Cipher implementation ruby

ruby_cipher.rb

def rotx(x, string, encrypt=true)
  offset = encrypt ? x : -x
  uppers = Hash[("A".."Z").zip(("A".."Z").to_a.rotate(offset))]
  lowers = Hash[("a".."z").zip(("a".."z").to_a.rotate(offset))]
  dictionary = uppers.merge(lowers)
  output = ""
  string.length.times do |idx|
    char = string[idx]
    if dictionary[char]
      output += dictionary[char]
    else
      output += char
    end
  end
  output
end


p rotx 10, 'Hello, World'
# => "Rovvy, Gybvn"
p rotx 10, 'Rovvy, Gybvn', false
# => "Hello, World"

# Rotation numbers greater than 26 should work as well
p rotx 36, 'Hello, World'
# => "Rovvy, Gybvn"