Liang Jin,Xiaoyan Hu,Yangming Lou,Zhou Zhong,Xiaoli Sun,Huiming Wang,Jiangxing Wu,3

1 PLA Strategic Support Force Information Engineering University,Zhengzhou 450002,China

2 Xi’an Jiaotong University,Xi’an 710049,China

3 Purple Mountain Laboratories:Networking,Communications and Security,Nanjing 211111,China

Abstract: The information security and functional safety are fundamental issues of wireless communications sytems.The endogenous security principle based on Dynamic Heterogeneous Redundancy provides a direction for the development of wireless communication security and safety technology.This paper introduces the concept of wireless endogenous security from the following four aspects.First,we sorts out the endogenous security problems faced by the current wireless communications system,and then analyzes the endogenous security and safety attributes of the wireless channel.After that,the endogenous security and safety structure of the wireless communications system is given,and finally the applications of the existing wireless communication endogenous security and safety functions are listed.

Keywords: wireless communication; endogenous security;information security;functional safety

I.INTRODUCTION

Wireless signals use electromagnetic waves as the carrier to transmit information freely and openly at the speed of light in space,which greatly promotes the progress and development of society.At the same time,information security issues faced by wireless communications have also received widespread attention[1].The free propagation of wireless signals also exposes the endogenous“gene”defects of electromagnetic waves,that is,anyone within the signal coverage area can eavesdrop or attack the signal at the physical layer[2].However,the existing security mechanisms mainly follow the encryption mechanism in traditional wired communication and are designed at the high level,which can not response accurately against security issues caused by the openness of wireless channels[3].With the improvement of computing power,encryption algorithms will inevitably have the risk of being cracked in the future[4].For example,the A51 and A52 encryption algorithms in 2G had been cracked long ago,and the KASUMI encryption algorithm in 3G was also conditionally cracked due to loopholes in 2014[5].Faced with such problems,the existing security mechanisms always adopt the remedy/patching method to solve the exposed security problems,e.g.,4G uses technologies such as Snow3G/AES/Zuc-based hierarchical keys to defense security attacks such as SS7 signaling hijacking in 3G,which makes it difficult to deal with the potential risks and vulnerabilities/loopholes in the current system.Furthermore,as future wireless devices become more diverse and wireless networks become more open and integrated,communication links are facing severe security threats and the security deficiencies of the air interface will be more significant[4].Therefore,it is urgent to study new security mechanisms from the essential attributes of wireless communication security to deal with known and unknown security threats in wireless communications systems[6].

The endogenous security theory proposed by Wu[7-13]may be an ideal way to solve the above problems.Endogenous safety and security (ESS or endogenous security) theory is to use the endogenous security structure with dynamic,heterogeneous,and redundant(DHR)attributes to realize the endogenous security function.Its main feature is to dynamically select the executor set from the heterogeneous and redundant executors,which can achieve the expected function of the system and make its structure more uncertain to the adversary.Under this mechanism,it not only ensures the reliability of the system,but also makes the attacker confused about the system structure and operation mechanism,which makes it difficult to carry out effective attacks.Therefore,endogenous security theory not only can be used to resist known security threats,more importantly,but also can resist the unknown security threat and the unknown attack.In recent years,both the fundamental theory and the potential applications have been greatly developed and received great progress[9].

Inspired by the endogenous security,the research on wireless endogenous security emerges.Different from the classical endogenous security,wireless channel naturally has endogenous security attributes with dynamic,heterogeneous and redundant.Essentially,this is because of the refraction,scattering,diffraction,reflection and other effects of electromagnetic wave propagation,which cause the wireless channel to naturally have time-varying,heterogeneous and redundant.Based on this,this paper propose a unique endogenous security structure of wireless communications system to provide endogenous security functions and ensure the security and reliability of information transmission from transmitter to receiver.

