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RE: [Asrg] Re: [Politech] Congress finally poised to vote on anti -spam bill [sp]

2003-11-21 17:21:31
We need to consider the technical workings of the do-not-spam list and the
requirements that we would like the FTC to meet.

I propose as a minimum:

1) Allow individual subscribers to list their email addresses with the
service.
2) Permit mail sender to quickly determine whether a given email is on the
list
3) Be distributable in a form that does not permit use as a mailing list.
4) Permit the storage of attributes in association with each listing,
minimally the date of subscription.

In addition we might add:

5) Allow domain name owners to list their domains.
6) Provide for authentication of listing requests


These requirements can be met using completely generic and to my knowledge
unencumbered technology. For the purposes of avoiding patent encumberabces I
disclose the following - I published note on the basic idea of using a one
way hash to conceal an email address on a do not spam list in 1995, I also
implemented the scheme at that time. The idea is not entirely novel, hash
databases have been used for at least twenty years, there may also be
similar ideas in the cryptography litterature.

My proposal would be to use a message authentication function such as
HMAC-SHA1 with a  key such as SHA1 ("FTC Do Not Spam List") to create a
unique digest function for the purpose. There is a security consideration
here, use of a digest such as SHA1(email) might lead to chosen protocol
attacks.

To add an individual email address "alice(_at_)example(_dot_)com" to the list we
calculate HMAC ("alice(_at_)example(_dot_)com") to create the key. A domain may 
be
represented by the string "example.com".

To determine whether the address "bob(_at_)example(_dot_)com" is on the list it 
is
necessary to test for both the specific email address and the domain.

[This can be made to meet arbitrarily complex requirements]


The list is distributed as a set of key/value pairs. Sorting the list
according to the key values allows rapid lookups by means of binary search,
or since the hash function is guaranteed homogenous using ranged search
using the hash value as an estimator for the index position. It is not
necessary to distribute the list sorted.

There are also a few tricks that can be used to reduce the usefulness of
such a list for address validation.

This same concept can be used to conceal the filter terms used in
cersorware.

                Phill

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