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technospheramag
technospheramag
ТЕХНОСФЕРА_РИЦ
Issue #6/2022
V. V. Grishachev, A. D. Zabolotskaya
Information Security Concern of Fiber-Optic Technologies
Information Security Concern of Fiber-Optic Technologies
DOI: 10.22184/1993-7296.FRos.2022.16.6.484.500
The paper presents an analysis of information security threats to the critical information infrastructure operating on the basis of fiber-optic technologies. The proposed model identifies three areas of privacy threats, including traffic interception in the optical networks; fiber optic channel of information leakage circulating at the protected facility; unauthorized access to the information using the fiber-optic technical intelligence means.
The paper presents an analysis of information security threats to the critical information infrastructure operating on the basis of fiber-optic technologies. The proposed model identifies three areas of privacy threats, including traffic interception in the optical networks; fiber optic channel of information leakage circulating at the protected facility; unauthorized access to the information using the fiber-optic technical intelligence means.
Теги: fiber-optic information leakage channel fiber-optic technical intelligence means information security of fiber-optic technologies traffic interception in the optical networks волоконно-оптические средства технической разведки волоконно-оптический канал утечки информации информационная безопасность волоконно-оптических технологий перехват трафика в оптических сетях
Information Security Concern of Fiber-Optic Technologies
V. V. Grishachev, A. D. Zabolotskaya
Russian State University for the Humanities,
Institute of Information Science and Security Technologies, Moscow, Russia
The paper presents an analysis of information security threats to the critical information infrastructure operating on the basis of fiber-optic technologies. The proposed model identifies three areas of privacy threats, including traffic interception in the optical networks; fiber optic channel of information leakage circulating at the protected facility; unauthorized access to the information using the fiber-optic technical intelligence means.
Key words: information security of fiber-optic technologies, traffic interception in the optical networks, fiber-optic information leakage channel, fiber-optic technical intelligence means
Received on: 05.04.2022
Accepted on: 04.05.2022
Introduction
Improvement of the processing base of information systems, telecommunication networks, automated control systems leads to the occurrence of previously unknown new threats to information security. The information process technologies based on new physical principles are of particular danger. An internal contradiction is manifested in new technologies and techniques related to the lack of knowledge about all the functioning features. On the one part, introduction of new technologies creates an illusion of greater information security that is associated with novelty of the principles used, for which the threat models have not yet been developed. On the other part, there is a danger of occurrence of the leakage channels that have not yet been identified and that are based on the physical principles not previously considered in the regulatory and methodological documents.
A similar problem occurs due to the use of photonic technologies in the data collection, processing, transmission and storage systems, in particular, in connection with the successful introduction of fiber-optic technologies in the communication, measurement and security systems that have significant advantages in comparison to other technologies. The problem can be solved by a physical and technical analysis of possible information leakage channels in the new technologies, generation of the relevant threat models, development of the up-to-date technical facilities and information security systems, and notification of a wide range of security specialists.
1. Information security
of fiber-optic technologies
Photonics is one of the main areas of development not only in the field of information technology, but also in the general technological field. It can conditionally be divided into the laser, optoelectronic, fiber-optic and integrated-optical technologies. The fiber-optic communication technologies are widely used in computer science. At present, the cable infrastructures are mainly based on the fiber-optic technologies. All new telecommunications are designed and developed using the optical cables [1]. The most promising subscriber access (first / last mile) is optical access in the form of passive optical networks (PON) that allows to use fiber optics for connection of the central network terminal with the subscriber without any intermediate active equipment. In the future, the entire communication system (both local and distant), must be all-optical (All-Optical Network, AON). The share of the optical component in modern communications is determined by the development level of the information component in a given territory; moreover, it is constantly growing.
Such a prospect is related primarily to the advantages of photonic transport over electronic transport in the cable networks. It means the lower energy losses, greater information capacity of the communication channel, durability, reliability, inertness to the superimposed fields and aggressive mediums. Very important advantages include the well-established installation and operation technologies for the optical cable networks. The construction produce-ability of the optical networks of different levels is related to a wide range of installation, testing and operational equipment that allows the construction of underwater, underground, overhead telecommunication lines. The total length of optical cable networks exceeds 4 billion kilometers, while traversing the continents and oceans.
In addition to the information communications, fiber optic technologies are widely applied in the measurement systems [2, 3]. Fiber optics can be used to produce a wide range of sensors, distributed measuring systems of almost all physical values for mechanical impacts, acoustic, thermal, radiation, electromagnetic fields, etc. The advantage of an optical fiber as a sensor is its high sensitivity to the superimposed fields and influences, distribution of measurements, and possible provision of several values on a single optical fiber. The optical fiber can be used as a basis for possible generation of distributed measuring networks to control the environmental condition of territories and the process condition of industrial facilities. For example, it is possible to monitor the coating condition by laying fiber optics inside the motorway coating. Similar problems can be solved in the field of railway and pipeline transport, or construction monitoring services. One of the important applications of optical fiber is its use for solving the security problems [4, 5]. By using the advantages of optical cable, it can be applied in the video surveillance systems, access control, perimeter guarding, fire alarm systems and other areas.
Such a widespread use of fiber optic technologies leads to the new types of information security threats that can be divided into three groups:
threats of traffic interception in the optical networks for various purposes;
threats of unauthorized data collection at the facilities using the standard optical networks;
threats to use the technical intelligence means based on the fiber-optic technologies.
The classification provided makes it possible to cover all aspects of the problem, each of which has an important significance with some independent technical implementation of both attack and defense instruments.
2. Threats of traffic interception in the optical networks [6–11]
Traffic interception is an illegal information sourcing using a technical tool that detects, receives and processes the informative signals from the data networks (Fig. 1). When intercepted, the object of threat is information transmitted over the regular optical networks.
The optical cable system of the facility can include not only telecommunications and local networks, but also the special-purpose networks such as audio communications, cable TV, video surveillance systems, various measuring systems and other cable systems. The traffic transmitted over the optical cables is confidential, and therefore, it is important for the facility operation, regardless of the network type. Traffic can be exposed to various hazards such as breach of confidentiality, integrity, and availability. The threats are perpetrated in various ways, but one of the main methods is interception through the unauthorized data retrieval, i. e. breach of confidentiality during data transmission using the technical intelligence tools. When intercepted, the intruder has technical capabilities at the modern technological level and is able to implement any scenario for gaining access to the confidential information that does not contradict the physics laws [6–8].
