Network Physical Layer Attack in the Very High Capacity Networks

OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH Ne wo k Physical Laye A ack in he Ve y High Capaci y Ne wo ks Da id GRENAR1, Jakub FROLKA1, Ka el SLAVICEK 2, O o DOSTAL2, Ma in KYSELAK 3 1Depa men o Telecommunica ions, Facul y o Elec ical Enginee ing and Communica ion, B no Uni e si y o Technology, Technicka 12, 612 00 B no, Czech Republic 2Ins i u e o Compu e Science - IT In as uc u e Di ision, Masa yk Uni e si y, Bo anicka 554/68a, 602 00 B no, Czech Republic 3Depa men o Elec ical Enginee ing, Facul y o Mili a y Technology, Uni e si y o De ence, Kounico a 65, 662 10 B no, Czech Republic [email p o ec ed], olk[email p o ec ed], sla[email p o ec ed]uni.cz, [email p o ec ed]uni.cz, [email p o ec ed] DOI: 10.15598/aeee. 21i1.4973 A icle his o y: Recei ed Dec 15, 2022; Re ised Dec 27, 2022; Accep ed Jan 16, 2023; Published Ma 31, 2023. This is an open access a icle unde he BY-CC license. Abs ac . This pape ocuses on he analysis o ibe op ic line ea esd opping op ions based on cheap and easy- o-use equipmen - o example, he commonly used ibe op ic spli e s wi h sui able op ical powe di ision a ios. The ibe op ic spli e akes a small po ion o he op ical powe su icien o he ea esd oppe o ead he da a and le s as much signal powe as possible pass in he o iginal di ec ion. We a emp ed o de ec he p esence o ibe op ic spli e -based ea esd opping poin s on he communica ion line by using common echniques designa ed o ibe op ic quali y measu emen and aul de ec ion. The esul s a e summa ised in his pape . Keywo ds Ea esd opping de ec ion, ibe op ics, e y high capaci y ne wo k, ne wo k a ic ea esd opping. 1. In oduc ion Wi h he cons an de elopmen o new communica ions se ices ha place g ea e demands on ansmission pa ame e s, op ical ne wo ks a e massi ely used in access ne wo ks. The secu i y conce ns a e eno mous - each yea , companies spend billions o dolla s secu ing hei ne wo ks, and each yea billions o dolla s a e los due o in usions in o hose same ne wo ks. A i s , ibe op ic ne wo ks we e ou ed as one o he mos secu e in as uc u e op ions. In he las couple o yea s, i has been sugges ed ha ibe is almos as easy o ap as coppe [1] and [2]. Today, he e a e millions o miles o ibe cable spanning he globe. La ge amoun o da a a e being ansmi ed ac oss hese cables daily, including sensi i e go e nmen da a, and pe sonal inancial, and medical in o ma ion. Fibe op ic communica ion is widely and publicly unde s ood as a medium ha is di icul o ea esd op on. Un o una ely, his common concep ion is a om he echnical eali y. In his pape , we s udy some cheap and easily accessible ools o ea esd opping on ibe op ic communica ions and explo e he chances o he au oma ic de ec ion o hei placemen on li e ibe op ic lines. I is e y likely ha , in a couple o yea s, con empo a y c yp og aphy used o p o ec communica ion will be ulne able due o he cu en p og ess in quan um compu ing. Fo he ime being, communica ion p o ec ion elies on p o ec ing physical lines agains ea esd opping un il new c yp og aphy algo i hms a e de eloped. Resea ch in his ield is mainly ocused on ad anced echniques based on leading bu cos ly echnology [3]. Howe e , he h ea o cheap and easy ea esd opping is mo e o less unno iced. This pape in ends o illumina e his possibili y. ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 37 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH In o de o ensu e communica ion secu i y, i is necessa y o ocus on physical access o he communica ion in as uc u e. In case o a se e and deli e y in as uc u e, access is loca ed in da a cen e s ha a e unde he cons an supe ision o p o isioning ope a o s. An unimaginable amoun o da a, including sensi i e da a, a e being ansmi ed ac oss hese cables daily. I he wi ing is in a publicly-accessible space, his da a may be comp omised. Thus, igh e access con- ol o he cabling mus be implemen ed. Mo e com- panies need o employ physical laye secu i y sys ems in conjunc ion wi h hei exis ing da a laye secu i y sys ems because physical laye secu i y sys ems a e be e able o de ec and deal wi h in usions o he cables ha do no in ol e an easily measu able amoun o da a in e up ion [4]. Also, i may be ad an ageous o no publish ibe op ic communica ion in as uc u es on he In e ne . This can p o ide a oadmap and b ing a en ion o ibe op ic ulne abili ies. Access ne wo ks a e o en loca ed in public a eas bu a e no p ope ly secu ed. To gain access o da a anspo ed o e he ibe , i is enough o connec an op ical spli e o he ansmission pa h. Then i is possible o ea esd op on all a ic. In o de o o ally block cybe -a acks and hacking, he access ne wo k should be p o ec ed. I a company enc yp s i s ansmi ed da a, i could p o e o be a s umbling block o in ude s. Depending on he enc yp ion me hods used, i may only be a ma e o ime be o e he in ude b eaks he enc yp ion and ob ains hei desi ed da a. Ou mo i a ion o his wo k is he MeDiMed in as uc u e used o medicine pic u e da a anspo and p ocessing (documen ed in [5], [6], [7], [8], [9], and many o he s). MeDiMed is a sha ed egional Pic u e A chi ing and Communica ion Sys em (PACS) se ing hospi als in B no and he su ounding a ea. The sys em acili a es as and secu e commu- nica ion among indi idual hospi als, enables deli e y o some se ices h ough he compu e ne wo k, and o e s o he capabili ies o oday’s compu e sys ems and da a ne wo ks o medical use s [10]. The sys em deals wi h he secu e ansmission, a chi ing, and sha ing o medical image da a o igina ing om a ious modali ies (compu ed omog aphy, magne ic esonance, mammog aphy, e c.). The secu i y needs o he MeDiMed sys em a e he mo i a ion o his a icle. In his e- sea ch, we ha e made use o he expe ience gained du ing he de elopmen and deploymen o he op ical backbone o he Czech NREN ne wo k CESNET [11], [12], [13] and [14]. 1.1. S a e o he A and Rela ed Wo k Cu en ly, scien i ic pape s ocus mainly on sophis ica ed ibe op ic line ea esd opping echnologies. Fo example, in [15], ad anced deep lea ning algo i hms a e discussed. In [16], he au ho s ocus on ea esd opping and espec i e de ense measu es using ibe bending and simila echnologies. In [17], he possible u iliza ion o in-band c oss alk o op ical anspo line ea esd opping is discussed. In [18], he au ho s discuss possibili ies o ibe op ics bending u iliza ion. All o hese ela ed wo ks u ilize ela i ely expensi e echnology and complica ed p ocedu es. Howe e , he bigges isk o cu en ly used ibe op ic ne wo ks lies in cheap and easy- o-use echnologies. This pape demons a es he ea esd opping capabili ies o e y simple equipmen - a ibe op ic powe spli e . The e a e se e al ela ed wo ks dealing wi h ibe op ics in as uc u e secu i y in gene al, [19] and [20], ela ed echnologies [21], [22] and [3], o secu i y in DWDM backbone ne wo ks ([23] and access ne wo ks - GPON [24] and [25]. Ou ocus is en e p ise and me opoli an ne wo ks. These ne wo ks commonly use gigabi and en-gigabi e he ne o e singlemode ibe and a e mo e suscep ible o a acks as he p o ec ion o cabine s wi h pa ch panels is no as s ic as in he case o backbone anspo ne wo ks, and he echnology is no as igh as in he case o GPON ne wo ks. An a acke can use any main enance window o ins all ibe op ic spli e s in o he line o in e es . Ano he ac o wo king o he e en ual a acke is a highe equency o changes in his ype o ne wo k so ha e en sho unannounced in e up s can pass wi hou no ice om he side o he ne wo k ope a o and adequa e secu i y checks. We ha e expe imen ally app o ed ha in he case o gigabi e he ne e en a spli e wi h a 5:95 op ical powe dis ibu ion can p o ide enough op ical powe o an ea esd oppe , allowing him o he o cap u e da a a ic using common ne wo k equipmen wi hou he need o op ical ampli ica ion o any o he ad anced ool o gea . 