Securing Short Message Service Using Vernam Cipher in Android Operating System

IOSR Journal of Mobile Computing & Application (IOSR-JMCA)
e-ISSN: 2394-0050, P-ISSN: 2394-0042.Volume 3, Issue 4 (Jul. - Aug. 2016), PP 11-16
www.iosrjournals.org
DOI: 10.9790/0050-03041116 www.iosrjournals.org 11 | Page
Securing Short Message ServiceUsing Vernam Cipher in
Android Operating System
Andysah Putera Utama Siahaan
Faculty of Computer Science, Universitas Pembangunan Panca Budi
Jl. Jend. Gatot Subroto Km. 4,5 Sei Sikambing, 20122, Medan, Sumatera Utara, Indonesia
Abstract: Although many ways to communicate with someone, SMS is still one of the popular media to send a
message to someone. Not unlike the others, the messages sent can be known by the third party either tapping or
the investigation. Unencrypted SMS can be easily obtained from communication providers so that they may be
misused. Since the communication devices have been using Android operating system, they are programmable.
There is various script can be inserted to devices to protect the data. One of them is Vernam Cipher. This
method offers how to protect personal messages sent via SMS easily. It converts the message into an encrypted
message shortly before sent. At the moment there tapping on the outside, the information is not easily
understood its contents. The message is entirely secure.
Keywords: Vernam, Mobile, SMS, Cryptography, Security, Encryption, Decryption
I. Introduction
Information security means securing information systems from unauthorized access, use, disclosure,
disruption, modification, perusal, inspection, recording or destruction [7].Despite the emergence of digital media
to communicate, SMS is still used as a system that is popular among social media. SMS has a major role in
communication. Not everyone has a sophisticated device that supports internet facility. For owners of older
model devices, SMS is a way that always used to deliver the message to the listener. The security of data on
SMS delivery is not guaranteed. Everyone can steal the message. Although the message is personal, the message
can be retrieved from a provider. When there is an investigation, the message might be generated from the
database. Whatever happens at the talks, if everyone wants, the message is still readable. This method does not
teach how to send the crime message, but it explains how to keep a secret message is not misused by the
irresponsible parties. This research tries to modify the bits order by encrypting and providing a password.
II. Theories
2.1 Android Short Message Service
SMS stands for Short Message Service. It is a facility to send and receive a short text message via the
wireless devices or cellular phone communication device. One of the advantages of SMS is cost. SMS is a
service that is widely applied in wireless communication system. SMS enables sending messages in
alphanumeric. SMS mechanism is sending a short message from one subscriber terminal to another terminal.
Short Message Service Centre (SMSC) is the device that handles this operation. It is also known as Message
Centre (MC). It includes the determination of search or sorts the final destination of the message.Figure 1
illustrates how the GSM Network handles the SMS.
Figure 1.SMS Architecture
SMS service is a non-real time service where a short message can be submitted to a destination, no
matter if the destination is ready or not. When it is not active, the system will delay the delivery to the
destination until the destination is active again. The SMS system guarantees the delivery of a short message to
get to the destination. Temporary delivery failures always identified as a pending message. Short retransmission

