cipher.rb

# Some very simple 'encryption' operations.
# Just for some dumb obsfucation.
class Cipher
	def initialize(shuffled)
		normal = ('a'..'z').to_a + ('A'..'Z').to_a + ('0'..'9').to_a + [' ']
		@map = normal.zip(shuffled).inject(:encrypt => {} , :decrypt => {}) do |hash,(a,b)|
			hash[:encrypt][a] = b
			hash[:decrypt][b] = a
			hash
		end
	end

	def encrypt(str)
		str.split(//).map { |char| @map[:encrypt][char] }.join
	end

	def decrypt(str)
		str.split(//).map { |char| @map[:decrypt][char] }.join
	end

end

generate.rb

require_relative './trie'
require_relative './cipher'
t = Trie.new
t.push("rbc4pr050n1y", "this isnt the flag")
t.push("m4tz i5 my h3r0", "neither is this")
t.push("d1dy0u r4d4r3 y0ur ruby?", "nope lots of fake flags")
t.push("b3c4u5e 17 uses llvm th15 me4nz sp33d", "wow not this either")
t.push("d1d y0u tr13 be1ng m04r 2337?", "good boy this is the flag")
t.push("d1d y0u kn0w tr13d n07 b31n6 a n00b?", "lole n1c3 try")
t.push("rbx 1z e4zy 2 r34d", "1 c4n r34d th15 ju57 l1k3 x86 0r 3n6L15h!")
t.push("d1d y0u h4xd 17 y3t", "stop being such a n00b and get the flag")
t.push("python is for noobs", "not the flag but a true statement ;)")

m = Marshal.dump(t)
File.open('trie.dump', 'w') {|f| f.write(m) }

trie.rb

# a simple prefix tree data structure
require './cipher'

class Trie
	def push_recursive(node, string, index, value)
		char = string[index]
		node = Node.new(char, value) if node.nil?
		if (char < node.char)
			node.left = push_recursive(node.left, string, index, value)
		elsif (char > node.char)
			node.right = push_recursive(node.right, string, index, value)
		elsif (index < string.length - 1)
			node.mid = push_recursive(node.mid, string, index + 1, value)
		else
			node.end = true
			node.value = value
		end
		return node
	end

	def get_recursive(node, string, index)
		return nil if node.nil?
		char = string[index]
		if (char < node.char)
			return get_recursive(node.left, string, index)
		elsif (char > node.char)
			return get_recursive(node.right, string, index)
		elsif (index < string.length - 1)
			return get_recursive(node.mid, string, index + 1)
		else
			if node.last?
				return [node.char, node.value]
			else
				return nil
			end
		end
	end
	def initialize
		@root = nil
	end

	def push(key, value)
		cipher = Cipher.new ["K", "D", "w", "X", "H", "3", "e", "1", "S", "B", "g", "a", "y", "v", "I", "6", "u", "W", "C", "0", "9", "b", "z", "T", "A", "q", "U", "4", "O", "o", "E", "N", "r", "n", "m", "d", "k", "x", "P", "t", "R", "s", "J", "L", "f", "h", "Z", "j", "Y", "5", "7", "l", "p", "c", "2", "8", "M", "V", "G", "i", " ", "Q", "F"]
		key = cipher.encrypt key.to_s
		return nil if key.empty?
		@root = push_recursive(@root, key, 0, value)
		return value
	end
	alias_method :[]=, :push

	def has_key?(key)
		key = key.to_s
		return false if key.empty?
		nope = get_recursive(@root, key, 0).nil?
		return !nope
	end

	def get(key)
		cipher = Cipher.new ["K", "D", "w", "X", "H", "3", "e", "1", "S", "B", "g", "a", "y", "v", "I", "6", "u", "W", "C", "0", "9", "b", "z", "T", "A", "q", "U", "4", "O", "o", "E", "N", "r", "n", "m", "d", "k", "x", "P", "t", "R", "s", "J", "L", "f", "h", "Z", "j", "Y", "5", "7", "l", "p", "c", "2", "8", "M", "V", "G", "i", " ", "Q", "F"]
		key = cipher.encrypt key.to_s
		return nil if key.empty?
		node = get_recursive(@root, key, 0)
		if node != nil
			return node.last
		else
			return nil
		end
		alias_method :[],:get
	end

	class Node
		attr_accessor :left, :mid, :right, :char, :value, :end

		def initialize(char, value)
			@char = char
			@value = value
			@left = @mid = @right = nil
			@end = false
		end

		def last?
			return @end == true
		end
	end
end

trie_harder.rb

require_relative './trie'
require_relative './cipher'

puts "            [*] Greetings to all of the eiltes here [*]"
puts "--- I heard you guys all hate ruby, so I have decided to be nice---"
puts "            --- enjoy this great bytecode instead! ---"
puts ""
puts ""
print "So, you can tell me now... what's the flag? "
flag = gets.chomp
dumped = File.read('trie.dump')
t = Marshal.load dumped
res = t.get(flag)
if not res.nil?
	puts res
else
	puts "nop"
end