1. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies
International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies
http://www.TuEngr.com, http://go.to/Research
A Review on Quantum Cryptography Technology
a*
Piya Techateerawat
a
Department of Electrical and Computer Engineering Faculty of Engineering, Thammasat University,
THAILAND
ARTICLEINFO A B S T RA C T
Article history: Nowadays, the information is exchanged among the
Received 2 August 2010
Received in revised form computer network. These data and information are involved in
23 August 2010 business, military, academic education, research and etc. which are
Accepted 27 August 2010 shared around the world in both private and public network. Since,
Available online
10 September 2010 many categories of data are required restriction on authorization of
Keywords: access, modify, delete and insert, security in communication is
Quantum Cryptography increasingly important to the network communication. Currently,
QKD
Quantum Key Distribution
computer security applies mathematic theory to computer security
BB84 for encrypting and decrypting on both sender and receiver. To use
BB92 security attack with high performance computer (e.g. quantum
computer), attacker can find a key and then obtains the data in
feasible period. Quantum cryptography is one of the solutions that
use property of polarization to ensure that transmitted data is not
trapped by eavesdropper. Quantum cryptography is improved
significantly in the last decades including the most two dominant
protocol BB84 and BB92.
2010 International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Some Rights Reserved.
1. Introduction
In general cryptography can be categorized as symmetric and asymmetric cryptography.
Symmetric cryptography uses one key in decrypting and encrypting data such as DES (Eli and
Shamir, 1993), 3DES (Merkle and Hellman, 1981) and AES (Ferguson et al., 2001). In contrast,
*Corresponding author (P. Techateerawat). Tel/Fax: +66-2-5643001 Ext.3246. E-mail addresses:
tpiya@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Volume 1 No. 1. eISSN: 1906-9642
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2. asymmetric cryptography uses one key to encrypt and another key to decrypt. These two keys in
asymmetric cryptography are related in mathematically method where one encryption key has
only one decryption key that can reveal the encrypted data. An example of asymmetric
cryptography is RSA (Rivest et al., 1978) which contains public key and private key. In the
security perspective, asymmetric cryptography is more secured than symmetric cryptography and
reduces the chance that eavesdropper breaks the security because of increasing domain of
available keys and complex computing.
However, if computing power is increasing significantly such as quantum computer, the time
to reveal the key can be reduced significantly from million years in today computer to seconds in
quantum computer. As a result communication needs a new technique to transmit data securely
other than depending on mathematically method and large set of keys.
Quantum cryptography uses a property of laws of quantum mechanics to inform sender and
receiver (Alice and Bob) if other person attempts to retrieve transmitting data. If this case is
occurred, both sender and receiver will ignore this part of data or this key. Then, they will re-start
transmitting a new key for encrypting data again. To compare with current cryptography, both
symmetric cryptography and asymmetric cryptography have no information when eavesdropper
intercepts the transmitting key.
2. Quantum Cryptography
Quantum cryptography contains a key distribution system that uses the laws of quantum
mechanics to guarantee secure communication. The crucial element of quantum mechanics such a
Heisenberg’s uncertainty principle (Heisenberg, 1927) prevents anyone directly measuring the bit
value without introducing errors that can be detected. A single photon is indivisible which means
that an eavesdropper cannot split the quantum signal to make measurements covertly. Quantum
cryptography has a quantum no-cloning theory. This theory shows that it is not possible to
receive a single photon and duplicate the photon without giving the notice to others. There are
two dominant schemes for quantum key distribution protocols which are the BB84 protocol and
the BB92 protocol.
2.1 BB84 Protocol
BB84 (Bennett and Brassard, 1984) protocol is the first quantum cryptography protocol
36 Piya Techateerawat

