Re: Opportunistic signatures - a proposed design

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On Sun, 29 Aug 2004, Eric S. Johansson wrote:
> Atom 'Smasher' wrote:
>> 
>> let's say i send an email to my mom, and her MUA recognizes a pgp email 
>> header on my signed email. whether the mail was signed manually or 
>> automatically doesn't matter, here. anyway, her MUA informs her:
>>     This email includes key information for "Atom Smasher". Would
>>     you like to accept all emails signed by "Atom Smasher"?
>> 
>> that's all it takes. then her MUA creates a key-pair for her, and 
>> automatically signs outgoing messages... same thing happens when 
>> someone gets a message form her.
>
> OK, I'll argue that you do not even need to see that message in the 
> first place.  Why not have her MUA look at recent traffic and say "she 
> has sent e-mail to atom smasher three times.  I've seen the same key 
> from atom with a stamp three times.  Therefore, let's assume any 
> signatures created by this key is equivalent to a stamp made by atom. no 
> need to bother mom.  She has more important things to do."
>
> seriously, the whole notification accept request messages would only 
> serve to confuse and not enlightened.  This is not to say you should not 
> keep track of all of this information and making available on user 
> requests but there's no need to throw in their face.  Remember that 
> users hate pop-ups of all forms whether they be from Web browsers or 
> from alert boxes in the application.
================

hhmmm... let the dancing paperclip dude handle it behind the scenes... i 
guess that would be fine for >90% of users....


>> so, the obvious weakness in automatically signing emails is that 
>> viruses will steal the key (large keys don't help), and then use it to 
>> send mail to everyone in that user's address book.
>
> just as much as they can steal cycles from a users machine (100 
> addresses is not that much) and send hashcash stamped messages to 
> everyone in your address book.
=================

well, if a signing key is used against everyone in the address book...
   1) the virus/spammer can send a LOT of spam (to those users) before 
being detected and
   2) every now and again, it will find HUGE address books (aka mailing 
lists).

re example #1, let's say my mom's computer gets infected, and at 3am the 
virus starts sending out mail to everyone in the address book... i come 
into the office at 9am and have a few hundred spams (signed by her) trying 
to sell me things that i would have rather never heard of. that barrage 
could actually be *worse* than the handful of spams that typically get 
past a filter.

hashcash, however, would force the virus/spammer to mint a stamp for EVERY 
email that's sent out... slowing down the computer and making it more 
likely that the virus/spammer will be discovered (and maybe even removed).


>> as an end user, do i benefit more from hashcash or signatures? i 
>> ~think~ hashcash is, overall, better. as a bank whose customers are 
>> targeted in phishing scams, do i benefit more from hashcash or 
>> signatures? i can protect myself much better if a PKI allowed customers 
>> to quickly identify if an email is *really* from me... domain-keys and 
>> SPF will both help with the problem of forgeries.
>
> hashcash is an introducer.  Opportunistic signatures allow for efficient 
> distribution of mail to people who agreed to know each other 
> (individuals and mailing lists).  you can never really know if e-mail is 
> "really" from you. They're too many ways for the identity process to be 
> corrupted even if you meet the person face-to-face with appropriate 
> documentation.  You have no of knowing it's truly accurate.  You need to 
> understand where false information can be injected into the system and 
> if you can corrupt human processes long before you ever go digital, then 
> there is no hope.  All you can do is trust people based on repeated 
> exposure.
=================

both technologies have their strengths and weaknesses... it will come down 
to what becomes widely implemented, and what proves easily defeated. if a 
PKI proves too easy to break, because it's being used on insecure systems, 
then hashcash gains credibility... OTOH if a method of quickly finding 
SHA-1 collisions is found, hashcash can either implement a stronger hash 
function or hashcash users can require more valuable stamps... only one 
thing is certain: the more widely any technology is used, the more effort 
will be put into attacking it.



         ...atom

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