The informative signals and access methods to them play an important role in the interception structure. In the optical networks, the parameter registration methods for an informative signal can be divided into the contact and remote ones. In the case of contact access, the intruder needs to gain physical access to the optical fiber in the cable, including the need to search for the cable, destroy the protective sheaths, select the required fiber, and then remove part of the optical informative signal by installing a special fiber optic insert into the fiber optic gap or by influencing the optical fiber for output of the optical signal parts, for example, at the fiber bend, optical tunneling, etc. In the case of remote interception, the intruder requires the closest possible contact with the optical cable, only without destruction or with slight destruction of its protective sheaths based on the spurious optical radiation, spurious electromagnetic radiation, etc. Further, we will discuss the main types of interception.
Threat Models of Contact Traffic Interception in the Optical Networks
1. Contact Interception with Fiber Breakage
The simplest and most effective registration method for information signal is related to the use of a standard traffic control device that is a fiber channel traffic access point (TAP). It can be inserted into a regular network breakage or connected using a welded joint to a fiber breakage made. The insert can be made on the basis of optical couplers.
2. Contact Interception by Influencing the Fiber Without Breakage [9]
The condition for the optical radiation propagation in a fiber is determined by total internal reflection at the core-cladding boundary. Any influences can cause impairment of total internal reflection and occurrence of the spurious optical radiation coming from the fiber. It can be easily implemented under mechanical impact by bending the fiber. The bend I / O devices, such as the FOD‑5503 fiber optic pin, are used in the optical networking for audio communications between the installers using the fiber optic phones without breaking the optical line.
3. Contact Interception Based on the Optical Tunneling [10]
Optical tunneling represents the transition of part of the optical radiation from one channel to another closely located channel separated by an optical layer with a lower refractive index, providing the total internal reflection. In the case of this phenomenon, the couplers are made using the lateral fiber fusion technology without the optical channel crossing. When intercepted by this method, the fibers of the communication and leakage channels are brought into a fixed optical contact that does not require significant damage to the protective sheaths of the cable and fiber. Using a thin metal tube, the communication channel fiber is captured. Then the optical adhesive and the leakage channel fiber are introduced through the tube. When the adhesive is set, a fixed optical contact is established between the fibers of the communication and leakage channels (Fig. 2).
Threat Models of Remote Traffic Interception in the Optical Networks
1. Remote Interception Based on the Tunnelling Modes
The tunnelling mode is the optical radiation emerging from the communication channel when the junction of the light source and fiber is unmatched and the source aperture exceeds the fiber aperture. The optical radiation introduced into the fiber and went out beyond the fiber aperture, will fall on the core-cladding boundary at the angles smaller than the critical one. It will be also exposed to the Fresnel reflection with non-zero refraction. The effect of tunnelling modes can be observed not only for the input information signal, but also along the entire fiber-optic communication line at the connection points of amplifiers and repeaters, as well as at the defective connection points of the fibers or fibers with various apertures. Generation of a remote leakage channel is possible in the presence of optical windows in the protective cable sheaths or partial optical transparency of the sheaths.
2. Remote Interception Based on the Spurious Optical Radiation
The spurious optical radiation can be any radiation localized along the optical communication channel, caused by the Rayleigh scattering, Fresnel reflection on optical inhomogeneities, etc. that can go beyond the fiber and cable through the optical windows of the protective sheaths and the cable system layers (Fig. 3).
In particular, the spurious radiations can be generated in the case of an inconsistent welded joints of fibers, i. e. when the fibers are displaced relative to each other, welded at an angle to each other, etc. Even a high-quality connection leads to the localized losses of about 0.01 dB. Some of them are captured by the fiber, and other can go beyond the fiber cladding. The spliced fibers are placed in the cable glands of underground, underwater and overhead telecommunication networks that can be located every 3–5 km. It allows the intruder to select the most suitable interception point, while requiring the available optical windows in the cable and gland.
3. Remote Interception Based on the Spurious Electromagnetic Radiation [11]
The spurious electromagnetic radiation is generated in the optical fiber due to the nonlinear optical transformations, leading to demodulation of the information optical signal at the frequencies close to the optical carrier modulation frequency, i. e. in the millimeter and centimeter wavelength range, for which the dielectric protective cable sheaths can be transparent. The spurious electromagnetic radiation power is determined by the coherence of the direct information optical flow and the value of the scattered information optical flow.
4. Remote Interception Based on the Parametric Methods
The parametric methods for the information signal registration in an optical communication channel are caused by modulation of the fiber parameters by the optical radiation of the information signal. It can be the precession modulation of electronic or nuclear magnetic moments, acousto-optic effects, X-ray diffraction effects, etc. The parametric interception structure applies the superimposed electromagnetic, X-ray, acoustic fields that can pass through the protective cable sheaths without its destruction that makes it possible to implement remote interception without the direct need to destroy the cable.
We will assess the reconnaissance accessibility area for remote interception using the spurious optical radiation as the most efficient of the described methods. Let the spurious radiation be formed by a plane discontinuity in the fiber core due to the Fresnel reflection of 30 dB (i. e. 1 / 1000 of the information signal). Due to the diffraction divergence of radiation, the attenuation will be 100 dB at a distance of 1 m from the discontinuity with a size of about 10 μm. If other losses are neglected, then, as a rough approximation, the intensity of the informative spurious optical radiation will be –130 dB of the information signal intensity. Thus, the reconnaissance accessibility area will not exceed a cylinder with a radius of about 1 m and an axis in the form of a cable. Therefore, determination of the remote interception in the threat model can be considered conditional, since the efficient interception is possible with the direct physical contact with the optical cable.
