Shift Ciphers

Shift Ciphers gem is simple, yet complete, implementation of Caesar and Vigenère ciphers.

Installation

gem install shift_ciphers

Basic usage

require 'shift_ciphers'

plaintext = "Attack at dawn!"

encrypted = ShiftCiphers::Caesar.encrypt(plaintext, offset: 5)
decrypted = ShiftCiphers::Caesar.decrypt(encrypted, offset: 5)
decrypted == plaintext  # Should be true

encrypted = ShiftCiphers::Vigenere.encrypt(plaintext, "my keyword")
decrypted = ShiftCiphers::Vigenere.decrypt(encrypted, "my keyword")
decrypted == plaintext  # Should be true

... or instantiate cipher, and benefit from stored configuration info (e.g. offset for Caesar cipher, or key for Vigenère cipher):

caesar = ShiftCiphers::Caesar.new
caesar.offset = 5
encrypted = caesar.encrypt(plaintext)
decrypted = caesar.decrypt(encrypted)
decrypted == plaintext  # Should be true

vigenere = ShiftCiphers::Vigenere.new("my keyword")
encrypted = vigenere.encrypt(plaintext)
decrypted = vigenere.decrypt(encrypted)
decrypted == plaintext  # Should be true

You can customize alphabet used by cipher:

plaintext = "ATTACKATDAWN"
encrypted = ShiftCiphers::Vigenere.encrypt(plaintext, "KEYWORD", alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
decrypted = ShiftCiphers::Vigenere.decrypt(encrypted, "KEYWORD", alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
decrypted == plaintext  # Should be true

When you attempt to encrypt a string, which contains character that is not in the cipher's alphabet, then ShiftCiphers::CipherError is rised:

plaintext = "ATTACK!"
encrypted = ShiftCiphers::Vigenere.encrypt(plaintext, "KEYWORD", alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
# Raises ShiftCiphers::CipherError: Invalid input "ATTACK!". Character "!" is not in the alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

You can avoid this exception by telling cipher to not encrypt characters which are not in its alphabet. This is done by passing nonalphabet_char_strategy argument to encrypt/decrypt class method (or by using nonalphabet_char_strategy= instance method):

plaintext = "ATTACK AT DAWN!"
encrypted = ShiftCiphers::Vigenere.encrypt(plaintext, "KEYWORD", alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ", nonalphabet_char_strategy: :dont_encrypt)
decrypted = ShiftCiphers::Vigenere.decrypt(encrypted, "KEYWORD", alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ", nonalphabet_char_strategy: :dont_encrypt)
puts plaintext  # => ATTACK AT DAWN!
puts encrypted  # => KXRWQB DD HYSB!
decrypted == plaintext  # Should be true