The Kish cypher is a statistical physical key exchange scheme (invented by Laszlo B. Kish) that offers information theoretic security. The offered information theoretic security is perfect in the mathematical model scheme and imperfect with practical, non-ideal building elements; see these attacks and the related responses below in the section dealing with attacks. In other words, the Kish cypher is a physical secure layer (hardware-based technique) where the conceptual security is based on the laws of classical physics (the second law of thermodynamics and Kirchhoff's laws). It should not be confused with a software-based approach called the Kish–Sethuraman (KS) cypher.
Read more about Kish Cypher: The Kish Cypher Scheme, Attacking Physical Realizations of The Kish Scheme, Privacy Amplification For The Kish Cypher, Securing Computers and Hardware By Integrating The Kish Cypher On Chips, Teleportation of Classical Bits