Slide Attack

plaidCTF 2014 - wheeeee (crypto375)

For PlaidCTF2014, Eindbazen and fail0verflow joined forces as 0xffa, the Final Fail Alliance. Don't miss out on other write-ups at Eindbazen's site!
Crypto (375 pts)
Although it seems like The Plague's messaging service is secure, 
there are bound to be bugs in any 20th century crypto system. 
We've recovered a version of the block cipher The Plague implemented. 
Use their online encryptor tool, at, to break the 
cipher and figure out Plague's secret plans. NOTE: When the service 
sends you a hex-encoded string, respond with a hex-encoded string.