Securing Short Message ServiceUsing Vernam Cipher in Android Operating System
message will always be possible unless the applicable rules that the short message has exceeded a certain limit
should be removed and otherwise failed to send.
In Android Operating System, we can use SMSManager API or devices Built-in SMS application to
send SMS. However, it uses a phone number system to find people and send them a message. SMS using the
conventional phone is similar to using the Android one. The difference is that the Android phone is
programmable. We can build a script to monitor the activity of the phone or maybe we can filter the SMS
content which is delivered to the inbox. The Android SMS is more flexible than the predecessor. We can attach
them to the function that we wish such as auto send, block, and many other functions.
Figure 2. SMS Interception
There are many attacks possible to SMS [2]. Figure 2 shows how the SMS can be attacked in the air.
Since SMS is wireless signal, everyone can intercept the signal and turn into the original information.
2.2 Vernam Cipher
The data security is the most significant issue in networking problem. A specific cryptography
algorithm must protect the data to maintain the integrity. One of them is Vernam Cipher. It produces the
ciphertext by doing modulo in its bits. Every character is turned into an 8-bit binary and converted into cipher
bits. The SMS will work if combined with this algorithm. In producing the ciphertext, we must provide a key to
keeping the ciphertext unbreakable. Vernam Cipher uses a very simple formula as showed next.
𝐶𝑇 = 𝑃𝑇 ⊕ 𝐾𝑒𝑦 (1)
𝑃𝑇 = 𝐶𝑇 ⊕ 𝐾𝑒𝑦 (2)
Where:
CT : bit of aftercode message
PT : bit of original message
Key : bit of password
PT is filled with the bit of the plaintext. For example, the character “A” is 65 where the binary is
01000001. To produce the ciphertext, it performs an 8-time looping. It carries out from bit 1 to bit 8. Every bit is
calculated. Formula 1 and 2 are identical. They are using the same technique to manipulate the bits. XOR is
used to encrypt and decrypt the bit.
Figure 3. Vernam Cipher bit operation
Vernam uses XOR operation to produce the ciphertext. The resulting bit "1" if the input bits are
different while "0" if they are same. Figure 3 shows the result of the bit operation. It describes how the set of
binary (A) are encrypted (G) and return to plain binary back.

III. Proposed Work
SMS sent will be forwarded to a cellular provider. GSM network will search for the destination number
and then send the message to the number. When the message arrives at the destination, the number sends an
acknowledgment back to the operator. This research proposes the method encrypts the message before
broadcasted. The message must be encrypted when the user has finished typing the content. By encrypting the
message, it is hard to convert it back without knowing the algorithm and password used before. The attacker
must know at least some of the plaintext character.
Figure 4. GSM encryption and decryption
Figure 4 describes the flow of sending and receiving a message. It must be encrypted before sent to a
destination and must be decrypted as well when receiving it. When the message is in the air, it is entirely secure.
Every attacker can steal the information, but they will have got nothing since the message is encrypted.
IV. Interface Design
The interface is designed to put the application in the mobile system. Figure 5 shows the home screen
of the application. The display consists of the message, password, phone number text boxes and three buttons of
command buttons. The application is build by using Basic4Android version 4. It is a very familiar interface to
construct the Android application. We can build either using the designer mode or even generating a toolbox
script.
Figure 5. Vernam Cipher SMS display
V. Software Testing
Now we test the apps with serveral characters. Assume we have “Hello, My Name is Andysah Putera
Utama Siahaan”. Figure 6 explains that the input characters are put in the message box.
Figure 6. Initial input (message, password and phone number)

There are two more input boxes such as password and phone number. The password is a set of
characters provided to protect the encryption. It is used to decrypting the message back to plain text after it has
arrived at the destination. The phone number is the destination itself.
Figure 7. Encrypted Message
After the Encrypt Button is pressed, the algorithm converts the plain text into cipher text by using the
separated password provided earlier. Figure 7 shows the message box is showing the illegible characters. Some
of them are illustrated like boxes. Separate applications do not show the same shape. Pressing the Decrypt
Button will get the text back to its original information. When the text is in a cipher mode, the Send Button is to
send the message to the destination number. Both participants must have the same applications to communicate
each other. Otherwise, the receiver will not understand the word that has been displayed.
VI. Evaluation
Let’s take a look at the previous example. Tabel 1 is some of the plaintext ASCII code.
Table 1. Plaintext ASCII code
H e l l O , M y
72 101 108 108 111 44 32 77 121
Table 2. Key ASCII code
K e y s h a K e y
75 101 121 115 104 97 75 101 121
Table 2 is the code of the key. The key is repeated until the length of the plaintext is met. Formula 1 is
to encrypt the plaintext into the ciphertext. To reconstruct it back to the plaintext, we can apply Formula 2.
The encryption calculation:
CT[1] = PT[1] ⊕K[1]
= 72 ⊕75
= 3
CT[2] = PT[2] ⊕K[2]
= 101⊕101
= 0
CT[3] = PT[3] ⊕K[3]
= 108⊕121
= 21
CT[4] = PT[4] ⊕K[4]
= 108⊕115
= 31
CT[5] = PT[5] ⊕K[5]

