Problem Set 4

Caesar Cipher and Substitution Cipher with OOP

A recursive permutation generator connected to two encryption systems built with OOP. Demonstrates class inheritance and composing components across files.

Implementation

Part A — Recursive Permutations (ps4a.py)

• get_insertions(letter, permutations) — inserts a letter at every position in every string in a list
• get_permutations(sequence) — base case returns a single-character string; recursive case inserts the first character into all permutations of the remaining characters

Part B — Caesar Cipher (ps4b.py)

• Message — base class with build_shift_dict() (creates a shift mapping for all 26 letters, preserving case) and apply_shift() (applies the cipher)
• PlaintextMessage(Message) — stores shift value, builds encryption dict, generates encrypted text
• CiphertextMessage(Message) — decrypt_message() tries all 26 shifts and returns the one producing the most valid English words. Successfully decrypts an encrypted story file

Part C — Substitution Cipher (ps4c.py)

• SubMessage — build_transpose_dict() maps vowels according to a given permutation while consonants remain unchanged; apply_transpose() applies the mapping
• EncryptedSubMessage(SubMessage) — decrypt_message() tries all 120 vowel permutations (5! = 120, generated by get_permutations from Part A) and returns the decryption yielding the most valid English words