The technical information (traffic) security facilities can be based on the features of an optical communication channel, such as its small cross section, when the entire information signal in the form of a light flux is enclosed inside the fiber or cable. The first safety layer is related to technical means for controlling access to the cable and to the fiber, as well as the optical communication channel condition. Another way to protect traffic is the noise contamination or signal distortion when it is transmitted through the communication channel and its cleaning from noise or restoration when received from the communication channel.
The standard encryption methods can be applied in a fiber-optic communication line to protect traffic. Such methods can be used for any other communication systems. Recently, the transmitted data protection systems against interception based on the quantum cryptography have been developed and offered at the market. There are some reasons to consider such protection systems absolute by the very nature of their implementation.
3. Threats of unauthorized data collection through the regular optical networks
Unauthorized data collection is an illegal information sourcing using the technical tool that detects, receives and processes informative signals from the controlled area based on the convergence of transmission and measurement functions in the regular optical networks (Fig. 4). In this case, the object of threat is information circulating at the facility near the optical networks in the form of various physical fields, such as speech, heat, electromagnetic fields, radiation fields, etc.
At the facilities, not only internal and external traffic is confidential, but also information circulating inside the facility in the form of the employees’ speech, various sounds of operating equipment, electromagnetic fields, physical parameters of the external environment, etc. The regular fiber optic communications are the distributed fiber optic measuring networks with non-standard measuring capabilities. Being located inside the facility, the communications pass through or near the protected premises where the confidential information can freely circulate. An intruder can gain access to it through the regular optical networks, using the regular light fluxes of the network or external probe radiation. In contrast to the traffic threat, such an information leakage channel can be considered a technical one (TCIL), using the undeclared, or unknown, or uncontrolled capabilities of the optical cable infrastructure due to the convergence of the transport and measurement network functions.
The generalized TCIL structure based on the facility’s fiber-optic communications requires a regular / irregular input / output system for the probe optical radiation with generation of the informative leakage signals when the optical fiber is exposed to the physical field related to the confidential information. The impact causes the light flux modulation in the optical fiber that transfers data outside the controlled area, i. e. being an informative signal for the modulating field. The transforming capabilities of fiber optics determine the danger level of fiber-optic TCIL. The network topology plays an important role in the threat to information security, since the optical cable laying near or through the protected premises significantly affects the protection against leaks.
Other features are related to the possible use of external non-regular sources creating the probe radiation in addition to the regular radiation for the informative signal generation. Moreover, the difficulties of connecting to an optical fiber are remained, the optical circuit can be complicated, but the intruder’s capabilities are increased due to variation in the radiation source parameters. The TCIL implementation scenarios using the fiber-optic communications can differ depending on the possible light modulation in the optical fiber by the informative fields and the aims pursued by the intruder.
Thus, the main areas for threat activities can be identified in the structure of the fiber-optics TCIL, including the probing methods for the regular optical network that is used for the informative signal recording, and the optical network facilities, at which the probing radiation is modulated. The probing methods and objects can be used for development of the threat models relating to the data security circulating at the protected facility.
Threat Model of Unauthorized Data Collection Through the Regular Optical Networks
1. Optical method probing methods
Based on the available fiber optic technology used for the unauthorized data collection, the following intelligence techniques can be identified:
for transmission, i. e. measurement of the optical radiation parameters that has passed through the probed facility, used to record an informative signal at the short distances between the source and the receivers, when the noise modulations do not exceed the informative signal value;
for reflection, i. e. optical reflectometry of the probed facility that is used to record an informative signal at the maximum distances determined by the optical reflectometry devices, since it allows to determine the response from a specific probed facility.
All the main optical radiation parameters and their combinations can be used for the transmission and reflection probing, including the intensity, phase, frequency, and polarization modulation, selected based on the modulation efficiency (depth) at the probing facility. In some cases, both optical radiation from the technical reconnaissance equipment (non-regular sources) and regular sources can be used for probing. In the case of regular sources and receivers, i. e. the optical network transceivers, probing is highly concealed, but requires access to the optical network technology (an insider).
The basis for the leakage channel functioning is optical reflectometry [3]. It is used for possible localization of the optical network response that is most sensitive to the influence of informative signals, for measurement of one informative signal from several probing facilities, for increase of the signal-to-noise ratio, for performance of real-time measurements, etc. The development of optical reflectometry technology is one of the most significant threats to unauthorized data collection.
2. Probing Objects
The passive optical network elements are the main objects of probing that determine the leakage channel efficiency. They can be grouped as follows:
regular passive elements of the optical network that are sensitive to the informative physical fields. During the optical network production and installation, as a rule, no researches of the possible response of passive optical elements to all possible external informative physical fields are conducted, so they may have undeclared opportunities not related to the main network functions, for example, the detachable connection design largely coincides with the design of a fiber-optic microphone with amplitude modulation, but the acoustic parameters are not indicated in the declared specifications of detachable connectors;
fiber-optic markers, i. е. the structural changes in the optical network passive elements made in order to increase sensitivity to the surrounding informative physical fields that can be introduced into the optical network.
3. Fiber Optic Markers
The structural changes in the optical network passive elements can be made during manufacture, installation, operation of the optical network. Each of such network has its own specifications and capabilities that makes it possible to divide the threat into three groups:
fiber-optical production markers – during the production of optical elements, the manufacturer can make changes to the passive element design that does not affect its functionality, but increases sensitivity to the superimposed physical fields.
The changes made may be applied to the optical fiber, to the protective sheaths and other elements of the optical cable. One such possibility is generation of the Bragg gratings in the fiber core with a resonant reflection wavelength at the wavelengths within the fiber material absorption range (Fig. 5). Having considered the small spectral width of the grating resonant reflection, it will not affect the radiation transmission at the operating wavelengths of the communication channel in the area of the material transparency windows. Availability of such gratings every 100–200 m along the cable length makes it possible to locate them near the informative signals when the cable system is installed. Thus, monitoring of an optical cable system will not detect such fiber optic markers, since monitoring at the wavelengths beyond the fiber transparency windows is not performed over the long distances due to high absorption values. If the absorption in amorphous quartz is decreased to 0.125 dB / km at a wavelength of 1550 nm, then it exceeds 1 dB / km at the absorption peaks of 1383 nm, and it exceeds 3 dB / km in the visible range. The fiber-optic marker in the form of a Bragg grating makes it possible to manufacture an informative signal sensor that is highly sensitive to the acoustic and thermal fields.
fiber-optic installation markers – during the process of intrafacility installation of a fiber-optic structured cable system, by intentional or unintentional violation of the work performance requirements, the cable system susceptibility to the external influences that may not be initially know (among other things) can be changed.
