A General Session Based Bit Level Block Encoding Technique Using Symmetric Key Cryptography to Enhance the Security of Network Based Transmission

International Journal of Computer Science, Engineering and Information Technology (IJCSEIT), Vol.2, No.3, June 2012
DOI : 10.5121/ijcseit.2012.2302 31
A General Session Based Bit Level Block
Encoding Technique Using Symmetric Key
Cryptography to Enhance the Security of Network
Based Transmission
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 Permutation Technique (MBBPT). MBBPT 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 ( 1 , 1 ) cell in a left to right
trajectory into a square matrix of suitable order n. Then the bits are taken from the square matrix
diagonally upward starting from ( n , n ) cell in a right to left trajectory 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 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 diagonally upward starting from
( 1 , 1 ) cell in a left to right trajectory to form the decrypted binary string . Plain text is regenerated from
this binary string. Comparison of MBBPT with existing and industrially accepted TDES and AES has been
done.
KEYWORDS
Matrix Based Bit Permutation Technique (MBBPT), Cryptography, Symmetric Key, Session Based Key,
TDES, AES.
1. INTRODUCTION
The people all over the world are engaged in communication through internet every day. It is very
important to secure our essential documents from unauthorized users. Hence network security is
looming on the horizon as a potentially massive problem. So network security is the most focused
topic among the researchers [1, 2, 3, 4]. Various algorithms have developed in this field but each
of them has their own merits and demerits. As a result researchers are working in this field of
cryptography to enhance the network based security further.
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 shuffled to generate the cipher text. A

32
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 MBBPT with TDES [5], AES [6]. Conclusions
are drawn in the section 6.
2. THE SCHEME
The MBBPT 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.
Cipher
Text
Key (K)
Plain
Text
Plain
Text
Key
Generator
Key (K)
Plain
Text
Key (K)
Cipher
Text

33
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.
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 ( 1 , 1 ) cell in a left to right
trajectory into this square matrix.
Step 4. From the square matrix bits are taken diagonally upward starting from ( √y , √y ) cell in a
right to left trajectory 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 diagonally upward starting from ( √y , √y ) cell in a right to left
trajectory.
Step 4. The decrypted binary string is generated after taking the bits diagonally upward starting
from ( 1 , 1 ) cell in a left to right 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:
A session key is generated for one time use in a session of transmission to ensure much more
security to MBBPT. 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 MBBPT, 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 Now these bits from MSB to LSB fit diagonally upward starting from ( 1 , 1 ) cell in a
left to right trajectory into this square matrix of order 4 as follows:

34
0 0 1 1
1 0 0 1
0 1 0 1
1 1 1 1
The encrypted binary string is formed after taking the bits diagonally upward starting from ( 4 , 4
) cell in a right to left trajectory from above the square matrix as follows:
1 1 1 1 0 1 1 1 0 1 0 0 1 1 0 0
The equivalent decimal no. of two 8 bit binary numbers 11110111 and 01001100 are 247 and 76
respectively. 247 and 76 are the ASCII values of the characters ÷ (Division Sign) and L (Latin
Capital Letter L) respectively. So the word Go is encrypted as ÷L.
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 MBBPT
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 MBBPT against the different files. Proposed MBBPT 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 MBBPT algorithms)
Sl.
No.
Source File Size
(in bytes)
File
type
Encryption Time (in seconds)
TDES AES MBBPT
1 330 Dll 0.001 0.001 0.006
2 528 Txt 0.001 0.001 0.010
3 96317 Txt 0.034 0.004 0.036
4 233071 Rar 0.082 0.011 0.086
5 354304 Exe 0.123 0.017 0.146
6 536387 Zip 0.186 0.023 0.232
7 657408 Doc 0.220 0.031 0.341

