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Copyright (C) 1995
Article appeared in The Expositor, Brantford, Ont., Canada
June 10th, 1995
- COMPUTER CRYPTOGRAPHY -
- PROTECTING YOUR PRIVACY -
Last week I discussed ways that the computer has
made our lives less private. Today we take up that thread and
talk about the stuff of spy novels.Cryptography, in the context
that we are discussing it, is a means of preventing
unauthorized people from reading our files or correspondence.
Cryptography is not new. It has been used throughout history
and has played its part in shaping events. Mary Queen of Scots
was beheaded because the cipher that she used to arrange a
rebellion against Elizabeth I was decoded by the government.
Julius Caesar used a primitive cipher, now known as a
Caesar Cipher, to disguise his messages to Rome during his
military campaigns. Every letter in his messages was replaced
by the letter three letters farther in the alphabet. Thus A would
become D, B would become E, until you reached the end of the
alphabet. You would then wrap around to make X equal to A,
Y equal to B and Z equal to C. In this way the word CAESAR
would become FDHVDU. Simple substitution ciphers like this
one are easily broken and today are used in puzzle books to
provide a few moments diversion to puzzle fanciers.
The role of computers in cryptography goes back to
the early days of computers. One of the first computers was
used to help decode enemy messages in England during the
second world war. The 'boffins of Bletchley' were the true
progenitors of the computer, not IBM.
Cryptography has progressed far beyond the simple
Caesar Cipher. Indeed, today's methods of encoding messages
have progressed to the point where the ciphers are unbreakable
within any reasonable amount of effort. It does no good to
break a cipher if it takes 1500 years of computer time to do it!
Of interest to computer users is the development of a
type of cryptography called Public Key Cryptography. With
this method you have two keys, a public key and a private key.
Simply speaking, a key is a very long number that is used by
your program to encode and decode messages. Each person
that you want to communicate with has a public key that is
published and is known by everyone.
To send a message to your friend you would use his
public key to encode the message. Your friend receives the
message and uses his private key to decode the message.
The beauty of this technique, is an eavesdropper can
intercept the encoded message and the public key of the
recipient, but he cannot use this information to decode the
message without the secret key of the recipient.
In older systems you had to transmit the secret key to
the recipient. The secret key could be intercepted and used to
decode the messages. Public key systems require that only the
public key be transmitted to the recipient. The message cannot
be decoded using only the public key and the message.
The availability to the general public of secure,
military grade cryptographic methods has generated
considerable controversy. The US government has placed this
software under export control and has suggested the use of
their own system called Clipper. Clipper has a 'backdoor' that
will allow the government to decode secret messages. They
claim that they need this power to combat drugs and crime.
Civil libertarians claim that the government has no business
intercepting private communications.
Cryptography can be used to protect E-Mail messages
and computer files. The software to do this is freely available
on the Internet (search for PGP). The US government, it
seems, is locking the barn door after the horses have escaped.
This file may not be reproduced by any means without the
permission of the author
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