2. Technology o Op ical Ne wo ks Ea esd opping This sec ion discusses he key echnologies and p ocesses sui able o cos -e ec i e op ical ne wo k ea esd opping. ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 38 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH The main ad an age o physical line ea esd opping is he long- e m a ailabili y o da a. Once he ea es- d opping poin is ins alled, i can p o ide a copy o all he da a anspo ed un il i is disco e ed and emo ed. The main d awback o ea esd opping is ha he a acke canno gain access o any da a hey choose, bu only ha anspo ed o e he a ec ed communica ion media. O cou se, he a acke has o ully unde s and he communica ion p o ocol s ack in use and needs enough compu ing powe o eassemble he sensi i e da a om communica ions p o ocols, packe s, and ames. Gaining access o da a anspo ed o e he ibe op ic line is much easie han commonly belie ed. An essen ial ool is a gene al ibe op ic spli e wi h he p ope coupling a io. An example o such a spli e is in Fig. 1. Equipped wi h he p ope ibe ype and casing, i is di icul o dis inguish he spli e om he pa chco d i placed in o a ibe op ic ack. This componen is a ailable in se e al e-shops o less han 15 USD. As men ioned be o e, we ocus on cheap and easy- o-use ea esd opping equipmen . This kind o equipmen can be used in many ins ances and doesn’ equi e in-dep h knowledge o i s use s. Fo his eason, we conside his kind o ea esd opping isk se e e compa ed o o he , mo e ad anced echnologies. Fig. 1: An example o a ibe op ic spli e equipped wi h p ope ibe ype and casing, making i di icul o be de ec ed in a ibe op ic ack. The same componen , usually encased in a ack-moun able chassis, is commonly used by secu i y inciden esponse eams o ne wo k a ic analysis. The echnology used by secu i y moni o ing eams o gain ne wo k a ic samples o analysis and he echnology used by a acke s o ne wo k a ic ea esd opping is almos he same. The main di e ences a e he encasing and, o cou se, he eason o apping he ne wo k a ic. The ollowing sec ions discuss possible ways o de ec ing spli e s inside a ibe op ic line. As discussed la e , he echnical capabili ies o de ec ing spli e s in ibe op ic lines a e limi ed. The e is no way o dis inguish he eason o he p esence o a spli e . Howe e , e en o ne wo k a ic analysis pe o med by he ne wo k ope a o , he ne wo k moni o ing de ice has access o he whole da a a ic, like an illegal ea esd oppe , bu commonly only p o ides agg ega e ou pu in he o m o ne wo k and low s a is ics, like Ne low o IPFIX. The way o u ilizing a ne wo k moni o is, o some ex en , up o he conscience and choices o he ne wo k ope a o . 100% 70% 30% 100% 70% 30% Ne wo k T a ic Moni o TX RX RX TX Fig. 2: An example o a ypical ne wo k a ic moni o ing TAP connec ion. 100% 5% 95% Illegal Moni o TX RX Fig. 3: Basic ea esd opping TAP connec ion. 100% 5% 95% Illegal Moni o 100% 5% 95% TX/RX TX/RX Fig. 4: Bidi ec ional ea esd opping TAP connec ion. 3. Ea esd opping Poin De ec ion The cos o an op ical spli e is insigni ican , and i s ins alla ion is almos e o less. Le us conside he op ions o op ical spli e de ec ion ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 39 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH 100% 5% 95% 