Nonlinearity Attack Against the Kichhoff–Law–Johnson-Noise (KLJN) Secure Key Exchange Protocol

This paper introduces a new attack against the Kirchhoff–Law–Johnson-Noise (KLJN) secure key exchange scheme. The attack is based on the nonlinearity of the noise generators. We explore the effect of total distortion ([Formula: see text]) at the second order ([Formula: see text]), third order ([Formula: see text]) and a combination of the second and third orders ([Formula: see text]) on the security of the KLJN scheme. It is demonstrated that as little as 1% results in a notable power flow along the information channel, which leads to a significant information leak. We also show that decreasing the effective temperature (that is, the wire voltage) and, in this way reducing nonlinearity, results in the KLJN scheme approaching perfect security.

Rectifying effect in high-performance ballistic diode bridge with a unique design for thermal energy harvesting

The long mean free path close to a micrometer in encapsulated graphene enabled us to rectify currents ballistically at room temperature. In this study, we introduce a ballistic rectifier that resembles a diode bridge and is based on graphene encapsulated using hexagonal boron nitride. Our device’s asymmetric geometry combined with the exploitation of the ratcheting effect means that it can operate successfully and provides excellent performance. The device’s estimated responsivities at 38,000 V/W for holes and 23,000 V/W for electrons at room temperature, are among the highest values for a ballistic device reported to date. Due to the device’s zero threshold voltage, it is able to rectify Johnson noise signals converting thermal excitation to electrical energy at room temperature. The bandwidth of the device at the ballistic regime is estimated at ~ 1.1 GHz for holes and 2 GHz for electrons. The device developed in this study is an important step along an innovative pathway that will lead to harvesting electrical energy directly from thermal energy.

Deterministic Random Number Generator Attack Against the Kirchhoff-Law-Johnson-Noise Secure Key Exchange Protocol

This paper demonstrates the vulnerability of the Kirchhoff-Law-Johnson-Noise (KLJN) secure key exchanger to compromised random number generator(s) even if these random numbers are used solely to generate the noises emulating the Johnson noise of Alice’s and Bob’s resistors. The attacks shown are deterministic in the sense that Eve’s knowledge of Alice’s and/or Bob’s random numbers is basically deterministic. Moreover, no statistical evaluation is needed, except for rarely occurring events of negligible, random waiting time and verification time. We explore two situations. In the first case, Eve knows both Alice’s and Bob’s random noises. We show that, in this situation, Eve can quickly crack the secure key bit by using Ohm’s Law. In the other situation, Eve knows only Bob’s random noise. Then Eve first can learn Bob’s resistance value by using Ohm’s Law. Therefore, she will have the same knowledge as Bob, thus at the end of the bit exchange period, she will know Alice’s bit.

Alternating (AC) Loop Current Attacks Against the KLJN Secure Key Exchange Scheme

Recently, several passive and active attack methods have been proposed against the Kirchhoff–Law–Johnson–Noise (KLJN) secure key exchange scheme by utilizing direct (DC) loop currents. The DC current attacks are relatively easy, but their practical importance is low. On the other hand, parasitic alternating (AC) currents are virtually omnipresent in wire-based systems. Such situations exist due to AC ground loops and electromagnetic interference (EMI). However, utilizing AC currents for attacks is a harder problem. Here, we introduce and demonstrate AC current attacks in various frequency ranges. The attacks exploit a parasitic/periodic AC voltage-source at either Alice’s or Bob’s end. In the low-frequency case, the procedure is the generalized form of the former DC ground-loop-based attack. In the high-frequency case, the power density spectrum of the wire voltage is utilized. The attack is demonstrated in both the low and the high-frequency situations. Defense protocols against the attack are also discussed.