Proposing an Encryption Algorithm based on DES

International Journal of Science and Research (IJSR), India Online ISSN: 2319-7064
Volume 2 Issue 9, September 2013
www.ijsr.net
Proposing an Encryption Algorithm based on DES
Omar Zughoul1
, Hajar Mat Jani2
1
Universiti Tenaga Nasional, College of Graduate Studies,
Jalan IKRAM-UNITEN, 43000 Kajang, Selangor, Malaysia
2
Universiti Tenaga Nasional, College of Information Technology,
Jalan IKRAM-UNITEN, 43000 Kajang, Selangor, Malaysia
Abstract: In this paper, a new method for key generation using Data Encryption Standard (DES) is proposed in order to make it more
secure than DES algorithm, but at the same time faster than 3DES algorithm. Some parts of the DES are modified to improve its
security and performance aspects. The proposed algorithm is named XS-DES (Extra Secure DES). We modify the process of key
generation to improve its level of security, and present the proposed algorithm’s design structure in more detail. We increase the size of
the key from 64 bits into 128 bits, and then split the key into two halves, left and right (Kl, Kr), and each one consists of 64 bits. XS-DES
will be used to encrypt some important information inside the database, like passwords, exam scores, and other confidential details. In
other words, to increase the security in the database and protect it from attackers, all critical information must be encrypted using a
strong encryption algorithm and a more secure algorithm (XS-DES) is proposed here. A workable Online Examination System (OES)
that applies XS-DES and the original DES algorithms is developed. It has gone through some preliminary testings and a comparison is
performed between the results of these algorithms based on their strengths in handling database attackers.
Keywords: Database Security, DES, 3DES, and XS-DES.
1. Introduction
The challenges for the security of databases increased
because of the enormous popularity of e-business. In these
days, the insider attacks gathered more attention than
outsider attacks [1]. The insiders have a big opportunity to
attack and it is difficult to compromise them. The attackers
can steal the information from the database in many ways
and it is easy for them because the information and data are
stored as plain text.
Cryptography is the art and science of protecting
information from undesirable individuals by converting the
information into a form non-recognizable by its attackers
while the information are being stored and transmitted [2].
There are two basic techniques for encrypting data and
information; the first one is “Symmetric cryptography”,
which means using the same key to encrypt/encode and
decrypt/decode its data. The second one is “Asymmetric”,
which needs the usage of both public and private keys.
Symmetric requires knowing the private key by the party
encrypting the data and the party decrypting the data.
Asymmetric permits the use of your public key by anyone to
encrypt the data but the only person who can decrypt it is the
one who has the private key.
2. Database Security
The security of database becomes so important in industrial,
government domain and in organizations and companies.
There are huge amounts of data and confidential information
stored in organizations’ databases and some of these data
and information are considered sensitive and important. In
other words, these details should not be readable except for
authorized people.
One of the solutions for avoiding the risk of attackers is to
encrypt the data inside the database, which means that there
is a need to create a cipher text from plain text or in other
words convert a plain text (original text) to cipher text (text
after encrypt) to make the original text unreadable and
without any meaning.
There are three major elements of data security; the first is
“confidentiality”, which means that the data is only readable
by authorized people; the second is “integrity”, which
ensures that the data sent and received are the same without
any interferences or changes. And the third is
“authentication”, which ensures that users are well-identified
[3].
3. Data Encryption Standard (DES)
Data encryption standard (DES) algorithm is a strong cipher;
however, according to Grabbe [4], its key length is too short
to provide much security against a “well-ﬁnanced” attacker.
In addition, DES is a block cipher algorithm which means
that it takes a fixed length of the message and encrypts it
(encrypts the block), and returns a string in the same size.
DES is the first encryption algorithm recommended by NIST
(National Institute of Standards and Technology).
It has been developed in the early 1970s by IBM for NBS
(National Bureau of standards). After that, in 1976 the NBS
selected a modified version of DES after deliberation with
the NSA (National Security Agency) and published for the
US in 1977 as a Federal Information Processing Standard
(FIPS) [5]. After 25 years of researching and analyzing,
researchers found that the only security problem with DES is
its key length, which is, too short [6].
