[hashcash] new format tweak coming...

Hi

I'm thinking that we need one more tweak to the hashcash format to
make it extensible -- a format change to end all format changes, and
allow people to add their extensions and have the extension
information cryptographically linked to the hashcash.

The current format is:

version:date:resource:random

(the resource is the email address, but in other contexts could be
URL, web site hostname, IP address, IRC nickname etc)

the new format will be:

version:date:resource:[extension]:random

a where the extension is optional.

the suprising things or gotchas are that (a) the resource can contain
':' char.  The rule is: the version and date are : separated from the
left, the random and extension are : separated from the right, and the
bit in the middle is the resource name.

The extension format will be something like:

name1=val1,val2;name2=val3 

etc name, value pairs with values being, separated list; name-value
pairs separated by ;s.

But you can ignore them if you're not using any extensions, I just
want an extensible format to allow developers to design and use their
own extensions.

This could be eg a camram public signing key, hmac based thing, or
perhaps might help tmda authenticate it's whitelist or something, last
bit speculation... don't know enough about tmda, but you get the idea)

I don't think it's worth a format number change as it's very similar
(and actually compatible with pre 0.14, post 0.14 I introduced allowed
: delimeter inside the resource) and current user base is small.

Adam

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