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Abstract—After decades of research, computer scientists have
in recent years come close to reaching substantive results which
prove the usability of quantum key distribution (QKD). Several
QKD protocols and different schemes have surfaced since the last
century. Additionally, some of these protocols were created in
new algorithms and up until now, have been proven to be secure;
however, other scientists only made modifications to previous
original protocols. This paper seeks to create a new scheme in
QKD that will communicate between two parties and will give
them a high level of security against any well-known attacks
while handling both of parties in a manner that will reduce their
dependency on both classic communication and the classical
channel.
Index Terms—Quantum key distribution, EPR pair,
Entanglement state, QKD attacks.
I. INTRODUCTION
OR several centuries, cryptography has been, and still
remains, a challenge to many computer scientists as well
as physicists. As long as more information and data are
transferred from one party to another, there is the need for
even more security for the data and information being
transferred. With regards to security, several schemes were
proven to be either new complicated computing algorithms or
improving existing ones. Cryptography is considered as the art
of encoding and decoding messages, and will remain
necessary as long as cyber eavesdroppers exist. Therefore, the
science of cryptography deals with keeping these information
secure [1].
Today, majority of the biggest systems and applications are
still being run using conventional cryptography, which is still
powerful enough to keep attackers away from stealing or
tapping into any important information. As compared to
quantum computing, classical security systems that depend
upon complicated computing algorithms are extremely weak.
Furthermore, if quantum cryptography became tangible and
useable, conventional cryptography would easy to break [2].
Classical security is still in wide use and several schemes have
shaken up the whole community of security. One of these
schemes was invented by Shor in 1994 and is not only based
on the factorization of prime numbers but still occupies a top
rank in classical cryptography. Also, most encryption theories
are based on mathematical operations, which are usually
capable of being attacked [3]. Quantum Mechanics is a ray of
hope which seeks to change several weaknesses in the
classical system.
II. QUANTUM KEY DISTRIBUTION
A. BB84 protocol
Quantum key Distribution permits in general two parties
so-named Alice (the sender) and Bob (the receiver) to
communicate over the quantum channel with the ability to
realize the occurrence of any form of eavesdropping as Eve
(the eavesdropper), may or may not disturb the established
connection [4]. BB84 protocol, which is still a unique QKD
protocol, is the first step in this approach. Most of today’s
protocols have been designed on the same idea. Bennett and
Brassard in [5] came up with an innovative protocol that
uses the polarization of photons. They also divided the
communication between Alice and Bob into two channels
(Quantum and public channel).
In 2000, Shor and Preskill in [6] proved the BB84
protocol to be a secure quantum protocol. In [7] Gottesman
and others again proved that the security of the BB84 is the
source and detector under a limit control of an adversary.
Also, the above mentioned protocol is still considered as
one of spotlights in the last two decades and has seen
unique transformations between the two parties.
Additionally, [8] proved the BB84 as still standing against
the King Mean Problem that was created by J. Bub in 2001.
Most scientists are of the conviction that quantum
computing is the future for this field. In QKD, if for any
reason interruption occurs, the system will in turn realize it
immediately.
Even though in recent times certain protocols have been
created because the authors mentioned above announced
that the BB84 is unsecure, the BB84 and other protocols
started as first a generation commercial system [9]. In [10]
Scarani et al. implemented another QKD protocol that was
extracted from the previous protocol BB84. SARG04 has
the same features as the BB84 protocol except in a classical
sifting procedure, in which the SARG04 is considered as
robust against the optimal individual eavesdropping as well
as photon-number splitting (PNS) attacks. The existence of
PNS will result in dramatic consequences in security
analysis [11].
This paper will discuss the advantages of BB84 and EPR in
order to improve the new scheme. The new scheme derives
its robustness from the advantages that have already been
discovered in either the BB84 or EPR.
Initiated decoy States in Quantum Key
Distribution Protocol by 3 ways channel
Abdulbast Abushgra, Khaled Elleithy
F
Abdulbast Abushgra Khaled Elleithy
aabushgr@my.bridgeport.edu elleithy@bridgeport.edu
Department of Computer Science & Engineering
University of Bridgeport, CT USA
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B. EPR Protocol
EPR in [12] was invented by Einstein, Podolsky, and
Rosen, who presented the EPR paradox in 1935. In their
paper, they argued about the completeness of physical
theory in quantum mechanics. Basically, the EPR protocol
is defined by EPR pair as:
|>
>>,
|>
>>.
Where |0> and |1> are the eigenvectors of the Pauli
operator, which the single photon will be measured by one
of the legitimate parties that end up destroying the
measurement state, and also determine the measurement of
a particular state. For instance, measuring one of the created
photons in the Bell’s state |> and getting |1> that means
the other photon will collapse to the state |0> [13]. To
authenticate the communication, Alice can follow this
scenario by using redundant coding, which she can encode
one bit by two qubits [14].