Data Encryption Standard (DES) algorithm has been a
popular secret key encryption algorithm and it is used in
many commercial and financial applications. Although it
was introduced in 1976, it has proven resistant to all forms
of cryptanalysis. However, as stated by Chang [7], its key
size is too small by current standards and its 56-bit key space
can only be searched in approximately 22 hours”. Fig.1
below shows how DES algorithm works:
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Figure 1: DES algorithm
3.1 DES encryption
There are two steps to encrypt the message using DES, the
first one is the key generation, and the second one is the
message. We will start with the key generation.
3.1.1 Key generation
The key of DES algorithm originally consists of 64 bits. It is
reduced to 56 bits through a fixed table, which is called PC1
(Table 1). The new key has 56 bits; here, the key splits into
two parts or two 28-bit halves. The first one is called C0 and
the second one called D0 where each one consists of 28 bits.
To get C1, D1, both C0 and D0 are rotated one bit to the left
using a fix table which is called shifting table or iteration
(Table 2). Then, C1and D1 are combined to get the 56 bits,
out of which we choose the 48-bit key K1 using the key
choice table called the permuted choice table 2, or PC-2
(Table 3). To generate all keys, the same steps in generating
the first key are repeated for 16 rounds [8].
In general, for each key Ki (i > 0), Ci and Di must first be
obtained by rotating each Ci-1and Di-1 one bit to the left,
respectively, using the shifting table (Table 4), i.e., C1and
D1 is obtained from C0, D0, C2 and D2 from C1, D1 and
subsequently, Cn, Dn is obtained from Cn-1, Dn-1 where n
takes the value from 1 to 16, because DES has to undergo 16
rounds for the keys and messages. Then, the 48-bit key Ki is
produced by combining Ci and Di and using PC-2. That is,
C1 and D1 are used to generate the key output K1 by
combining them and permuted the combination using PC-2,
C2 and D2 to generate K2, and so on until finally, Cn, Dn
are combined and permuted to get Kn, where n is from 1
to16.
Table 1: PC-1
57 49 41 33 25 17 9
1 58 50 42 34 26 18
10 2 59 51 43 35 27
19 11 3 60 52 44 36
63 55 47 39 31 23 15
7 62 54 46 38 30 22
14 6 61 53 45 37 29
21 13 5 28 20 12 4
Table 2: Iteration
Round Left Shifts
1 1
2 1
3 2
4 2
5 2
6 2
7 2
8 2
9 1
10 2
11 2
12 2
13 2
14 2
15 2
16 1
Table 3: PC-2
14 17 11 24 1 5
3 28 15 6 21 10
23 19 12 4 26 8
16 7 27 20 13 2
41 52 31 37 47 55
30 40 51 45 33 48
44 49 39 56 34 53
46 42 50 36 29 32
3.1.2 The message
DES (and most of the other major symmetric ciphers) is
based on a cipher known as the Feistel block cipher. The
basic principle of Feistel ciphers is that the plain text block is
split into two halves and each half is used to encrypt the
other half over a predetermined number of rounds. Thus,
DES is a symmetric, 64-bit block cipher as it uses the same
key for both encryption and decryption and only operates on
64-bit blocks of data at a time. In general, DES algorithm
divides a message into blocks where each block consists of
64 bits.
The encryption begins with an initial permutation using
the fixed initial permutation (IP) table, which rearranges the
64 bits of the message data in a fixed pattern. The result of
the initial permutation is divided into two blocks L0 and R0,
and each block consists of 32 bits. Subsequently, DES
generates L1 to L16 and R1 to R16 using the formula, which
is given as the following:
L j = R j-1 (1)
R j = L j-1 (+) F(E(R j-1), K j) (2)
where j = 1, 2, ... , 16. (2)
Thus, for example, from equation (1), when j = 1, L1 = R0
while R1= L0 (+) F(E(R0), K1) according to equation (2).