3. which is proposed by Charles Bennett and Gilles Brassard in 1984. This protocol employs two
polarization bases of single photon; rectilinear basis and diagonal basis. The single photon may
be polarized with four states: horizontal |h>, vertical |v>, left circle polarized |lcp>, and right
circle polarized |rcp>. Polarization state horizontal |h> and left circle polarized |lcp> represent a
‘0’. Polarization state vertical |v> and right circle polarized |rcp> represent a ‘1’.
To exchange secret key between sender and receiver (Alice and Bob) needs two channels,
quantum channel and public channel, process as follow: Alice sends a random sequence polarize
photons to Bob via quantum channel. After transmission is completed, Bob randomly chooses his
detector either rectilinear basis or diagonal basis and then reports his detector to Alice via public
channel. After that Alice responds the correct basis to Bob. Finally, Alice and Bob share the
correct bits which are used as the key for the secure encryption. The procedure of BB84 protocol
is shown in figure 1.
Alice Bob
Random Sequence Photons
Source Basis
Polarization
Random Detector Basis
Measure Polarization
Interpret as Bit Sequence
Detector Basis
Correct Basis
Discard Incorrect Bits
Shared Secret Key Shared Secret Key
Figure 1: An example of key exchange between Alice and Bob by using BB84 protocol.
*Corresponding author (P. Techateerawat). Tel/Fax: +66-2-5643001 Ext.3246. E-mail addresses:
tpiya@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Volume 1 No. 1. eISSN: 1906-9642
37
Online Available at http://tuengr.com/V01-01/01-01-035-041{Itjemast}_Piya.pdf

4. 2.2 BB92 Protocol
BB92 (Bennett and Brassard, 1982) protocol is proposed by Charles Bennett and Gilles
Brassard in 1992, similar to BB84 protocol but uses only two non-orthogonal quantum state |h>
represent a ‘0’ and |rcp> represent a ‘1’, half of the BB84 protocol to transmit the key.
The process of secret key transmission: Alice sends a random sequence of photons, |h> and
|rcp>.Bob randomly chooses his detector basis from |lcp> or |v> and interprets as a quantum bit
sequence, ‘0’ and ‘1’. Alice and Bob share the same quantum bits, discarding all other bits. The
BB92 protocol is shown in figure 2.
Alice Bob
Random Sequence Photons
Polarization
Random Detector Basis
Figure 2: An example of key exchange between Alice and Bob by using BB92 protocol.
3. Cryptography Attack
In general cryptography, key or password is the target of an intruder which attempts to reveal
the encrypted data. There are several methods to attack by using the opportunity in transmitting
data in network as shown below.
3.1 Brute Force Attack (BFA)
This method defeats cryptography by trying every possible key. It expects to find a correct
key approximately at half of key domain (e.g. if there is 2n possible keys, BFA will average be
founded correct key at 2n-1). However, this theory has a limitation in real world that array
processors require a large amount of energy and continuous operation for a long period (Blaze,
1993).
38 Piya Techateerawat

5. 3.2 Known Plain Text Attack (KPA)
KPA is attacking model where adversary has samples of plaintext (e.g. sensing data in
network) and uses them to reveal secret key. As a result, an adversary could translate all the
encrypted messages and also transmit fraudulent messages to the network (Meyer and Wetzel ,
2004).
3.3 Replay Attack (RPA)
RPA is an attack against the message which is repeated or delayed. It could be using as
duplicated authentication or malicious data. In network communication, RPA can use for creating
a new session or to bypass authentication (Kwon and Song , 1999).
3.4 Man­in­the­middle Attack (MITM)
MITM has the intent to read, add and modify messages between two parties. It requires
intercepting messages between two parties (Meyer and Wetzel , 2004).
3.5 Denial of Service Attack (DoS)
DoS is an attack to disrupt computer resource or obstruct communication between user and
service. DoS in network can be in the form of flooding network which disturbs communication
between nodes, or continuous communication burns out the equipment’s battery (Deng et al.,
2005).
4. Discussion
Since Brute Force Attack (BFA) is focused on the key, quantum cryptography is increasing
the computation time that BFA required to decrypt an entire set of information because the
frequency of key changing in quantum cryptography is increasing more than general
cryptography. Known Plain Text Attack (KPA) is more difficult in quantum cryptography
because rapidly key change during the session increasing more varieties of encrypted pattern, so
attack in quantum cryptography is required more processing time significantly than general
cryptography. However, Man-in-the-middle Attack (MITM) and Denial of Service Attack (DoS)
still able be occurred in this quantum cryptography because these two attacks are not focused in
cryptography method but rely on trust and network protocol mechanisms.
*Corresponding author (P. Techateerawat). Tel/Fax: +66-2-5643001 Ext.3246. E-mail addresses:
tpiya@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Volume 1 No. 1. eISSN: 1906-9642
39
Online Available at http://tuengr.com/V01-01/01-01-035-041{Itjemast}_Piya.pdf

