A few weeks ago I stumbled across a thread on hacker news that referenced the Matasano Cyrpto Challenge. I find myself unable to resist this type of problem so I decided to make an attempt. It teaches you to find vulnerabilities in crypto systems by starting with simple attacks and building up to more complex ones. Early on in the project it has you start breaking ecryption that uses the AES cypher in ECB mode. It specifically asks you not to implement the cypher yourself but to use a known-correct implementation like OpenSSL.
I tend to try to solve programming challenges in python, because the coding goes much more quickly. I checked the pyOpenSSL docs (which I have used before) to determine the call for encryption in ECB mode.