Introducing an Encryption Algorithm based on IDEA

International Journal of Science and Research (IJSR), India Online ISSN: 2319-7064
Volume 2 Issue 9, September 2013
www.ijsr.net
Introducing an Encryption Algorithm based on
IDEA
Osama Almasri1
, 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: International Data Encryption Algorithm (IDEA) is one of the encryption algorithms that is widely used for security
purpose. IDEA block cipher operates with 64-bit plain text block and 64-bit cipher text block, and a 128-bit key controls it. The
fundamental design of the algorithm is using three different algebraic operations: bitwise Exclusive OR, multiplication modulo, and
addition modulo. Having the largest number of weak keys is one of the drawbacks of IDEA. In addition, a new attack during round six
of IDEA’s operations has been detected. In this paper, we propose and describe the new design and preliminary implementation of a
more secure encryption algorithm based on IDEA, and it is named DS-IDEA. Increasing the size of the key from 128 bits to 512 bits
will increase the complexity of the algorithm. The algorithm’s complexity is increased by increasing the amount of diffusion
(multiplicative additive block) in a single round. It is implemented to provide better security to the user’s password within the Online
Password Management System (OPMS) in order to protect the user’s data within the database from hackers and other forms of
unauthorized access.
Keywords: International Data Encryption Algorithm (IDEA), Double Secure-IDEA (DS-IDEA), Multiplicative Additive (MA), Online
Password Management System (OPMS)
1. Introduction
Single key encryption or conventional encryption are terms
that are often used to refer to symmetric encryption. It was
the only type of encryption in use in the development of
public-key encryption. It remains the most widely used of the
two types of encryption: symmetric encryption and
asymmetric encryption [1]. Symmetric encryption has five
components as illustrated in Fig. 1:
• Plain text: This is the original message that is intelligible
and is fed into the algorithm as input.
• Encryption algorithm: It performs various operations and
transformations on the original message (plain text).
• Secret key: It is shared between the sender and the
recipient, and is used as an input to the algorithm.
• Cipher text: It is the algorithm’s output. It is scrambled
message and unintelligible that depends on the plain text
and encryption key.
• Decryption algorithm: The reverse operation is applied
on the cipher text to get the plain text (original).
The International Data Encryption Algorithm (IDEA) is one
of the symmetric encryption algorithms that can be
implemented in e-learning systems [2]. It is a post Data
Encryption Algorithm (DES) that has better security and
covers some of the DES problems. It is characterized by
high-speed encryption/decryption process, with resisting and
correlation analysis [3]. Because of the weaknesses in the
algorithm’s keys, and the attack in round six of its operations,
the necessity to increase the algorithm’s security has become
paramount [4].
The proposed scheme of algorithm is named Double Secure-
IDEA or DS-IDEA. It is a modified version of IDEA; a
modification is done by increasing the key size and the
amount of the diffusion process (MA blocks). Any
organization over the world must protect their user’s data by
the fulfillment of three major factors: confidentiality,
integrity, and availability (CIA). Password confidentiality is
more challenging, and this involves a number of security
controls along with decisions involving the characteristics of
the passwords themselves. Those CIA factors are applied by
implementing the proposed algorithm within a workable
prototype named Online Registration System, in which the
component of the proposed Online Password Management
System (OPMS) is embedded.
Figure 1: General model of symmetric encryption [1]
2. Background and Related Work
2.1 Brief description of IDEA algorithm
IDEA is a symmetric block cipher that was published in 1991
by Lai, Massey, and Murphy [5]. IDEA is a modification of
Proposed Encryption Standard (PES) that was published by
Lai and Massey in 1990 [6]. PES is a replacement of DES,
and IDEA was originally named Improved Proposed
Encryption Standard (IPES), but was later changed to IDEA
in 1992 [7].
The block cipher IDEA encrypts a 64-bit block of plain text
and a 64-bit of cipher text, and a 128-bit key controls it. The
algorithm (refer to Fig. 2) consists of eight identical rounds
plus a half round for output transformation. The fundamental
Paper ID: 12013164 334

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design in IDEA is the use of the mixing of three incompatible
algebraic groups: bit-by-bit XOR, addition modulo 216, and
multiplication modulo 216+1. There are 216 possible 16-bit
blocks: 0000000000000000… 1111111111111111. Schneier
[8] breaks the algorithm into fourteen steps for each eight
complete rounds. The plain text is a fixed size (64-bit block)
that is divided into four 16-bit blocks (X1|| X2|| X3|| X4). The
key is a 128-bit block. It is divided into eight 16-bit sub keys.
