A tool to evaluate symmetric key algorithms

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A Tool to Evaluate Symmetric Key Algorithms
Article · February 2014
DOI: 10.11591/ijins.v3i1.5043
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Institute of Advanced Engineering and Science
w w w . i a e s j o u r n a l . c o m
International Journal of Information & Network Security (IJINS)
Vol.3, No.1, February 2014, pp. 26~32
ISSN: 2089-3299  26
Journal homepage: http://iaesjournal.com/online/index.php/ IJINS
ATooltoAnalyzeSymmetric KeyAlgorithms
T.D.B Weerasinghe
MSc.Eng, BSc.Eng(Hons), C|EH, MIEEE, AMIE(SL), AMCS(SL)
Software Engineer – IFS R&D International (Pvt) Ltd, Sri Lanka.
Article Info ABSTRACT
Article history:
Received Nov 12th
, 2013
Revised Dec 20th
, 2013
Accepted Jan 26th
, 2014
With the growth of the internet and the interconnectivity of computer
and data networks, security of data transmission has always been a
concern of many stakeholders of information and communication
arena. Among them, the researchers who work in the field of
Cryptography and Network Security pay a lot attention to deliver
highly secured and cost effective security mechanism and/or systems.
Many types of cryptographic tools are available in open
literature/internet, but this tool provides a mechanism to visualize the
security levels of the symmetric key algorithms w.r.t Shannon’s
theories on secrecy of ciphers. The tool can be used to analyze the
secrecy and performance levels of many symmetric key algorithms
and it is capable of analyzing plaintext in the form of character inputs
(passwords). More importantly this tool and can be extended to
evaluate combined algorithms as well as new symmetric key
algorithms, hence the targeted users of this tools are researches and
software engineers who are in the field of Cryptography and Network
Security
Keywords:
Symmetric key ciphers
Cryptogrpahic tools
Secrecy of ciphers
Copyright @ 2014 Insitute of Advanced Engineeering and Science.
All rights reserved.
Corresponding Author:
T.D.B Weerasinghe
MSc.Eng, BSc.Eng(Hons), MIEEE, AMIE(SL), AMCS(SL),
Software Engineer – IFS R&D International (Pvt) Ltd, Sri Lanka.
Email: tharindu.weerasinghe@gmail.com
1. INTRODUCTION
The tool introduced by this paper, will be helpful to researchers, software engineers who work in the
field of Cryptography as they need to analyze security levels of the algorithms. Especially in circumstances
where they need to have numerical values to describe the secrecy. Since this tool can be extended to develop
hybrid algorithms (combining symmetric key algorithms) without developing an attack on those new
algorithms they will be able to analyze the secrecy and performance by using this tool. This is an outcome of
some literature analysis of crypto tools available in the internet [4, 5, 6, 7, 8, and 9]. As many of them are
encryption tools that gives a secure cipher-text as outputs but this tool is for research and software
engineering community who works in the area of cryptography, especially in the area of symmetric key
algorithms.
In open literature, when we search cryptographic tools we find many software products that help the
users to get encrypted material. In other words, there are a lot of tools to make use of the existing encryption
algorithms. In this research the focus was to provide a tool evaluate existing algorithms with some new
algorithms (combined algorithms like AES+RC4 as well as new symmetric key algorithms)with the existing
algorithms. This tool can be used by the researchers who havejava programming knowledge, i.e. to extend
the tool’s behavior to analyze newly created algorithms (since this open source anyone can use and edit the

IJINS ISSN: 2089-3299 
A Tool to Analyze Symmetric Key Algorithms (T.D.B Weerasinghe)
27
code). The other idea was to give a numerical output to depict the secrecy of each cipher rather than
simulating some known attacks. That reduces the complexity of the tool and makes it more sensible. If a new
symmetric key algorithm is introduced by someone, then surely this tool can be used to analyze its secrecy
and performance with respect to other ciphers. (For example if it is a new stream cipher or a variant of an
existing one, then it can be compared with the other stream ciphers which are already in the forefront.)
Technology used to develop this tool:
Core Java
Java Cryptography Package (Javax Crypto)
Netbeans IDE
Platform:
Intel® Core™ i3 CPU, M370 @ 2.40 GHz with 1.86 GB usable RAM in Microsoft Windows 7 Home Basic
(32 bit)
Special Features:
 User friendly interface.
 Can be used to combine block or stream ciphers and analyze them.
 Since Javax crypto package is used the correctness of the algorithms can be trusted.
 Since this tool is dedicated for researchers and software engineers who work in the field of
Information Security, they can extend this tool to analyze the secrecy and performance of symmetric
key algorithm they create!
 Not complex. Secrecy is analyzed using theoretical definitions of Shannon, but it is a good measure
to get an idea about the ciphers. Higher the secrecy (numerical value) higher the security!
2. OTHER TYPES OF TOOLS AVAILABLE
Tool introduced by Bozga L et al mainly focuses on cryptographicprotocols and their
implementation. So, it does not purely targetalgorithms but set of protocols like Schroeder-Loweprotocol.
And also it focuses on secrecy not the performance [1]. Tool introduced by Blanchet also focuses on
protocols andverifying their authenticity. In this tool, pi calculus is used torepresent each protocol with some
fairly random cryptographic primitives [2]. Tools described in the reference [3] which is freely available
online, aresome e-Learning tools related to Cryptography. They can bevery useful to learn about
Cryptographic algorithms.Although they have many features, there is a lack of focustowards secrecy analysis
using Shannon’s theories as well asthe performance of the algorithms and most of them arelimited for
Windows operating system. On the other handthere are limitations when it comes to develop newalgorithms
and analyze them.Thus it is obvious that each tool is different and has differentobjectives. Tools described
above are pretty good tools thatcan be used to various purposes. The tool presented in thispaper mainly
focuses on a simple way to depict the secrecyand performance of symmetric key ciphers and this tool ismade
for people who have programming knowledge so thatthey can extend the tool for new algorithms. Secrecy
andperformance calculations are written in separate classes sothat those can be easily used to analyze new
algorithms.
3. TOOL DESCRIBED IN THIS PAPER
This tool consists of two parts.
1. Calculation of Secrecy: Depends of theories of secrecy of ciphers by Shann
2. Calculation of Performance
The following two figures show how the tool looks like in run time:

