Güvenli şekilde dost uçakları tanıma
Secure identification friendly aircraft
Yazar: BUSE TEKİN AYDIN
Danışman: DOÇ. DR. ENVER ÖZDEMİR
İstanbul Teknik Üniversitesi / Bilişim Enstitüsü / Bilişim Uygulamaları Ana Bilim Dalı / Bilgi ve Haberleşme Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol = Computer Engineering and Computer Science and Control

Özet:
Son yıllarda havacılık sektörünün popülerliği hem sivil hem de askeri alanda artmıştır.
Sivil havacılıkta kullanımları yoğun bir şekilde devam eden ve her geçen yıl
kullanımları giderek artan yolcu taşıma uçaklarına, kargo taşıma uçaklarına ek olarak;
insansız hava araçları gibi araçların giderek yaygınlaşmaya başlaması ve drone gibi
yeni nesil insansız hava araçlarının da popülerliğinin artması (gözlem ve insan-yük
taşıma faaliyetlerindeki kullanımlarının artması) bu sektörü her geçen yıl daha da
güçlü kılmaktadır ve sektörün zorlukları da giderek artmaktadır. Askeri havacılıkta
ise kullanımları yıllardır süregelen savaş uçakları, helikopterler gibi hava araçlarına
ek olarak; yine gözlem için kullanılan insansız hava araçları ve savunma-saldırı
için kullanılan silahlı insansız hava araçları, askeri havacılık alanını devletler için
takip edilmesi kaçınılmaz bir alan kılmaktadır. Sektörün mevcut alanlarındaki hava
araçlarının kullanımının artması ve yeni hava araçlarının kullanılmaya başlanması her
ne kadar herkesi memnun etse de, artan trafiğin yönetiminin her geçen gün zorlaşması
sektörün sorunlarından bir tanesi haline gelmiştir. Ayrıca artan bu kullanımla birlikte
güvenlik konusu da gittikçe önem kazanmaktadır. Bu çalışmamızda savaş uçaklarında
bulunan dost - düşman tanıma sistemlerine alternatif olabilecek aynı zamanda sivil
havacılıktaki güvenlik problemlerini de giderebilecek bir tanıma şeması geliştirdik.
Bu tezde yetkisi olmayan uçakların kendilerini diğer uçaklara "dost" olarak tanıtmasını
engellemek amacıyla uçak filoları arasında kullanılabilecek bir tanıma (identification)
şeması tasarlanmıştır. Bu şema havacılık iletişimdeki tanıma sorununa bir çözüm
olarak kullanılabilir. Yöntemimiz klasik şifreleme yöntemlerinin ve sıfır bilgi ispatı
yöntemlerinin bir birleşimidir. Dost filolarda yer alan uçaklara, aynı filo içinde
yer alan uçaklara aynı anahtarlar dağıtılmak üzere, birbirleriyle belirlenen benzerlik
oranında benzeşen gömülü anahtarlar dağıtılmış ve kullandığımız matematiksel modelle
iki filo arasında anahtarlarının benzerliğini anlama kıstası üzerinden bir tanımlama
şeması tasarlanmıştır. Zero Knowledge Proof tekniği sayesinde iki hava aracı arasında
gömülü anahtarına dair hiçbir bilgi paylaşımı olmadan "dost" veya "bilinmeyen"
olarak kategorileştirme işlemi yapılması amaçlanmıştır. Dost kategorisine giren hava
araçlarının mesajları bu iletişim sonrasında işlenirken, bilinmeyen olarak işaretlenen
hava araçlarının mesajlarının dikkate alınmaması sağlanacaktır. Genel olarak bu
çalışmada sıfır bilgi ispatına dayanan yöntemle daha güvenilir bir tanıma sistemi sistem
sunduk.

Abstract:
In last years, aviation industry has become more and more popular. In addition
to being extensively used in air transportation and cargo transportation areas which
are continuing to be used intensively in civil aviation; the increasing popularity of
new generation unmanned aerial vehicles such as drone (observation, human-cargo
transport activities) makes this sector stronger and more challenging every year.
Besides, the air vehicles such as combat aircraft, helicopters, which have been in use
for years in military aviation; the unmanned aerial vehicles that used for observation
and armed unmanned aerial vehicles that used for defense-attack make the military
aviation an inevitable subject to follow closey.
Technological developments have undoubtedly improved their accuracy, consistency,
effectiveness and system continuity of aviation navigation systems. System security
has become a necessity in the sector to eliminate the threats of the aviation
infrastructure. Currently, there is no common vision, common strategy, objectives,
standards, implementation models or international policies defining cyber security for
commercial aviation. It is a common responsibility of governments, airlines, airports
and manufacturers to ensure a safe aviation system and prevent cyber threats.
Avionics which means aviation electronics covers all electronic systems used in an
aircraft. These systems mainly perform navigation, communication, display and other
flight and duty functions. Military avionics systems are indispensable for manned,
unmanned aircraft, missiles and weapons. These systems allow the aircraft to perform
defense, attack and surveillance tasks. The main difference between the Avionics
software and the conventional embedded software is that the avionic software is
optimized for security and the legal arrangements that require the development process
of the software. Avionics become an important discipline with the rapid development
of new generation computers, communication hardware, software languages and
development tools. With these developing areas, the avionics has expanded and
become multi-disciplined.