The most evident changes may be related to non-observance of the regulatory and methodological recommendations and requirements, for example, the optical cable bending value exceeds the regulatory requirements, the cable wiring is made with tension, the cable is rigidly fastened to the walls, etc. Such facts significantly increase sensitivity to the acoustic fields. On the one part, the deviations made may not be noted in the installation requirements, since they do not affect the main function of the cable system, namely the data transmission. On the other part, their availability does not yet pose a threat to the security of information circulating at the facility, if their location relative to the protected premises is not considered.
One of such deviations that increase the acoustic sensitivity of the cable system, is the installation point of cable channels. Rigid fastening of the optical cable to the fundamental building structures, such as reinforced concrete load-bearing walls, leads to the distributed measuring system of vibroacoustic oscillations in the walls. It is a highly informative structural sound that is poorly absorbed by the monolithic building structures. To demonstrate the reduced acoustic contact of the cable channel with the walls, we can suggest using a corrugated pipe fastened to the wall using the clips that are made of plastic with increased elasticity (Fig. 6). In such cable conduits, it is possible to make the additional acoustic insulation in relation to the walls (clip) and inside the corrugated pipes using the special mineral fiber pads.
fiber-optic operation markers – they are made by an insider using the local mechanical, thermal, magnetic, electrical and other physical impact on the cable conduits, optical cable of the structured cable systems of the protected facility at the optical network operating stage.
When the fiber-optic subsystems of the structured cabling systems at the facility are functioning, it is always possible to increase the efficiency of unauthorized data collection by having an impact on it. The type of impact depends on the intruder’s aims and capabilities, however, the main purpose of such impact is to create local optical inhomogeneities of the cable system near the protected premises or near dangerous elements of building structures. For example, the threat to the negotiations confidentiality can be determined not only by proximity to the protected premises, but also to the acoustic waveguides in the form of cast-in-place walls, air ducts, water and other utility pipelines in the building. Compliance with the requirements for threat manageability at the installation stages can minimize the threats. However, the insider can mechanically affect the cable system, place the field sources near it in the most sensitive places, cause an increase in the threat level.
Threat Model of a Fiber-Optic Channel of Verbal Information Leakage [12]
A separate technical intelligence area is the fiber-optic channel for the acoustic (verbal) information leakage that is determined by the spurious acoustic modulation of the light flux parameters in the optical fiber (Fig. 7). In this case, the optical cable and its fibers represent a non-regular distributed fiber-optic converter (microphone) of the air acoustic vibrations or vibrations of the building structures with high sensitivity. Selection of the probing signal parameters, increased acoustic or vibroacoustic contact with the optical fiber, topology and other cable infrastructure specifications that are usually not considered can create a threat of interception of the confidential conversations. As the experimental studies show, the greatest danger is posed by the light modulations in the inhomogeneous sections of an optical cable related to the vibroacoustic effects (structural sound), as well as the possible use of the regular fiber-optic equipment as the technical reconnaissance equipment, for example, a Rubin‑021 fiber-optic testing telephone with an amplitude modulation.
The implementation of the verbal information leakage channel is possible by the optical radiation transmission method or optical reflectometry, by using the parameters (intensity, phase, polarization and wavelength) of the regular or non-regular optical radiation. In fact, any section of the cable system is used as a source of informative signals, and application of optical reflectometry makes it possible to create a distributed fiber-optic measuring system for acoustic vibrations.
The acoustic data protection methods against leakage through an acoustic and optical (fiber) channel are divided into the passive (soundproofing of an optical cable, «correct» network installation, etc.) and active ones (filtering, masking, noise contamination of an information signal, etc.). It is possible to emphasize an additional method that consists in inclusion of the light flux continuous monitoring function in each optical transceiver for the possible use of technical acoustic reconnaissance means. The interception danger level can be lowered by developing new recommendations for the installation and operation of optical cable systems.
4. Threats of using technical intelligence tools based on the fiber-optic technologies
The fiber-optic technical intelligence tools mean the fiber-optic technical devices (sensors) designed to receive, record and process the informative signals (Fig. 8), while the object of the threat is information circulating at the protected facility in the form of various physical fields, such as acoustic, electromagnetic, optical fields.
The advantages of fiber optic technologies can be used to produce the fiber optic technical intelligence tools in the form of fiber optic sensors and measuring systems adapted to perform special functions [2, 3]. Initially, the fiber optic sensors and measurement systems have the properties required for these purposes. They are highly sensitive to a wide range of physical fields; they are multifunctional, i. e. allow the measurements of various physical valies using one optical fiber; they can perform both point-by-point and distributed measurements; they are not detected by the regular electromagnetic methods, since they do not contain any conductive elements; they are passive and insensitive to the superimposed electromagnetic fields; they are fire-safe; very small, etc. All these advantages make them a very effective technical intelligence tool. In particular, the fiber-optic microphones can be used in operational activity for surreptitious conversation listening.
Possible increase in the laser microphone efficiency for surreptitious remote listening of confidential conversation can be used as an example of one of the applications of fiber-optic technical intelligence tools. One of the difficulties in the laser probing of vibrating surfaces is diffuse reflection of laser radiation from an unprepared surface or, vice versa, a narrow directivity of the reflected radiation from a prepared surface (mirror). Removal of such restrictions can be done by introducing into the building walls with a dedicated premises a sensor fiber optics without any protective shields with the microlenses at the ends that have optical contact with the environment. Then illumination with the infrared laser radiation on one end can lead to the optical radiation modulated by the structural sound that is easily detected as the laser radiation aimed at a well-known direction with a well-known wavelength.
The countermeasures against the fiber-optic technical reconnaissance tools require special studies on the detection of optical fiber and cable, impact on its conversion capabilities for neutralization, etc.
