A Universal Bit Level Block Encoding Technique Using Session Based Symmetric Key Cryptography to Enhance the Information Security

International Journal of Advanced Information Technology (IJAIT) Vol. 2, No.2, April 2012
DOI : 10.5121/ijait.2012.2203 29
A Universal Bit Level Block Encoding Technique
Using Session Based Symmetric Key Cryptography
to Enhance the Information Security
Manas Paul1
and Jyotsna Kumar Mandal2
1
Dept. of Comp. Application, JIS College of Engineering, Kalyani, West Bengal, India
manaspaul@rediffmail.com
2
Dept. of C.S.E., Kalyani University, Kalyani, West Bengal, India
jkmandal@rediffmail.com
ABSTRACT
In this paper a session based symmetric key cryptographic algorithm has been proposed and it is termed as
Matrix Based Bit Jumbling Technique (MBBJT). MBBJT consider the plain text (i.e. the input file) as a
binary bit stream with finite number bits. This input bit stream is divided into manageable-sized blocks with
different length. The bits of the each block fit diagonally upward starting from ( n , n ) cell in a right to left
trajectory into a square matrix of suitable order n. Then the bits are taken from the square matrix column-
wise from top to bottom to form the encrypted binary string and from this encrypted string cipher text is
formed. Combination of the values of block length and the no. of blocks of a session generates the session
key. For decryption the cipher text is considered as a stream of binary bits. After processing the session key
information, this binary string is divided into blocks. The bits of the each block fit column-wise from top to
bottom into a square matrix of order n. Now bits are taken diagonally upward starting from ( n , n ) cell in
a right to left trajectory from the square matrix to form the decrypted binary string. Plain text is
regenerated from this binary string. Comparison of MBBJT with existing and industrially accepted TDES
and AES has been done.
KEYWORDS
Matrix Based Bit Jumbling Technique (MBBJT), Cryptography, Symmetric Key, Session Based Key, TDES,
AES.
1. INTRODUCTION
Day by day our communication becomes faster and simpler for internet. Every computer is
connected virtually to each other through internet. Securing electronic data is gradually becoming
important with the increasing dependency on the data interchange by the internet. Hence network
security is the most focused topic among the researchers [1, 2, 3, 4]. Various cryptographic
algorithms are available but each of them has their own merits and demerits. As a result
continuous research works are going on in this field of cryptography to enhance the network
security.

30
Based on symmetric key cryptography a new technique has been proposed where the plain text is
considered as a stream of binary bits. Bit positions are jumbled up to generate the cipher text. A
session key is generated using plain text information. The plain text can be regenerated from the
cipher text using the session key information.
Section 2 of this paper contains the block diagram of the proposed scheme. Section 3 deals with
the algorithms of encryption, decryption and key generation. Section 4 explains the proposed
technique with an example. Section 5 shows the results and analysis on different files with
different sizes and the comparison of the proposed MBBJT with TDES [5], AES [6]. Conclusions
are drawn in the section 6.
2. THE SCHEME
The MBBJT algorithm consists of three major components:
• Key Generation
• Encryption Mechanism
• Decryption Mechanism
Key Generation:
Encryption Mechanism:
Decryption Mechanism:
3. PROPOSED ALGORITHM
3.1. Encryption Algorithm:
Step 1. The plain text i.e. the input file is considered as a binary bit stream of finite no. of bits.
Step 2. This binary stream breaks into manageable-sized blocks with different lengths like 4 / 16 /
64 / 144 / 256 / 400 / ……….. [ (4n)2
for n = 1/2, 1, 2, 3, 4, 5, ……. ] as follows:
First n1 no. of bits is considered as x1 no. of blocks with block length y1 where n1 = x1 * y1. Next
n2 no. of bits is considered as x2 no. of blocks with block length y2 where n2 = x2 * y2 and so on.
Finally nm no. of bits is considered as xm no. of blocks with block length ym (= 4) where nm = xm *
ym . So no padding is required.
Cipher
Text
Key (K)
Plain
Text
Plain
Text
Key
Generator
Key (K)
Plain
Text
Key (K)
Cipher
Text