 ISSN: 2089-3299
IJINS Vol. 3, No. 1, February 2014 : 26 – 32
28
Fig.1. Algorithm List
Fig.2. A Sample Output
a. SHANNON’S SECRECY OF CIPHERS
Secrecy of a cipher: Secrecy of a cipher is described in terms of the key equivocation, H (K) c
of a key K for a given cipher text C; that is the amount of uncertainty in K given C. [Equivocation is
the uncertainty of a message, reduced when there is additional information; Uncertainty of a
message is the number of plaintext bits that must be recovered when the message is encrypted, in-
order to obtain the plaintext. The uncertainty of a message is measured by its entropy. Higher the
number, higher the uncertainty; Entropy of a message X is called H(X), which is the minimum

IJINS ISSN: 2089-3299 
29
number of bits needed to encode all possible meanings of the message assuming the occurrences of
all messages are equally likely.] [8]
Mathematical Equation:
All the above definitions and equations are illustrated from the lecture notes of Dr.Issa Traore on Shannon’s
secrecy, University of Victoria, British Columbia, Canada, which were available online.
b. METHOD OF CALCULATING SECRECY IN THIS RESEARCH
 Consider the Part 1 first: It is the entropy of K given the relevant cipher. (Cipher text C, has been
obtained using this particular key K)
o Calculate how often each key byte is appeared in the key.
o And then calculate the probability of each byte appears (given the cipher) in the key and
get the summation of Pc(K) * log2Pc(K).
 After that consider the other part: Calculating P(C) and then the summation.
o Calculate how often each cipher byte has appeared in the cipher text.
o And then calculate the probability of each byte appeared in the key and get the summation
(for all possibilities of the cipher bytes). This cipher is obtained after the plaintext
operations with the key; i.e. this cipher is correlated to the above key.
o Then get the multiplication of “Part 1” and P(C) is calculated and finally the summation of
all possibilities is calculated.
Important: Higher the value, higher the secrecy. i.e. The cipher is better!
c. IMPLEMENTATION OF SECRECY CALCULATION IN JAVA
public class SecrecyCalculator
{
private static int[]
countByteDistribution(byte[] data, int start, int length)
{
final int[] countedData = new
int[256];
for (int i=start; i<start+length; i++)
{
countedData[data[i] & 0xFF]++;
}
return countedData;
}
private static double log2(double d)
{
return Math.log(d)/Math.log(2.0);
}
public static double calculateEntropy(byte[]data, int start, int length)
{
double entropy = 0;
final int[] countedData = countByteDistribution(data, start, length);
for (int i=0;i<256;i++)
{
final double p_k = 1.0 * countedData[i] / length;
if (p_k > 0)
{

 ISSN: 2089-3299
30
entropy += -p_k * log2(p_k);
}
}
return entropy;
}
public static double calculateSecrecy(byte[] key, byte[] cipher, int start)
{
double entropy = 0;
double secrecy = 0;
System.out.println("nttKey Length: " + key.length);
final int[] countedKey = countByteDistribution(key, start,
key.length-1);
final int[] countedCipher = countByteDistribution(cipher, start,
cipher.length-1);
for (int i=0;i<256;i++)
{
final double p_k = 1.0 *
countedKey[i] / key.length;
final double p_c = 1.0 *
countedCipher[i] / cipher.length;
if (p_k > 0)
{
entropy += p_k * log2(p_k);
secrecy += -p_c * entropy;
}
}
return secrecy;
}
}
4. VERIFICATION AND ANALYSIS OF THE TOOL
Average secrecy and performance analysis were performed using the tool. Similar numbers of
experiments/tests were considered for all circumstances to calculate the average values in-order to obtained
reasonable outputs. Input: A password which has alphanumeric characters with special characters, which
meant to be a strong password. (Example: #abc123%)
Table 1. Algorithm Vs Average Secrecy
Algorithm Average Secrecy
DES 0.211263
3DES 0.255173
AES 0.268375
RC2 0.165872
RC4 0.140538
3DES+RC4 0.286776
AES+RC4 0.32096
Table 2. Algorithm Vs Average Encryption Time
Algorithm Average Encryption
Time
DES 25
3DES 22
AES 24.8
RC2 15.4
RC4 9.4
3DES+RC4 25.2
AES+RC4 40

