[147067] in cryptography@c2.net mail archive
Re: [Cryptography] Impossible trapdoor systems (was Re: Opening
daemon@ATHENA.MIT.EDU (Ray Dillinger)
Thu Sep 12 10:37:19 2013
X-Original-To: cryptography@metzdowd.com
Date: Wed, 11 Sep 2013 20:37:03 -0700
From: Ray Dillinger <bear@sonic.net>
To: "Perry E. Metzger" <perry@piermont.com>
In-Reply-To: <20130908144953.63f7f313@jabberwock.cb.piermont.com>
Cc: cryptography@metzdowd.com
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
On 09/08/2013 11:49 AM, Perry E. Metzger wrote:
> That said, your hypothetical seems much like "imagine that you can
> float by the power of your mind alone". The construction of such a
> cipher with a single master key that operates just like any other key
> seems nearly impossible, and that should be obvious.
True. A universal key that uses the same decryption operation as
a normal key is clearly stupid.
I guess the thing I was thinking of is that the "attacker" knows
a method that allows him to decrypt anything if he knows the IV,
but cannot recover the key used to encrypt it.
Which is of course a public-key system, where the decryption
method is the "private" key and the IV is the "public" key.
The thing I was thinking of as a "key" functions as a "nonce"
or subkey which allows people unrelated to the private key
holder to communicate semi-privately by shared secret, but
the private key is a backdoor on their communication.
Duh. Sorry, just wasn't thinking of the right "parallel mapping"
of what I described. For the cipher itself to function as a key
sort of escaped my attention.
Sorry to waste time.
Ray.
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