100% 5% 95% Illegal Moni o Fibe Op ics Isola o TX/RX TX/RX Fig. 5: Ea esd opping TAP wi h p o ec ion agains he OTDR de ec o . u ilizing equipmen and echniques commonly used in elecommunica ion ne wo k deploymen and ope a ion. The i s and p obably he mos ob ious way is op ical pe o mance moni o ing. The second me hod is Op ical Time-Domain Re lec ome e (OTDR) u iliza ion. We ha e se up a simple es ing scena io based on a simple ansmi e and ecei e using he SFP module wi h a 1550 nm wa eleng h and ibe op ic lines used as pa o he physical ne wo k in as uc u e in he com- pu e cen e . We ins alled a ibe op ic spli e inside he line ins ead o he pa chco d. A spli e wi h a coupling a io o 5:95 was used, and gigabi e he ne a ic was success ully ea esd opped on and ead by he simula ed boo leg de ice. All es s we e pe o med on legacy ITU-T G.652 ibe op ic lines and pa chco ds based on a G.657 ibe . We pe o med a se o measu emen s o analyze he di e ences in de ec ing he spli e by bo h op i- cal pe o mance moni o ing and OTDR measu emen s. The EXFO FTB-7300D-234B-EI OTDR was used o ou expe imen s. This ype o OTDR is used o he daily ope a ion o he uni e si y’s ibe op ic ne - wo k. We used h ee scena ios o spli e placemen s, as shown in Fig. 3, Fig. 4 and Fig. 5, whe e Fig. 5 is ele an only o OTDR measu emen s. To demon- s a e he eal capabili ies o ibe op ic ea esd opping componen s and he limi ed possibili ies o hei de- ec ion, we se up a lab model and pe o med a se o measu emen s. The lab model is shown in Fig. 6. The esul s a e summa ized in he ollowing sec ions. We used h ee local op ical loops: wo o hem simula ing communica ion lines on he igu e deno ed as lines 1–2 and 3–4, and one used as a simula ion o an a acke on he igu e line 5–6. A ixed a enua o o 5 dB was inse ed in he middle o line 1–2; ano he a enua o o 10 dB was inse ed in he middle o line 124 3 56 100% 5% 95% 2 5 3 100% 5% 95% 23 5 DUT−A 100% 5% 95% 100% 5% 95% 2 5 3 DUT−C 5 100% 5% 95% 100% 5% 95% 23 DUT−D DUT DUT−B Fig. 6: LAB model used o op ical ea esd opping componen s analysis. 3–4; line 5–6 was s aigh . The o e all a enua ion o line 1–2 was 8.6 dB, he a enua ion o line 3–4 was 12.7 dB, and he a enua ion o line 5–6 was 1.4 dB. 3.1. Ea esd opping Poin De ec ion by Op ical Pe o mance Moni o ing The op ical spli e in oduces addi ional inse ion loss in o he ibe op ic line. The added inse ion loss is gi en by he connec o s and he coupling a io o he inse ed spli e . The line inse ion losses o he cases o he s aigh line, one spli e usage, and wo spli e usage o gaining independence on he ansmission di ec ion a e gi en in he ollowing Tab. 1: Tab. 1: Spli e inse ion loss balance. Line se up A enua ion A enua ion inc emen s aigh 21.8 dB – (pa chco d only) single spli e 22.3 dB 0.5 dB (Fig. 3) wo spli e s 22.9 dB 0.9 dB (Fig. 4) ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 40 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH Tab. 2: Gigabi e he ne SFP op ical pe o mance moni o ing p ecision analysis. DUT DUT Pw me e DUT RX TX RX RX balanced (dBm) (dBm) (dBm) (dBm) min 2.45 −13.90 −13.90 −14.32 max 2.45 −12.72 −13.86 −13.10 a g 2.45 −13.32 −13.88 −13.72 s dde 0dB 0.22 dB 0.01 dB 0.22 dB I is easy o see ha he a enua ion inc emen is no la ge. Fu he , we analyzed he op ical pe o mance moni o ing p ecision o some commonly-used SFP modules. We measu ed he gigabi e he ne modules used o a ic ea esd opping in ou expe imen , a mul i- a e 100 Mbps o 2.4 Gbps SFP module, and a en-gigabi e he ne SPF+, all o hem ansmi ing on a p ecise wa eleng h in a 100 GHz DWDM g id. These SFP and SFP+ modules will be also called a De ice Unde Tes (DUT). Fo measu emen , we used he lab se up p