The division into 16 bits is because all of the algebraic
operations used in the encryption and decryption process
operate at 16-bit numbers. The last output round is four 16-
bit sub keys. Each round uses six 16-bit sub keys and the
remaining two sub keys are used in the next round by
implementing left shifting by 25 positions. The total sub keys
is 52 {52=8 rounds*6 sub keys + (4 sub keys “output
transformation”)} [3]. The encryption and decryption of sub
keys are shown in Table 1.
Table 1: Encryption and decryption of the sub keys [3]
Round
No.
Sub keys of Encryption Sub keys of Decryption
1 Z1
(1)
Z2
(1)
Z3
(1)
Z4
(1)
Z5
(1)
Z6
(1) Z1
(9)-1
–Z2
(9)
–Z3
(9)
Z4
(9)-1
Z5
(8)
Z6
(8)
2 Z1
(2)
Z2
(2)
Z3
(2)
Z4
(2)
Z5
(2)
Z6
(2) Z1
(8)-1
–Z2
(8)
–Z3
(8)
Z4
(8)-1
Z5
(7)
Z6
(7)
3 Z1
(3)
Z2
(3)
Z3
(3)
Z4
(3)
Z5
(3)
Z6
(3) Z1
(7)-1
–Z2
(7)
–Z3
(7)
Z4
(7)-1
Z5
(6)
Z6
(6)
4 Z1
(4)
Z2
(4)
Z3
(4)
Z4
(4)
Z5
(4)
Z6
(4) Z1
(6)-1
–Z2
(6)
–Z3
(6)
Z4
(6)-1
Z5
(5)
Z6
(5)
5 Z1
(5)
Z2
(5)
Z3
(5)
Z4
(5)
Z5
(5)
Z6
(5) Z1
(5)-1
–Z2
(5)
–Z3
(5)
Z4
(5)-1
Z5
(4)
Z6
(4)
6 Z1
(6)
Z2
(6)
Z3
(6)
Z4
(6)
Z5
(6)
Z6
(6) Z1
(4)-1
–Z2
(4)
–Z3
(4)
Z4
(4)-1
Z5
(3)
Z6
(3)
7 Z1
(7)
Z2
(7)
Z3
(7)
Z4
(7)
Z5
(7)
Z6
(7) Z1
(3)-1
–Z2
(3)
–Z3
(3)
Z4
(3)-1
Z5
(2)
Z6
(2)
8 Z1
(8)
Z2
(8)
Z3
(8)
Z4
(8)
Z5
(8)
Z6
(8) Z1
(2)-1
–Z2
(2)
–Z3
(2)
Z4
(2)-1
Z5
(1)
Z6
(1)
Output
transfor-
mation
Z1
(9)
Z2
(9)
Z3
(9)
Z4
(9)
Z1
(1)-1
–Z2
(1)
–Z3
(1)
Z4
(1)-1
The following steps are the encryption process in each round
[3]:
1.First multiplication between X1 and the first sub key Z1.
2.Addition operation of X2 with the second sub key Z2.
3.Addition operation between X3 and the third sub-key Z3.
4.Second multiplication between X4 and the fourth sub-key
Z4.
5.Calculating Bitwise XOR from the results of steps 1 and 3.
6.Calculating Bitwise XOR from the results of steps 2 and 4.
Figure 2: Structure of IDEA encryption process [3]
The decryption process is an essential process that is applied
on cipher text to transform it into the original message (plain
text). The computational process for the decryption is the
same as that used for the encryption of the plain text. The
difference compared to the encryption is that the 16-bit sub
keys are generated in reverse order.
The IDEA encryption algorithm has some features which
claim for use [9]:
• High level security not keeping the algorithm a secret, but
rather upon ignorance of the secret key.
• Easily understood.
• Available online.