Although increased usage of vehicles in the existing areas and the newly coming
aircrafts pleased everyone, overseeing and controlling of air traffic has become one
of the biggest problems in the sector. Even if we have developed PSR (Primary
Surveillance Radar) and SSR (Secondary Surveillance Radar) to control the air traffic,
afterwhile these developed technologies become insufficient because of the increased
aircrafts. These radar systems were highly costly and inappropriate for the newly
coming air vehicles. In these radar systems, the vehicles has to communicate with
the ATC (Air Traffic Controller) tower to inform other air crafts and also has to
communicate with ATC tower again to get the information from other air crafts.
In order for the ATC towers to manage the airspace safely, each control unit must understand the status of each aircraft. Traditionally, the PSR and the SSR have fulfilled
this role in various ways since World War II. Both systems are designed at a time
when radio transmission requires a great deal of financial investment and expertise.
Therefore, these old systems were not given any security considerations because they
were assumed to be inaccessible. The rise of Software-Based Radio (SDR) overrides
this assumption and has enabled potential attackers to compromise the system with
fewer resources. Without authentication of the basic protocols, data link level attacks
are more difficult to detect for both aviation systems and users of these systems than
for attacks on traditional analog technologies such as the audio communication system
or primary surveillance radar (PSR).
A new communication technology named ADS-B (Automatic Dependent
Surveillance-Broadcast) has developed and started to be used in air craft vehicles.
Using the global navigation system, ADS-B helps aircraft find their position
independently. Aircrafts can periodically send their altitude, speed and other relevant
data with the help of a digital data connection that communicates with air-to-air and
air-to-land systems. ADS-B is a completely new paradigm for air traffic control. Each
participant gets their position and speed using a built-in GPS ( Global Positioning
System) receiver. The location is then periodically broadcasted by a transmitter
subsystem called ADS-B Out with a message (typically twice per second). The
messages are received and processed by ATC towers on the ground or by nearby
aircraft if the air craft is equipped with ADS-B In. One of the security problem of
ADS-B is that it is impossible to detect the identification of the ADS-B message
sender aircraft.
The critical importance of IFF (Identification Friend or Foe) systems has led to many
studies for it. IFF system is installed in vehicles such as warplanes and warships. It is a
radar transponder that responds correctly with an encrypted message that describes the
aircraft or ship "friend" when interrogated by appropriate radar signal. Interrogative
devices are placed in search, surveillance and capture radars. It is also installed in the
guidance systems of certain antiaircraft missiles. All aircraft and ships equipped with
the IFF may be targetted if they do not react correctly when detected by the radar. In
Air Defense Systems, identification and access control of friendly-foe aircraft are the
necessary protection mechanisms.
Furthermore, security in communication is becoming more and more important with
this increased usage. We have created an identification scheme that can be an
alternative to the identification of friend or foe systems in combat aircraft, which can
also solve the security problems in civil aviation.
There are many different algorithms that provide secure communication in
cryptography. In this study, we will use two algorithms, namely Secret Sharing and
Zero Knowledge Proof (ZKP). ZKP systems were introduced in 1985 by Goldwasser,
Micali and Rackoff. This protocol is based on a Prover convincing a Verifier to validate
knowledge without revealing any information beyond the reality of information. ZKP
techniques are important techniques used in cryptographic algorithms.
Interpolation is a basic mathematical technique to bring something complicated to a
simple or at least less complex structure.Interpolation is an effective tool to make high
precision approximations. These methods generally provide numerical approaches to
calculate complex function values and to evaluate differential equations. Polynomial
interpolation methods date back to 17th century. Polynomial interpolation provides a simple and good way to predict the analytical expression, specifically a function, in a
region stretched by the measured points. The Newton Divided Difference method is a
numerical procedure that is used to interpolate a given set of points.
In this thesis, an identification scheme that can be used between aircraft fleets is
designed to prevent unauthorized aircraft from introducing themselves as "friends" to
other aircraft. This scheme can be used as a solution to the identification problem in
aviation communication. Our method is a combination of classical encryption methods
and zero knowledge proof methods. The method we recommend is not as complicated
as other ZKP methods using graph isomorphism. Moreover, it is not only available for
military aircraft. The identification scheme which we use can also be used by other
non-aeronautical systems, eg on IoT devices. Because we do not use time-varying IFF
codes, the cost of implementation is lower than other methods. This also makes the
operational cost lower. It is more reliable for secret listening attacks. Because we use
the ZKP, the attacker cannot capture or manipulate any confidential information.
In this method, embedded keys similar to each other with the already agreed similarity
ratio are distributed to the aircraft in the friendly fleets. The same keys were
distributed to the aircrafts in the same fleet. Thanks to the mathematical model
designed the identification scheme provides a method to understand the similarity
ratio of the keys between the two aircrafts. In this method, both sides (interrogating
and responding) make polynomial interpolation with the values installed or given.
Interrogator investigates whether the value calculated with a set of values at a certain
point is the same as the responder part. When the values taken from responder includes
the one that was calculated after interpolating polynomial, the responder is marked
as "friend". If the set of values doesn't include the value calculated by interrogator,
then the responder is marked as "foe". The Zero Knowledge Proof technique made it
possible to mark an aircarft vehicle "friend" or "foe" without sharing any information
about their embedded keys.
Thanks to this method, the messages of the aircrafts that belong to "friend" category
will be processed after this communication and the messages of the aircraft marked as
"unknown" will be ignored.
In general, we have presented a more reliable identification system in this study which
is based on zero knowledge proof and classical encryption methods.
The software to be used in this identification model that we have developed can be
dealt with in future studies in a way that is in compliance with DO-178B standard.