Signing keys for nyms

[hfinney at shell.portal.com]

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Eric Hughes writes, regarding the problem of determining whether the
key of a "nym" is valid:

> If a provider of any sort is the sole means of access to a series of
> communications, there will be the possibility of tampering.  If some
> public key must issue forth through this channel only, it is possible
> to alter the pseudonym's public key each time it is passed throught
> that channel.  Since every protocol which uses communications only
> through the server won't work, every solution needs another channel.

Eric goes on to describe a solution based on sending the key through
two different channels, with a return message via the pseudonym server
channel.  I think this is a good solution, but there is the possibility
that the evil pseudonym server could corrupt the return message so that
the nym did not find out that his key was being mangled (although other
people would find out, which may be good enough).

A more general solution is to use more than one pseudonym server.
Assuming they aren't both colluding, you can send your nym1 key to nym2,
and vice versa.  By providing two or more channels back to you as well
as out from you, you are able to detect corruption of your messages.

Eric suggested that if the pseudonym server signed the user's key, then
corruption of the key could be proven to third parties.  I'm not sure this
is the case, because it would seem that a user could falsely incriminate
a pseudonym server by claiming that he had never created the key which the
pseudonym server signed, that it was a bogus key.  I suppose reputations
would have to play a role then, in weighing the credibility of the pseudonym
server against that of the nym.

Hal
hfinney at shell.portal.com

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