You're pre-judging your hypothetical court case rather, aren't you?
IANAL, but in the UK at least, I gather this would only be an issue with
*some* *public* services. I'm not required to provide (for instance)
wheelchair ramps at my front door.
Besides, reasonable alternative provisions might cover you (depending on
your local laws) - a multi-modal "sound or vision" puzzle perhaps.
Any successful system should allow the recipient to send back multiple
challenges and the recipient could then take their pick as to which one
they would like to solve. Thus they could have a CPU based system (penny
black), a sight based system (decode graphic), sound based system,
something for cell phones, or ..... this could even be done / offered in
multiple languages.
Thus the protocol shouldn't make life difficult for people with
disabilities. It would be up to the recipient to provide an access method
for each of the disabilities that they choose to address -- or none at
all. But that should be left to the recipient not the protocol.
Personally, I think an XML schema should be created that defines the
different challenges. The sender or sender's client could then (perhaps
automatically) select the challenge they wish to solve.
Also, the issue of keeping the challenge response system from being used as
an advertising mechanism can be easily solved by having the original
application include a "password" (which can be a random number). Then when
the challenge is sent, it can reference this password. If the challenge
does not reference the password, it is considered bogus and dropped. The
passwords can be one time only passwords so they do not run the risk of
being compromised.
-Art
--
Art Pollard
http://www.lextek.com/
Suppliers of High Performance Text Retrieval Engines.
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