Thermal noise informatics: Totally secure communication via a wire; Zero-power communication; and Thermal noise driven computing

Abstract

Very recently, it has been shown that thermal noise and its artificial versions (Johnson-like noises) can be utilized as an information carrier with peculiar properties therefore it may be proper to call this topic Thermal Noise Informatics. Zero Power (Stealth) Communication, Thermal Noise Driven Computing, and Totally Secure Classical Communication are relevant examples. In this paper, while we will briefly describe the first and the second subjects, we shall focus on the third subject, the secure classical communication via wire. This way of secure telecommunication utilizes the properties of Johnson(-like) noise and those of a simple Kirchhoff's loop. The communicator is unconditionally secure at the conceptual (circuit theoretical) level and this property is (so far) unique in communication systems based on classical physics. The communicator is superior to quantum alternatives in all known aspects, except the need of using a wire. In the idealized system, the eavesdropper can extract zero bit of information without getting uncovered. The scheme is naturally protected against the man-in-the-middle attack. The communication can take place also via currently used power lines or phone (wire) lines and it is not only a point-to-point communication like quantum channels but network-ready. Tests have been carried out on a model-line with ranges beyond the ranges of any known direct quantum communication channel and they indicate unrivalled signal fidelity and security performance. This simple device has single-wire secure key generation/sharing rates of 0.1, 1, 10, and 100 bit/second for copper wires with diameters/ranges of 21 mm / 2000 km, 7 mm / 200 km, 2.3 mm / 20 km, and 0.7 mm / 2 km, respectively and it performs with 0.02% raw-bit error rate (99.98 % fidelity). Comment: Plenary Talk at the 4th International Symposium on Fluctuations and Noise, Florence, Italy, May 23, 2007. Results are featured in New Scientist (technology section), May 23, 2007, by Jason Palmer

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Thermal noise informatics: Totally secure communication via a wire;
Zero-power communication; and Thermal noise driven computing
Laszlo B. Kish(+), Robert Mingesz(x), Zoltan Gingl(x)
(+)Texas A&M University, Department of Electrical and Computer Engineering, College Station,
TX 77843-3128, USA
(x)University of Szeged, Department of Experimental Physics, Dom ter 9, Szeged, H-6720,
Hungary.
ABSTRACT
Very recently, it has been shown that thermal noise and its artificial versions (Johnson-like noises) can be utilized as an
information carrier with peculiar properties therefore it may be proper to call this topic Thermal Noise Informatics. Zero
Power (Stealth) Communication, Thermal Noise Driven Computing, and Totally Secure Classical Communication are
relevant examples. In this paper, while we will briefly describe the first and the second subjects, we shall focus on the
third subject, the secure classical communication via wire. This way of secure telecommunication utilizes the properties
of Johnson(-like) noise and those of a simple Kirchhoff's loop. The communicator is unconditionally secure at the
conceptual (circuit theoretical) level and this property is (so far) unique in communication systems based on classical
physics. The communicator is superior to quantum alternatives in all known aspects, except the need of using a wire. In
the idealized system, the eavesdropper can extract zero bit of information without getting uncovered. The scheme is
naturally protected against the man-in-the-middle attack. The communication can take place also via currently used
power lines or phone (wire) lines and it is not only a point-to-point communication like quantum channels but network-
ready. We report that a pair of Kirchhoff-Loop-Johnson(-like)-Noise communicators, which is able to work over
variable ranges, was designed and built. Tests have been carried out on a model-line with ranges beyond the ranges of
any known direct quantum communication channel and they indicate unrivalled signal fidelity and security
performance. This simple device has single-wire secure key generation/sharing rates of 0.1, 1, 10, and 100 bit/second
for copper wires with diameters/ranges of 21 mm / 2000 km, 7 mm / 200 km, 2.3 mm / 20 km, and 0.7 mm / 2 km,
respectively and it performs with 0.02% raw-bit error rate (99.98 % fidelity). The raw-bit security of this practical
system significantly outperforms raw-bit quantum security. Current injection breaking tests show zero bit
eavesdropping ability without setting on the alarm signal, therefore no multiple measurements are needed to build an
error statistics to detect the eavesdropping as in quantum communication. Wire resistance based breaking tests of
Bergou-Scheuer-Yariv type give an upper limit of eavesdropped raw bit ratio is 0.19 % and this limit is inversely
proportional to the sixth power of cable diameter. Hao's breaking method yields zero (below measurement resolution)
eavesdropping information.
Keywords: Secret key distribution, classical information, stealth communication.
1. INTRODUCTION
Very recently, it has been shown that thermal noise and its artificial versions (Johnson-like noises) can be utilized as an
information carrier with peculiar properties therefore it may be proper to call this topic Thermal Noise Informatics.
Thermal Noise Driven Computing, Zero Power Communication, and Totally Secure Classical Communication are
relevant examples. In this paper, while we will briefly describe the first and the second subjects, we shall focus on the
third subject, the secure communication via wire.
The secure communication results were featured in the technology section of the New Scientist magazine on May 23, 2007, by Jason Palmer.
This manuscript was a plenary talk at the 4th International Symposium on Fluctuation and Noise, Florence, Italy, (May 23, 2007).