Equation (2) can be further described as follows. For any j,
F(E(R j-1), K j) means that the function F takes the 32-bit R
half, i.e., R j-1, and 48-bit sub-key Kj, in which E(R j-1)
denotes that the 32-bit R j-1 is expanded to 48 bits using the
E-box expansion permutation table.
The expansion of R j-1 to 48 bits is because K1 is 48 bits.
The result of E(R j-1) is then XORed (+) to the key Kj.
Next, the XOR result will then be grouped to 8 blocks where
each block consists of 6 bits. This result is then passed
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through S-Box substitution to get 32-bit result and then the
permutation using the P-box permutation is applied to
permute the output of the S-box without changing the size of
the data. Finally, this result is then XORed (+) to the key L
j-1 in order to get Rj as in equation (2). These steps are then
iterated 15 more rounds to produce L2 and R2, L3 and R3
and so on until L16 and R16. The total number of iteration
is 16 rounds if including L1 and R1.
At the end of the 16th round, the 32-bit Li and Ri output
quantities are swapped to create what is known as the pre-
output. Finally, the pre-output is passed through the final
permutation (Fb) using the (IP-1
). In other words, the final
permutation is the inverse of the initial permutation; the table
is interpreted similarly, that is IP-1
is the inverse of the IP
table. This final process is converting the Fb into
hexadecimal (the encrypted text) such that the output of IP−1
is the 64-bit cipher text.
3.2 DES decryption
Any symmetric algorithm has only one key for encryption
and decryption (Feistel cipher block), and uses similar
algorithms for encryption and decryption, but the application
of the sub keys is reserved [9].
4. TDES (3DES)
TDES or 3DES is the American National Standards
Institute’s (ANSI)-sanctioned encryption algorithm standard
used by all debit-capable transaction terminals for PIN
encryption. TDES (also known as Triple-DES) was
developed to add more security protection in combating
potential security breaches by being more secure than its
predecessor, Data Encryption Standard (DES).
The 3DES was developed after it became clear that DES
by itself was too easy to crack. It uses three 56-bit DES keys,
giving a total key length of 168 bits. Encryption using 3DES
is simply encryption using DES with the first 56-bit key,
decryption using DES with the second 56-bit key, and
encryption using DES with the third 56-bit key. Because
3DES applies the DES algorithm three times (hence the
name), 3DES takes three times as long as standard DES [10].
Decryption using 3DES is the same as the encryption,
except it is executed in reverse order. In other words, 3DES
means you need to encrypt with key 1, decrypt with key 2,
and again encrypt it with key 3. Fig. 2 below shows a
general architecture of 3DES.
Figure 2: 3DES algorithm
5. Online Examination System (OES)
There are many application software or applications created
for online examinations and in this section some of them are
described.
TCExam [11], is open source software (free) which is
simple and efficient, it is developed using popular LAMP
platform (GNU-Linux, Appache server, MySQL, and PHP
programming language). Any server that can run PHP can
support this software.
SpeedExam [12] is not an open source but it is also not
expensive. It is customized for schools, colleges, and
universities. It was designed for practice and tests.
Multiple-choice questions, multiple answers, true/false
questions, and yes/no question are supported by this
software. It can also import questions from Excel sheet.
This software can be installed into mobile devices.
VirtualX [13] is an online examination system, which is
open source; it is an effective system for saving the time, and
also in getting fast result. It supports 12 different types of
questions and 5 different types of reports for examinees with
graphical analysis. It also supports a feedback management.
It is useful for universities, schools, companies, and E-
learning organizations.
Exambuilder [14] supports multiple-choice questions,
true/false question, multiple correct answers, fill-in the blank
and matching; the software will distribute the question
randomly. This software supports gap analysis reports -
“These reports grade the student on each question pool and
provide remediation activities if the performance is below a
threshold that you set”.
The first version of Adit [15] was created in 2006 and the
last one in 2012. And the requirements for this system are:
any windows operating system except windows 95/98/ME,
the processor is 1 GHz or higher, memory 512 or higher, and
80 MB of disk space. The last version is comprehensive,
which means that it supports all kinds of examination
questions. In addition, it supports four kinds of tests, which
are assessment, survey, personality, and script.
