Secure Channel for Molecular Communications
S. M. Riazul Islam
Dept. of Computer Engineering
Sejong University
Seoul, South Korea
riaz@sejong.ac.kr

Farman Ali
UWB Wireless Research Center
Inha University
Incheon, South Korea
farmankanju@gmail.com

Abstract—Molecular communication in nanonetworks is an
emerging communication paradigm that uses molecules as
information carriers. Achieving a secure information exchange is
one of the practical challenges that need to be considered to
address the potential of molecular communications in
nanonetworks. In this article, we have introduced secure channel
into molecular communications to prevent eavesdropping. First,
we propose a Diffie–Hellman algorithm-based method by which
communicating nanomachines can exchange a secret key through
molecular signaling. Then, we use this secret key to perform
ciphering. Also, we present both the algorithm for secret key
exchange and the secured molecular communication system. The
proposed secured system is found effective in terms of energy
consumption.
Keywords— Nanonetworks, molecular
security, secure channel, eavesdropping.

communications,

Hyeonjoon Moon
Dept. of Computer Engineering
Sejong University
Seoul, South Korea
hmoon@sejong.edu

Kyung-Sup Kwak
UWB Wireless Research Center
Inha University
Incheon, South Korea
kskwak@inha.ac.kr

key (a key only known to them). Then, information is encrypted
using the key before transmission. However, in molecular
communications, the main challenge is how to generate a private
key so that the adversary cannot learn the exchanged key.
Moreover, both key exchange process and encryption
algorithms should be cost-effective in terms of computational
complexity, and energy consumption. Authors in [8] make use
of radio-frequency identification (RFID) noisy tags, similar to
blocker tag suggested by authors in [9], to exchange secret key.
These tags intentionally generate noise on the channel so that
intruders in RFID communications can’t understand the key.
The same idea has been tailored to security requirements in near
field communication (NFC) [10]. However, these works have
been performed in the context of EM communications. In this
article, we try to establish a secure channel in molecular
communications to defend against eavesdropping.

I. INTRODUCTION

II. SYSTEM MODEL

Molecular communication is promising to provide
appropriate solutions for a wide range of applications including
biomedical, industry, and environmental areas [1], [2]. Even, it
can be integrated with the Internet of Things (IoT) to provide
IoT-based healthcare services [3], [4] by implementing the
concept of Internet of NanoThings [5]. This is an
interdisciplinary research field and is significantly different
from the electromagnetic (EM) communication system, since it
utilizes molecules as carriers of information. However,
molecular communication has a number of technical challenges
to overcome. Introducing security into molecular
communications is a fundamental challenge for researchers.
There exist very few papers that focus on security aspects of this
promising technology [6], [7]. These papers discuss several
security and privacy issues and challenges in the context of
molecular communications, in general. To the best of our
knowledge, there exists no prominent work which attempts to
mitigate any particular security risk.

We consider that the underlying system is time-slotted with
specific slot duration and the participating nanomachines are in
a stationary fluidic medium at any distance within the network
coverage. We also consider that these nanomachines are
perfectly synchronized and communicate with each other using
same types of messenger molecules. Symbols are supposed to
be transmitted upon on-off keying (OOK) modulation through
the memoryless channel. In this scheme, information bit 1 is
conveyed by liberating an impulse of 𝑧1 number of molecules at
the start of the slot, whereas no molecule is released for
information 0. For the simplicity of presentation, we consider a
full-duplex system; participating nanomachines can transmit
and receive information at the same time. However, the
proposed method, with a slight modification, can also equally be
applied in a half-duplex system.

In this article, we deal with eavesdropping, a special class of
threats, that might exploit vulnerabilities to breach security in
molecular communications. It is the act of secretly listening to
an ongoing communication between two nanomachines. In EM
communications, a secure channel is established to prevent
eavesdropping. To do this, two communicating parties follow
Diffie–Hellman key exchange protocol and generate a private
This work was supported in part by National Research Foundation of
Korea-Grant funded by the Korean Government (Ministry of Science and ICT)NRF-2017R1A2B2012337) and in part by Sejong University Faculty Research
Fund.

Fig. 1. Molecular communication with eavesdropping (A sends violet
molecules, C-green molecules).