• Widely used range of application and efficiently such as
distance learning.
2.2 A proposed encryption algorithm based on IDEA
The drawback of IDEA is that large numbers of weak keys
were found in the algorithm. In addition, the attack that has
been detected in round 6 is also one of the algorithm’s
drawbacks [10], [11]. This paper discusses the improvement
that is made to the IDEA algorithm to make it more secure.
Increasing the key size from 128 bits to 512 bits is a main
factor in algorithmic complexity. Also, increasing the
IDEA’s strength can be made by exploiting the operations of
confusion and diffusion. The modified design is named
Double Secure-International Data Encryption Algorithm
(DS-IDEA). The block size of the sub keys in the modified
version will be increased due to the key size. So, to ensure
decreasing the number of sub key blocks, this will increase
the sub key block size to become more than 16-bit. The block
size should be 16-bit because of the algebraic operations that
operate on 16-bit numbers. The other modification in the
design is using S-Box to decrease the number of bits from 32
bits to 16 bits of each sub key block.
The encryption process consists of eight identical steps
(named encryption rounds) and followed by last round called
output transformation. The key size is 512 bits, and the plain
Paper ID: 12013164 335

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text size is 128 bits. The plain text is processed in 8 blocks of
16 bits each. DS-IDEA (proposed method) can be processed
as two sub blocks of 64 bits. Two sub blocks are running in
parallel with each other. Each round uses two MA blocks and
12 sub keys of 32 bits each. In IDEA 128-bit key is divided
into 8 sub keys of 16 bits each; each round uses 6 sub keys
and the remaining two sub keys are used in the next round
after applying left shifting by 25 positions. In the proposed
design 512-bit key is divided into 16 sub keys of 32-bit each.
Each round uses 12 sub keys of 32-bit each; the remaining
four sub keys are used in the next round. S-box should
implement on the 16 sub keys to transform 32-bit to 16-bit of
each sub key, then 12 sub keys are processed by applying the
addition and multiplication modulo.
In the first round, the first four 16-bit sub key is combined
with two of 16-bit plain text blocks using addition modulo
216
, and with another two 16-bit plain text blocks using
multiplication modulo 216
+1. The results are then processed,
whereby two more 16-bit sub keys are included in the
calculation and the third algebraic group operator, the bitwise
XOR, is used. Each round consists of two further divisions
i.e. transformation, followed by sub encryption.
Transformation uses 8 sub key, whereas sub encryption uses
4 sub keys. The process of the first round of encryption is
illustrated in Fig. 3. The last round of output transformation
uses 8 sub keys, whereas the total keys will be 104 sub keys
of 16 bits each that gives the cipher text. The decryption
process is almost the same as the encryption process, but in a
reverse sequence. Fig. 3 describes the structural design of the
encryption round of DS-IDEA. From Fig. 3 the following
relations can be written:
• W11 = I11 ⨁ MAR1 (I11 ⨁ I13 , I12 ⨁ I14)
• W12 = I13 ⨁ MAR1 (I11 ⨁ I13 , I12 ⨁ I14)
• W13 = I12 ⨁ MAL1 (I11 ⨁ I13 , I12 ⨁ I14)
• W14 = I14 ⨁ MAL1 (I11 ⨁ I13 , I12 ⨁ I14)
• W15 = I15 ⨁ MAR2 (I15 ⨁ I17 , I16 ⨁ I18)
• W16 = I17 ⨁ MAR2 (I15 ⨁ I17 , I16 ⨁ I18)
• W17 = I16 ⨁ MAL2 (I15 ⨁ I17 , I16 ⨁ I18)
• W18 = I18 ⨁ MAL2 (I15 ⨁ I17 , I16 ⨁ I18)
“W11” denotes the word that is 16-bit, and the first index on
the left means the first word. The right index refers to the
round number. “I” refers to the input ( plain text) that is 16-
bit block. The processes of round one that described above
are repeated in each of the subsequent seven encryption
rounds using 16-bit sub keys for each combination.
Figure 3: Structural design of first encryption round of DS-
IDEA
3. Research Methodology for Implementing the
Proposed Algorithm
Fig. 4 depicts the research methodology in the
implementation of DS-IDEA within the prototype.
