Unconditional Security by the Laws of Classical Physics

Abstract

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).

Enhanced Secure Key Exchange Systems Based on the Johnson- Noise Scheme

“…The goal is to have a key exchange where either the exchange cannot be measured/recorded, or when the information measured/recorded by Eve is zero; a situation called perfect information theoretic security; or this information is practically miniscule, a situation is practically-perfect information theoretic security. If the information extracted by Eve is zero or small and, its amount does not depend on Eve's accessible resources when she is approaching the limits imposed by the laws of physics, the security is called unconditional [2,3]. In practical cases "unconditional" and "information theoretic" security are interchangeable terms [1].…”

“…Thus the security classification can be classified as perfect unconditional (perfect information theoretic), imperfect unconditional (imperfect information theoretic) or conditional, where "perfect" with practical elements can only be "practically perfect", and only simplified mathematical models of the system may offer really perfect security at the theoretical level. With other words, perfect unconditional security can only be defined at the (simplified) conceptual level in any physical system while imperfect unconditional security is the level that any real physical system can aim to reach due to the limitations posed by non-ideal elements and situations [2,3]. Perfect security is like infinity, it can be approached but never reached.…”

“…Thus, these methods offer only conditional security because, with sufficient computing power (for example by having a hypothetical quantum computer or its noise-based-logic version), the key would instantaneously be cracked by Eve. Due to the unexpected progression of computing technologies, this type of security is not only conditional but also it is not a future-proofsecurity [2]: Eve can potentially crack the recorded key exchange and communication in the near future even if presently such task looks hopeless.…”

“…However, in 2005, the Kirchhoff-Law-Johnson-(like)-Noise (KLJN) secure key exchange [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] scheme was introduced [4] and later it was built and its security demonstrated [7]. These ideas have inspired new concepts also in computing, particularly noise-based logic and computing [17][18][19][20][21][22][23][24], where not the security of data but complexity of data processing has been the issue.…”

“…(2,3,7,8) with the actually measured mean-square channel voltage and current to decide if the situation is secure (LH or HL) while utilizing the fact that these mean-square values are different in each of these three situations (LL, LH/HL and HH). If the situation is secure, Alice and Bob will know that the other party has the inverse of his/her bit, which means, a secure key exchange takes place.…”