I'm calling it "recursive key" ciphering since the plaintext provides its
own key. So the situation could look like (all emerging ciphertext is
for illustration only, so don't take literally).
Starting key: COMET

Plaintext: SENDSUPPLIESTOMORLEYSSTATI...

Recursivekey: COMETSENDSUPPLIESTOMORLEYS...

Cipher (something like): USZHLMTCOAYHIZUSJESKGJEERA...

How about that? Brilliant, no? If each member of the class ponies up $1000 we can launch our company.

But before committing your gasoline money you may want to do just a little technical investigation to convince yourself of the soundness of this scheme. Therefore you should prepare a technical analysis of this scheme, outlining as many exploitable weaknesses and resulting attacks on this cipher as you can.

STOP PRESS: Darn! I just found out that this scheme was known in 1577. Somehow work in cryptography did not stop there....?? Well, I can't understand that myself, but maybe you can.

OK, OK, so maybe you can find some problems with my
soon-to-be-patented
recursive keying scheme. But how about **This?** I call this
little doozy the "Recursive encrypted key" cypher and it's even
more diabolically clever... BWAH-Hah-hah-hahaha!

The trick here is to use the
emerging **cipher** itself as a key! Is that devious or what?
Something like

Starting Key: COMET

Plaintext: SENDSOMEAPPLECIDERANDDONUTS...

Recursive key (given cipher...): COMETUSZHLOOOIODIUYNTQWVB...

Cipher (something like) : USZHLOOOIODIUYNTQWVB...

So analyze this idea too. Turn in to WebCT the usual nicely-written and formatted TR-style paper. Your hypothesis might be that something is wrong with this idea. References supporting or opposing your hypothesis would be good, as would your own thoughts (in a page or two) on this problem.

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*Last update: 21.8.03.*