Text 7695, 51 rader
Skriven 2010-05-10 19:07:50 av Robert Bashe (2:2448/44)
   Kommentar till text 7686 av Ward Dossche (2:292/854)
Ärende: Cryptology (was: No blanket right for press to protect sources)
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Ward Dossche wrote to Robert Bashe on Monday May 10 2010 at 13:21:

RB>> But _no_ cypher is "unbreakable", given enough resources and time -
RB>> and considering the advances in computer technology that are made
RB>> year for year.

WD> That only works if that cypher is used repeatedly and there is enough
WD> to work from.

No, it depends on the method, as I mentioned in my earlier message.

WD> What the USSR did was encrypt the messages using a very short
WD> algorithm that changed with every message. Such messages were mostly
WD> short and already coded to begin with so there is no material to work
WD> with even for the most powerful number-cruncher available.

I also pointed out the weakness of this method in my other method. One-time pad
cyphers must be transmitted to the receiver at some point, and such
transmission can never be totally secure.

WD> It's not as if they were sending "Pride and Prejudice" in one stream
WD> of data, because such amounts indeed are breakable, there's enough
WD> material embedded.

That's not even necessary, Ward. Read some more about cryptography and you'll
find that there are various ways of attacking encrypted messages. The easiest
is to clandestinely break into the sender's office or home and examine his
computer or copy the hard disk - that's much easier than trying to break a
cypher.

Public key encryption is very good with long keys, but nowadays can be broken
if the keys are too short - and doesn't have the disadvantage that the private
key must be transmitted to the receiver through a secure channel.

Anything that has to be transmitted, though, can be intercepted. That's a weak
point.

As for the case you cited, it appears that the Soviets simply didn't use the
system properly. If the had, and if the key had not been intercepted, the code
would have been secure.

The whole subject of cryptology is fascinating, and Phil Zimmermann (the author
of PGP - an open-source public key enryption method - has written extensively
on this:

http://www.philzimmermann.com/EN/background/index.html

Cheers, Bob

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