Conclusion
The provided analysis of the information security threat model for the facilities with the fiber optic technologies shows a wide range and a high level of possible threats that need to be investigated, with development of the possible threat models, training and retraining of the specialists in this area.
REFERENCES
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AUTHORS
Vladimir V. Grishachev, Cand.of Sc. (Phys.& Math.), docent, associate professor Institute for Information Sciences and Security Technologies (IISST) Russian State University of the Humanities (RSUH), Moscow, Russia.
ORCID: 0000-0002-7585-7282
Anna D. Zabolotskaya, student Institute for Information Sciences and Security Technologies (IISST) Russian State University of the Humanities (RSUH), Moscow, Russia.
V. V. Grishachev, A. D. Zabolotskaya
Russian State University for the Humanities,
Institute of Information Science and Security Technologies, Moscow, Russia
The paper presents an analysis of information security threats to the critical information infrastructure operating on the basis of fiber-optic technologies. The proposed model identifies three areas of privacy threats, including traffic interception in the optical networks; fiber optic channel of information leakage circulating at the protected facility; unauthorized access to the information using the fiber-optic technical intelligence means.
Key words: information security of fiber-optic technologies, traffic interception in the optical networks, fiber-optic information leakage channel, fiber-optic technical intelligence means
Received on: 05.04.2022
Accepted on: 04.05.2022
Introduction
Improvement of the processing base of information systems, telecommunication networks, automated control systems leads to the occurrence of previously unknown new threats to information security. The information process technologies based on new physical principles are of particular danger. An internal contradiction is manifested in new technologies and techniques related to the lack of knowledge about all the functioning features. On the one part, introduction of new technologies creates an illusion of greater information security that is associated with novelty of the principles used, for which the threat models have not yet been developed. On the other part, there is a danger of occurrence of the leakage channels that have not yet been identified and that are based on the physical principles not previously considered in the regulatory and methodological documents.
A similar problem occurs due to the use of photonic technologies in the data collection, processing, transmission and storage systems, in particular, in connection with the successful introduction of fiber-optic technologies in the communication, measurement and security systems that have significant advantages in comparison to other technologies. The problem can be solved by a physical and technical analysis of possible information leakage channels in the new technologies, generation of the relevant threat models, development of the up-to-date technical facilities and information security systems, and notification of a wide range of security specialists.
1. Information security
of fiber-optic technologies
Photonics is one of the main areas of development not only in the field of information technology, but also in the general technological field. It can conditionally be divided into the laser, optoelectronic, fiber-optic and integrated-optical technologies. The fiber-optic communication technologies are widely used in computer science. At present, the cable infrastructures are mainly based on the fiber-optic technologies. All new telecommunications are designed and developed using the optical cables [1]. The most promising subscriber access (first / last mile) is optical access in the form of passive optical networks (PON) that allows to use fiber optics for connection of the central network terminal with the subscriber without any intermediate active equipment. In the future, the entire communication system (both local and distant), must be all-optical (All-Optical Network, AON). The share of the optical component in modern communications is determined by the development level of the information component in a given territory; moreover, it is constantly growing.
Such a prospect is related primarily to the advantages of photonic transport over electronic transport in the cable networks. It means the lower energy losses, greater information capacity of the communication channel, durability, reliability, inertness to the superimposed fields and aggressive mediums. Very important advantages include the well-established installation and operation technologies for the optical cable networks. The construction produce-ability of the optical networks of different levels is related to a wide range of installation, testing and operational equipment that allows the construction of underwater, underground, overhead telecommunication lines. The total length of optical cable networks exceeds 4 billion kilometers, while traversing the continents and oceans.
In addition to the information communications, fiber optic technologies are widely applied in the measurement systems [2, 3]. Fiber optics can be used to produce a wide range of sensors, distributed measuring systems of almost all physical values for mechanical impacts, acoustic, thermal, radiation, electromagnetic fields, etc. The advantage of an optical fiber as a sensor is its high sensitivity to the superimposed fields and influences, distribution of measurements, and possible provision of several values on a single optical fiber. The optical fiber can be used as a basis for possible generation of distributed measuring networks to control the environmental condition of territories and the process condition of industrial facilities. For example, it is possible to monitor the coating condition by laying fiber optics inside the motorway coating. Similar problems can be solved in the field of railway and pipeline transport, or construction monitoring services. One of the important applications of optical fiber is its use for solving the security problems [4, 5]. By using the advantages of optical cable, it can be applied in the video surveillance systems, access control, perimeter guarding, fire alarm systems and other areas.
Such a widespread use of fiber optic technologies leads to the new types of information security threats that can be divided into three groups:
threats of traffic interception in the optical networks for various purposes;
threats of unauthorized data collection at the facilities using the standard optical networks;
threats to use the technical intelligence means based on the fiber-optic technologies.
The classification provided makes it possible to cover all aspects of the problem, each of which has an important significance with some independent technical implementation of both attack and defense instruments.
2. Threats of traffic interception in the optical networks [6–11]
Traffic interception is an illegal information sourcing using a technical tool that detects, receives and processes the informative signals from the data networks (Fig. 1). When intercepted, the object of threat is information transmitted over the regular optical networks.
The optical cable system of the facility can include not only telecommunications and local networks, but also the special-purpose networks such as audio communications, cable TV, video surveillance systems, various measuring systems and other cable systems. The traffic transmitted over the optical cables is confidential, and therefore, it is important for the facility operation, regardless of the network type. Traffic can be exposed to various hazards such as breach of confidentiality, integrity, and availability. The threats are perpetrated in various ways, but one of the main methods is interception through the unauthorized data retrieval, i. e. breach of confidentiality during data transmission using the technical intelligence tools. When intercepted, the intruder has technical capabilities at the modern technological level and is able to implement any scenario for gaining access to the confidential information that does not contradict the physics laws [6–8].
