Modified caesar shift

encryptio.rb

Alphabet = Struct.new :chars do
	def [] v
		case v
		when Fixnum
			chars[v]
		when String
			chars.index v
		end
	end
end

Alphabet::UTF8 = Alphabet.new (0...256).map(&:chr).join("")
alphabet = Alphabet.new "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890.!?,;'\"()- \n"

def encode str, alphabet: Alphabet::UTF8, fixed_key: 0, variable_key: 0
	str
		.split("")
		.map(&alphabet.method(:[]))
		.each_with_index
		.map { |v, i| v + fixed_key + (i * variable_key) }
		.join(",")
end

def decode str, alphabet: Alphabet::UTF8, fixed_key: 0, variable_key: 0
	str
		.split(",")
		.map(&:to_i)
		.each_with_index
		.map { |v, i| v - fixed_key - (i * variable_key) }
		.map(&alphabet.method(:[]))
		.join("")
end

fixed_key = 0
variable_key = 1

encoded = encode("The quick brown fox jumped over the lazy dog.", fixed_key: fixed_key, variable_key: variable_key, alphabet: alphabet)

ap encoded
ap decode(encoded, fixed_key: fixed_key, variable_key: variable_key, alphabet: alphabet)