In order to introduce the concept of wireless endogenous security proposed in this paper,we start from the four aspects of wireless communication endogenous security problems,attributes,structure,and functions.The rest of this paper is organized as follows.Section II introduces the basic concept of ESS and the wireless endogenous security problems caused by the endogenous defects in electromagnetic wave.Section III explores the endogenous security attributes in the wireless communications system and operation mechanism,and then constructs the endogenous security structure based on these attributes.Section IV introduces several existing key technologies of wireless endogenous security.Finally,the conclusion remarks of this paper are given in Section V.

II.THE ENDOGENOUS SAFETY AND SECURITY PROBLEM

2.1 Basic Concept

Wireless communication network is one of the important components of cyberspace[14].To discuss the wireless endogenous safety and security (WESS)problem,we should first clarify what is the endogenous safety and security(ESS)problem in cyberspace.The functional safety problem refers to the damage to the expected function of the system,and information security problem refers to the information leakage.In essence,the endogenous security problem and the cyberspace are interrelated and interdependent.This is because in addition to the expected function(EF),any natural or artificial system also has the associated visible side effect function(VSEF)or invisible dark function(IDF).As shown in Figure 1,the VSEF and IDF are represented by white dots and gray circles,respectively,and they are widely distributed around the expected function.The current methodology is to design security patches once these VSEFs are discovered.But this is only a small part of the undiscovered functions.Moreover,the additional security patches may also bring new security issues.This shows that when various software and hardware perform their expected functions,the VSEF and IDF generated by loopholes and backdoors cannot be eradicated[10].If the VSEF and IDF have an adverse effect on the system,they become the endogenous safety and security problems.The ESS problems include not only functional safety problems that affect the robustness and reliability,but also information security problems that affect the privacy and credibility.Once endogenous security problems are caused by artificial or natural disturbances(for example,active attacks or natural interference),undesired security events will be triggered.This type of disturbance is called general uncertain disturbance[12].Many cybersecurity incidents have shown that ESS problems in cyberspace are usually caused by the general uncertain disturbance,VSEF and IDF[13].Such endogenous security issues cannot be thoroughly solved by the traditional patching or plug-in security mechanisms.

Figure 1. The relationship among EF,VSEF and IDF.

2.2 The WESS Problem

Different from the ESS problem in cyberspace,the wireless communication network is faced with unique endogenous security problems caused by the inherent defects of electromagnetic propagation.As shown in Figure 2,the desired function is to transmit information safely and reliably on the reachable path between the transmitter and receiver.However,due to the multipath propagation characteristics of electromagnetic waves and the uncertainty and uncontrollability of the electromagnetic environment,random fading and noise (i.e.,VSEF)are inevitable at the receiver.At the same time,the broadcast characteristics of electromagnetic waves will also cause unpredictable dark functions,that is,passive eavesdropping can be implemented in any unknown place within the broadcast range,and unknown wireless access attacks can be launched.

Figure 2. Causes of WESS problems.

Figure 3 shows the causes of WESS problems of wireless communication.Safety problem mainly refers to random fading,natural and man-made interference; security problem mainly refers to man-made eavesdropping and access attacks.Due to the multipath effect of electromagnetic waves,after the signal is sent from the transmitter,it will go through many different paths to different locations.We expect that the signals pass through some reachable paths and converge at the legal receiver with greater energy.However,the phases of signals from different reachable paths are different,and fading may occur after superposition (i.e.,VSEF).Fading occurs on the reachable path of the desired function,so this kind of side effect can also be called as on-path VSEF.On the other hand,attackers may also receive signals from the unknown path(i.e.,off-path)to eavesdrop the signals or to launch attacks,which is the off-path IDF of wireless communications.It can be seen from Section 2.1 that once the above VSEF and IDF are triggered,there will be endogenous security problems.Wireless endogenous security problems can also be divided into two categories.The relationship between them is shown in the figure below.Among them,the general uncertainty disturbance in wireless communication represents the safety problem caused by natural and man-made interference,and the security problem caused by manmade attack.

Figure 3. The WESS problem of wireless communications system.

Figure 4. Classic cyberspace endogenous security structure.