Our system is created to increase the efficiency of OES by
using a secure algorithm, which is XS-DES. Fig. 3 below
shows the main interface of our system.
Figure 3: The main page of OES
Here, we will explain where we can apply our proposed
method to make an OES more secure. When a student enters
into an OES, there are two options; the first one is Login,
which includes the Admin, Examiner and Student logins,
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and each one has a specified level of authority to perform
some tasks. Admin can add or delete students, he/she also
can add or delete Examiner, and he/she can approve the
exams. The Examiner can just evaluate the exam paper and
send the result; he/she cannot see the students’ name,
because the system will generates fake name to the students’.
The second option is Register, which is meant for new
students (without an account).
Once a student logs into the system, he/she has three tasks
that he/she can perform. He/she can first select the desired
exam file, and secondly (second task), answer and submit the
exam; after that he/she can request (third task) for the results.
Whenever there is a request for exam results, the OES will
send an email containing the decrypted results.
It should be noted that the student has to register first to
allow him/her to take the exam, and during the registration
process he/she must enter his/her name, filed, password, and
email, when he/she login in the first time he/she will choose
security question and answer it. If all fields were filled and
the ID does not exist, then the student’s information will be
created and stored in the database to allow him/her take the
exam later.
6. Extra Secure DES (XS-DES)
Researchers found that the only security problem in DES is
its key, which is not very powerful and also too short, as
stated by Deshmukh and Qureshi [16].
Thus, the 3DES becomes the choice to solve this problem
of DES. 3DES uses three keys (K1, K2, K3) where each key
consists of 56 bits. The plain text block is encrypted with
the first key (K1), then decrypted with the second key (K2)
and, finally, encrypted with the third key (K3). To decrypt
the cipher text, the steps are reversed, that is decrypt with
K3, encrypt with K2, decrypt with K1 and XOR the previous
cipher text block.
DES is faster than 3DES but, 3DES is more secure than
DES [17]. Our system needs an encryption algorithm, which
is more secure than DES, but at the same time faster than
3DES. So, in order to accomplish this objective, we propose
a new algorithm named XS-DES (Extra Secure-DES).
We propose to increase the size of the key from 64 bits to
128 bits, and split the key into two halves: left and right (Kl,
Kr), and each one consists of 64 bits. Here, the proposed
algorithm will decrease each key to 56 bits by applying the
PC-1; after that it will divide each key into two parts (C0,
D0). Then, (C1, D1) will be generated from (C0, D0) and
the next (Ci, Di), i = 2, 3, ..., 16 will be obtained through
similar step iteration. K1 will be produced by combining the
left side from Kl (C0 from left key) and right side from Kr
(D0 from right key). The last operation is to decrease the
size of a key to 48 bits to encrypt the message. Fig. 4 shows
our proposed method for the key generation in DES.
Figure 4: XS-DES
7. Comparison: DES and XS-DES
In this section we present a comparison between DES and
our proposed algorithm, which is XS-DES. We perform this
comparison to show that our proposed algorithm is more
secure than DES, and at the same time faster than 3DES.
In terms of time, our method will be faster than 3DES,
because 3DES will encrypt using key one, then decrypt
using key two, and encrypt again using key three; this
process will take more time. In XS-DES, it just encrypts
using the same key, and there is no need to perform 3
processes. From the reduction of the number of steps, XS-
DES will require less execution time (faster).
In terms of security level, we test these algorithms using
an online tool, which is the website
“howsecureismypassword.Net”; this website shows how
many years attackers need to hack the encrypted password
[18]. Many researchers like Judge Herbert [19] and Tony de
Souza-Daw [20] also used this tool to test their passwords.
We choose five passwords and encrypt them through
DES, and XS-DES. Then, we put the cipher text for each one
in this tool. Table 4 and Table 5 below show these results.
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Table 4: Results [18]
Plain text Algorithm Cipher text Time To Hack
omarzug8
7!