6. 5. Conclusion
Quantum cryptography is alternative security solution for computer network. Instead of
using general encryption and decryption technique, quantum cryptography can verify that key is
transmitted without interception from eavesdropper. In the case that key is intercepted, both
sender and receiver are simple drop the key and re-send the new key.
BB84 is the protocol that introduces the method to transmit the key with quantum technique.
However, BB84 requires four polarization states: horizontal |h>, vertical |v>, left circle polarized
|lcp>, and right circle polarized |rcp> comparing to two non-orthogonal quantum state |h>
represent a ‘0’ and |rcp> represent a ‘1’ in BB92. Also, the procedure during setting up the shared
key for both sender and receiver, BB92 is simplified with more effective of transmission.
This quantum cryptography can be applied to application and superior secure channel. In the
future, this protocol is also prepared for the upcoming high performance computer (e.g. quantum
computer).
6. Acknowledgements
For this paper, we would like to thank Optical and Quantum Communication Research Lab,
National Research Council of Thailand, Faculty of Engineering Thammasat University and
Thammasat University for the support and cooperation.
7. References
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Physical Review Letters, Vol. 68, 1992; 3121-3124.
Bennet, C.H., and G. Brassard. Quantum Cryptography: public key distribution and coin
tossing, Proceeding of IEE International Conference on Computers, Systems and Signal
Processing, India 1984; 175-179.
Blaze, M. A cryptographic file system for UNIX ,in Proceedings of the 1st ACM conference on
Computer and communications security Fairfax, Virginia, United States ACM Press,
1993; 9-16.
Deng, J., R. Han, and S. Mishra, Defending against pathbased DoS attacks in wireless sensor
networks, in Proceedings of the 3rd ACM workshop on Security of ad hoc and sensor
networks Alexandria, VA, USA ACM Press, 2005; 89-96.
40 Piya Techateerawat

7. Eli B., and A. Shamir, Differential Cryptanalysis of the Data Encryption Standard, Springer
Verlag, 1993.
Ferguson, N., R. Schroeppel, and D. Whiting, A simple algebraic representation of Rijndael,
Proceedings of Selected Areas in Cryptography, 2001, Lecture Notes in Computer
Science., Springer-Verlag, 2001;103–111.
Heisenberg, W., Über den anschaulichen Inhalt der quantentheoretischen Kinematik und
Mechanik, Zeitschrift für Physik, 1927; 172–198.
Kwon, T., and Song J., Clarifying straight replays and forced delays, SIGOPS Oper. Syst. Rev. ,
vol. 33, 1999;47-52.
Merkle R., and M. Hellman. On the Security of Multiple Encryption, Communications of the
ACM, Vol 24, 1981; 465–467.
Meyer U., and S.Wetzel. A man-in-the-middle attack on UMTS ,in Proceedings of the 2004
ACM workshop on Wireless security, PA, USA ACM Press, 2004; 90-97.
Rivest R., A. Shamir, and L. Adleman. A Method for Obtaining Digital Signatures and Public-
Key Cryptosystems, Communications of the ACM ,Vol 21,1978; 120–126.
P. Techateerawat is a lecturer of Computer Engineering at Thammasat University. He received his B.Eng. from
University of New South Wales, Australia with Honors in 2004. He continued his PhD study at Royal Melbourne
Institute of Technology University, Australia, where he obtained his PhD in Wireless Sensor Network Security. Dr.
Piya Techateerawat current interests involve applications of Sensor Network, Security and Quantum Cryptography.
*Corresponding author (P. Techateerawat). Tel/Fax: +66-2-5643001 Ext.3246. E-mail addresses:
tpiya@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Volume 1 No. 1. eISSN: 1906-9642
41
Online Available at http://tuengr.com/V01-01/01-01-035-041{Itjemast}_Piya.pdf