esen ed in Fig. 7. The ou pu o he measu ed SPF was a enua ed by a ixed 10 dB a enua o . SFP TX RX Spli e 50:50 49.2 50.8 IN PM−212 Fig. 7: SFP module op ical pe o mance measu emen p ecision analysis. To ob ain p ecise measu emen s, we i s analyzed he coupling a io o he spli e used in his se up. The coupling a io o he spli e (A:B) was de e mined o be 49.2:50.8. The esul s om ou measu emen s a e summa ized in Tab. 2, Tab. 3, and Tab. 4. The o iginal measu ed da a a e a ailable upon eques o e i ica ion o u he p ocessing. In all cases, he measu emen was 20 minu es long wi h a 10 s ime delay. This was enough o see he ins abili y o he SFP module measu emen esul s. Tab. 3: Mul i a e SFP op ical pe o mance moni o ing p ecision analysis. DUT DUT Pw me e DUT RX TX RX RX balanced (dBm) (dBm) (dBm) (dBm) min 1.91 −13.30 −13.70 −13.43 max 1.96 −13.21 −13.61 −13.39 a g 1.93 −13.26 −13.66 −13.41 s dde 0.01 dB 0.02 dB 0.02 dB 0.01 dB F om he abo e-men ioned measu emen s, i is e iden ha he commonly used op ical pe o mance measu emen o e ed by SFP op ical modules is no p ecise enough o eliably de ec op ical line pe o mance dec eases caused by ea esd opping equipmen inse ion. The only excep ion is he Tab. 4: Tengigabi e he ne SFP+ op ical pe o mance moni o ing p ecision analysis. DUT DUT Pw me e DUT RX TX RX RX balanced (dBm) (dBm) (dBm) (dBm) min 1.43 −14.88 −15.33 −14.63 max 1.49 −14.01 −14.43 −14.48 a g 1.45 −14.41 −14.84 −14.54 s dde 0.02 dB 0.18 dB 0.19 dB 0.03 dB mul i- a e SFP. Mo eo e , he a enua ion o he ibe op ic line changes in ime due o he change o mechanical s ess caused by, o example, empe a u e changes o o he ex e nal in luences. In ou long- e m expe ience, he daily a ia ion o a 40 km long op ical line a enua ion is abou 0.6 dB. Adding a simple ibe op ic spli e causes only a e y small inc ease in he communica ion line inse ion loss (0.5 dB). This inse ion loss is ypically below he common daily luc ua ion o communica ion line inse ion loss. Mo eo e , he p ecision o ypical op ical pe o mance moni o ing pe o med by SFP and simila op ical modules is beyond his ma gin as well. Fo his eason, a simple analysis o op ical pe o mance is no enough o de ec a ibe op ic spli e inse ed in o he communica ion line. Fo a mo e sophis ica ed cons uc ion based on wo op ical spli e s, he inse ion loss inc ease (0.9 dB) is somewha de ec able, bu a basic op imiza ion o he cons uc ed ea esd opping equipmen can sligh ly dec ease he inse ed loss and make his cons uc ion almos in isible as well. 3.2. Ea esd opping Poin De ec ion by OTDR The u iliza ion o OTDR could be used o de ec ea esd opping poin s inside a ibe op ic line. We es ed he lab se up as desc ibed in Fig. 6 wi h OTDR as well. To achie e he bes possible esolu ion, we used he smalles possible pulse du a ion o e ed by OTDR. The measu emen was pe o med on h ee commonly used wa eleng hs: 1310 nm, 1550 nm, and 1625 nm. The esul s we e almos iden ical. To imp o e he eadabili y o he g aphs and ables, we used he 1550 nm measu emen in he ollowing explana ion and discussion. Acco ding o he sho leng h o he es ed ibe , we used he sho es a ailable pulse du a ion (5 ns), co esponding o a pulse leng h o 1 m. The leng h o he launch cable used was 500 m and he measu emen a e aging pe iod was 30 s. We used he es se up desc ibed in Fig. 6. The es ed ibe op ic lines we e simula ed on se e al looped oom- o- oom cables in ou compu e cen e . We had wo cables a ailable, wi h leng hs o 20 m and 30 m, espec i ely. Se e al lines om hese ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 41 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 8: Re e ence measu emen o ea esd opped line. 0 5 10 15 20 25 