III.ENDOGENOUSSECURITYATTRIBUTES AND STRUCTURE

3.1 Classic DHR Structure

In the face of endogenous security problems,the traditional network security methods mostly use precise defense based on threat perception,such as patching the system and checking poison.These methods can only implement effective defense on the premise of acquiring prior knowledge of attack sources,characteristics,approaches,behaviors and mechanisms.However,they can neither eradicate the uncertain threats caused by VSEF or IDF,nor predict or resolve the attacks against unknown threats.In order to deal with this network security problem,the idea of existing works[7,8,11]is that since the endogenous security problem comes from the structure itself,we should follow the endogenous security mechanism of“structure determines function”,and design the information system structure with the attributes of endogenous security.

The classic cyberspace endogenous security structure is shown in Figure 4,which mainly includes input agent,heterogeneous executor and output agent.The region of the three is called mimicry bound,which is the region protected by endogenous security mechanism.The advantages of the structure are mainly reflected in the following two aspects:first,the“relatively correct”axiom can transform an unknown problem scene in a single space into a perceptible scenario under the consensus mechanism in a functionally equivalent multi-dimensional heterogeneous redundant space.In other words,unless multiple unknown problems produce wrong results at the same time,the safety and security of the system will not be affected.The other is dynamic multimode consensus mechanism,which can endow the system an“uncertainty”effect.Therefore,even if the attacker knows a certain dark function,his“trial and error tactics”will fail because he does not know which heterogeneous executors the system has selected.It can be seen that the endogenous security mechanism can deal with unknown security threats and uncertain random disturbances without relying on prior knowledge about vulnerabilities,backers or attackers.

3.2 Wireless Endogenous Security Attributes

The key to solve the problem of endogenous security is to explore the attributes of endogenous security,construct the structure of endogenous security and realize the function of endogenous security.Inspired by this idea,this section first discusses the endogenous security attributes of wireless communication.Different from wired communications system,wireless communications system itself has endogenous security attributes.This is caused by the propagation characteristics of electromagnetic wave and electromagnetic environment.The propagation mode of electromagnetic wave can be expressed by Maxwell equation as follows

whereEis the electric field intensity,Bis the magnetic induction intensity,ρis the charge density,and J is the current density;ε0andμ0are the permittivity and permeability in vacuum,respectively,∇,∇·and∇×are the vector differential operator,divergence and curl,respectively; Δζis a set of boundary conditions,which is a set of equations that determine the relationship between the electromagnetic field on both sides of the interface.According to the completeness of Maxwell’s equations,when the initial conditions and boundary conditions are determined,the equations set has a unique solution.The boundary conditions are determined by the various medium in the propagation of electromagnetic waves,i.e.,electromagnetic environment.Generally speaking,the medium experienced by the electromagnetic wave received at each point in space is different.This means that the boundary conditions at different locations are different,resulting in different solutions to equation (1).Moreover,the complexity of the electromagnetic environment makes it difficult for us to determine the boundary conditions and predict electromagnetic waves at different locations.Therefore,the unpredictability of the electromagnetic environment is the endogenous security attribute of wireless communications.One of the usual concrete manifestations of the electromagnetic environment is the wireless channel.In the following,we introduce the DHR characteristics in the endogenous security properties of the wireless channel in detail.

3.2.1 Heterogeneity

The heterogeneity stems from the unique propagation mode and complicated propagation environment of electromagnetic wave.The refraction,scattering,diffraction,and reflection effects of electromagnetic wave propagation reach the receiver in different paths and at different times,which leads to random multipath fading after the signals of each path are superimposed according to their phases[15].From the above analysis,it can be seen that the boundary conditions of the two points with large differences in space are different,so the fading of the wireless channels are also different.Unless the attacker and the legitimate user are exactly the same in the time,frequency,and space domains,there must be a certain difference between the legitimate and illegitimate channels[16].The diversity and complexity of the wireless channel makes it difficult to predict the boundary conditions.Therefore,the wireless channel between legitimate communication nodes has non-replicable and non-measurable heterogeneity to third parties at different locations.

