02 / ROTATE THE ALPHABET

ROT13 replaces A with N, B with O, and so on. Applying it twice returns the
original letters. Our signal has nine letters:

  nsgretybj

Let the shell turn the dial:
  printf '%s\n' nsgretybj | tr 'A-Za-z' 'N-ZA-Mn-za-m'

Use the decoded word when sudo asks for guest's password. Password input is
hidden in a Unix terminal; the lack of dots or stars is normal.

  sudo su

Want the answer directly? cat ~/clues/03-open-door.txt