Quantum Passwords
  A quantum password is a quantum mechanical analogue of the classical password. Our proposal is completely quantum mechanical in nature, i.e. at no point is information stored and manipulated classically. We show that, in contrast to quantum protocols that encode classical information, we are able to prevent the distribution of reusable passwords even when Alice actively cooperates with Eve. This allows us to confront and address security issues that are unavoidable in classical protocols. 
Mile Gu, Christian Weedbrook