3.2.2 Redundancy

Compared with traditional wired communication,the broadcasting characteristic of electromagnetic waves obscures the limitations of communication boundaries to a certain extent,which enables the signals from the transmitter to be received at multiple points in space.When considering the multi-antenna system,each antenna within the array can acquire signals and decode information.In addition,the channels of the antennas at different locations are also different,which enables the multi-antenna system to use redundant space resources to achieve diversity or multiplexing gain.Therefore,the wireless channel has redundancy in the spatial domain[17].

3.2.3 Dynamic

The dynamic nature of the wireless channel comes from its inherent time-varying nature.Time-varying is caused by the movement of transceivers,scatterers,and changes of the propagation medium in the electromagnetic environment.The real-time changing electromagnetic environment leads to different channels at different times for the same location,which makes the channel dynamic.Although the dynamics of wireless channels is often regarded as a factor that is detrimental to reliability in wireless communications systems,we can use natural or man-made dynamics to construct endogenous security mechanisms inspired by the concept of endogenous security.Specifically,the wireless channel can be used as a heterogeneous executor with dynamic and redundant characteristics to construct the DHR structure shown in Section 3.1,which makes the protected system obtain the“unpredictable”attribute and increase the difficulty of successful attack.

3.3 Wireless Endogenous Security Structure

Utilizing the inherent security attributes of wireless channel in Section 3.2,we can construct a wireless endogenous security structure to inherit the security effects of classic DHR structure and cope with unknown security threats.As shown in Figure 5,the heterogeneous executor corresponding to the classic DHR structure is the wireless channel,the input agent is the transmitter,and the output agent is the receiver.The area covered by the above three is called the mimicry bound,which is the range that our wireless endogenous security mechanism needs to protect.In addition,the diversity technology performed by the output agent(such as maximum ratio combining,etc.) can reduce the impact of random noise(VSEF),similar to the ruling mechanism output agent in Figure 4.The beamforming technology after the transmitter estimates the channel can be compared with the policy scheduling and feedback control of DHR structure.

Figure 5. The WESS structure.

If we compare the wireless endogenous security with the classical wireless communication,we can find that the essence of wireless endogenous security is based on using endogenous security attribute of the channel to solve the natural and man-made general uncertain disturbances.Nevertheless,the essence of classical wireless communication is to fight against the disturbance caused by the uncertainty of natural channel.The difference between the two lies in the design concept.The wireless endogenous safety based on the fine cognition,optimizing customization and fine control of the electromagnetic environment,while the classic wireless communication is passively adapted to the electromagnetic environment.What they have in common is that they both make use of the endogenous security properties of the channel.A symbiotic relationship that is different from the traditional binding and splicing security mechanism exists between wireless endogenous security and classic wireless communication.They are both endogenous integration and can symbiotic development.For example,the Channel State Information(CSI)estimation technology not only can better combat the random channel fading,but also make better use of CSI to scramble the signal and enhance the endogenous security.Similarly,as for the channel coding technology,a good coding method not only can improve the robustness of the communication system,but also help to realize the physical layer secure transmission(a kind of wireless endogenous information security)technology.

3.4 Imagination of Wireless Endogenous System and Mechanism

Based on the wireless endogenous security architecture,we envision the expected endogenous security system,mechanisms and technical characteristics.

3.4.1 Expected wireless endogenous security system The expected wireless endogenous security system includes the following five aspects:

1.The wireless endogenous security system should be an open air interface signal processing architecture,which does not exclude any endogenous security issues involved in wireless signal transmission.

2.The wireless endogenous security system should be an integrated structure,which can simultaneously provide high-reliability,high-credibility,and high-availability functions.

3.The wireless endogenous security system should be able to coordinate the use of the defense elements of diversity,randomness,and dynamics.

4.The wireless endogenous security system should have the structural elements of heterogeneous,redundant,dynamic,adjudication and feedback control at the same time.