The informative signals and access methods to them play an important role in the interception structure. In the optical networks, the parameter registration methods for an informative signal can be divided into the contact and remote ones. In the case of contact access, the intruder needs to gain physical access to the optical fiber in the cable, including the need to search for the cable, destroy the protective sheaths, select the required fiber, and then remove part of the optical informative signal by installing a special fiber optic insert into the fiber optic gap or by influencing the optical fiber for output of the optical signal parts, for example, at the fiber bend, optical tunneling, etc. In the case of remote interception, the intruder requires the closest possible contact with the optical cable, only without destruction or with slight destruction of its protective sheaths based on the spurious optical radiation, spurious electromagnetic radiation, etc. Further, we will discuss the main types of interception.
Threat Models of Contact Traffic Interception in the Optical Networks
1. Contact Interception with Fiber Breakage
The simplest and most effective registration method for information signal is related to the use of a standard traffic control device that is a fiber channel traffic access point (TAP). It can be inserted into a regular network breakage or connected using a welded joint to a fiber breakage made. The insert can be made on the basis of optical couplers.
2. Contact Interception by Influencing the Fiber Without Breakage [9]
The condition for the optical radiation propagation in a fiber is determined by total internal reflection at the core-cladding boundary. Any influences can cause impairment of total internal reflection and occurrence of the spurious optical radiation coming from the fiber. It can be easily implemented under mechanical impact by bending the fiber. The bend I / O devices, such as the FOD‑5503 fiber optic pin, are used in the optical networking for audio communications between the installers using the fiber optic phones without breaking the optical line.
3. Contact Interception Based on the Optical Tunneling [10]
Optical tunneling represents the transition of part of the optical radiation from one channel to another closely located channel separated by an optical layer with a lower refractive index, providing the total internal reflection. In the case of this phenomenon, the couplers are made using the lateral fiber fusion technology without the optical channel crossing. When intercepted by this method, the fibers of the communication and leakage channels are brought into a fixed optical contact that does not require significant damage to the protective sheaths of the cable and fiber. Using a thin metal tube, the communication channel fiber is captured. Then the optical adhesive and the leakage channel fiber are introduced through the tube. When the adhesive is set, a fixed optical contact is established between the fibers of the communication and leakage channels (Fig. 2).
Threat Models of Remote Traffic Interception in the Optical Networks
1. Remote Interception Based on the Tunnelling Modes
The tunnelling mode is the optical radiation emerging from the communication channel when the junction of the light source and fiber is unmatched and the source aperture exceeds the fiber aperture. The optical radiation introduced into the fiber and went out beyond the fiber aperture, will fall on the core-cladding boundary at the angles smaller than the critical one. It will be also exposed to the Fresnel reflection with non-zero refraction. The effect of tunnelling modes can be observed not only for the input information signal, but also along the entire fiber-optic communication line at the connection points of amplifiers and repeaters, as well as at the defective connection points of the fibers or fibers with various apertures. Generation of a remote leakage channel is possible in the presence of optical windows in the protective cable sheaths or partial optical transparency of the sheaths.
2. Remote Interception Based on the Spurious Optical Radiation
The spurious optical radiation can be any radiation localized along the optical communication channel, caused by the Rayleigh scattering, Fresnel reflection on optical inhomogeneities, etc. that can go beyond the fiber and cable through the optical windows of the protective sheaths and the cable system layers (Fig. 3).
In particular, the spurious radiations can be generated in the case of an inconsistent welded joints of fibers, i. e. when the fibers are displaced relative to each other, welded at an angle to each other, etc. Even a high-quality connection leads to the localized losses of about 0.01 dB. Some of them are captured by the fiber, and other can go beyond the fiber cladding. The spliced fibers are placed in the cable glands of underground, underwater and overhead telecommunication networks that can be located every 3–5 km. It allows the intruder to select the most suitable interception point, while requiring the available optical windows in the cable and gland.
3. Remote Interception Based on the Spurious Electromagnetic Radiation [11]
The spurious electromagnetic radiation is generated in the optical fiber due to the nonlinear optical transformations, leading to demodulation of the information optical signal at the frequencies close to the optical carrier modulation frequency, i. e. in the millimeter and centimeter wavelength range, for which the dielectric protective cable sheaths can be transparent. The spurious electromagnetic radiation power is determined by the coherence of the direct information optical flow and the value of the scattered information optical flow.
4. Remote Interception Based on the Parametric Methods
The parametric methods for the information signal registration in an optical communication channel are caused by modulation of the fiber parameters by the optical radiation of the information signal. It can be the precession modulation of electronic or nuclear magnetic moments, acousto-optic effects, X-ray diffraction effects, etc. The parametric interception structure applies the superimposed electromagnetic, X-ray, acoustic fields that can pass through the protective cable sheaths without its destruction that makes it possible to implement remote interception without the direct need to destroy the cable.
We will assess the reconnaissance accessibility area for remote interception using the spurious optical radiation as the most efficient of the described methods. Let the spurious radiation be formed by a plane discontinuity in the fiber core due to the Fresnel reflection of 30 dB (i. e. 1 / 1000 of the information signal). Due to the diffraction divergence of radiation, the attenuation will be 100 dB at a distance of 1 m from the discontinuity with a size of about 10 μm. If other losses are neglected, then, as a rough approximation, the intensity of the informative spurious optical radiation will be –130 dB of the information signal intensity. Thus, the reconnaissance accessibility area will not exceed a cylinder with a radius of about 1 m and an axis in the form of a cable. Therefore, determination of the remote interception in the threat model can be considered conditional, since the efficient interception is possible with the direct physical contact with the optical cable.
The technical information (traffic) security facilities can be based on the features of an optical communication channel, such as its small cross section, when the entire information signal in the form of a light flux is enclosed inside the fiber or cable. The first safety layer is related to technical means for controlling access to the cable and to the fiber, as well as the optical communication channel condition. Another way to protect traffic is the noise contamination or signal distortion when it is transmitted through the communication channel and its cleaning from noise or restoration when received from the communication channel.
The standard encryption methods can be applied in a fiber-optic communication line to protect traffic. Such methods can be used for any other communication systems. Recently, the transmitted data protection systems against interception based on the quantum cryptography have been developed and offered at the market. There are some reasons to consider such protection systems absolute by the very nature of their implementation.
