A class containing methods that can be used to run additive and subtractive one-time pad operations, both on characters and strings.

onetimepad.rb

#  These methods are all class methods. To convert to instance methods, remove the "self." portion of the method names.

#  In order to decrypt, utilize the opposite method you used to encrypt, and pass the method the encrypted text, followed by the key.

#  You can use these methods to determine the key used to encrypt if you have both the plain text and ciphertext.
#  - If an additive method was used to encrypt, call the subtractive method, passing in the ciphertext, followed by the plaintext
#  - If a subtractive method was used to encrypt, call the subtractive method, passing in the plaintext, followed by the ciphertext

class OneTimePad
  
    def self.to_num(a)
        index = ('a'..'z').to_a
        return index.index(a) + 1
    end
    
    def self.to_alpha(i)
        index = ('a'..'z').to_a
        return index[i-1] 
    end
    
    def self.char_add(p,k)
        plain = to_num(p)
        key = to_num(k)
        cipher = plain + key
        cipher %= 26
        return to_alpha(cipher)
    end
    
    def self.char_sub(p,k)
        plain = to_num(p)
        key = to_num(k)
        cipher = plain - key
        cipher %= 26
        return to_alpha(cipher)
    end
    
    def self.string_add(plain,key)
        plain = plain.chars
        key = key.chars
        cipher = ""
        plain.zip(key).each do |p,k|
            cipher += char_add(p,k)
            end
        return cipher
    end
    
    def self.string_sub(plain,key)
        plain = plain.chars
        key = key.chars
        cipher = ""
        plain.zip(key).each do |p,k|
            cipher += char_sub(p,k)
            end
        return cipher
    end
end