5.The wireless endogenous security system should be able to naturally absorb traditional security protection technologies or other technologies and gain exponential defense gains.

3.4.2 Expected wireless endogenous security mechanism

The expected wireless endogenous security mechanism includes the following five aspects:

1.There should be man-machine,machine-machine,machine-man game relations between the endogenous security mechanism and the generalized uncertainty disturbance.

2.The endogenous security mechanism should be able to conditionally control or suppress generalized uncertain disturbances without attempting to eliminate its influence.

3.The effectiveness of the endogenous security mechanism should not rely on any prior knowledge about the attacker,and any additional,builtin,or endogenous security measures or technical means.

4.The security of the endogenous security mechanism should have stable robustness and quality robustness with quantifiable design and verifiable metrics.

5.The effectiveness of the endogenous security mechanism should be irrelevant or weakly related to the technical capabilities and experience of the maintenance manager.

3.4.3 Expected technical characteristics

The expected technical characteristics of the wireless endogenous security architecture includes the following four aspects:

1.The wireless endogenous security belongs to the intrinsic security function of electromagnetic objects,which has the fusion defense function similar to the non-specific and specific immune mechanism of vertebrate organisms,and is inseparable from the intrinsic function of target objects.

2.The wireless endogenous security function does not rely on any prior knowledge and behavioral characteristics of the attacker,so it has a natural inhibitory effect on independent attack techniques and methods.

3.Only precise coordinated attacks with time and space consistency can crack the wireless endogenous security architecture.However,in order to achieve this goal,the attacker must first overcome the“unpredictable”effect of temporal and spatial inconsistency,and must exceed the“physical isolation distance formed by a heterogeneous environment”.

4.Theoretically,the success of an attack is a very small probability event,and none of the attack actions or results in the wireless endogenous security environment has stable robustness and quality robustness.

IV.WESS FUNCTION AND TECHNOLOGY

4.1 Wireless Endogenous Information Security

The purpose of wireless endogenous information security technology is to protect the confidentiality,reliability and integrity of information.As shown in Figure 6,we use the wireless channel as the executor to realize the secure transmission technology based on random signal scrambling[18-23],and can also realize the physical layer key generation technology based on“one time pad”[14,24,25].

Figure 6. Wireless endogenous information security technology based on wireless channel.

Figure 7.The reconfigurable intelligent surface aided wireless communication.

Figure 8. The DHR antenna array.

Among them,the essence of the physical layer security transmission technology is to design a signal transmission and processing mechanism that is strongly associated with the wireless channel,so that only users on the legal channel can correctly demodulate the signal,while the signals on the channels in other locations are scrambled and unrecoverable.The essence of the physical layer key generation technology is to directly use the CSI to generate keys[26].The key can be seen as a simplified representation of the executor.After the key is used for authentication or encryption,the information can be bound to the executor,thereby preventing attacks or eavesdropping from other unknown locations.The realization of the above two wireless endogenous security functions does not rely on any prior knowledge and behavior characteristics of the attacker,so it can defense unknown security threats.

Moreover,reference[14]points that physical layer key generation technology can be used to realize“one time pad”.Because the amount of information of the electromagnetic environment itself is large enough,and the communication process of transmitting the source naturally contains the same amount of electromagnetic environment information,which can provide enough keys.Therefore,as long as we can realize the precise and meticulous cognition and shaping of the environment,no matter how high the communication rate is,we can obtain the matching key rate from the endogenous electromagnetic environment.And the extracting procession does not dissipate additional energy or occupy additional resources.

The reference[14]also shows that we can improve the randomness and dynamics of channel fingerprints by some enabling techniques.As shown in Figure 7,the Reconfigurable Intelligent surface (RIS) of metamaterial has the characteristics enabling to control electromagnetic waves effectively,fast and flexibly,which can enrich and amplify the DHR characteristics of electromagnetic environment to improve information security and functional safety[27].In general,RIS related information security and functional safety are called RIS-based information transaction (RBIT)and RIS-assisted wireless communications (RAWC)[28],respectively.Reference[29]also gives a method to improve the key generation rate in static environment by fully exploring the electromagnetic environment and signal entropy.These enabling technologies are helpful to realize the“one time pad”endogenous security function based on the endogenous security attributing of electromagnetic environment.

