Re: [secdir] [taugh.com-standards] Re:Security review of draft-levine-herkula-oneclick-05

["John R. Levine" <[e-mail]>]

One other thought -- I think the most common thing that mailers do is to 
put the subscriber info into a database where each record includes a 
randomly generated key unrelated to anything else.  Then you put that key 
into the URI, no HMAC needed.

R's,
John

>>> It's only a goal here because they have other ways to do it if it's not
>>> one-click.
>> 
>> Ok, then in that case it seems like you only need to secure the POST
>> arguments, not the URI.
>
> There's several scenarios that this draft is addressing:
>
> A) bad guy sends fake mail with real insecure opt-out link, MUA clicks it
> indirectly when user hits the junk button
>
> B) real message with real link is clicked by helpful anti-spam software, not 
> the user
>
> The hash stuff is for A, the POST is for B.  Since the POST gets both the URI 
> and the arguments, the hash can be in whichever is operationally easier.  All 
> the places that have rules about commercial junk mail say that if the 
> recipient tells you to stop, you have to stop and "the link was in a fake 
> message" isn't a defense. It's quite common now for the unsubscribe URI to be 
> totally opaque, e.g., with a hash and a key the mailer looks up in a database 
> to find the recipient's address, so that malicious parties can't guess other 
> subscribers' addresses.  If they add POST arguments for one-click, they'll 
> likely keep the existing opaque URI, and with the secure URI, the POST 
> arguments tell it nothing beyond the fact that this is a one-click 
> transaction.
>
> In the two decades since 2369 came out, the URI stuff has become common 
> knowledge among the narrow group of people for whom "deliverability" is an 
> adjective.  I really don't want to open up 2369 with this draft, because I 
> don't think the small amount this draft says would be helpful.  It doesn't 
> change the way people use 2369, it only adds a new way to do 
> list-unsubscribe.

Regards,
John Levine, [e-mail], Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly