Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
Text File Encryption and Decryption by FFT and IFFT
Algorithm Using Lab view
D Narmatha, W Jenifa, M Merlin Moses, J Prem Kumar
Assistant Professor, Department of Electronics and Communication Engineering, Einstein College of
Engineering, Tamil Nadu, India
Email: niranjnarmi@gmail.com
DOI: http://doi.org/10.5281/zenodo.3525834
Abstract
An approach to encrypt and decrypt the text files using FFT and IFFT algorithm respectively.
Cryptography involves encryption and decryption process. The use of data encryption is to
provide security to the confidential data from unauthorized access. Decryption is the
conversion of encrypted data into original information. The design is implemented in Lab
VIEW software. The basic operations include conversion of characters from text file into
encrypted data in encryption module. The retrieval of original information is done at the
decryption module.
Keywords: Decryption, encryption, FFT, IFFT
INTRODUCTION
Security is the most important aspect in the
field of internet and network application.
To facilitate secret communication by the
government and Militaries encryption is
used. Teodorescu et al explains presents a
software application for studying of the
most
used
methods
for
text
encryption/decryption these techniques are
applied to encryption of a text files. The
main aspects of encryption techniques can
be analyzed, like the text encryption
strength as well as the complexity of
algorithm implementation and processing
resources involved. Because of the
advantages of visual programming
languages like Lab VIEW, users can easily
understand programming techniques for
different encryption/decryption methods
and data manipulation, and they can
modify the application to add new
functionalities or to implement other
algorithms [1]. Sarma et al., deals with text
8
file encryption and decryption. Encryption
has always been very important part of
military communication. To achieve a very
high degree of security digital encryption
techniques
being
used.
Digital
transmission adopts scrambling technique
which provide high level security for
communication.
There
are
many
traditional scrambling methods used in
single dimension such as time or
frequency domain scrambling [2]. Arpneek
Kaur et al., approaches briefly about the
symmetric key cryptography algorithms
such as AES, DES, 3DES, Blowfish etc. It
explains
the
individual
algorithm
characteristics and methods. It also
highlights the character of symmetric
cryptography as it is almost impossible to
break the encryption algorithm without
knowing the exact key value because of
internal key generation with the reference
of entered key. The memory requirement
of symmetric algorithms is lesser than
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
asymmetric encryption algorithms and a
symmetric key algorithm runs faster than
asymmetric key algorithms. Nithya
Chidambaram et al., deals with the data
partitioning, shuffling and encryption
techniques that are used to preserve
confidentiality [3]. In the proposed
method, the data is encrypted through the
deterministic algorithm. Four different
keys are used for encryption and
decryption Two of the keys are used for
achieving confusion for numeric data and
the remaining three keys are used for
encrypting alpha-numeric data when the
data is not highly sensitive and for lowlevel security is sufficient. The plain text
which is to be converted to cipher text is
loaded to the encryption system and the
encrypted file is stored. The cipher text
from the storage system is loaded to the
decryption system and it is decrypted back
to plain text. Secret key is always to the
data owner or the Administrator. This
approach provides a hybrid scheme for
information security using Laboratory
Virtual Information Engineers workbench
(Lab-View) tool [4].
PROPOSED METHODOLOGY
Cryptography involves two processes
namely, encryption and decryption. Data
encryption translates data into another
form called a decryption key or cipher text
can read it. Data or plaintext is encrypted
with an encryption algorithm and an
encryption key. The main purpose of data
encryption
is
to
maintain
the
confidentiality of the digital data.
In our proposed system, the characters
from the original text file are extracted.
The next step involves the application of
ASCII codes for the respective characters
of the plain text. The codes are subjected
to FFT algorithm for further process of
encryption. A series of complex numbers
are obtained as the result of frequency
domain conversion.
The obtained complex numbers are
multiplied with a desired key number.
Thus the obtained complex numbers are
the required encrypted data. These
numbers are converted into a binary data.
This binary data is overwritten in new text
file which acts as the transmitting file. Fig.
1 represents the flow diagram of
encryption process.
The discrete Fourier transform can be
computed in more efficient way by means
of fast Fourier transform. Generally, N
complex valued numbers X (k) is
computed by the data sequence x(n) of
length N is given by the formula:
( )
Where,
∑ ( )
⁄
.
is the twiddle factor. The fast Fourier
transform can be computed in two ways,
either by using the formula represented
above or known as direct computation
method or by using the butterfly diagram
or known as radix algorithm method.
Encryption Process
9
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
ORIGINAL TEXT FILE
EXTRACTING THE
CHARACTERS
CONVERT THE
CHARACTERS TO
ASCII CODE
CONVERT THE ASCII
CODE TO FREQUENCY
DOMAIN
ENCRYPTION
PROCESS
KEY
WRITE THE
ENCRYPTED DATA
INTO A FILE
ENCRYPTED TEXT
FILE
Figure 1: Flow diagram for encryption.
