Charles Lindsey wrote: > On Tue, 31 Mar 2009 06:13:41 +0100, Jim Fenton <[email protected]> wrote: > > >> The second two cases are not my example. Concern #2 in my message has >> to do with messages where the signing address is a different address in >> the same domain as the From address. The correct test case is: >> >> >>> From [email protected] >>> >> Valid signature from [email protected] >> >> Let's also use "all" instead of "discardable" as the test case because >> it's the harder problem to solve. As you point out, the mailing list >> should be acting on the Discardable practice rather than trying to send >> the message to the list. >> >> Let's say that [email protected] is a mailing list that re-signs >> mail sent to the list (or it could be a forwarder or similar agent). >> foo.example's mail server gets a message from an address in the same >> domain, [email protected], that has no Author Signature or has a >> broken one. ... >> > > But how come it had no Author signature? Presumably because it arrived > over some internal LAN, and internal mail is not signed (or all signing is > done at the point where mail is finally dispatched to the Big Wide World > outside). >
Perhaps that was the reason, but it could be a lot of things. The notion of "internal" is becoming harder and harder to define. > >> ... In accordance with the domain's policy, it subjects the >> message to additional scrutiny because of the "all" practices and lack >> of an Author Signature. The message passes this test and is sent to the >> mailing list manager. >> > > So the mailing list manager, or some agent just prior to it, has satisfied > itself that it was a valid message from [email protected] (hence no > reason not to send it out to the mailing list). > Right. >> At this point, the mailing list manager would normally sign the >> message. Let's examine this with the i= and d= choices: >> >> Using i= as the basis for Author Signature, the list can sign the >> message, and the eventual verifier/assessor that does an ADSP check will >> see that it (still) lacks an Author Signature since >> [email protected] does not match [email protected]. >> > > But we are agreed that (at least for now) we don't use i= as the basis for > Author Signature. The mailing list expander may well add > [email protected], but that is just so humans (and maybe some > super-smart Assessors) can observe what has been happening. But, for > normal Assessors, that i= is just "opaque" stuff that it can ignore. > Go back and look at the message from the Chair that started this thread. I had thought that we were debating the merits of the current wording vs. an alternative that I offered that replaces the definition of Author Signature and that means we're still discussing i= vs. d= as a basis for Author Signature. >> Using d= as the basis for Author Signature, if the list signs the >> message, an eventual verifier/assessor will erroneously see that >> signature as an Author Signature, and therefore might not give the >> message the desired treatment. ... >> > > Why ever not? It is From: [email protected]. The agent that signed it > has already satisfied itself that it is genuine ("additional scrutiny" > maybe), and it is signed with d=foo.example. It looks like a Author > Signature, it quacks like an Author Signature, therefore it IS an Author > Signature. Subsequent Assessors should be perfectly happy to accept it > (whether the ADSP for foo.example is "All", "Discardable", or anythng > else). > > So where is your problem? > My problem is that the semantics of the signature that the mailing list applies shouldn't depend on whether the original author happens to be in the same domain as the list. > >> ... Another option would be for the mailing >> list manager not to sign this message, which means it needs to do a >> special case not to sign messages if they're from the same domain and >> lack an Author Signature. This is certainly possible, but would be more >> challenging if the MTA manages many domains. I also think it's the >> wrong place to solve the problem. >> > > Why should that be? It is either signed by the mailing list manager, or it > is signed by the outgoing gateway to the Big Wide World, or maybe both. So > who cares? Either way, it is sufficiently well signed for it to be > acceptable everywhere. > Perhaps. Or the eventual verifier/assessor may have different criteria that it uses to evaluate messages from ADSP=all domains that don't have valid author signatures. -Jim _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html