3. Threats of unauthorized data collection through the regular optical networks
Unauthorized data collection is an illegal information sourcing using the technical tool that detects, receives and processes informative signals from the controlled area based on the convergence of transmission and measurement functions in the regular optical networks (Fig. 4). In this case, the object of threat is information circulating at the facility near the optical networks in the form of various physical fields, such as speech, heat, electromagnetic fields, radiation fields, etc.
At the facilities, not only internal and external traffic is confidential, but also information circulating inside the facility in the form of the employees’ speech, various sounds of operating equipment, electromagnetic fields, physical parameters of the external environment, etc. The regular fiber optic communications are the distributed fiber optic measuring networks with non-standard measuring capabilities. Being located inside the facility, the communications pass through or near the protected premises where the confidential information can freely circulate. An intruder can gain access to it through the regular optical networks, using the regular light fluxes of the network or external probe radiation. In contrast to the traffic threat, such an information leakage channel can be considered a technical one (TCIL), using the undeclared, or unknown, or uncontrolled capabilities of the optical cable infrastructure due to the convergence of the transport and measurement network functions.
The generalized TCIL structure based on the facility’s fiber-optic communications requires a regular / irregular input / output system for the probe optical radiation with generation of the informative leakage signals when the optical fiber is exposed to the physical field related to the confidential information. The impact causes the light flux modulation in the optical fiber that transfers data outside the controlled area, i. e. being an informative signal for the modulating field. The transforming capabilities of fiber optics determine the danger level of fiber-optic TCIL. The network topology plays an important role in the threat to information security, since the optical cable laying near or through the protected premises significantly affects the protection against leaks.
Other features are related to the possible use of external non-regular sources creating the probe radiation in addition to the regular radiation for the informative signal generation. Moreover, the difficulties of connecting to an optical fiber are remained, the optical circuit can be complicated, but the intruder’s capabilities are increased due to variation in the radiation source parameters. The TCIL implementation scenarios using the fiber-optic communications can differ depending on the possible light modulation in the optical fiber by the informative fields and the aims pursued by the intruder.
Thus, the main areas for threat activities can be identified in the structure of the fiber-optics TCIL, including the probing methods for the regular optical network that is used for the informative signal recording, and the optical network facilities, at which the probing radiation is modulated. The probing methods and objects can be used for development of the threat models relating to the data security circulating at the protected facility.
Threat Model of Unauthorized Data Collection Through the Regular Optical Networks
1. Optical method probing methods
Based on the available fiber optic technology used for the unauthorized data collection, the following intelligence techniques can be identified:
for transmission, i. e. measurement of the optical radiation parameters that has passed through the probed facility, used to record an informative signal at the short distances between the source and the receivers, when the noise modulations do not exceed the informative signal value;
for reflection, i. e. optical reflectometry of the probed facility that is used to record an informative signal at the maximum distances determined by the optical reflectometry devices, since it allows to determine the response from a specific probed facility.
All the main optical radiation parameters and their combinations can be used for the transmission and reflection probing, including the intensity, phase, frequency, and polarization modulation, selected based on the modulation efficiency (depth) at the probing facility. In some cases, both optical radiation from the technical reconnaissance equipment (non-regular sources) and regular sources can be used for probing. In the case of regular sources and receivers, i. e. the optical network transceivers, probing is highly concealed, but requires access to the optical network technology (an insider).
The basis for the leakage channel functioning is optical reflectometry [3]. It is used for possible localization of the optical network response that is most sensitive to the influence of informative signals, for measurement of one informative signal from several probing facilities, for increase of the signal-to-noise ratio, for performance of real-time measurements, etc. The development of optical reflectometry technology is one of the most significant threats to unauthorized data collection.
2. Probing Objects
The passive optical network elements are the main objects of probing that determine the leakage channel efficiency. They can be grouped as follows:
regular passive elements of the optical network that are sensitive to the informative physical fields. During the optical network production and installation, as a rule, no researches of the possible response of passive optical elements to all possible external informative physical fields are conducted, so they may have undeclared opportunities not related to the main network functions, for example, the detachable connection design largely coincides with the design of a fiber-optic microphone with amplitude modulation, but the acoustic parameters are not indicated in the declared specifications of detachable connectors;
fiber-optic markers, i. е. the structural changes in the optical network passive elements made in order to increase sensitivity to the surrounding informative physical fields that can be introduced into the optical network.
3. Fiber Optic Markers
The structural changes in the optical network passive elements can be made during manufacture, installation, operation of the optical network. Each of such network has its own specifications and capabilities that makes it possible to divide the threat into three groups:
fiber-optical production markers – during the production of optical elements, the manufacturer can make changes to the passive element design that does not affect its functionality, but increases sensitivity to the superimposed physical fields.
The changes made may be applied to the optical fiber, to the protective sheaths and other elements of the optical cable. One such possibility is generation of the Bragg gratings in the fiber core with a resonant reflection wavelength at the wavelengths within the fiber material absorption range (Fig. 5). Having considered the small spectral width of the grating resonant reflection, it will not affect the radiation transmission at the operating wavelengths of the communication channel in the area of the material transparency windows. Availability of such gratings every 100–200 m along the cable length makes it possible to locate them near the informative signals when the cable system is installed. Thus, monitoring of an optical cable system will not detect such fiber optic markers, since monitoring at the wavelengths beyond the fiber transparency windows is not performed over the long distances due to high absorption values. If the absorption in amorphous quartz is decreased to 0.125 dB / km at a wavelength of 1550 nm, then it exceeds 1 dB / km at the absorption peaks of 1383 nm, and it exceeds 3 dB / km in the visible range. The fiber-optic marker in the form of a Bragg grating makes it possible to manufacture an informative signal sensor that is highly sensitive to the acoustic and thermal fields.
fiber-optic installation markers – during the process of intrafacility installation of a fiber-optic structured cable system, by intentional or unintentional violation of the work performance requirements, the cable system susceptibility to the external influences that may not be initially know (among other things) can be changed.
The most evident changes may be related to non-observance of the regulatory and methodological recommendations and requirements, for example, the optical cable bending value exceeds the regulatory requirements, the cable wiring is made with tension, the cable is rigidly fastened to the walls, etc. Such facts significantly increase sensitivity to the acoustic fields. On the one part, the deviations made may not be noted in the installation requirements, since they do not affect the main function of the cable system, namely the data transmission. On the other part, their availability does not yet pose a threat to the security of information circulating at the facility, if their location relative to the protected premises is not considered.