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 9: Re e ence measu emen o an ea esd oppe . cables we e in e connec ed by pa chcables e mina ing in ei he APC polished connec o s (E2000) i we in ended he connec o o be almos in isible on a e lec og am, o PC polished connec o s (PC/APC) i we in ended he connec o o be s ongly isible. The i s segmen (1–2 in Fig. 6) was 64 m in leng h wi h APC connec o s only and simula ed a clean segmen om he a acked da a sou ce. The second segmen (3–4) simula ed a con inua ion o he line om he ea esd opping poin owa d he da a des ina ion unde a ack. This line had a o al leng h o 232 m and PC connec o s a e 64 m, hen 50 m and 25 m wi h a 5 dB a enua o inse ed. Line 5–6 simula ed he pa h om he ibe op ic spli e owa d he ac i e ea esd oppe de ice. This line con ained 3 PC-based in e connec ions o be e isibili y on he OTDR. ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 42 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 10: Ea esd opping equipmen a ian A - simple op ical spli e . 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 11: Ea esd opping equipmen a ian B - simple op ical spli e equipped wi h a ci cula o used as an isola o . The e e ence OTDR measu emen on lines 1–2 and 3–4 in e connec ed ia a simple 2 m pa chcable is shown in Fig. 8. The i s 500 m segmen is he launch cable. The i s peak is he beginning o he emula ed communica ion line. The big peak ep esen s he end o he clean line and he beginning o he segmen wi h impe ec connec o s. The mos impo an pa o he measu emen is emphasized by he dashed box. I ep esen s he pa whe e he op ical pa chco d was eplaced by a ibe op ic spli e o a se o spli e s and ci cula o s as deno ed in Fig. 6. Line 5–6 was used o emula e he ea esd oppe communica ion line. The e e ence OTDR measu e- men is p esen ed in Fig. 9. In e es ingly, lines wi h impe ec connec o s, such as his se up, can cause be e e lec ions in OTDR. I is expec ed ha he pa e n in he dashed box will be p esen on e lec og ams om se ups using ibe op ic spli e s. ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 43 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 12: Two op ical spli e s connec ed in opposi e di ec ions o ob ain di ec ion-independen ea esd opping. 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Signal s eng h (dB) Dis ance (km) Fig. 13: Two op ical spli e s equipped wi h an op ical ci cula o . The OTDR measu emen s o he ou possible modes o ea esd opping as depic ed in Fig. 6 and e e ed o as connec ions A, B, C, and D a e in Fig. 10, Fig. 11, Fig. 12 and Fig. 13, espec i ely. I is easy o see ha he pa e n o he ea esd oppe ’s communica ion line ep esen ed in Fig. 9 is di icul o ind in he e lec og ams; his is ue, especially in he case o ci cula o u iliza ion, whe e his line is comple ely in isible on he e lec og ams. E en when u ilizing a spli e di ec ly wi hou hiding he ea esd opping communica ion line behind an isola o o ci cula o , i is no easy o no ice he ea esd opping poin . I an isola o o ci cula o is used, he spli e is almos in isible o commonly used measu emen s as can easily be seen om e lec og ams Fig. 10, Fig. 11, Fig. 12 and Fig. 13 - emphasized by he dashed box. ©2023 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 44 OPTICS AND OPTOELECTRONICS VOLUME: 21 |NUMBER: 1 |2023 |MARCH All he op ical equipmen used a e easy o acqui e om many online componen s o es o e y low p ices compa ed o commonly used ne wo k equipmen . The ac i e ne wo king de ices needed o op ical communica ion ea esd opping migh be he same as he ones used o igh ul ne wo k a ic moni o ing. Ea esd opping on op ical communica ion lines is echnically much easie and, a he same ime, cheape han mos o i s use s commonly belie e. Mo eo e , de ec ing op ical ea esd opping is e y di icul and almos impossible o achie e using common measu emen equipmen , as he key componen s beha e oo simila ly o gene al op ical pa chcables. 