In case of reception, a nanomachine counts the total number
of messenger molecules received during the time slot. This
received number of molecules, denoted by 𝑧2 , is then compared
to z, a threshold number of molecules. If 𝑧2 is less than z, the
machine considers the received bit to be 0; otherwise, it decodes
the received bit to be 1. We further assume that there exists at
least a malicious nanomachine which uses a suitable detector to
receive the transmitted molecules with the purpose of
eavesdropping (see Fig. 1).
III. EAVESDROPPING DISTANCE
This is very noticeable that eavesdropping is a significant
matter, since molecular communication is a wireless approach
in practice. A question that may arise is how a malicious
nanomachine can decode the transmitted data out of received
molecules. This can be achieved by two ways. First, the intruder
can do required experiments prior to an attack. Second, the
attacker can have prerequisite knowledge from literature
investigation. Also, it’s not unusual that the intruder will have
the required detector to receive the molecules and the
hardware/software arrangements to decode the received
molecules, since this doesn’t need any special kit.
Molecular communication is typically occurred between two
nanomachines in near vicinity. A reasonable question is how
close the malicious machine needs to be to be capable to detect
the transmitted molecules. However, there is no exact answer to
this question. The reason why we can’t answer this question
accurately is that there is a number of factors which determine
the said distance. For instance, the distance might be influenced
by the following factors, among others: molecular
characteristics of the given transmitting nanomachine, number
of molecules sent by transmitting nanomachine, detector
characteristics of the intruder, quality of the intruder’s
nanomachine itself and location of the attack. Thus, any
particular distance specified would only be usable for a definite
set of the aforementioned parameters and cannot be utilized to
develop common security strategies. Nevertheless, we can
arguably say that eavesdropping can be performed up to a
distance of more than a typical distance between two authentic
nanomachines. In other words, a powerful attacker can still
decode the information even when it operates from a relatively
larger distance compared to intended receiving nanomachine..
IV. PROPOSED SECURE CHANNEL
The idea is that both nanomachine A and nanomchine C
transmit random data simultaneously. This is conceivable as

Fig. 2. The secret key exchange in molecular communication.

nanomachines can launch and collect the molecules at the same
time. In the setup phase, these two nanomachines synchronize
on the exact timing of the bits and also on the energies (number
of molecules) of the transmitted molecular signal. After the
synchronization phase, machines A and C are able to send
molecules at the same time with the same number of molecules.
At the time of transmitting random bits of 0 (sending no
molecules) or 1 (sending some predetermined number of
molecules), both nanomachines also listen to molecular signal.
Now, we consider all the possible cases below:
Case 1: When both machines transmit a zero molecular
signal, the sum of these two molecular signals is zero and a
malicious nanomachine, who is eavesdropping, would recognize
that both nanomachines sent a zero. This case does not help the
malicious machine B to understand that which machine is
sending a bit of the secret key.
Case 2: When both machines transmit a one molecular
signal, the sum of these two molecular signals is the double (two
times the number of molecules set for sending a one) and the
malicious nanomachine would recognize that both
nanomachines sent a one. This case also does not help the
malicious machine B to recognize that which machine is sending
a bit of the secret key.
Case 3: An interesting case is happened when nanomachine
A sends a one whereas nanomachine C sends a zero or when
machine A sends a zero whereas machine C sends a one. In this
situation, both nanomachines can find what the other machine
has transmitted, since both machines are aware of what
information they themselves have just sent. Conversely, the
malicious node B only understands the sum of two molecular
signals and it cannot factually find out which machine sent the
one and which machine sent the zero.
This concept has been demonstrated in Fig. 2. While the top
part of the figure shows the molecules released (violet color) by
nanomachine A, whereas the middle part shows the molecules
released (green color) by C. Machine A randomly transmits the
eight bits: 1, 0, 1, 1, 0, 1, 0, and 1. Machine B randomly transmits
the eight bits: 0, 1, 0, 1, 1, 1, 0, and 1. The bottom part of the
figure displays the sum of the molecules released by both
machines. This is the ultimate signal as observed by the
malicious machine B. It clearly shows the resultant signal in case
of A transmits 0, and C transmits 1 is the same as in the case of
A transmits 1, and C transmits 0. Therefore, the malicious
machine B can’t differentiate between these two cases. Then, the

two authentic machines now abandon all bits, where they
transmitted the same number of molecules (corresponding to
both A and C sent 0, and both A and C sent 1). However, both
machines accept all bits, where they transmitted different
number of molecules (corresponding to A sent 1 and C sent 0,
and A sent 0 and C sent 1). They can consider either the bits
transmitted by machine A or the bits transmitted by machine C
as the secret key. This is basically a prior agreement as per
security policies. In this fashion, both machines can exchange an
encryption key of any desired length. Thus, in this example,
transmitted bits, by the selected nanomachine, at bit indexes 0,
1, 2, and 4 constitutes the secret key, since the participatory
machines sent different number of molecules at these bit
indexes. Now, if a security scheme selects the nanomachine C
for this purpose, the encryption key will be 0101. However, if
the machine A is selected, the key is 1010. The key we have just
obtained is 4-bits in length. Note that a secret key of any desired
length can be achieved if both machines continue their
operations until the target number of bits are stored. The
flowchart in Fig. 3 shows the generalized algorithm of our
proposed technique as described above. In this article, we will
assume the desired key is 8 bits in length.
The next step after the private key generation is to encrypt
the information bit to be transmitted before it goes onto the
channel through molecular modulation. For this purpose, we use
Exclusive OR (XOR) cipher, since it is simple to implement and
XOR operation is inexpensive in terms of computation. The
encrypted bits are obtained by using the following logical
operations,
𝑥𝑗 = 𝑏𝑘𝑗 ⊕ 𝑏𝑖𝑗 for 𝑗 = 0,1, … ,7