One of such deviations that increase the acoustic sensitivity of the cable system, is the installation point of cable channels. Rigid fastening of the optical cable to the fundamental building structures, such as reinforced concrete load-bearing walls, leads to the distributed measuring system of vibroacoustic oscillations in the walls. It is a highly informative structural sound that is poorly absorbed by the monolithic building structures. To demonstrate the reduced acoustic contact of the cable channel with the walls, we can suggest using a corrugated pipe fastened to the wall using the clips that are made of plastic with increased elasticity (Fig. 6). In such cable conduits, it is possible to make the additional acoustic insulation in relation to the walls (clip) and inside the corrugated pipes using the special mineral fiber pads.
fiber-optic operation markers – they are made by an insider using the local mechanical, thermal, magnetic, electrical and other physical impact on the cable conduits, optical cable of the structured cable systems of the protected facility at the optical network operating stage.
When the fiber-optic subsystems of the structured cabling systems at the facility are functioning, it is always possible to increase the efficiency of unauthorized data collection by having an impact on it. The type of impact depends on the intruder’s aims and capabilities, however, the main purpose of such impact is to create local optical inhomogeneities of the cable system near the protected premises or near dangerous elements of building structures. For example, the threat to the negotiations confidentiality can be determined not only by proximity to the protected premises, but also to the acoustic waveguides in the form of cast-in-place walls, air ducts, water and other utility pipelines in the building. Compliance with the requirements for threat manageability at the installation stages can minimize the threats. However, the insider can mechanically affect the cable system, place the field sources near it in the most sensitive places, cause an increase in the threat level.
Threat Model of a Fiber-Optic Channel of Verbal Information Leakage [12]
A separate technical intelligence area is the fiber-optic channel for the acoustic (verbal) information leakage that is determined by the spurious acoustic modulation of the light flux parameters in the optical fiber (Fig. 7). In this case, the optical cable and its fibers represent a non-regular distributed fiber-optic converter (microphone) of the air acoustic vibrations or vibrations of the building structures with high sensitivity. Selection of the probing signal parameters, increased acoustic or vibroacoustic contact with the optical fiber, topology and other cable infrastructure specifications that are usually not considered can create a threat of interception of the confidential conversations. As the experimental studies show, the greatest danger is posed by the light modulations in the inhomogeneous sections of an optical cable related to the vibroacoustic effects (structural sound), as well as the possible use of the regular fiber-optic equipment as the technical reconnaissance equipment, for example, a Rubin‑021 fiber-optic testing telephone with an amplitude modulation.
The implementation of the verbal information leakage channel is possible by the optical radiation transmission method or optical reflectometry, by using the parameters (intensity, phase, polarization and wavelength) of the regular or non-regular optical radiation. In fact, any section of the cable system is used as a source of informative signals, and application of optical reflectometry makes it possible to create a distributed fiber-optic measuring system for acoustic vibrations.
The acoustic data protection methods against leakage through an acoustic and optical (fiber) channel are divided into the passive (soundproofing of an optical cable, «correct» network installation, etc.) and active ones (filtering, masking, noise contamination of an information signal, etc.). It is possible to emphasize an additional method that consists in inclusion of the light flux continuous monitoring function in each optical transceiver for the possible use of technical acoustic reconnaissance means. The interception danger level can be lowered by developing new recommendations for the installation and operation of optical cable systems.
4. Threats of using technical intelligence tools based on the fiber-optic technologies
The fiber-optic technical intelligence tools mean the fiber-optic technical devices (sensors) designed to receive, record and process the informative signals (Fig. 8), while the object of the threat is information circulating at the protected facility in the form of various physical fields, such as acoustic, electromagnetic, optical fields.
The advantages of fiber optic technologies can be used to produce the fiber optic technical intelligence tools in the form of fiber optic sensors and measuring systems adapted to perform special functions [2, 3]. Initially, the fiber optic sensors and measurement systems have the properties required for these purposes. They are highly sensitive to a wide range of physical fields; they are multifunctional, i. e. allow the measurements of various physical valies using one optical fiber; they can perform both point-by-point and distributed measurements; they are not detected by the regular electromagnetic methods, since they do not contain any conductive elements; they are passive and insensitive to the superimposed electromagnetic fields; they are fire-safe; very small, etc. All these advantages make them a very effective technical intelligence tool. In particular, the fiber-optic microphones can be used in operational activity for surreptitious conversation listening.
Possible increase in the laser microphone efficiency for surreptitious remote listening of confidential conversation can be used as an example of one of the applications of fiber-optic technical intelligence tools. One of the difficulties in the laser probing of vibrating surfaces is diffuse reflection of laser radiation from an unprepared surface or, vice versa, a narrow directivity of the reflected radiation from a prepared surface (mirror). Removal of such restrictions can be done by introducing into the building walls with a dedicated premises a sensor fiber optics without any protective shields with the microlenses at the ends that have optical contact with the environment. Then illumination with the infrared laser radiation on one end can lead to the optical radiation modulated by the structural sound that is easily detected as the laser radiation aimed at a well-known direction with a well-known wavelength.
The countermeasures against the fiber-optic technical reconnaissance tools require special studies on the detection of optical fiber and cable, impact on its conversion capabilities for neutralization, etc.
Conclusion
The provided analysis of the information security threat model for the facilities with the fiber optic technologies shows a wide range and a high level of possible threats that need to be investigated, with development of the possible threat models, training and retraining of the specialists in this area.
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AUTHORS
Vladimir V. Grishachev, Cand.of Sc. (Phys.& Math.), docent, associate professor Institute for Information Sciences and Security Technologies (IISST) Russian State University of the Humanities (RSUH), Moscow, Russia.
ORCID: 0000-0002-7585-7282
Anna D. Zabolotskaya, student Institute for Information Sciences and Security Technologies (IISST) Russian State University of the Humanities (RSUH), Moscow, Russia.
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