Bad/Crackable Encryption Example? I've been tasked with building up some security exercises (basic CTF training kind of stuff) for work. This should contain a bit of crypto, but my knowledge in this space has been limited to using the right tools, not trying to roll my own, etc, so coming up with an example of bad crypto, but believably real, has been tough.

Specifically one of the flags would be encrypted, say a simple sentence, in a way that would be crackable, allowing for recovery of the plaintext with a bit of know how and some burned cpu.

Could someone point me to an example like that?

Thanks for any input.
Start with the Caesar Cipher.  It is important to know the flaws and important for students to know the history of it.  It would be quite easy to break considering the background of the learners.  You probably want to include the algorithm as well as the cipertext.

From here you can build more advanced problems since they have the basic understanding of what's going on. 


LM Hash
Small Keys
WEP


Simple problems, but we must crawl before we can walk.