TY - JOUR N2 - There is an ongoing debate about the fundamental security of existing quantum key exchange schemes. This debate indicates not only that there is a problem with security but also that the meanings of perfect, imperfect, conditional and unconditional (information theoretic) security in physically secure key exchange schemes are often misunderstood. It has been shown recently that the use of two pairs of resistors with enhanced Johnsonnoise and a Kirchhoff-loop ‒ i.e., a Kirchhoff-Law-Johnson-Noise (KLJN) protocol ‒ for secure key distribution leads to information theoretic security levels superior to those of today’s quantum key distribution. This issue is becoming particularly timely because of the recent full cracks of practical quantum communicators, as shown in numerous peer-reviewed publications. The KLJN system is briefly surveyed here with discussions about the essential questions such as (i) perfect and imperfect security characteristics of the key distribution, and (ii) how these two types of securities can be unconditional (or information theoretical). L1 - http://www.czasopisma.pan.pl/Content/90055/PDF/Journal10178-VolumeXX%20Issue1_01.pdf L2 - http://www.czasopisma.pan.pl/Content/90055 PY - 2013 IS - No 1 EP - 16 DO - 10.2478/mms-2013-0001 KW - information theoretic security KW - unconditional security KW - secure key exchange KW - secure key distribution KW - quantum encryption A1 - Mingesz, Robert A1 - Kish, Laszlo Bela A1 - Gingl, Zoltan A1 - Granqvist, Claes-Göran A1 - He Wen A1 - Peper, Ferdinand A1 - Eubanks, Travis A1 - Schmera, Gabor PB - Polish Academy of Sciences Committee on Metrology and Scientific Instrumentation DA - 2013 T1 - Unconditional Security by the Laws of Classical Physics SP - 3 UR - http://www.czasopisma.pan.pl/dlibra/publication/edition/90055 T2 - Metrology and Measurement Systems ER -