Take the 2-minute tour ×  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.  share|improve
this question What should we assume about the mathematical
background of the readers? Believably real cryptography (even
solved problems which are totally crackable) often involves at
basic number theory and abstract algebra. –  Alexander Nikolas
Gruber Feb 23 '13 at 23:13 Sorry, background should be assumed
to be typical intermediate software engineer. Some exposure to
basic number theory