Another task to do on stream? 👀

• Refactor CLI to take fitness function at each of the 3 stages of decryption.
  • Maybe a separate binary? Since we'll want to output fitness data at various stages.
• Set up test runner to randomize a bunch of texts and store rotor/key/ring value.
• Plot performance over each combination of fitness functions.

Feeling inspired to write some more cryptanalysis code in Rust after seeing this Computerphile video and finishing reading The Code Book. This is a rough list of TODOs to organize the process, since I might feel like coding this on stream...

• Update project to build on latest stable rust (bump dependencies).
• Implement Plugboard::unplugged to get currently unused plugboard characters.
• Add ability for plugboard randomization via --randomize.
• Find import bigram/trigram data, similar to existing quadgram data.
• Create Fitness trait.
• Implement bigram and trigram fitness functions.
• Refactor quadgram code into fitness module.
• Implement index of coincidence fitness function.
• Rewrite main decryption loop (see https://github.com/mikepound/enigma/blob/main/src/com/mikepound/Main.java)
  • Uses IoC for rotor config, bigrams for ring settings, and quadgrams for plugboard breaking.
  • Should probably implement as a new method and a new CLI flag if it will be a lot slower.
• Experiment with trying different fitness functions from the above, possibly in parallel.
  • Come up with some weighted "overall fitness" function that accumulates the results of all existing ones.
• Improve decryption ergonomics to re-insert original whitespace & punctuation.
• Implement Display trait on Enigma (will want debug messages for printing the top N candidates at each step).
  • Something like Rotors: I-II-III / Key: 4-5-6 / Ring: 7-8-9 / Plug: WX YZ
  • Implement Display for Plugboard (non-trivial due to currently only storing explicit mapping in the struct).
    • Just store the explicit pairs as part of the struct; will be useful for implementing Plugboard::unplugged.
• Move setting randomization to Enigma::random() constructor.
• Add methods to Enigma to get settings from current configuration (useful to reverse-engineer key/ring for Display).
• Just return an Enigma instance from decrypt() methods.
• Find more passages for end-to-end decryption tests, seed and randomize many decryptions.
• Make test macro for fairly close decryption (>0.95%).
• Add integration tests for randomly encrypted messages.
• Update README.
• Update release notes for 0.6.0.
• Add decrypt example in docstring.
• Benchmark decryption and decryption submethods.
• Attempt to optimize parallelized loops.
• Refactor decryption into 3 explicit steps to make it easier to pass in fitness functions.

References:

• Ciphertext-only Cryptanalysis of Enigma
• https://github.com/mikepound/enigma

This might be faster as an explicit loop where the outgoing character is modulo'd off the accumulated index, the index is multiplied by 26, then the incoming character is added in.