Figure 4: Research methodology
3.1 Implementing DS-IDEA within OPMS
The online system is a platform that provides data and
information online with the objective of improving the user’s
experience. Nowadays, the most appropriate way to
disseminate and present information to a large group of
people in the world is using websites. The goal of the website
design is to provide plenty information to visitors or users in
an organized manner. In addition, there must be a reliable
Paper ID: 12013164 336

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transfer of secure information. There are other factors such as
simplicity, user friendliness, layout, ease of rendering in the
browser and so on that are closely related with the quality of
the website.
Organizations must protect the password by three major
factors, which are confidentiality, integrity, and availability,
so that all authorized users can use passwords successfully as
needed. Reducing the risk of compromise of password-based
authentication systems are an effective password
management.
Password confidentiality is more challenging and involves a
number of security controls along with decisions involving
the characteristics of the passwords themselves. Ensuring
integrity and availability using typical data security controls,
such as imposing privileges and access controls to prevent
attackers from overwriting the password are in place.
The objective of the research is to implement the proposed
encryption method in providing better security to users’
passwords within the Online Password Management System
(OPMS) in order to protect the user’s data within the
database from hackers or attackers.
The protection process is done by implementing a symmetric
encryption algorithm named International Data Encryption
Algorithm (IDEA) on the passwords. The algorithm will be
improved by modifying the size of the secret key that is used
in both the encryption and decryption operations on the data.
The proposed algorithm is known as Double-Secure IDEA
(DS-IDEA).
The research elaborates on a number of issues that are related
to web design and development, and it focuses on the
security measures that are applied within OPMS. These
concepts will be illustrated and demonstrated in the design of
system that we have designed so far. Testing results from
implementing the proposed method of the encryption
algorithm on system password fields for evaluating the
security strength is the one of the primary aims of this
research. The system can be considered as a working
prototype. It deals with the maintenance of university, staff,
and students’ information through the Online Registration
website. This system involves the automation of registration
process that is used by the administrators and students. Fig. 5
shows a simplified structure of the OPMS, which implements
the proposed algorithm, DS-IDEA.
Figure 5: A simplified structure of Online Password
Management System (OPMS) [3]
Fig. 6 shows a prototype of an online course registration
using OPMS [3]
Figure 6: A simplified course registration prototype [3]
Fig. 7 illustrates a diagram representing OPMS within a
workable online registration prototype.
Figure 7: The framework of the online registration system
using OPMS and DS-IDEA
Fig. 8 shows the home page interface of the system coded
with Active Server Page (ASP).
Figure 8: The home page of online registration prototype
Paper ID: 12013164 337

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3.2 Preliminary experimental results
In this section, we discuss the results that we obtained from
implementing the standard algorithm (IDEA) and the
proposed modified algorithm, DS-IDEA. We implement both
algorithms on the password field in the prototype to compare
the results. The password is stored in the database in
encrypted form under two fields; one uses the IDEA
algorithm and the other uses DS-IDEA.
The aim of the comparison is to get results to demonstrate
that the modified algorithm is stronger and more secure than
the original IDEA algorithm. The comparison is conducted
only on the cipher text using an online tool named “HOW
SECURE IS MY PASSWORD?”[12]. This site can accept any
password to be analyzed, and an estimation of how long it
would take for a personal computer to crack each one of
them is produced.
Judge Herbert B. Dixon Jr [13], Tony de Souza-Daw [14],
and Scott Granneman [15] have recommended using this site
to test the passwords’ security and strength. Table 2
demonstrates using 5 different passwords as plain text and
cipher text, and shows the time the cracker needs in order to
breach the password through the implementation of IDEA
[12]. Table 3 shows the same five passwords encrypted using
DS-IDEA [12]. Each password is comprised of at least 8
characters containing at least one digit and one special
character.
Table 2: Five different passwords encrypted using IDEA
[12]
Plain text Cipher text Time to Crack
ghaleb2!