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2. Zero Power Classical Communication, Zero-Quantum Quantum communication, Stealth Communication
Recently, it has been shown that the equilibrium thermal noise in information channels can be utilized to carry
information. In this case, the transmitter does not emit any signal energy into the channel however it only modulates the
existing noise there. This issue is completely different from the earlier Porod-Landauer debate about the question if
communication without net energy cost is possible by gaining back the energy spent in the communicator devices.
(Porod is right, energy-free communication is impossible just like energy-free computing). In our system, the noise is
used as information carrier and no effort is made to restore the energy dissipated in the communicator devices.
Therefore, this communicator is not energy-free communication but it is free of emitted signal energy.
CHANNEL
SYSTEM
IN THERMAL
EQUILIBRIUM
RECEIVER
MEASURING
AND ANALYZING
THERMAL NOISE
SENDER
MODULATING A
PARAMETER
CONTROLLING
THERMAL NOISE
Figure 1.
CHANNEL
QUANTUM
SYSTEM IN
GROUND STATE
RECEIVER
MEASURING
AND ANALYZING
ZERO-POINT
FLUCTUATIONS
SENDER
MODULATING A
PARAMETER
CONTROLLING
ZERO-POINT
FLUCTUATIONS
Figure 1.
R
C1
(T)
u1(t)
R
(T)
u2(t)
2
1
C2
Ground
To channel
Classical: (kT>>h/(RC))Quantum: (kT<<h/(RC))
SENDER
Figure 3. A possible realization of stealth communication with zero power classical communication or zero-quantum quantum
communication utilizing classical thermal noise and zero-point quantum fluctuations with bandwith modulation. Classical or
quantum, it depends on the upper cutoff frequency fc and the temperature. Classical: hfc << kT; quantum: hfc << kT .

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3. THERMAL NOISE DRIVEN COMPUTING?
Because thermal noise turned out to be a special information carrier with low energy density in the information channel,
it is natural to pose the question: can we use it for information processing and computing? At thermal noise driven
computing, an idea further inspired by the fact that the neural signals in the brain are noise, certain statistical parameters
of the thermal noise is the information carrier.
The information may be carried by the bandwidth as at the zero power communication example above or in other way.
To study the minimal energy requirement of requirement/dissipation, another specific realization was used, a simple
digital system with zero threshold voltage, when the thermal noise is equal to or greater than the digital signal. Under
these conditions, when the digital signal amplitude is less than the variance of the noise, classical digital information is
usually considered to be zero or useless.
We would like to note that in a different class of efforts many notable scientists, including John von Neumann [11];
Forshaw and coworkers [12,13]; and Palem and coworkers [14,15] have been proposing efficient ways of working with
probabilistic switches, which are noisy digital logic units with relatively high error probability. For example, Palem and
coworkers have pointed out that this may be a way to reduce power dissipation [14,15] if we give up our requirement of
data accuracy. However, though these approaches can be relevant to future developments of thermal noise driven
computing, they are very different from our present approach. In a thermal noise driven computer, the voltage in the
channel is dominantly noise and the modulation of the statistical properties of this noise carry the information.
Therefore, the way of extracting the information is not by "error correcting the information" like the efforts mentioned
above do but by "decoding the information in the noise". The realization example we analyzed is working in the regime
of huge error probability, p ? 0.5 , with zero logic threshold voltage and in the sub-noise signal amplitude limit; and all
these parameters are very unusual.
Even though that at this stage there are more open questions than answers and we were are at the moment unable to
show a functioning thermal noise driven logical circuitry, certain questions can already be answered about it.
Estimations were given about the information channel capacity and the minimal energy dissipation E1 given in
Energy/bit unit. The minimal energy requirement, which is the deterministic energy carried by the signal (which is
buried by thermal noise) is given as:

h =
Ps
Cdigpº0.5
=p ln2
2
kT / bit º1.1 bit / kT

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The main advantage of such a hypothetical thermal noise driven computer would be a potentially improved energy
efficiency and an obvious lack of leakage current, cross-talk and ground EMI problems due the very low DC voltages.
An apparent disadvantage is the large number of extra (redundancy) elements required for error reduction [11-13].
From the long list of open questions, we list some of the most important ones:
1. Do we need error correction at all (except input/output operations) in such a computer or when we want to simulate
the way the brain works?
2. Is there any way to realize a non-Turing machine with stochastic elements without excessive hardware/software
based redundance?
3. How should redundancy and error correction be efficiently used to run the thermal noise driven computer as a Turing
machine?
4. How much energy would such error correction cost?
5. How much energy is needed to feed the active devices processing and producing the sub-thermal noise signals or the
bandwidth control of thermal noise?
6. What is the impact of the internal noise of these devices?
Though, all these questions are relevant for the ultimate energy dissipation of thermal noise driven computers, the lower
limit given for that specific arrangement with DC signal buried by thermal noise stays valid because this is the minimal
energy needed to generate itself the digital signal.
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.40.5 0.60.7 0.8 0.91
The theoretical information content of the noisy bit
C / fc (bit)
p (probability of correct state)
Thermal noise
driven computing
Classical
computing
Figure 1. Illustration of the range of error probabilities of classical computing and that of the thermal noise driven computing. A
thermal noise driven computer will supposedly work in that range where the information content/ single switching is low, the signal
looks like noise and no classical computer could work.

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Introduction.
Recently, a totally secure classical communication scheme, a statistical-physical competitor of quantum communicators,
was introduced, see Figure 1, [1,2], the Kirchhoff-loop-Johnson(-like)-Noise (KLJN) communicator, with two identical
pairs of resistors and corresponding Johnson(-like) noise voltage generators. The KLJN communicators are utilizing the
physical properties of an idealized Kirchhoff-loop and the statistical physical properties thermal noise (Johnson noise).
The resistors (low bit = small resistor, high bit = large resistor) and their thermal-noise-like voltage generators (thermal
noise voltage enhanced by a pre-agreed factor) are randomly chosen and connected at each clock period at the two sides
of the wire channel. A secure bit exchange takes place when the bit states at the two line ends are different, which is
indicated by an intermediate level of the rms noise voltage on the line, or that of the rms current noise in the wire. The
most attractive properties of the KLJN cipher are related to its security [1,3] and to the extraordinary robustness of
classical information when compared that to the fragility of quantum information. To provide security against arbitrary
types of attacks, the instantaneous currents and voltages are measured at both end by Alice and Bob and they are
published and compared. In the idealized scheme of the KLJN cipher, the passively observing eavesdropper can extract
zero bit (zero-bit security) of information and the actively eavesdropping observer can extract at most one bit before
getting discovered (one-bit security) [1]. The system has a natural zero-bit security against the man-in-the-middle attack
which is a unique property among secure communicators [3]. The KLJN system has recently became network-ready [4].
This new property [4] opens a large scale of practical applications because the KLJN cipher can be installed as a
computer card [4], similarly to Eternet network cards. Other practical advantages compared quantum communicators
are the high speed, resistance against dust, vibrations, temperature gradients, and the low price [1]. It has recently been
shown [5] that the KJLN communicator may use currently used wire lines, such as power lines, phone lines, internet
wire lines by utilizing proper filtering methods.
Figure 1. The outline of the KLJN communicator. The line below 2000 km in the relevant frequency range can be represented by
distributed resistors and capacitors and below 200 km as a simple resistor. The instantaneous current and voltage data are measured
and compared at the two ends and, in the case of deviance; the eavesdropping alarm goes on and the currently exchanged bit is not
used. The low-pass line filters are against necessary to protect against out-of-alarm-frequency-band breaking attempts and false
alarms due to parasite transients. False alarms would occur due to any wave effect (transient or propagation effects), illegal frequency
components or external disturbance of the current-voltage-balance in the wire.
Concerning the security of the KLJN system, the basic rule of any physical secure communication holds here, too: If
you compromise it you lose it. Though there have been several attempts to break in the KJLN line, so far, no proposed
method has been able to challenge the total security of the idealized KLJN system. All these breaking attempts have
used certain assumptions which are directly violating the basic model of the idealized KLJN method. These assumptions
are as follows:
i. Allowing non-negligible wire resistance (Bergou [2], Scheuer and Yariv [6]). For the evaluation of this claim at
practical conditions, see the response in [7].
ii. Allowing high-enough bandwidth for wave (transient propagation) effects (Scheuer and Yariv [6]). This possibility
has been explicitly excluded since the original article [1]. For further refusal of this claim, see the response in [7].
Moreover, and this is the most direct practical argument, in this case the standard current and voltage protection of the