35
8 682496 Dll 0.248 0.031 0.368
9 860713 Pdf 0.289 0.038 0.403
10 988216 Exe 0.331 0.042 0.466
11 1395473 Txt 0.476 0.059 0.518
12 4472320 Doc 1.663 0.192 0.714
13 7820026 Avi 2.626 0.334 1.226
14 9227808 Zip 3.096 0.397 1.338
15 11580416 Dll 4.393 0.544 1.542
16 17486968 Exe 5.906 0.743 3.381
17 20951837 Rar 7.334 0.937 3.568
18 32683952 Pdf 10.971 1.350 4.027
19 44814336 Exe 15.091 1.914 5.992
20 62657918 Avi 21.133 2.689 10.244
TABLE II
File size v/s decryption time (for Triple-DES, AES and MBBPT algorithms)
Sl.
No.
Source File Size
(in bytes)
File type
Decryption Time (in seconds)
TDES AES MBBPT
1 330 Dll 0.001 0.001 0.005
2 528 Txt 0.001 0.001 0.009
3 96317 Txt 0.035 0.008 0.031
4 233071 Rar 0.087 0.017 0.072
5 354304 Exe 0.128 0.025 0.132
6 536387 Zip 0.202 0.038 0.218
7 657408 Doc 0.235 0.045 0.333
8 682496 Dll 0.266 0.046 0.348
9 860713 Pdf 0.307 0.060 0.386
10 988216 Exe 0.356 0.070 0.447
11 1395473 Txt 0.530 0.098 0.502
12 4472320 Doc 1.663 0.349 0.706
13 7820026 Avi 2.832 0.557 1.211
14 9227808 Zip 3.377 0.656 1.318
15 11580416 Dll 4.652 0.868 1.526
16 17486968 Exe 6.289 1.220 3.364
17 20951837 Rar 8.052 1.431 3.549
18 32683952 Pdf 11.811 2.274 4.004
19 44814336 Exe 16.253 3.108 5.937
20 62657918 Avi 22.882 4.927 10.168

36
Fig. 1(a). Encryption Time (sec) vs. File Size (bytes) in logarithmic scale
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
MBBPT. 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 MBBPT. All three
algorithms show a distributed spectrum of characters. From the above observation it may be
conclude that the proposed MBBPT may obtain very good security.
Fig. 2(a). Distribution of characters in source file

37
Fig. 2(b): Distribution of characters in TDES
Fig. 2(c). Distribution of characters in AES
Fig. 2(d). Distribution of characters in MBBPT
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

38
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 MBBPT against the
different files.
From Table III it may conclude that the Chi-Square values of MBBPT 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 & MBBPT.
Table III
Chi-Square values for Triple-DES, AES and MBBPT algorithms
Sl.
No.
Source File
Size (bytes)
File
type
Chi-Square Values
TDES AES MBBPT
1 330 dll 922 959 868
2 528 txt 1889 1897 1929
3 96317 txt 23492528 23865067 20843454
4 233071 rar 997 915 958
5 354304 exe 353169 228027 213002
6 536387 zip 3279 3510 3291
7 657408 doc 90750 88706 86657
8 682496 dll 29296 28440 26403
9 860713 pdf 59797 60661 56762
10 988216 exe 240186 245090 254747
11 1395473 txt 5833237390 5545862604 5657405581
12 4472320 doc 102678 102581 99191
13 7820026 avi 1869638 1326136 1139029
14 9227808 zip 37593 37424 36497
15 11580416 dll 28811486 17081530 16614547
16 17486968 exe 8689664 8463203 8096422
17 20951837 rar 25615 24785 26131
18 32683952 pdf 13896909 13893011 14977606
19 44814336 exe 97756312 81405043 76958249
20 62657918 avi 3570872 3571648 3834862
Fig.3 Chi-Square values for TDES, AES & MBBPT in logarithmic scale.

39
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 MBBPT algorithms
Sl.
No.
Source File Size
(in bytes)
File
type
Avalanche achieved
TDES AES MBBPT
1 330 dll 0.99591 0.98904 0.98381
2 528 txt 0.99773 0.99852 0.98542
3 96317 txt 0.99996 0.99997 0.99618
4 233071 rar 0.99994 0.99997 0.99689
5 354304 exe 0.99996 0.99999 0.99592
6 536387 zip 0.99996 0.99994 0.99818
7 657408 doc 0.99996 0.99999 0.99726
8 682496 dll 0.99998 1.00000 0.99847
9 860713 pdf 0.99996 0.99997 0.99816
10 988216 exe 1.00000 0.99998 0.99840
11 1395473 txt 1.00000 1.00000 0.99766
12 4472320 doc 0.99999 0.99997 0.99714
13 7820026 avi 1.00000 0.99999 0.99828
14 9227808 zip 1.00000 1.00000 0.99924
15 11580416 dll 1.00000 0.99999 0.99873
16 17486968 exe 1.00000 0.99999 0.99939
17 20951837 rar 1.00000 1.00000 0.99941
18 32683952 pdf 0.99999 1.00000 0.99958
19 44814336 exe 0.99997 0.99997 0.99948
20 62657918 avi 0.99999 0.99999 0.99964

