Re: public key BATV isn't useful

Dave Crocker wrote:
> Paul Smith wrote:
> > Tony Hansen wrote:
> > > Paul, The original idea behind BATV was so that 1) the original 
> > > sending MTA can protect itself such that 2) non-delivery reports for 
> > > messages originally sent from there can be differentiated from 3) 
> > > non-delivery reports that are being sent in response to messages 
> > > *not* originating from that sending MTA. That is, NDRs from your 
> > > users (#2) will come back using your BATV tagging, whereas NDRs from 
> > > spammers (#3) will come back without using your BATV tagging, and 
> > > your system (#1) can happily ignore the #3 NDRs.
> > Ah. I think I seem my problem... I looked at the BATV spec as a 
> > newcomer to BATV rather than someone who had known about it for ages...
> > The BATV introduction is misleading. It doesn't mention anything 
> > about the reasoning behind BATV that you state, 
>
> #2 and #3, above, are two types of bounce messages that are invalid, 
> because they result from unauthorized creation of the bounce address 
> (MailFrom).  The Introduction says:
>      "existing Internet mail permits unauthorized use of addresses in 
> the MailFrom command, which results in having notices sent to 
> unwitting and unwilling recipients."
> which seems to state exactly that condition, and:
No. To me, that is still talking about people SENDING notices to 
unwitting and unwilling recipients. Note that it says that the 
unauthorised use results in notices being *SENT* to unwitting and 
unwilling recipients. So, I read BATV as being a solution to prevent 
these notices being *SENT*.
Nowhere does it say anything about BATV being checked by the *recipient* 
MTA of the bounce messages.
>      "Bounce Address Tag Validation (BATV) defines a framework for 
> mechanisms that validate the value in this command."
> says that BATV seeks to remedy that problem.
Again, to me, that looks like it's a framework for use by the SENDER of 
the notices.
As I said, I think my problem is that I'm looking at this as someone who 
knows nothing about BATV, rather than someone who has known about it all 
along.
> How should the Introduction be different?
Just words along the lines of those that you used would help.

Eg, something like "BATV is intended primarily to be used by the MTA 
receiving a bounce message to determine whether the bounce message is in 
response to a message sent by an authorised sender for that domain. It 
will allow the MTA receiving the bounce message to discard bounce 
messages due to blowback/back-scatter from messages using forged return 
path addresses"
Some examples of use would also be useful.

eg

"An MTA receiving a bounce message like:

MAIL FROM:<>
RCPT TO:<private-key-tagged-localpart(_at_)domain>
DATA
...bounce message...

could accept the message, where as an MTA receiving a bounce message like:

MAIL FROM:<>
RCPT TO:<untagged-localpart(_at_)domain>
DATA
...bounce message...

could decide to reject the bounce message as it doesn't appear to have 
been in response to an authorised message sent from this domain"

> and the introduction says
> > things like "This assessment could aid in deciding whether to *send* 
> > a bounce message, thereby reducing the Internet mail infrastructure 
> > cost for transmitting notification messages in response to addresses 
> > used without permission." (emphasis mine) - thus implying that the 
> > thing sending the bounce message (ie NOT your own server - that 
> > should already know that the address was used legitimately) is the 
> > thing checking the BATV tags. To do that, you MUST have public key 
> > BATV tagging, private key tagging doesn't make sense.
> Right.  And since the sentence before the one you cite says:
>
>      "Enhancements would permit processing agents that are along the 
> original message's transfer path to determine whether the MailFrom 
> adress is likely to be valid.",
> it is meant to be clear that this portion of the discussion is 
> referring to something beyond the current specification.  So I'm not 
> sure I understand your concern.
Because that's the ONLY thing in the introduction (AFAICS) which states 
how BATV could be used... I did initially read it as 'this is something 
for the future', but when I looked for 'something for now', I couldn't 
find anything, so I assumed I'd misunderstood, and the above was 
actually for now as well.
> > So, I think the introduction needs to have something in it about the 
> > rationale, reasoning and purpose behind BATV, as I obviously 
> > misunderstood it, and even though I've now had my mistake explained 
> > to me, I still can't see anything in the spec which explains it...
> I do not understand what it should say that it does not already say.  
> Please offer suggested text.
It doesn't say ANYTHING about how BATV could/should be used in its 
current state (AFAICS). See above for the sort of thing I think should 
be there.
--
Paul Smith

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