and that must have been relayed
(direct or indirectly) to them by the owner of that mail address. The
recipient needs to take care that a key exists for that very mail
address.
I think the last sentence exactly captures the difference between the
two approaches.
Who needs to take care that a key exists / pick an existing key for a
different email address routed to the same mailbox.
One of the use cases I have for the '+' syntax is registering to
services with email addresses that allow me to remember where i used
them and filter mails based on them.
One example would be using 'azul+conference_name(_at_)riseup(_dot_)net' to
register
to a conference.
It's low overhead. I can just come up with a addition to my email
address when filling in a web form. If I later receive spam to that
address I know who leaked my email address.
Providing a key for the new address or even publish all those addresses
in my key do not seem like an option for me. Therefor the party I
submitted the form to will not be able to get back to me with an
encrypted email even if i have a key in the wkd.
I don't quite understand the downside of relaxing the spec in this
regard. As far as i understand it it would not require implementations
to lookup which mailbox an address would route to. It would just allow
it. For some providers / implementations this may be trivial and other
may choose to not do it.
Where does the need for the matching user_id come from?
One downside I see is that the mechanism could be used to detect where
an email address routes to. In the case of azul+conf this may be easy to
guess. But for aliases users do not expect them to be linkable without
any interaction on their side.
Cheers,
Azul
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