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firstly described the weakness of transmission data in
the downstream direction. The work (Froehlich et al.,
2005) employs a patented Optical Tapped Delay Line
(OTDL) channelizer. This technology is able to chan-
nelize an information-carrying light into many narrow
spectral subbands and change a phase of each of them.
OTDL can be used in fibre and free-space optical
communication transmission systems. They present
the option of using these systems for Wavelength-
Division Multiplexing (WDM) systems but do not
show how the management changes the key for a sep-
arate wavelength in real time applications. Further,
the paper (Kochman and Wornell, 2012) introduces
the key distribution in free-space optical communi-
cation. The authors incorporate Pulse-Position Mod-
ulation (PPM) over multiple spatial degrees of free
spaces. They use the quantum key distribution model
to establish a key in a quantum channel and a classi-
cal channel. The work (Martinez-Mateo et al., 2014)
deals with the quantum key distribution in passive op-
tical networks. The authors present how to implement
the quantum cryptography into the standard access
optical networks. They present a solution for Time
Division Multiplexing (TDM) based PON. For exam-
ple, in TDM-Based PON with 128 ONUs, a quantum
emitter (and a receiver) has to be connected to one
port of an optical splitter. In general, current networks
are combination of TDM and WDM networks.
The papers (Hajduczenia et al., 2007), (Mendonca
et al., 2012) and (Xu et al., 2010) introduce the se-
curity issues in passive optical networks and the en-
cryption method of next generation PON systems. In
the paper (Hajduczenia et al., 2007), the security is-
sues of Ethernet PON (EPON) are discussed. On the
other hand, the article describes security issues and
attacks in EPON networks: eavesdropping, denial-
of-Service, masquerading and theft-of-service. The
paper (Mendonca et al., 2012) introduces security is-
sues which address reflection. In general, the au-
thors describe dividing the signal in the optical splitter
and the measurement of reflection in a PON physical
medium. The knowledge of the frame structure and
a sensitive detector are required for the detection of
transmitted data.
The authors (Eun and Kwon, 2006) analyze the
design of key security in EPON. They use a pseudo
random function for generating keys. The output of
the function is a 160 bit random. Their solution needs
some requests of ONU and OLT to change a key. In
EPON and all others PON networks, downstream is
transferred as broadcast, which means that all nodes
receive the whole signal. Only ONU with the same
ONU-ID can decode the frame. On the other hand,
the EPON networks use the well-known structure of
the frame. Optical traffic analyzer enables to read the
parameters of the network (source and destination ad-
dresses, lengths, types, timestamps, data etc.).
The article (Xu et al., 2010) deals with high speed
encryption methods for next generation PON systems.
The designed method is divided into 3 parts: key gen-
eration, key synchronization and key exchange. Se-
cret encryption keys are sent from ONUs to OLT to
prevent other ONUs from eavesdropping these keys.
Nevertheless, the authors do not describe the first
communication states between OLT and ONU units.
In these states, the first key establishment is realized.
Further, the possibility of upstream eavesdropping has
not been considered in the paper.
In GPON networks, the frames have the compli-
cated structure, i.e., many encapsulations with vari-
able lengths of parts. Nevertheless, ONUs are able to
listen the downstream communication in PONs and
GPONs. Further, we assume the presence of an adver-
sary who is able to listen both directions and read data
from ONUs, including keys that are sent in upstream
like in (Xu et al., 2010). Due to this fact, we deal with
more robust key establishment. The goal of this paper
is to provide secure GPON systems by a proposed se-
cure key establishment protocol and data encryption.
1.2 Our Contributions
The contributions of this paper are summarized in the
following text:
1. We analyze security in gigabit passive optical net-
works and emphasize some security flaws of the
ITU-T G.984 standard (ITU, 2014) that occur dur-
ing the establishment of the session secret keys.
2. We propose a novel key establishment protocol
which is based on secure assumptions and uses
the signal propagation measurement to establish
a common value between two communication
nodes. The propagation value between certain
ONU and OLT serves as a weak password and
an identifier and protects against impersonating
attacks. Our key establishment protocol protects
against passive adversaries.
2 SECURITY IN GIGABIT
PASSIVE OPTICAL
NETWORKS
The communication units (OLT and ONU) need to be
synchronized in the downstream direction (from an
OLT view). The synchronization process starts in the
first state called Initial state (O1). ONU asserts LOS
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