what fields to hash with hashcash (Re: A Trial Balloon to Ban Email?)

[Adam Back]

Well there are different things you could hash.  This simplest is just
to hash the recipient address and the current time (to a day
resolution).

The recipient looks at the token and knows it is addressed to him
because it's his address.  He stores it in his double spend database
and won't accept the same token twice.

After the validity period of a token has expired he can remove it from
his double-psend database to avoid the database growing indefinately.
(He can reject out-of-date mail based purely on it's date).

Hashing the message body is generally a bad idea because of minor
transformations that happen as mail traverses MTAs and gateways.

In fact I don't see a need to hash anything else if you're happy
keeping a double-spend database.

Adam

On Mon, May 12, 2003 at 11:52:57PM -0500, Roy M.Silvernail wrote:
> On Monday 12 May 2003 07:09 pm, Joseph Ashwood wrote:
> 
> > That one's easy. Use a problem that is not in P but is in NP. To make it
> > clearer to most people, use a problem that can be verified cheaply, but
> > that can't be solved cheaply. 
> 
> Please permit me to join the dense crowd.  Now that I've proved my labor, how 
> do I attach the proof to the email?  Obviously, some parts of the message are 
> added to a hash, but which parts? If it's the body, is whitespace damage 
> still an issue?