31
Step 3. Square matrix of order √y is generated for each block of length y. The binary bits of the
block from MSB to LSB fit diagonally upward starting from ( √y , √y ) cell in a right to left
trajectory into this square matrix.
Step 4. From the square matrix bits are taken column-wise from top to bottom to generate the
encrypted block of length y.
Step 5. The cipher text is formed after converting the encrypted binary string into characters.
3.2. Decryption Algorithm:
Step 1. The encrypted file i.e. the cipher text is considered as a stream of binary bits.
Step 2. After processing the session key information, this binary string breaks into manageable-
sized blocks.
Step 3. Square matrix of order √y is generated for each block of length y. The binary bits of the
block from MSB to LSB fit column-wise into the square matrix.
Step 4. The decrypted binary string is generated after taking the bits diagonally upward starting
from ( √y , √y ) cell in a right to left trajectory from the square matrix.
Step 5. The plain text is reformed after converting the decrypted binary string into characters.
3.3. Generation of Session Key:
During encryption a session key is generated for one time use in a session of transmission to
ensure much more security to MBBJT. This technique divides the input binary bit stream
dynamically into 16 portions, each portion is divided again into x no. of blocks with block length
y bits. The final (i.e. 16th
) portion is divided into x16 no. of block with block length 4 bits (i.e. y16
= 4). So no padding is required. Total length of the input binary string is
x1 * y1 + x2 * y2 + …….. + x16 * y16.
The values of x and y are generated dynamically. The session key contains the sixteen set of
values of x and y respectively.
4. EXAMPLE
To illustrate the MBBJT, let us consider a two letter’s word “Go”. The ASCII values of “G” and
“o” are 71 (01000111) and 111 (01101111) respectively. Corresponding binary bit representation
of that word is “0100011101101111”. Consider a block with length 16 bits as
0 1 0 0 0 1 1 1 0 1 1 0 1 1 1 1
Now these bits from MSB to LSB fit diagonally upward starting from ( 4 , 4 ) cell in a right to left
trajectory into this square matrix of order 4 as follows:
1 1 1 1
1 0 0 1
1 1 0 0
1 0 1 0
The encrypted binary string is formed after taking the bits column-wise from top to bottom from
above the square matrix as follows:
1 1 1 1 1 0 1 0 1 0 0 1 1 1 0 0

32
The equivalent decimal no. of two 8 bit binary numbers 11111010 and 10011100 are 250 and 156
respectively. 250 and 156 are the ASCII values of the characters ú (Latin small letter u with
acute) and œ (Latin small ligature oe) respectively. So the word Go is encrypted as úœ.
For decryption, exactly reverse steps of the above are followed.
5. RESULTS AND ANALYSIS
In this section the comparative study between Triple-DES (168bits), AES (128bits) and MBBJT
has done on 20 files of 8 different types with file sizes varying from 330 bytes to 62657918 bytes
(59.7 MB). Analysis includes comparison of encryption time, decryption time, Character
frequencies, Chi-square values, Avalanche and Strict Avalanche effects, Bit Independence. All
implementation has been done using JAVA.
5.1. ANALYSIS OF ENCRYPTION & DECRYPTION TIME
Table I & Table II shows the encryption time and decryption time for Triple-DES (168bits), AES
(128bits) and proposed MBBJT against the different files. Proposed MBBJT takes very less time
to encrypt/decrypt than Triple-DES and little bit more time than AES. Fig. 1(a) and Fig. 1(b)
show the graphical representation of encryption time and decryption time against file size in
logarithmic scale.
TABLE I
File size v/s encryption time(for Triple-DES, AES and MBBJT algorithms)
Sl.
No.
Source File Size
(in bytes)
File
type
Encryption Time (in seconds)
TDES AES MBBJT
1 330 Dll 0.001 0.001 0.003
2 528 Txt 0.001 0.001 0.005
3 96317 Txt 0.034 0.004 0.021
4 233071 Rar 0.082 0.011 0.054
5 354304 Exe 0.123 0.017 0.078
6 536387 Zip 0.186 0.023 0.131
7 657408 Doc 0.220 0.031 0.181
8 682496 Dll 0.248 0.031 0.198
9 860713 Pdf 0.289 0.038 0.215
10 988216 Exe 0.331 0.042 0.254
11 1395473 Txt 0.476 0.059 0.273
12 4472320 Doc 1.663 0.192 0.369
13 7820026 Avi 2.626 0.334 0.648
14 9227808 Zip 3.096 0.397 0.676
15 11580416 Dll 4.393 0.544 0.786
16 17486968 Exe 5.906 0.743 1.799
17 20951837 Rar 7.334 0.937 1.597
18 32683952 Pdf 10.971 1.350 1.992
19 44814336 Exe 15.091 1.914 2.934
20 62657918 Avi 21.133 2.689 5.288

33
TABL II
File size v/s decryption time (for Triple-DES, AES and MBBJT algorithms)
Sl.
No.
Source File Size
(in bytes)
File type
Decryption Time (in seconds)
TDES AES MBBJT
1 330 Dll 0.001 0.001 0.003
2 528 Txt 0.001 0.001 0.006
3 96317 Txt 0.035 0.008 0.024
4 233071 Rar 0.087 0.017 0.062
5 354304 Exe 0.128 0.025 0.089
6 536387 Zip 0.202 0.038 0.146
7 657408 Doc 0.235 0.045 0.198
8 682496 Dll 0.266 0.046 0.226
9 860713 Pdf 0.307 0.060 0.238
10 988216 Exe 0.356 0.070 0.277
11 1395473 Txt 0.530 0.098 0.298
12 4472320 Doc 1.663 0.349 0.407
13 7820026 Avi 2.832 0.557 0.712
14 9227808 Zip 3.377 0.656 0.535
15 11580416 Dll 4.652 0.868 0.866
16 17486968 Exe 6.289 1.220 1.974
17 20951837 Rar 8.052 1.431 1.768
18 32683952 Pdf 11.811 2.274 2.192
19 44814336 Exe 16.253 3.108 3.249
20 62657918 Avi 22.882 4.927 5.857
Fig. 1(a). Encryption Time (sec) vs. File Size (bytes) in logarithmic scale

34
Fig. 1(b). Decryption Time (sec) vs. File Size (bytes) in logarithmic scale
5.2. ANALYSIS OF CHARACTER FREQUENCIES
Analysis of Character frequencies for text file has been performed for T-DES, AES and proposed
MBBJT. Fig.2(a) shows the distribution of characters in the plain text. Fig.2(b), 2(c), 2(d) show
the characters distribution in cipher text for T-DES, AES and proposed MBBJT. All three
algorithms show a distributed spectrum of characters. From the above observation it may be
conclude that the proposed MBBJT may obtain very good security.
Fig. 2(a). Distribution of characters in source file
Fig. 2(b): Distribution of characters in TDES

35
Fig. 2(c). Distribution of characters in AES
Fig. 2(d). Distribution of characters in MBBJT
5.3. TESTS FOR NON-HOMOGENEITY
The test for goodness of fit (Pearson χ2
) has been performed between the source files and the
encrypted files. The large Chi-Square values (compared with tabulated values) may confirm the
high degree of non-homogeneity between the source files and the encrypted files. Table III shows
the Chi-Square values for Triple-DES (168bits), AES (128bits) and proposed MBBJT against the
different files.
From Table III it may conclude that the Chi-Square values of MBBJT are at par with &
sometimes better than that of T-DES and AES. Fig. 3 graphically represents the Chi-Square
values on logarithmic scale for T-DES, AES & MBBJT.

36
Table III
Chi-Square values for Triple-DES, AES and MBBJT algorithms
Sl.
No.
Source File
Size (bytes)
File
type
Chi-Square Values
TDES AES MBBJT
1 330 dll 922 959 874
2 528 txt 1889 1897 1938
3 96317 txt 23492528 23865067 20949798
4 233071 rar 997 915 963
5 354304 exe 353169 228027 214087
6 536387 zip 3279 3510 3308
7 657408 doc 90750 88706 87099
8 682496 dll 29296 28440 26536
9 860713 pdf 59797 60661 57051
10 988216 exe 240186 245090 256043
11 1395473 txt 5833237390 5545862604 5686269895
12 4472320 doc 102678 102581 99695
13 7820026 avi 1869638 1326136 1144840
14 9227808 zip 37593 37424 36682
15 11580416 dll 28811486 17081530 16699315
16 17486968 exe 8689664 8463203 8137730
17 20951837 rar 25615 24785 26267
18 32683952 pdf 13896909 13893011 15054022
19 44814336 exe 97756312 81405043 77350891
20 62657918 avi 3570872 3571648 3854424
Fig.3 Chi-Square values for TDES, AES & MBBJT in logarithmic scale.

