[3920] in cryptography@c2.net mail archive
[Ed Gerck ] Unicity, DES unicity, open trust and "open-keys"
daemon@ATHENA.MIT.EDU (Perry E. Metzger)
Thu Jan 7 14:29:11 1999
To: cryptography@c2.net
Reply-To: perry@piermont.com
From: "Perry E. Metzger" <perry@piermont.com>
Date: 06 Jan 1999 16:30:36 -0500
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Date: Wed, 6 Jan 1999 17:26:36 -0200 (EDT)
From: Ed Gerck <egerck@mcg.org.br>
To: "Perry E. Metzger" <perry@piermont.com>
Subject: Unicity, DES unicity, open trust and "open-keys"
Message-ID: <Pine.LNX.4.02.9901061724330.7588-100000@laser.cps.softex.br>
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Perry:
Would you so kind as to fwd this message and not the other one? This
is better ... and shorter ;-)
Thanks, Ed
-----------------------
List:
[ Complete text at http://www.mcg.org.br/unicity.txt ]
This exposition initially revisits the concept of "unicity" and shows
that key-length is not the most important parameter to evaluate the
security of cryptographic systems, discussing possible weaknessess in
current systems and alternatives as well.
Applying the concepts developed, the paper shows that DES English
messages can be brute-force attacked over a plaintext space of only 3
characters -- instead of the currently assumed limit of 20
characters. It also shows that the low-end limit of security/key-bit
is occupied by DES. This result immediately impacts the assumed
security of SSL, S/MIME and other protocols that use DES. It further
shows that re-keying is not of very much use under DES, even if done
out-of-band, since one would have to re-key after every two
characters of text.
The exposition also advances other topics to motivate discussion of
higher-security cipher systems, even when short key-lengths need to
be used. Specially, concrete examples show the usefulness of "open
trust" (i.e., open-keys) to increase security -- in addition to the
currently exclusive use of "closed trust" (i.e., secret-keys). Since
open-keys are public, the concept may afford a way to increase
security even within imposed secret-key key-length limitations.
By allowing the secure use of smaller secret-keys, the open-key
concept can have other applications, such as in smart-cards, digital
signatures, authentication, non-repudiation, etc.
Comments are welcome.
Cheers,
Ed Gerck
______________________________________________________________________
Dr.rer.nat. E. Gerck egerck@mcg.org.br
http://novaware.com.br
--- Meta-Certificate Group member -- http://www.mcg.org.br ---
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