caesar.rb

caesar.rb

def is_letter (x)
    return x.ord >= "a".ord && x.ord <= "z".ord
end

def encrypt (text, key, n, offset)
    encrypted_text = ""
    text.each_char do |x|
        if is_letter(x)
            code = (x.ord + key - offset) % n + offset
            encrypted_text += code.chr
        else
            encrypted_text += x
        end
    end
    return encrypted_text
end

def decrypt (encrypted_text, key, n, offset)
    text = ""
    encrypted_text.each_char do |y|
        if is_letter(y)
            code = (y.ord - key + n - offset) % n + offset
            text += code.chr
        else
            text += y
        end
    end
    return text
end

key = 123
offset = "a".ord
n = "z".ord - offset + 1
text = "helloz there"
encrypted_text = encrypt text, key, n, offset
puts encrypted_text
raise "fail" unless (decrypt encrypted_text, key, n, offset).eql? text