From: Anonymous <nobody@REPLAY.COM>
Date: Sat, 11 Oct 1997 11:05:44 +0800
To: cypherpunks@cyberpass.net
Subject: Re: do NOT escrow communications keys
Message-ID: <199710110255.EAA03590@basement.replay.com>
MIME-Version: 1.0
Content-Type: text/plain



> > There may be patents on these technologies, too.
>
> Don't think so.  It's simple enough technology.

Take a look at 5493614 : Private signature and proof systems

INVENTORS: Chaum; David, Sherman Oaks, CA 91403
ISSUED: Feb. 20, 1996
FILED: May 3 , 1994

ABSTRACT:   Cryptographic methods and apparatus for forming (102) and
verifying (103) private signatures and proofs (203,204, 207, and 209)
are disclosed. Such a signature convinces the intended recipient that it
is a valid undeniable or designated-confirmer signature. And such a proof
convinces the intended recipient, just as any cryptographic proof. Even
though the signatures and proofs are convincing to the intended recipient,
they are not convincing to others who may obtain them. Unlike previously
known techniques for convincing without transferring the ability to
convince others, those disclosed here do not require interaction--a
signature or proof can simply be sent as a single message. Because
the intended recipient can forge the signatures and proofs, they are
not convincing to others; but since only the intended recipient can
forge them, they are convincing to the intended recipient. Exemplary
embodiments use a cryptographic challenge value that is said to pivot on
a trap-door function, in that the value can be manipulated by those with
the corresponding trap-door information, and is believed impractical to
manipulate without it.