37
5.4. STUDIES ON AVALANCHE EFFECTS, STRICT AVALANCHE EFFECTS AND BIT
INDEPENDENCE CRITERION
Avalanche & Strict Avalanche effects and Bit Independence criterion has been measured by
statistical analysis of data. The bit changes among encrypted bytes for a single bit change in the
original message sequence for the entire or a relative large number of bytes. The Standard
Deviation from the expected values is calculated. The ratio of calculated standard deviation with
expected value has been subtracted from 1.0 to get the Avalanche and Strict Avalanche effect on
a 0.0 – 1.0 scale. The value closer to 1.0 indicates the better Avalanche & Strict Avalanche effects
and the better Bit Independence criterion. Table IV, Table V & Table VI show the Avalanche
effects, the Strict Avalanche effects & the Bit Independence criterion respectively. Fig.4(a),
Fig.4(b) & Fig4(c) show the above graphically. In Fig.4(a) & Fig.4(b), the y-axis which represent
the Avalanche effects & the Strict Avalanche effects respectively has been scaled from 0.97 – 1.0
for better visual interpretation.
Table IV
Avalanche effects for T-DES, AES and MBBJT algorithms
Sl.
No.
Source File Size
(in bytes)
File type
Avalanche achieved
TDES AES MBBJT
1 330 dll 0.99591 0.98904 0.98558
2 528 txt 0.99773 0.99852 0.98588
3 96317 txt 0.99996 0.99997 0.99643
4 233071 rar 0.99994 0.99997 0.99789
5 354304 exe 0.99996 0.99999 0.99774
6 536387 zip 0.99996 0.99994 0.99846
7 657408 doc 0.99996 0.99999 0.99795
8 682496 dll 0.99998 1.00000 0.99872
9 860713 pdf 0.99996 0.99997 0.99848
10 988216 exe 1.00000 0.99998 0.99873
11 1395473 txt 1.00000 1.00000 0.99896
12 4472320 doc 0.99999 0.99997 0.99824
13 7820026 avi 1.00000 0.99999 0.99863
14 9227808 zip 1.00000 1.00000 1.00000
15 11580416 dll 1.00000 0.99999 0.99898
16 17486968 exe 1.00000 0.99999 0.99964
17 20951837 rar 1.00000 1.00000 0.99967
18 32683952 pdf 0.99999 1.00000 0.99978
19 44814336 exe 0.99997 0.99997 0.99962
20 62657918 avi 0.99999 0.99999 0.99989

38
Table V
Strict Avalanche effect for T-DES, AES & MBBJT algorithms
Sl.
No.
Source File
Size (in bytes)
File type
Strict Avalanche achieved
TDES AES MBBJT
1 330 dll 0.98645 0.98505 0.97884
2 528 txt 0.99419 0.99311 0.97896
3 96317 txt 0.99992 0.99987 0.98434
4 233071 rar 0.99986 0.99985 0.99576
5 354304 exe 0.99991 0.99981 0.99798
6 536387 zip 0.99988 0.99985 0.99783
7 657408 doc 0.99989 0.99990 0.99797
8 682496 dll 0.99990 0.99985 0.99884
9 860713 pdf 0.99990 0.99993 0.99992
10 988216 exe 0.99995 0.99995 0.99878
11 1395473 txt 0.99990 0.99996 0.99882
12 4472320 doc 0.99998 0.99995 0.99898
13 7820026 avi 0.99996 0.99996 0.99886
14 9227808 zip 0.99997 0.99998 0.99967
15 11580416 dll 0.99992 0.99998 0.99896
16 17486968 exe 0.99996 0.99997 0.99959
17 20951837 rar 0.99998 0.99996 0.99962
18 32683952 pdf 0.99997 0.99998 0.99971
19 44814336 exe 0.99991 0.99990 0.99988
20 62657918 avi 0.99997 0.99998 0.99979
Table VI
Bit Independence criterion for T-DES, AES & MBBJT algorithms
Sl.
No.
Source File Size
(in bytes)
File
type
Bit Independence achieved
TDES AES MBBJT
1 330 Dll 0.49180 0.47804 0.43945
2 528 Txt 0.22966 0.23056 0.21867
3 96317 Txt 0.41022 0.41167 0.42849
4 233071 Rar 0.99899 0.99887 0.98972
5 354304 Exe 0.92538 0.92414 0.93688
6 536387 Zip 0.99824 0.99753 0.99594
7 657408 Doc 0.98111 0.98030 0.98583
8 682496 Dll 0.99603 0.99560 0.98990
9 860713 Pdf 0.97073 0.96298 0.97957
10 988216 Exe 0.91480 0.91255 0.94074
11 1395473 Txt 0.25735 0.25464 0.24994
12 4472320 Doc 0.98881 0.98787 0.96787
13 7820026 Avi 0.98857 0.98595 0.98766
14 9227808 Zip 0.99807 0.99817 0.98985
15 11580416 Dll 0.86087 0.86303 0.86868
16 17486968 Exe 0.83078 0.85209 0.85963
17 20951837 Rar 0.99940 0.99937 0.98858
18 32683952 Pdf 0.95803 0.95850 0.96881
19 44814336 Exe 0.70104 0.70688 0.82894
20 62657918 Avi 0.99494 0.99451 0.99788