operation is sufficient enough to hide the information from
unauthorized parties. This in turn ensures that frequent changes
of private key are not mandatory. Conversely, security-sensitive
applications will require relatively frequent changes of secret
keys. In the receiving side, decryption operation, presented in
(2), will be performed on the information bits after molecular
demodulation by using the same logical operations as applied in
(1).
𝑦𝑗 = 𝑏𝑘𝑗 ⊕ 𝑏𝑒𝑗 for 𝑗 = 0,1, … ,7

where 𝑦𝑗 , 𝑏𝑘𝑗 and 𝑏𝑒𝑗 are the j-th bit of the decrypted bits, the
secret key, and demodulated information block of 8-bit,
respectively. If there occurs error free communication, 𝑦𝑗
should be the same as 𝑏𝑖𝑗 . Our proposed secured molecular
communication system thus eventually takes the form of Fig. 4.
The serial-to-parallel (S/P) and parallel-to-serial (P/S)
converters have been used, since the hardware XOR cipher
performs 8-bit parallel XOR operations. However, this is a
design issue. The same XOR cipher can alternatively be
accomplished by using a single XOR gate. It is worth
mentioning that the processing time to place secured molecular
information onto the channel becomes negligible compared to
the usual baseband information processing time, since there is
no complicated computation in ciphering operations and
parallel-to-serial and serial-to-parallel operations also occur
instantly. Moreover, the use of hardware ciphering instead of
software counterpart further reduces the associated time. Thus,
our secured molecular communication system is effective in
terms of information processing time.

(1)

where 𝑥𝑗 , 𝑏𝑘𝑗 and 𝑏𝑖𝑗 are the j-th bit of the encrypted bits to be
modulated for molecular transmission, the secret key, and
information block of 8 bits, respectively. There will be many
applications of molecular communications where stringent
security will not be required. In those cases, a simple hiding

(2)

V. ENERGY CONSUMPTION ANALYSIS
𝐸𝑏𝑇

Let
and 𝐸𝑏𝐶 be the energy required to transmit one bit of
information, and energy required to compute one bit of
information, respectively. Also, 𝑁 denotes the total number of
information bits to be transmitted and the key length is
designated by 𝐾. And the number of key generation to complete
the information transmission is 𝑀. Since information bits (1’s or
0’s) are randomly generated on an equiprobable basis and
transmissions of two out of four possible cases (during key
exchange) are discarded, participating nodes should exchange
2𝑛 bits of information, on an average, to share 𝑛 bits of key.
Therefore, the required energy to exchange the desired key once
is 𝐸𝐾 = 2 × 𝐾 × 𝐸𝑏𝑇 . Ciphering and deciphering 𝑁 information
bits by using XOR logical operations require 𝐸𝐶 = 2 × 𝑁 × 𝐸𝑏𝐶
energy. Thus, the total energy required to transmit the
information with security becomes
𝐸𝑇𝑆 = Energy for Information Transmission
+𝑀 × 𝐸𝐾 + 𝐸𝐶
=𝑁×

𝐸𝑏𝑇

+ 𝑀 × (2 × 𝐾 × 𝐸𝑏𝑇 ) + 2 × 𝑁 × 𝐸𝑏𝐶 . (3)

Considering the fact that the energy required to transmit one
bit of information is analogous to the energy required to carry
1000 logical operations [11], we use 𝐸𝑏𝐶 = 0.001 × 𝐸𝑏𝑇 in (3)
and get
𝐸𝑇𝑆 = (1.002𝑁 + 2𝐾𝑀)𝐸𝑏𝑇
Fig. 3. The algorithm for secret key exchange.

(4)

In case of no security, the total energy required to transmit
the information is

for a long time. As a result, the amount of additional energy is
negligible compared to the total energy requirement for
information transmission. Even, the amount of extra energy
consumption is still very low for the cases where there might be
a provision of frequent changes of shared keys (different key
after a few frames), since the key is very short in length
compared to the total length of several frames of interest. Thus,
the proposed method is found energy efficient. Both simulated
and analytical results are well matched at every case.

Fig. 4. The molecular communication system with the secure channel.

