Re: Novel use of Usenet and remailers to mailbomb from luzskru@cpcnet.com

At 18:22 1/12/96, Alan Bostick wrote:
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>
>If "digital postage" is ever implemented, this sort of
>distributed-origin mailbomb-through-a-remailer would be stopped
>immediately.  All the messages that the horny net geeks send would
>necessarily contain the same postage stamp, and the remailer would
>notice this right away -- and throw away messages containing the used
>postage stamp.
>
>One more motivation for e$-like digital postage for remailers.

I am not sure that postage would solve this problem. The geeks would
individually pay for it. Still, nominal postage would solve a lot of the
problems that plague remailnet.


-- Lucky Green <mailto:shamrock@netcom.com>
   PGP encrypted mail preferred.

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People asked in earlier in this thread how remailers could issue digital
postage stamps without being able to know who is using which stamp issued.

One obvious approach is to use blind signatures.  Rather than issuing
a stamp to the user who requests/purchases it, the user could send
an unsigned stamp, encrypted in an RSA envelope, to the remailer.  The
remailer would then blind-sign the envelope and return it to the user.
The user then decrypts the envelope and has a stamp ready for use.

At the time of use, the remailer checks the signature.  If it is valid,
it checks to see if the stamp has been used before.  If so, it forwards
the message to /dev/null; if not, it records the stamp (or perhaps a
hash of the stamp) in its database.

How does the remailer know that it is signing a stamp rather than (say)
money orders, or a confession of sending kiddy porn over the net?  The
textbook answer is to use a cut-and-choose protocol -- which requires
some subsequent communication with the user.  But I'm not convinced that
this is necessary. If the remailer's postage key is used only for
postage and known to be used only for postage, then tricking it into
signing something else would have the same significance as "signing" a
paper check with the Pitney-Bowes postage meter.

I'm assuming that the postage stamp would look something like:

- -----BEGIN POSTAGE STAMP-----

Kibo's remailer <remailer@happy.net> 3FA610092DB3FE12554AE98F66705601

- -----END POSTAGE STAMP-----

where the random bits are generated by the user prior to submission to
the remailer.  (Actually its appearance would be
implementation-dependent, of course.)

This is all cryptology 101, of course, but hey, it's a start.

- -- 
   Alan Bostick             | He played the king as if afraid someone else 
Seeking opportunity to      | would play the ace.
develop multimedia content. |      John Mason Brown, drama critic
Finger abostick@netcom.com for more info and PGP public key

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Alan Bostick wrote:

| People asked in earlier in this thread how remailers could issue digital
| postage stamps without being able to know who is using which stamp issued.
| 
| One obvious approach is to use blind signatures.  Rather than issuing
| a stamp to the user who requests/purchases it, the user could send
| an unsigned stamp, encrypted in an RSA envelope, to the remailer.  The
| remailer would then blind-sign the envelope and return it to the user.
| The user then decrypts the envelope and has a stamp ready for use.

This is a lot of public key work for the remailer.

Take a look at Shamir's Micromint scheme, and sell coins for ecash on
the web.  Micromint coins are easy to verify, and thus could be resold
on peoples web pages.  They do have expiry dates though.

Adam


-- 
"It is seldom that liberty of any kind is lost all at once."
					               -Hume

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In article <v02120d02ad1ce02500bc@[192.0.2.1]>,
shamrock@netcom.com (Lucky Green) wrote:

> I am not sure that postage would solve this problem. The geeks would
> individually pay for it. Still, nominal postage would solve a lot of the
> problems that plague remailnet.

Maybe I'm misunderstanding how using digital postage with remailers would
work.  I was assuming that the postage stamp would be included *inside*
the encrypted envelope, that what the remailer would do on receipt of
mail would be: (a) decrypt the envelope; (b) validate the postage stamp;
and (if the stamp is valid) (c) forward the message according to the
now-decryped instructions.

Using this model, if the perpetrator doesn't include a postage stamp,
then the message is ignored.  If the perp includes a stamp, the first
horny net geek's message is relayed but subsequent ones get bounced for
invalid postage.

If the message requires external postage (remailer processing cycle is
process postage *before* decrypting envelope), then at the very least
the horny net geeks have to get their own postage stamps, putting a step
in the way of instant gratification.  What's more, doing this would
require *some* understanding of how the remailer network operates.  One
should never underestimate the degree of cluelessness present on the
net, but knowing how to use remailers makes it more likely that somebody
could recognize this as a mailbomb rather than a legitimate offer.

What's more, even external postage works to block this attack used with 
a chain of remailers, because the second remailer's stamp would have to
be provided by the perpetrator, inside the encrypted envelope sent to
the first one.

The very nature of this attack makes me wonder whether it would be
worthwhile to implement a digital postage scheme for remailers that
doesn't happen to be backed by real money.  The remailers would continue
to be free to use, and currency exchange hassles would be avoided, but
many of the benefits of abuse prevention would be in place.  So would
the infrastructure to upgrade to pay-to-play remailers at a later date.

- -- 
   Alan Bostick             | He played the king as if afraid someone else 
Seeking opportunity to      | would play the ace.
develop multimedia content. |      John Mason Brown, drama critic
Finger abostick@netcom.com for more info and PGP public key

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