EPR protocol has been modified in several researches
and papers as [15] where Hwang and Lee tried to add more
efficiency to the protocol. Both Alice and Bob are able to
generate the EPR pair which the receiver can preserve. One
of the assumptions here is that no collision occurs between
the photon states, and the used measurement system is
polarization as described above. Moreover, Dong and others
in [16] presented a multiparty Quantum Secret Sharing
(QSS) protocol that is based on entanglement swapping and
random EPR selection, which has raised the probability of
detecting the eavesdropper to 95.8%, which means more
efficiency.
III. THE NEW QUANTUM KEY SCHEME
As mentioned above, the new scheme can be reflected on
one of the protocols that are extracted by BB84, or more
precisely the new scheme can be transmitted into the
quantum channel initializing two, four, or six states.
Generally, computer scientists believe quantum mechanics
is not the whole solution but rather part of it. They also
know that the law of physics can be a major aspect of
creating a security system, where QKD protocols have
proved two parties as being able to establish a
communication under generating a secret binary string that
is totally random [17]. Now as cryptography, we still need
more of complicated computing as well as some tricks to
provide perfection to our protocols.
In this paper, we provide a new QKD protocol that will
use different systematic processes of submitting channels,
where we try to capitalize on the advantage of the law of
physics, the variety of BB84 and EPR protocol.
A. Proposal Scheme
The new protocol practically utilizes the features of EPR
pairs to ensure the authentication of the initiated
communication between the two parties that generally raises
the reliability and the accuracy of the protocol to more than
50% as compared to the other protocols such as regular BB84.
Moreover, The BB84 is used in this scheme as fundamental
polarization, in which the sender party can create the electron
(photon) in four bases by sending the photon randomly in
different states. Also, the length of the code depends upon the
text that Alice wants to share with Bob. Here, the steps of the
proposed protocol are explained in sequentially as follows:
- Step 1: Alice creates n EPR pair, keeps photon A and
sends photon B to Bob as shown in [18],[19] and [20],
this string of photons includes the authentication key,
the length (includes the dimension of the matrix) of
next sent qubits and the time when Alice starts
submitting the first qubit (giving the signature and
confidentiality to Bob).
|>
>>,
|>
>>,
|>
>>,
|>
>>.
- Step 2: Bob resends the authentication key and the
bases code into the first channel (orthogonal basis = 0,
and orthonormal = 1) this is done by creating an
auxiliary qubit and which is then transferred into C-
NOT gate.
- Step 3: Alice starts preparing the bits and passes them
through the polarization device. This process will be
done by entering the code bits randomly in lower
triangle (l) and filling in the upper triangle (u)
sequentially. After this, she modifies every row to be
even by filling the diagonal with (0 or 1); hence,
making the rows even.
Figure (1) shows the table that prepared by Alice
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- Step 4: Alice submits the rows of prepared matrix in
random selections, where she picks up different indices
every time, and then submits the whole string of
photons to Bob. Here, I would mention to Eve that she
cannot figure out the submitted qubits because they
have been submitted in the rows randomly.
Figure (2) shows the submitted string of qubits
- Step 5: Bob at the other side measures the upcoming
qubits from Alice that are supposed to be in either {|0>,
|1>, |+>, |–>} in random bases {+ or ×}. He measures
the qubits into Pauli-Matrices operators (z, x). Next, he
places the measured qubits in the well-known matrix
and then starts to sort the matrix as Alice mentioned in
EPR communication.
,
.
- Step 6: Bob sends just the upper triangle to Alice in a
sorted string of one basis (the agreement was fulfilled
since the first communication). If Alice agreed to the
received photons, she will end the quantum
communication and start the classical channel. On the
other hand, if Alice does not accept the upper triangle
that was sent by Bob, she will send the measured bases
in sequence to Bob by classical channel (1 and 0).
Where is the whole qubits that are represented
in one matrix and should be sent to Bob row by row.
- Step 7: Bob compares the measured qubits with those
sent by Alice. If the measured qubits contains
differences, he will then know that a third party was
existent and tapping or eavesdropping. In this case he
informs Alice to ignore the interrupted ones or rejects
the whole communication if the rate of interrupted
qubits is over 50%.
Figure (3) shows the new scheme diagram.
The new scheme demonstrates a protocol that contains
three ways of communication between two parties. It begins
by affirming the authentication prior to starting the transfer
of the encoded qubits by quantum channel. The first
communication will be processed by the EPR channel
where both of the legitimate parties do not need to keep
their information in the memory for a long time. In addition,
this information should be short and effective. The second
scenario of the communication is transferring the encoded
information into the two bases quantum system, which is
considered as BB84 in the polarization system. One of the
advantages in this protocol is the reduction of classical
communication to the last station in order to confirm the
previous transfers, and to combine the reconciliation and
error correction in the connection steps.