U2FsdGVkX1/EpfScwgj8
QDP2D+PBukw
VoA==
It would take a desktop PC
about 174 septendecillion
years to crack the password
osama87#
U2FsdGVkX19YI5tvCW7
LY6rOKHpbACQJ
18 duodecillion years
leb28-*&
U2FsdGVkX1917Hl3Bv5
Z/vh3HVzSLu99aQ==
16 sexdecillion years
_!omar87
3
U2FsdGVkX1/614cyIQa2
fsT1orHLTN7Bzw==
16 septendecillion years
2131987h
ey&
U2FsdGVkX1/eLhpdVNx
R1EnnNsGur3+GWA==
174 sexdecillion years
Table 3: Same passwords encrypted using DS-IDEA [12]
Plain text Cipher text Time to Crack
ghaleb2!
U2FsdGVkX1/ldmZTWQ
fHYZluqeIwoa7Lzw==
It would take a desktop
PC about 16
octodecillion years to
crack your password
osama87#
U2FsdGVkX18EVJrd6Slh
ER12F4gQoqZR
18 duodecillion years
leb28-*&
U2FsdGVkX18KuJOm8Q
giC4Wl6UEmY6ZL8A==
50 octodecillion years
_!omar873
U2FsdGVkX1+8GH12vH
mveKeg5LF1mmgVIQ==
296 octodecillion years
2131987hey
&
U2FsdGVkX19Wdxfm6O
nJiM7kLxM3cUXMzQ==
50 septendecillion
years
From Table 2 and Table 3, we discovered that the time to
crack each password requires many more years. The site uses
terms to express the number 10 raised to the power of 54, as
in the word “septendecillion”. “duodecillion” means 1039
,
“octodecillion” is 1057
, and “sexdecillion” means 1051
. By the
comparison between values of years, we proved that the
proposed algorithm (DS-IDEA) is more secure than IDEA.
4. Conclusion and Future Work
The proposed algorithm, DS-IDEA, has two features:
increasing the key size (512 bits) that leads to increasing the
degree of diffusion, and using the S-Box to reduce the key
block size from 32 bits to 16 bits. The total number of sub
keys becomes 104 compared to 52 sub keys with the original
IDEA to enhance the complexity of confusion. This will also
reduce the probability of attacks. Furthermore, using two
multiplicative additive blocks enhances the diffusion. This
contributes in making the algorithm to become more secure
and less susceptible to cryptanalysis. The development of the
Online Password Management System (OPMS) that
implements the DS-IDEA algorithm has started and is
progressing well. It has gone through some initial testing’s
and evaluations with very encouraging results, and we are in
the process of improving the algorithm’s performance.
In the future, the DS-IDEA is going to be enhanced by
including more security operations that can strengthen the
confidentiality, integrity and availability of data that are
encrypted using this algorithm. We also plan to apply this
modified version of IDEA to other web-based systems in e-
business, e-commerce, and e-learning environments with
slightly different methods of implementation.
Acknowledgment
This research is partially supported by the Ministry of
Education (MOE) Malaysia under the Fundamental Research
Grant Scheme (FRGS).
References
[1] S. William, S. Stallings, Cryptography and Network
Security, Pearson Education, India, 2006.
[2] H.S. Chang, “International Data Encryption Algorithm,”
jmu.edu, googleusercontent.com, Fall 2004. [Online].
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WXJPT0eEM7EJ:scholar.google.com/+International+D
ata+Encryption+Algorithm&hl=en&as_sdt=0,5
[Accessed: Feb. 15 2013]
[3] O. Almasri, H. Mat Jani, Z. Ibrahim, O. Zughoul,
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Journal of Computer Engineering (IOSR-JCE), 10 (4),
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Kaeslin, N. Felber, W. Fichtner, “A 177 Mb/s VLSI
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[11]X. Lai, J. Massy, S. Murphy, “Markov Ciphers and
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[13]J.H.B. Dixon Jr, “Cybersecurity ... How Important Is
It?,” The Judges’ Journal, 51 (4), pp. 36-39, 2012.
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Curriculum for an Introductory Course for Information
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Author Profile
Osama Almasri received the B.Sc. degree in
Computer Systems Engineering from Mamoun Private
University of Science and Technology in 2009. During
2011-2013, he is studying Master of Information
Technology (Coursework and Research) at Universiti
Tenaga Nasional.
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: 12013164 339

Introducing an Encryption Algorithm based on IDEA

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