Interesting series of articles on GCHQ, Public Key etc.

[Bo Elkjaer]

List:

This Is Gloucestershire has published an interesting little series of
articles commemorating the GCHQ 50 years anniversary. The articles can be
found at:

http://www.thisisgloucestershire.co.uk/displayNode.jsp?nodeId=110560&command=newModule&sourceNode=84282


Yours
Bo Elkjaer, Denmark



<QUOTE>
In 1965, James Ellis, who worked for CSG (GCHQ's codemaking department),
went back to first principles to solve the problem and dreamed up the
unthinkable. His vision was sending secret messages without the need for
exchanging a key. Suppose Alice wants to send a message to Bob. Alice
looks up Bob's "public" key and encodes her message using a standard
algorithm. Bob receives the message and decodes it using his "private" key
and another standard algorithm.

Anyone can intercept the message because the public key is widely known,
but only possession of the private key enables the decoding step.

The private key remains in Bob's possession throughout and never has to be
passed to Alice, thus guaranteeing confidentiality.

By 1967 public key cryptography had hit a brick wall. Mr Ellis was not
able to come up with a private key function to bring his theory to life.

But in September 1973 bright young Cambridge graduate Clifford Cocks
joined GCHQ. After six weeks, the puzzle was presented to Mr Cocks and
within half an hour he came up with a solution - an algorithm that made Mr
Ellis' theory a real possibility.

In 1975, these ideas were refined further by Mr Cocks' colleague Malcolm
Williamson.

Because they were employees of GCHQ, they were sworn to secrecy and their
brilliant idea was never made public.

In 1976, a trio of American academics, Diffie, Hellman and Merkle, filed a
patent for their version of public key cryptography which they developed
independently. They went on to claim the glory for developing the system.
</QUOTE>




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EOT