Are there any simple to understand and implement, but nontrivial cyphers and hash functions which are easily broken by modern cryptoanalysis methods (for example, ones listed in Wikipedia)?
Ideally it should be encryptable/decryptable/hashable using pen and paper (without computer), allow simple cracking using the methods also using pen and paper, but not trivially crackable by brute force (or at least requiring much more paper and tedious calculation if use dumb methods)?
Retired "production" cryptos look too complicated, and it's not obvious for non-specialist if they can be "downscaled" from some 64 bits to 4 bits while also preserving analysis-over-bruteforce advantage.
Maybe there are dedicated algorithms for this? Maybe some of them are specifically constructed to lead to analysis methods if one thinks about them, trying to crack?