Figure 9. The structure of the paper.

4.2 Wireless Endogenous Functional Safety

Wireless endogenous security can not only provide information security,but also provide reliability and availability of functional safety.Many traditional wireless communication technologies are designed to ensure the functional safety of communication,such as spread spectrum communication[30],multi-antenna diversity technology and so on.They are mainly against generalized uncertain disturbances which includes uncertain disturbances of natural channels and anthropogenic disturbances.These technologies generally use some DHR characteristics and belong to endogenous security technology based on atypical DHR structure.Take wireless communication antiinterference technology as an example.Anti-jamming the technique can generally be divided into time domain[31],spatial domain and frequency domain[32]anti-interference.Taking classical time-hopping,frequency-hopping and space-hopping communication as examples,they use time-domain,frequencydomain or spatial domain redundancy to randomly select different time,frequency points or actuators(i.e.,wireless channels)on the antenna to communicate according to the hopping image.Therefore,wireless communication anti-jamming technology introduces dynamic and random elements,which makes the defense mechanism have uncertainty effect and can effectively increase the interference difficulty of the attacking party.However,most of the existing arrays use isomorphic elements,which have the problems of heterogeneity and limited degree of freedom.[33]presents an array of space-time heterogeneous antennas,in which each heterogeneous antenna can scan quickly and distinguish multipath to realize fine sensing and manipulation of electromagnetic environment.Based on metamaterials,the DHR antenna array is constructed by spatial heterogeneity,which makes the array elements in different positions have heterogeneous and uncorrelated patterns.The array can make the spatial resources get rid of the limitation of the spatial spectrum wall and improve the efficiency under the condition of antenna aperture limitation.As shown in Figure 8,theoreticallyNarray elements andKheterogeneous degrees of freedom can achieve the actual degrees of freedom ofNK,and the receiving capacity increases linearly with the degree of isomerism(including time domain isomerism and spatial heterogeneity)[33].As a result,DHR antennas can not only achieve array gain,but also obtain the gain of array elements.Therefore,it can amplify the dynamic and heterogeneous nature of wireless endogenous security structure,and obtaining better wireless endogenous function security effect to improve the signal-tonoise ratio and anti-interference ability.

V.CONCLUSION

The structure of the whole paper is shown in the Figure 9.From the perspective of the principle of endogenous security,this paper first introduces the invisible dark functions and the visible side effect functions of wireless communication systems,and then combs the endogenous security problems they cause.Following that,we analyzes the attributes of wireless endogenous security and the characteristics of DHR to propose the structure of wireless endogenous security.Finally,the technologies and applications of wireless endogenous information security and functional security is introduced.It can be predicted that in the future development of wireless communication,the theory of endogenous security in cyberspace will play an important guiding role as described in this paper.Moreover,the DHR structure of wireless communications system will become an important supplement to the theory of endogenous security in cyberspace.Taking the massive machine type communication scenarios in 5G/B5G as an example,communication nodes have the characteristics of dense distribution,high concurrent communication,low communication delay,and dynamic migration.The artificial introduction of DHR features will inevitably increase the overhead.Fortunately,wireless channels naturally have endogenous security attributes.The endogenous security structure based on wireless channels can reduce the cost of introducing heterogeneous redundancy and relax the requirements on software,hardware and algorithms,which has important engineering significance.It can be seen that the integration and mutual penetration of ESS theory and WESS theory not only can provide guidance for the development of new wireless communication reliability and security methods,but also provide enlightenment for the further development of ESS.

ACKNOWLEDGEMENT

This work was supported by National Natural Science Foundation of China (No.61941114 and No.61521003) and Key Universities and Academic Disciplines Contruction Project.