Cipher challenge Spring 2007

Oops! I forgot to reinstate some of these ciphers. They should all be available now.

I have reopened ciphers 3, 7, 16, 19, 24, 29, 30, 37, 38, 39, 52, 58, 60, 69, 71, 79, and 82 to give people another chance to gain some marks. Only the first solution received to each of these from now on is likely to get any marks, however!

People seem to want to know if their own ciphers have been broken. So far the ciphers which have been broken at least once are: 3, 5, 6, 7, 8, 9, 10, 15, 16, 17, 18, 19, 24, 29, 30, 31, 35, 37, 38, 39, 42, 43, 46, 52, 53, 58, 59, 60, 61, 62, 64, 69, 70, 71, 73, 79, 82, 84, 85.

I have received a complaint that some people are breaking more ciphers than they need to. Apparently, this is considered to be greedy. However, I do not want to discourage you from trying your hand at breaking more ciphers, particularly the harder ones. Therefore my policy is (and always has been) not to count your solutions in the rankings, beyond a certain point. Those of you whose solution to a particular cipher was the fourth received *may* also, at my discretion, receive some consolation marks.

I have been asked to remove 'dead' ciphers from this web-page. This I have done. If you manage to click on a dead cipher you will get the message 'undefined'.

Marking of your decryptions will not take place until after the deadline for handing in solutions. As with other courseworks, you have to make your own judgement of the quantity and quality of the work that you hand in.

So far I have received approximately 140 decryptions of 36 different ciphers. Unfortunately about 50 of these arrived too late to get any marks. There are still plenty of relatively easy ciphers out there, though, so `get cracking`!

Correction: Cipher 56 was originally truncated. Now the full text is there, so it should be easier to decrypt than before!

Ciphers 3, 5, 7, 8, 9, 10, 15, 16, 17, 18, 19, 24, 29, 30, 31, 35, 37, 38, 39, 42, 43, 46, 52, 53, 58, 59, 60, 61, 64, 69, 70, 71, 73, 79, 82 and 84 have now been broken by three people. No more marks are available for breaking these ciphers!

Correction: I accidentally copied Cipher 53 into Cipher 86. This has now been corrected. If you are working on one of these please check which one it is.

I have received a total of 85 ciphers, 63 of which I have been able to check, and in some cases correct. They have been anonymised and randomised for fairness.

I have put up the remaining ciphers without checking them, as the authors have not provided me with enough information.

You may submit solutions (by email, as a plain text file, please) to any except your own cipher. The first correct solution with a full explanation of the method of crytanalysis may receive up to 20 marks, the second up to 10 marks, and the third up to 5 marks. Subsequent solutions to the same cipher receive no marks. You may accumulate up to 20 marks on this part of the challenge.

If you use a computer program, it must be one you've written yourself, and the program must be submitted along with your solution.

Please play fair and do not help anyone else to break your own cipher. I expect to be able to spot most cases of collusion and will punish them appropriately.

I shall attempt to keep this webpage reasonably up-to-date with information on which ciphers have been broken three times, to help you not to waste time on work which will earn you no marks.

Good luck!

Select a cipher from above

Robert A. Wilson
Created 19 February 2007
Updated 8.00am 12 March 2007