40
Table V
Strict Avalanche effect for T-DES, AES & MBBPT algorithms
Sl.
No.
Source File
Size (in bytes)
File type
Strict Avalanche achieved
TDES AES MBBPT
1 330 dll 0.98645 0.98505 0.97864
2 528 txt 0.99419 0.99311 0.98806
3 96317 txt 0.99992 0.99987 0.98827
4 233071 rar 0.99986 0.99985 0.99552
5 354304 exe 0.99991 0.99981 0.99648
6 536387 zip 0.99988 0.99985 0.99754
7 657408 doc 0.99989 0.99990 0.99728
8 682496 dll 0.99990 0.99985 0.99816
9 860713 pdf 0.99990 0.99993 0.99841
10 988216 exe 0.99995 0.99995 0.99518
11 1395473 txt 0.99990 0.99996 0.99762
12 4472320 doc 0.99998 0.99995 0.99676
13 7820026 avi 0.99996 0.99996 0.99622
14 9227808 zip 0.99997 0.99998 0.99965
15 11580416 dll 0.99992 0.99998 0.99861
16 17486968 exe 0.99996 0.99997 0.99948
17 20951837 rar 0.99998 0.99996 0.99864
18 32683952 pdf 0.99997 0.99998 0.99929
19 44814336 exe 0.99991 0.99990 0.99904
20 62657918 avi 0.99997 0.99998 0.99933
Table VI
Bit Independence criterion for T-DES, AES & MBBPT algorithms
Sl.
No.
Source File Size
(in bytes)
File
type
Bit Independence achieved
TDES AES MBBPT
1 330 Dll 0.49180 0.47804 0.42544
2 528 Txt 0.22966 0.23056 0.22602
3 96317 Txt 0.41022 0.41167 0.43706
4 233071 Rar 0.99899 0.99887 0.98665
5 354304 Exe 0.92538 0.92414 0.93618
6 536387 Zip 0.99824 0.99753 0.99621
7 657408 Doc 0.98111 0.98030 0.97588
8 682496 Dll 0.99603 0.99560 0.96852
9 860713 Pdf 0.97073 0.96298 0.96849
10 988216 Exe 0.91480 0.91255 0.93355
11 1395473 Txt 0.25735 0.25464 0.25632
12 4472320 Doc 0.98881 0.98787 0.97428
13 7820026 Avi 0.98857 0.98595 0.97316
14 9227808 Zip 0.99807 0.99817 0.99925
15 11580416 Dll 0.86087 0.86303 0.86211
16 17486968 Exe 0.83078 0.85209 0.85627
17 20951837 Rar 0.99940 0.99937 0.99928

41
18 32683952 Pdf 0.95803 0.95850 0.95858
19 44814336 Exe 0.70104 0.70688 0.82742
20 62657918 Avi 0.99494 0.99451 0.99776
Fig.4(a) Comparison of Avalanche effect between T-DES, AES and MBBPT
Fig4(b) Comparison of Strict Avalanche effect between TDES, AES and MBBPT
Fig.4(c) Comparison of Bit Independence criterion between TDES, AES and MBBPT
6. CONCLUSION
MBBPT, the proposed technique in this paper is simple and easy to implement. The key varies
from session to session for any particular file which may enhance the security features. Results
and Analysis section indicates that the MBBPT is comparable with industry accepted standards T-

42
DES and AES. The performance of MBBPT is significantly better than T-DES algorithm. For
large files, MBBPT 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.
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.

A General Session Based Bit Level Block Encoding Technique Using Symmetric Key Cryptography to Enhance the Security of Network Based Transmission

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