In radix algorithm method there are two
ways:
 Decimation in time-FFT
 Decimation in frequency-FFT
In DIT-FFT the input sequence, the input
sequence is shuffled and output sequence
is in order. In DIF-FFT the input sequence,
the input sequence is in order and output
sequence is in shuffled in manner.
Decryption Process
The conversion cipher text data into its
original form of plaintext is called
Decryption. During the process of
decryption, all the binary coded characters
are extracted from the transmitted binary
10
file. These binary characters are converted
into frequency domain values as complex
numbers. The following step involves
keying process in the decryption end.
Thus, the complex numbers are obtained
and they are converted into ASCII code
using IFFT process, i.e., the frequency
domain complex values are converted into
time domain values. The next step
involves representing the encrypted
characters for the respective ASCII codes.
The final step of decryption involves
writing the decrypted text data in new text
file.
Fig. 2 represents the flow diagram for
decryption process.
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
RECEIVED
ENCRYPTED FILE
DECRYPT THE
CHARACTERS
USING KEY
KEY
CONVERT THE
FREQUENCY
DOMAIN TO ASCII
CODE
EXTRACT THE
CHARACTERS
FROM ASCII
CODE
DISPLAY THE
DECRYPTED DATA
DECRYPTED TEXT FILE
OUTPUT
Figure 2: Flow diagram for decryption.
The process of converting the frequency
domain signal to the time domain signal is
called as inverse Fourier Transform. It is
the reverse process of Fourier Transform.
( )→
( )
The equation of inverse continuous time
Fourier transforms is given as:
( )
∫
(
( )
∑ ( )
)
The equation of inverse discrete time
Fourier transforms is given as:
( )
∑
( )
Inverse Fast
Fourier Transform is the reverse process of
fast Fourier transform is the inverse fast
11
Fourier transform. FFT algorithms can be
used to compute Inverse DFT (IDFT)
without any change in
the algorithm. The direct computation
method is performed by the formula given
below:
⁄
Where,
is the twiddle
factor. It can also computed by radix
algorithm.
RESULTS AND DISCUSSION
The result contains the output of text files
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
created during the process of encryption
and decryption. The first step involves the
creation of VI in the LabVIEW software
tool. This VI consists of two panel-front
panel and block diagram. The front panel
is the user interface which interacts with
the user. The block diagram consists of
internal parts which builds the whole
process.
The block diagram for the encryption
process is created. The file path of to be
encrypted was provided. Another path of
the empty text file was provided. In this
file, the encrypted binary output is
rewritten. The Fig. 3 shows block diagram
of the proposed encryption module. The
front panel is the user interface and the
front panel window is shown in the Fig. 4.
Figure 3: Block diagram of encryption module.
Figure 4: Front panel of the encryption module.
12
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
Figure 5: Original information text file.
As the result of encryption process, the
original text file information (Fig. 5), is
converted
into
the
cipher text
information and it is overwritten in the
empty text file path provided (Fig. 6).
Figure 6: Encrypted binary text file.
The created binary text file (Fig. 5), is
used for transmission. The path of this file
was provided at the decryptor module
front panel. The decryption process is done
and the resultant text is displayed. The
decryptor module performs the following
function:
 Extracting the characters from



encrypted file.
Conversion of Cipher text into numeric
data.
Performing the IFFT function.
Conversion of inverted answers into
characters and obtaining original
information.
Figure 7: Block diagram of decryption module.
13
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Journal of Communication Engineering and Its Innovations
Volume 5 Issue 3
Figure 8: Front panel of decryption module.
Figure 9: Decrypted information file.
The Fig. 7 and 8 represents block diagram
and front panel of decryption module
respectively. The information is decrypted
and displayed in the front panel. The
decrypted data is also written in a new text
file. The Fig. 9 represents the decrypted
text file.
CONCLUSION
The original data that is transmitted
through encryption is same as the retrieved
data after the decryption process. The
application designed provides a very high
security in transmission of a text file. As
information security is one of the growing
concern in various fields like nation
security, defense, banking and protection
of various confidential data this
application can be used in those sectors.
This application can be used as an
effective technique in programming
scenarios to secure vital codes and secure
transmission in research departments. The
high level of security is provided by the
scrambling patterns, user logins, domain
conversion, etc., the future scope of this
14
application relies the development of
higher order FFT algorithm. For higher
security, the number of scrambling
patterns are increased by means of FFT
algorithm. The application possesses
immense scope for further development.
The development relies on the factors
providing transmission security. The
application can be further designed for
word documents and other types of text
files (pdf, word document, etc.).
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