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TUCoPS :: Crypto :: des_prob.txt

Problems with DES encryption by Ratsnatcher




Problems with DES Encryption
by Ratsnatcher

..........................................................................

*** Quoting M. Stirner to All ***

 >   The Gov't. standard encryption scheme was proven breakable
 > before official adoption.  A guy @ Stanford busted it &
 > suggested that substitution of a 64-bit scheme would make it
 > actually unbreakable.  The NSA objected to that much
 > security.  Indeed, it is my understanding that pending
 > Federal legislation will make it illegal to transmit
 > encrypted data without a "backdoor."  It is widely believed
 > that the NSA currently has "backdoor" ability for the current
 > Gov't. encryption standard. .   ~ .   M.

Yeah... Scary stuff, yeah.  Well here's what my Tanenbaum Textbook on Computer
Networks says about the DES--which is what I think you're talking about.

..........................................................................

The DES Controversy

        Before leaving the subject of DES, it is worthwhile pointing out
that this cipher has been surrounded by controversy since its inception
(Branstad, 1979; et al., 1977; Davida, 1979; Diffie and Hellmen, 1976b, 1977;
[bunch of other refs...].  A number of computer scientists have made the claim
that 56 bits is too small a key size, that is, the cipher is too vulnerable to
attacks such as Hellman's.  The key size, in IBM's original design was 128
bits, which unquestionably eliminates any chance of an exaustive search of the
key space.  At the request of the U.S. National Security Agency, the key size
was reduced to 56 bits.  The reason the cipher was weakened has not been made
public.

        What has also bothered a number of scientists is IBM's refusal to
make public the reasons the specific S-boxes in the cipher were chosen. IBM
has said that the National Security Agency requested that it keep the design
principles secret.  Without knowing the design principles, it is difficult to
exclude the possibility that a trick exists by which the cipher can be easily
broken.  There was also an incident that some observers interpreted as an
attempt by a government employee to stifle publication of academic research
aimed at developing stronger ciphers (Shapley and Kolata, [bunch of other
refs...]).

        The net effect of a short key, secret design principles, and other
factors has led some critics (e.g., Hellmen [more refs...]) to believe that
the government might not be unhappy with a standard cipher just strong enough
to keep everyone except itself from breaking it.  To understand the
significance of these developments, you should realize that in the future,
telephones may contain microcomputers capable of digitizing and encrypting
speech, and mail may be send electronically, from home terminal to home
terminal.  If unbreakable encryption algorithms were used in these
applications, it would be impossible for governments to tap phone and
surreptitiously read mail.  As Kahn (1980) and [blaw blaw blaw...] point out,
electronic eavesdropping is currently practiced on a large scale, so technical
advances making it impossible in the future may not be viewed with great joy
in all quarters.
                                 -- Computer Networks
                                    Network Security and Privacy
                                    Andrew S. Tanenbaum
..........................................................................

Then he goes on to talk about other problems with DES, like distribution of
keys and more [blaw blaw blaw].  It gets extremely technical.

Scary stuff though... Another very interesting book about this kind of
stuff--scary stuff--is "The Rise of the Computer State" by David Burnham,
which is mostly about the uses of the NSA, CIAs, and FBIs computer resources.
Come to think of it, that's one of the scariest books I've ever read...

Spock protect us all!




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