𝐸𝑇0 = Energy for Information Transmission = 𝑁 × 𝐸𝑏𝑇 (5)
VI. PERFORMANCE E VALUATION
To assess the proposed method, we perform computer
simulation. We consider same types of molecules of the same
size with OOK modulation scheme in a 2-dimensional confined
space and 125 molecules/bit (𝐸𝑏𝑇 ) is used on an average. The
sizes of the messenger molecules are anticipated to be
analogous to that of the fluid molecules. The threshold number
of molecules is supposed to be 𝑧 = 20 . Transmitter and
receiver are synchronized [12] so that the starting time of each
molecular symbol at each communicating node becomes the
same and the track of secret key sharing is maintained. The 4K
information bits, divided into 4 frames, are transmitted. The
frequent change of secret key is implemented by generating
new keys after each 2 frames.
The Fig. 5 presents the total energy requirements for
secured molecular communication system under varying key
length. It clearly shows that no additional energy is required to
transmit secured molecular information in the proposed secure
channel fashion. This is because the number of bits to send the
same amount information remains unchanged. However, the
secured molecular communication system needs energy in
exchanging the secret keys and in processing the information
for encryption. In case of simple information hide operation,
where the key should be exchanged only once, prior to
information transmission, the same key can relatively be used

Fig. 5. Comparison of energy consumption.

VII. CONCLUDING REMARKS
In this article, we have proposed a secured molecular
communication system to defend against eavesdropping. The
participating nanomachines exchange a secret key through
molecular signaling in such a way that adversary cannot
understand the key. This key exchange mechanism doesn’t
require significant additional energy. Also, the use of XOR
ciphering to encrypt and decrypt the data using the generated
secret key make the system simple and effective in terms of
energy consumption. The proposed system can effectively be
used in molecular communication systems where simple hide
operations are sufficient or more stringent security are required.
REFERENCES
[1]

I.F. Akyildiz, F. Brunetti, and C. Blazques, “Nanonetworks: A New
Communication Paradigm,” Computer Networks, vol. 52, no. 12, pp.
2260-2279, Aug. 2008.
[2] T. Nakano, M.J. Moore, W. Fang, A.V. Vasilakos, and S. Jianwei,
"Molecular Communication and Networking: Opportunities and
Challenges," IEEE Transactions on NanoBioscience, vol. 11, no.2,
pp.135-148, Jun. 2012.
[3] S. M. R. Islam, D. Kwak, M. H. Kabir, M. Hossain, and K. S. Kwak, "The
Internet of Things for Healthcare: A Comprehensive Survey," IEEE
Access, vol. 3, pp. 678-708, Jun. 2015.
[4] S. M. R. Islam, M. N. Uddin, K. S. Kwak, "The IoT: Exciting Possibilities
for Bettering Lives," IEEE Consumer Electronics Magazine, vol. 5, no.
2, pp. 49-57, Apr. 2016.
[5] I. F. Akyildiz, M. Pierobon, S. Balasubramaniam and Y. Koucheryavy,
"The internet of Bio-Nano things," IEEE Communications Magazine, vol.
53, no. 3, pp. 32-40, March 2015.
[6] V. Loscri, C. Marchal, N. Mitton, G. Fortino, and A.V. Vasilakos,
"Security and Privacy in Molecular Communication and Networking:
Opportunities and Challenges," IEEE Transactions on NanoBioscience,
vol. 13, no. 3, pp. 198-207, Sep. 2014.
[7] F. Dressler, and F. Kargl, “Security in Nano Communication: Challenges
and Open Research Issues," in Proc. IEEE Int. Conf. on Communications,
pp. 6183-6187, Jun. 2012.
[8] C. Castelluccia, and G. Avoine, "Noisy Tags: A Pretty Good Key
Exchange Protocol for RFID Tags", in Proceedings of CARDIS 2006,
LNCS 3928, pp. 289-299, 2006.
[9] A. Juels, R. Rivest, and M. Szydlo, “The Blocker Tag: Selective Blocking
of RFID Tags for Consumer Privacy,” In: Atluri, V. (ed.) Conf. on
Computer and Communications Security, Washington, DC, USA, pp.
103–111. ACM Press, New York, Oct. 2003.
[10] E. Haselsteiner, and K. BreitfuB, “Security in Near Field Communication
(NFC): Strengths and Weaknesses,” In Workshop on RFID Security,
2006.
[11] H. Karl, and A. Willing, “Protocols and Architectures for Wireless Sensor
Networks,” John Wiley & Sons Ltd, Chichester, England, 2005.
[12] M. H. Kabir, S. M. R. Islam, and K. S. Kwak, "D-MoSK Modulation in
Molecular Communications," IEEE Transactions on NanoBioscience,
vol. 14, no. 6, pp. 680-683, Jun. 2015.

