[hashcash] Re: Pure Python implementation of hashcash v.1

David Mertz, Ph.D. wrote: 
On Sep 24, 2004, at 2:36 PM, Eric S. Johansson wrote:

I also check and write email on my Powerbook, with OSX and using Mail.app. Anyone know if anyone has figured out how to interface with Mail.app, it would certainly be nice to get hashcash integration there.


well, you could take my hacks on smtpd.py and the postfix stamping filter interface code and build yourself a stamping proxy. On the other hand, I have been intending to create a version of Camram that runs on client side machines and the mac is the most likely candidate.


Yeah, a proxy is a possibility. But it just seems so *fugly*! Adding a X-Hashcash: header doesn't have anything to do with the SMTP/IMAP/sendmail/whatever interface; it's just a text processing task on an email message.

well, you've just described a whole 'nother mission from God. Fix all MUA's to have a rational and consistent interface for processing messages at different points in the handling.

it's more than just a simple "plug in the header" filter. You really need to process things in background which means you have a queue and retry logic and a delivery agent etc. etc.. Without these things, you end up torturing the end-user, forcing them to wait for stamp generation to complete.

Ideally, a mailer should just be able to post-process a message before sending it (using all the network interface code already built into the mailer. Many *nix mailer let you specify an arbitrary filter for outgoing messages... but MacOSX isn't targeted this way, unfortunately (I understand novices don't want to be confused by that, but a buried preference wouldn't hurt them). Likewise, MUAs should be able to filter using an arbitrary external utility.

like I said. Mission from God project. The really annoying thing is that MUAs really aren't suited for this kind of filtering and that it is only because of the filters we're talking about here is there any need. Therefore, maybe a side project should be creating this kind of filter interface in Thunderbird. If anyone has any contacts in Eudora land, see if one could get them to put the same interface there.

FWIW, I will write a utility 'add_hashcash_stamps.py' that will simply take an rfc2822 message on STDIN, and write one with added headers on STDOUT. I reckon this utility will optionally use an external compiled minter (e.g. hashcash.exe) for speed, but use my hashcash.py if one is not available. Not sure the best way to configure the name/switches of the external tool, but I'll decide on something. 

simple modification to my hashcash module.

I guess while I'm at it, I might also do 'check_hashcash_stamp.py' that takes an rfc2822. This is a little tricker in a way though. How do you know whether a resource in an X-Hashcash: header is one you want to accept? For example, I use many different email addresses within my 'gnosis.cx' domain (for various contacts). In principle, I might accept a stamp with any of these resources, since I'll accept email to any of the addresses. But there are actually infinitely many resources I might accept inside a stamp (subject to it really having the right bits, date, etc). Then again, I don't want to accept just any resource... for example, what if a spammer CC:'s herself, and produces a valid stamp only for her own email address?

solved that problem in Camram as well. I force the user to enumerate all valid e-mail addresses and I iterate over the list of valid e-mail addresses whenever I find a stamp in a message. Again, check the hashcash module.

it would just take a simple wrapper to make them command line friendly.

---eric

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