IJINS ISSN: 2089-3299 
31
Fig. 3 Algorithm used in the tools Vs Secrecy value calculated by the tool for the sample input
Fig. 4 Algorithm used in the tools Vs Encryption Time (ms) calculated by the tool for the sample input
4.1 RELIABILITY OF THE RESULTS OF TOOL:
With respect to Secrecy: Since the experiments are carried-out for all known and well established
block and stream ciphers and according to the average secrecy values obtained the algorithms can be sorted
in the descending order as follows:
AES>3DES>DES>RC2>RC4
This result is acceptable as this kind is proved by many researches before (i.e block ciphers are
highly secured than stream ciphers and AES it the best block cipher around and also 3DES also commonly
used.)

 ISSN: 2089-3299
32
Combination of block and stream ciphers would give higher secrecy and as expected the tool has given the
results.
Hence the results obtained from the tool are reliable w.r.t Secrecy. With respect to Performance: It is
a known and proven fact that the block ciphers are complex than stream ciphers hence they are expensive
than stream ciphers. The encryption times obtained by the tool also prove it. If the algorithms are sorted
according to the cost effectiveness we have the following pattern: RC4>RC2>3DES>DES>AES Note:
Combination of block and stream ciphers would give lower performance and as expected the tool has given
the result. Hence the results obtained from the tool are reliable w.r.t Performance as well.
4.2 EXTENSIBILITY OF THE TOOL
As mentioned earlier, this tool can be extended if one wants to analyze a newly implemented symmetric key
algorithm in Java. Although Shannon’s theories are not 100% practical we can get an idea of the analysis.
Source code can be published online.
5. CONCLUSION
This tool will be helpful to the users to evaluate the secrecy and throughput of ciphers. It will help
the users to obtain numerical values for the secrecy of ciphers. The objective of this work is not to introduce
yet another tool to deliver cipher text of plain texts according to the ciphering algorithms, but to help the
users to use this as an analyzer which is fairly simple. Based on the Shannon’s theories and encryption times
an initial idea can be obtained if a new symmetric key algorithm is analyzed with the help of this tool.
The target users of this tool are software engineers in the felid of information security or information security
analysts because this tool can be customized in order adopt to the new symmetric key algorithms.
6. REFERENCES
[1] L. Bozga, Y. Lakhnech and M. Périn, “HERMES: An Automatic Tool for Verification of Secrecy in Security Protocols”,
Computer Aided Verification, Lecture Notes in Computer Science, Volume 2725, 2003, pp. 219-222 [15th
International Conference, CAV 2003, Boulder, CO, USA, July 8-12, 2003, Proceedings].
[2] Blanchet, “From Secrecy to Authenticity in Security Protocols”, Static Analysis, Lecture Notes in Computer
Science, Volume 2477, 2002, pp. 342-359 [9th International Symposium, SAS 2002 Madrid, Spain, September 17–
20, 2002, Proceedings].
[3] CRYPTOOL PORTAL: http://www.cryptool.org/en/
[4] Advanced Crypto Software Collection: http://hms.isi.jhu.edu/acsc/
[5] Cipher Tools: http://rumkin.com/tools/cipher/
[6] Cryptography Tools: http://msdn.microsoft.com/en-us/library/windows/desktop/aa380259%28v=vs.85%29.aspx
[7] JavaScrypt: Browser-Based Cryptography Tools: http://www.fourmilab.ch/javascrypt/
[8] Lecture notes of Dr.Issa Traore on Shannon’s theories, University of Victoria, British Columbia, Canada, which
were available online.
[9] T.D.B Weerasinghe, “Analysis of a Modified RC4 Algorithm”, International Journal of Computer Applications,
vol. 51, no. 22, pp. 13-17, available at http://www.ijcaonline.org/archives/volume51/number22/8341- 1617
BIOGRAPHY OF AUTHOR
T.D.B WEERASINGHE
MSc.Eng, BSc.Eng(Hons), C|EH, MIEEE, AMIE(SL), AMCS(SL)
Software Engineer, IFS R&D International, 363, Udugama, Ampitiya Road, Kandy.
Contact No: 0094 716 860 396
Email: tharindu.weerasinghe@gmail.com
Postal Address (Home): 296, Kandy Road, Millawa, Kurunegala 60000, Sri Lanka.
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