Completed File Crypt Program

# Code from this video : https://www.youtube.com/watch?v=RqbtV4cURI0
module CR
    def self.encrypt(x,key)
        result = ""
        srand(((954938*key)%0xFFFFFF)+2)
        x.each_byte{|y|
            result << ((y+rand(444)+3)%256).chr
        }
        return result
    end
    def self.decrypt(x,key)
        result = ""
        srand(((954938*key)%0xFFFFFF)+2)
        x.each_byte{|y|
            result << ((y-rand(444)-3)%256).chr
        }
        return result
    end
    def self.encrypt_file(x,y,k)
        file = File.open(x,'rb')
        data = file.read
        file.close
        file = File.open(y,'wb')
        file.write(CR.encrypt(data,k))
        file.close
    end
    def self.decrypt_file(x,y,k)
        file = File.open(x,'rb')
        data = file.read
        file.close
        file = File.open(y,'wb')
        file.write(CR.decrypt(data,k))
        file.close
    end
end

begin
print "Podaj metode :\n0-szyfruj\n1-deszyfruj\n"
mode = gets.chomp!.to_i
print "Podaj plik do szyfrowania :\n"
filename = gets.chomp.to_s
print "Podaj plik docelowy :\n"
dest = gets.chomp.to_s
print "Podaj klucz :\n"
key = gets.chomp.to_i
case mode
    when 0 then CR.encrypt_file(filename,dest,key);print "\nSzyfrowanie pomyslne.";$stdin.gets
    when 1 then CR.decrypt_file(filename,dest,key);print "\nDeszyfrowanie pomyslne.";$stdin.gets
    else
        print "Zly tryb"
end
rescue => e
    print "Wystapil blad : #{e}\n"
    print "Nacisnij ENTER by wyjsc\n"
    $stdin.gets
end