B. The simulation
The new protocol has been examined to have certain
common features with protocols such as the BB84. This
was done by creating a certain level of noise in the channels
of both protocols. The created noises comprised White
Gaussian Noise, Intercept-Resend (IRA) Attack and others.
Our protocol recorded a high ability to stand resist the IRA
attack when it was applied and measured with BB84. It also
recorded a higher ratio as compared to BB84 as shown in
table [1]:
TABLE I
THE RATIO OF THE SUBMITTED QUBITS.
Qubits\ Ratio
BB84
New Protocol
32
0.4063
0.5200
64
0.5000
0.5278
128
0.5703
0.5714
Therefore, as shown in Figure (4), the applied correlation
between the submitted and received photons is shown to be
more linear in BB84’s figure unlike new scheme. On the
other hand, the measurements were timed before
exchanging channels. This means, whereas in the BB84, the
attacker can gain some data by IRA, in the new scheme, it is
very difficult to monitor any data.
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Figure (4) shows the correlation between the BB84 and the new scheme.
Furthermore, the protocols were experimented under the
White Noise Gaussian (WNG), which assists to figure out
weakness through sending and receiving photons; especially
regarding submitting and exchanging channels as
mentioned in figure [3].
Figure (5) shows the WNG applied to both protocol.
As pointed above, the new protocol is more reliable and
efficient, due to the establishment the authentication that
verifies the two communicating parties before going
forward. Also, the decoy states that are initiated in a matrix
make eavesdropping very complicated to figure out at least
for now. Unlike the use of classical decoy that should be
created in well-known algorithms in quantum devices, one
of the advantages in the new protocol is its ability to exploit
the decoy states. In addition, the new protocol is guaranteed
by the strength of the matrix.
Figure (6) shows the NOISE to the BB84 and the new scheme.
Even though noise was created in both protocols, the
BB84 protocol demonstrated more weakness as compared
to the new scheme. This is because the new protocol is not
affected by noise that is either caused by the environment,
dark count probability or by an attacker. Reason being,
Alice and Bob ensure that both of them are the legitimate
parties; hence, making the next mechanism unknown except
to one of them.
IV. SECURITY ANALYSIS
This section discusses the scenario of the proposal protocol
and how the protocol is able to fight against many different
types of quantum attacks. As known, the fake-signal attack is
commonly seen in quantum security [21]. Supposing Eve is
able to copy some of these photons and and sends
fake-photons to Bob, the proposal scheme in turn will ensure
the inability of reaching Eve to the desired secret key. This is
due to the asymmetric decoy states that are embedded in the
submitted photons between Alice and Bob.
Men-In-Middle attack is a form of quantum attack [22], and
this attack depends totally on measuring the pulse that is
created with more than one photon, where Eve just keeps one
of these photons and leaves the other without any interruption.
The new scheme leaves MIM attack with nothing even if Eve
catches some photons. Next, due to the use of the asymmetric
decoy states in the new scheme, the Denial-Of-Service attack
(DoS) suffers strict processes that have been explained above.
The point here is when Bob measures the submitted photons in
sequence, he will realize whether Eve interrupted the
connection or not.
To increase the security of the proposed scheme, Alice and
Bob share the only function that forms the density of the
matrix (), where n is the length of text that is needed to
be encoded as well as this length is invisible except Alice and
Bob. As mentioned in [23] the Photon Number Splitting (PNS)
attack can be computed, and its efficiency determined by
computing the density matrices is associated with n photon-
pulses. Furthermore, PNS is still unable to be processed or
completely efficient by Eve without establishing another
attack that so-called Intercept-resend with unambiguous
discrimination (IRUD) attack, which is still possible in our
scheme; however, fortunately without gaining any
information.
V. THE CONCLUSION
The proposed scheme is proved to be more secure than
BB84, where the eavesdropper cannot realize the secret key
even with caching some of the photons and resending others.
Additionally, requesting the authentication at the beginning
increases the level of security, where at the first channel the
legitimate party can ignore the communication or resume it
and then move to the next step. Therefore, the protocol has
been designed for resisting attacks even in weak scenarios,
where Eve will not have any useful combination of submitted
data.
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VI. REFERENCES
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VII. BIOGRAPHY
Abdulbast A. Abushgra, He is a PhD
candidate in Computer Science &
Engineering at University of Bridgeport.
He has served as professor assistant at Al-
Mergib University in Libya since 2007.
Also, he has worked in the Railroad
Company for 10 years as an advisor. Now,
his work focuses on the quantum
cryptography, and how to make a sharing secret key by
Quantum Mechanics is possible in our classical system.
Khaled Elleithy, He is the Associate
Vice President for Graduate Studies and
Research at the University of Bridgeport.
He is a professor of Computer Science
and Engineering. He has research interests
in the areas of wireless sensor networks,
mobile communications, network
security, quantum computing, and formal
approaches for design and verification. He has published more
than three hundreds research papers in international journals
and conferences in his areas of expertise.