DES U2FsdGVkX1
8e9YPt/tWxfI
kHSJwM5kP1
Qjbbpk8jtfk=
It would take a
desktop PC about
A tresvigintillion
years to crack this
password
XS-DES U2FsdGVkX1
+MTV3/DFb6
z/Ynm9GVtf
VtBnAD68W
xgvo=
It would take a
desktop PC about
“121”
tresvigintillion
years to crack this
password
@OMAR
z87
DES U2FsdGVkX1
+97zSYAfnN
Yrhht4t9lkvva
KJsRL2tclU=
It would take a
desktop PC about
“61”
unvigintillion
years to crack this
password
XS-DES U2FsdGVkX1
+a7XZbFHW
oqhwezWoW
8A0t2x15Jpa7
/Po=
It would take a
desktop PC about
“121”
tresvigintillion
years to crack this
password
@zug12o
m$
DES U2FsdGVkX1
9z/tFTuIn8+Y
7aA/zLrwOlK
+iPI9nK4dBa
8li3ileIVg==
It would take a
desktop PC about
“773” trigintillion
years to crack this
password
XS-DES U2FsdGVkX1
8QgsWluh4Y
hIS06yj64d/r
CE++VnKR/e
fA+CKLfS4L
pg==
It would take a
desktop PC about
“68” googol years
to crack this
password
Table 5: Results [18]
Plain text Algorithm Cipher text Time To Hack
omar87_
_
DES U2FsdGVkX1
+MJ8GLaCot
CF4cDCOhw
7NtWwcWY0
Rc6FI=
It would take a
desktop PC about
“802” vigintillion
years to crack the
password.
XS-DES U2FsdGVkX1
8M/LlHMwL
v5R96YifxF8
RIIIXFryjQV
4c=
It would take a
desktop PC about
“13” duovigintillion
years to crack This
password.
_!omar87 DES U2FsdGVkX1
9cEJW3G4mf
46WctRFDUi
rEerd9eP6s+
Yc=
It would take a
desktop PC about
“4” duovigintillion
years to crack this
password
XS-DES U2FsdGVkX1
9JgNWrofyN
4ZqVB7Co3Z
/lAbHXpQGY
8eY=
It would take a
desktop PC about
“121”tresvigintillio
n years to crack this
password
8. Conclusion and Future Work
Encryption algorithms are important for any database for
encrypting confidential data, information, and more
importantly, the passwords. Encryption algorithms are used
to encrypt data and make it unreadable. This is done in order
to prevent any attackers from seeing these confidential
details.
In this paper, we propose a new method to encrypt the
data and information, and the encryption algorithm is named
XS-DES, which is originally based on DES. We increase
the key size of the algorithm and add a new method in the
key generation’s step. After applying our method to a
workable prototype and performing several preliminary
testings, we achieved positive results, which proved that our
method is more secure than DES algorithm.
A workable prototype of the Online Examination System
(OES) that uses the proposed XS-DES algorithm has been
developed. It has been tested to demonstrate if the
introduced XS-DES algorithm has achieved its objectives,
and the results are acceptable.
In the future, the XS-DES will be applied to other web-
based applications related to education and other types of
online business applications so that more people can benefit
from the proposed encryption method.
Acknowledgment
This research was partially supported by the Ministry of
Education (MOE) Malaysia under the Fundamental Research
Grant Scheme (FRGS).
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Authors Profiles
Omar Zughoul received the B.S degree in Computer
Information System from Yarmouk University in
2011, he stay in Malaysia to study Master of
Information Technology.
Dr. Hajar Mat Jani is currently a Senior Lecturer at Universiti
Tenaga Nasional (UNITEN), Malaysia. She received her Bachelor
of Science (Computer Science) and Master of Science (Computer
Science) degrees from The University of Georgia and Western
Michigan University, U.S.A., respectively. She holds a Ph.D.
degree in Software Engineering from University of Malaya,
Malaysia.
Paper ID: 02013299 326

Proposing an Encryption Algorithm based on DES

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