39
Fig.4(a) Comparison of Avalanche effect between T-DES, AES and MBBJT
Fig4(b) Comparison of Strict Avalanche effect between TDES, AES and MBBJT
Fig.4(c) Comparison of Bit Independence criterion between TDES, AES and MBBJT
6. CONCLUSION
MBBJT, the proposed technique in this paper is simple, easy to understand and easy to
implement. The key information varies from session to session for any particular file which may
enhance the security features. Results and Analysis section indicates that the MBBJT is
comparable with industry accepted standards T-DES and AES. The performance of MBBJT is
significantly better than T-DES algorithm. For large files, MBBJT is at par with AES algorithm.
Therefore the proposed technique is applicable to ensure high security in message transmission of
any form and is suitable for any sort of file transfer.

40
REFERENCES
[1] J.K. Mandal, P.K. Jha, Encryption through Cascaded Arithmetic Operation on Pair of Bits and Key
Rotation (CAOPBKR), National Conference of Recent Trends in Intelligent Computing (RTIC-06),
Kalyani Government Engineering College, Kalyani, Nadia, India, 17-19 November 2006.
[2] M.Paul, J.K.Mandal, “A Permutative Cipher Technique (PCT) to Enhance the Security of Network
Based Transmission”, in Proceedings of 2nd National Conference on Computing for Nation
Development, Bharati Vidyapeeth’s Institute of Computer Applications and Management, New Delhi,
pp. 197-202,08th -09th February 2008
[3] S. Som, D. Mitra, J. Halder, Session Key Based Manipulated Iteration Encryption Technique
(SKBMIET), International Conference on Advanced Computer Theory and Engineering (ICACTE
2008), Phuket, Thailand, 20-22 December 2008.
[4] S. Som, K. Bhattacharyya, R. Roy Guha, J. K. Mandal, Block Wise Bits Manipulations Technique
(BBMT), International Conference on Advanced Computing, Tiruchirappalli, India, 6-8 August 2009.
[5] “Triple Data Encryption Standard” FIPS PUB 46-3 Federal Information Processing Standards
Publication, Reaffirmed, 1999 October 25 U.S. DEPARTMENT OF COMMERCE/National Institute
of Standards and Technology.
[6] “Advanced Encryption Standard”, Federal Information Processing Standards Publication 197,
November 26, 2001
Authors
Mr. Manas Paul received his Master degree in Physics from Calcutta University in
1998 and Master degree in Computer Application with distinction in 2003 from
Visveswariah Technological University. Currently he is pursuing his PhD in
Technology from Kalyani University. He is the Head and Assistant Professor in the
Department of Computer Application, JISCE, West Bengal, India. His field of interest
includes Cryptography and Network Security, Operation Research and Optimization
Techniques, Distributed Data Base Management System, Computer Graphics.
Dr. JYOTSNA KUMAR MANDAL received his M.Tech. and PhD degree from
Calcutta University. He is currently Professor of Computer Science & Engineering &
Dean, Faculty of Engineering, Technology & Management, University of Kalyani,
Nadia, West Bengal India. He is attached with several AICTE projects. He has 25
years Teaching & Research Experiences. His field of interest includes Coding
Theory, Data and Network Security, Remote Sensing & GIS based Applications, Data
Compression error corrections, Watermarking, Steganography and Document
Authentication, Image Processing, Visual Cryptography.

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