= 111⊕104
= 7
CT[6] = PT[6] ⊕K[6]
= 44⊕97
= 77
CT[7] = PT[7] ⊕K[7]
= 32⊕75
= 107
CT[8] = PT[8] ⊕K[8]
= 77⊕101
= 40
CT[9] = PT[9] ⊕K[9]
= 121⊕121
= 0
After the above calculation, the ciphertext is obtained. There are several characters are illegible. It
shows on the screen. The ASCII 0 – 31 are usually unprinted. They are marked as or any other character. The
ASCII 32 – 127 are printed and primarily used. The ASCII 128 – 255 are the extended characters that show like
symbols.Table 3 shows the result after being encrypted.
Table 3. Ciphertext ASCII code
M k (
3 0 21 31 7 77 107 40 0
Table 4. Complete process of Vernam Cipher
PT A Key A CT A
H 72 K 75 3
e 101 e 101 0
l 108 y 121 21
l 108 s 115 31
o 111 h 104 7
, 44 a 97 M 77
32 K 75 k 107
M 77 e 101 ( 40
y 121 y 121 0
32 s 115 S 83
N 78 h 104 & 38
a 97 a 97 0
m 109 K 75 & 38
e 101 e 101 0
32 y 121 Y 89
i 105 s 115 26
s 115 h 104 27
32 a 97 A 65
A 65 K 75 10
n 110 e 101 11
d 100 y 121 29
y 121 s 115 10
s 115 h 104 27
a 97 a 97 0
h 104 K 75 # 35
32 e 101 E 69
P 80 y 121 ) 41
u 117 s 115 6
t 116 h 104 28
e 101 a 97 4
r 114 K 75 9 57
a 97 e 101 4
32 y 121 Y 89
U 85 s 115 & 38
t 116 h 104 28

a 97 a 97 0
m 109 K 75 & 38
a 97 e 101 4
32 y 121 Y 89
S 83 s 115 32
i 105 h 104 1
a 97 a 97 0
h 104 K 75 # 35
a 97 e 101 4
a 97 y 121 24
n 110 s 115 29
Table 4 is the complete process of encryption and decryption. The text “Hello, My Name is Andysah
Putera Utama Siahaan” turns into encrypted message and return back to the plaintext.
VII. Conclusion
PlainSMS is very dangerous. If the content does not consist of any important thing, it does not matter.
Otherwise, it brings into trouble. Encrypting the message is the only way to secure the information personally.
The cellular network provides the mobile encryption as well, but it does not guarantee the message safely. The
attacker can intercept the message at any time. Vernam Cipher is the great common encryption method to
implement. It does not need the complex mathematical calculation. It provides the ciphertext by doing XOR
operation. The text after encryption is completely secure to transmit.
References
[1]. B. Forouzan, Cryptography and Network Security, McGraw-Hill, 2006.
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[3]. H. M. E. Bakry, A. E. T. E. Deen dan A. H. E. Tengy, “Implementation of a Hybrid Encryption Scheme for SMS / Multimedia
Messages on AndroidI,” International Journal of Computer Applications, vol. 85, no. 2, pp. 1-5, 2014.
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Science and Information Technologies, vol. 6, no. 4, pp. 3855-3858, 2015.
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Research, vol. 5, no. 3, 2016.
[7]. R. Rayarikar, S. Upadhyay dan P. Pimpale, “SMS Encryption using AES Algorithm on Android,” International Journal of
Computer Applications, vol. 50, no. 19, pp. 12-17, 2012.
Author Profile
Andysah Putera Utama Siahaan was born in 1980, Medan, Indonesia. He received the
S.Kom. degree in computer science from Universitas Pembangunan Panca Budi, Medan,
Indonesia, in 2010, and in 2012, he obtained M.Kom. from the University of Sumatera
Utara, Medan, Indonesia. In 2010, he joined as a lecturer at the Department of
Engineering, Universitas Pembangunan Panca Budi. He has been a researcher since 2012.
He has studied his Ph. D. degree from 2016. He is now active in writing international
journals and conferences.

Securing Short Message Service Using Vernam Cipher in Android Operating System

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Securing Short Message Service Using Vernam Cipher in Android Operating System