4. Discussion We ha e measu ed he p ope ies o ibe op ic spli e s and hei simple cons uc ions which could be used o ibe op ic communica ion ea esd opping. As expec ed, e en a a he s ong spli a io (only 5 % o op ical powe used o he ea esd oppe ) is enough o ob ain a good quali y signal o he a acke while minimizing he impac o he ea esd opped line i sel . The spli e is almos unde ec able by common measu emen equipmen like OTDR and/o analysis o he op ical powe le el. Simply modi ying his elemen (adding an op ical isola o o ci cula o ) can make i mos ly in isible o common measu emen s. Al hough he ins alla ion o his ype o ea esd opping equipmen needs some speci ic knowledge and physical access o he cabling in as uc u e, he simplici y and p ice a ailabili y, oge he wi h he p og ess in quan um compu ing needed o con empo a y c yp og aphic p o ec ion mi iga ion, will make his h ea e y se ious in he nea u u e. The aim o his pape is o poin ou he p oblem o communica ion ne wo ks’ physical in as uc u e secu i y and especially o emphasize he isk o ea esd opping on ibe op ic communica ion lines. The echnical equipmen needed o ap he ne wo k a ic is o e y low cos . The cos o he equipmen needed o analyze he apped a ic co esponds o he used communica ion p o ocol and he cos o he equipmen used by he ea esd opping ic im. The mos impo an p ope y o op ical ne wo k ea esd opping in his con ex is he ac ha i is almos unde ec able by commonly used measu emen equipmen . To main ain p i acy, he use o s ong c yp og aphy is necessa y, e en in he case o communica ions o e ibe op ic lines. I is expec ed ha con empo a y enc yp ion algo i hms will be no mo e secu e in he nea u u e. Cu en ly, p ope ly inspec ing ibe op ic lines and en o cing he eplacemen o disman lable connec ions (connec o s) by non-disman lable ones (splices) will be c ucial. Acknowledgmen This wo k was suppo ed by he g an p ojec o he Minis y o In e io o he Czech Republic, no. VI20192022140. Au ho Con ibu ions K.S. concei ed o he p esen ed idea, D.G. de eloped he heo e ical o malism and pe o med he expe imen al wo k. E alua ion o he expe imen was by J.F. and K.S. e i ied he analy ical and nume ical me hods. D.G., M.K., and J.F. con ibu ed o he inal e sion o he manusc ip . O.D. supe ised he p ojec . Re e ences [1] SKOUBY, K. E., P. DHOTRE, I. WILLIAMS and K. K. HIRAN. 5G, Cybe secu i y and P i- acy in De eloping Coun ies. 1s ed. Boca Ra on: CRC P ess, 2022. ISBN 978-87-7022-647-9. [2] FUHR, P. L. A Sepa a e Ne wo k o Con ol Sys- em Cybe Secu i y. In: 6 h In e na ional Sympo- sium o ICS &SCADA Cybe Secu i y Resea ch 2019 (ICS-CSR). A hens: Science open, 2019, pp. 144–156. DOI: 10.14236/ewic/icscs 19.18. [3] NOVOTNY, V., P. SYSEL, J. PRINOSIL, J. MEKYSKA, K. SLAVICEK and I. LAT- TENBERG. C i ical In as uc u e Moni o - ing Sys em. In: 2021 IEEE 17 h In e na- ional Colloquium on Signal P ocessing & I s Applica ions (CSPA). Langkawi: IEEE, 2021, pp. 165–170. ISBN 978-1-66541-484-5. DOI: 10.1109/CSPA52141.2021.9377303. [4] CHYAD, R. M., A. H. ALI, N. H. KHALEF, A. A. HAMAD, A. I. MAHMOOD, B. R. MAHDI, W. H. RASHID and N. K. SHAIEE. Design and Cons uc ion o Secu i y Moni- o ing Sys em o Op ical Fib e Communica ions. Jou nal o Physics: Con e ence Se ies. 2019, ol. 1234, iss. 1, pp. 1–7. ISSN 1742-6596. DOI: 10.1088/1742-6596/1234/1/012008. [5] WANG, D. Selec ed Topics on Compu ed Tomog aphy. 1s ed. London: In echOpen, 2013. 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