Cracking DES as set 9 of cryptopals [0] :) ? Awesome challenges in general, of course, but iirc no actually breaking a symmetric key cipher ("actually" doing a lot of work here, I admit, since there's all kinds of oracle attacks which are awesome!).
[0] For the uninitiated: https://cryptopals.com, which is of the parent's and collaborators' creation!
Ninja edit to add: This is all in good fun, recognizing that cryptopals focuses on real-world crypto that actually is used today!
[0] For the uninitiated: https://cryptopals.com, which is of the parent's and collaborators' creation!
Ninja edit to add: This is all in good fun, recognizing that cryptopals focuses on real-world crypto that actually is used today!