A New Approach to Enhance the
Security and Performance of Blowfish Algorithm
1,2
Ashwak Mahmood ALabaichi , 3 Ramlan Mahmood, 4 Faudziah Ahmad 5,6 Mohammed S. Mechee
Information Technology Department- University Utara Malaysia-06010, Sintok, Malaysia
2
Department of computer science-Faculty of Sciences -University of Kerbala- Iraq
3
Faculty of Computer Science and Information Technology- University Putra Malaysia, Serdang,
Selangor, Malaysia
4
Information Technology Department- University Utara Malaysia-06010, Sintok, Malaysia
5
and Information Technology Institute of Mathematical Sciences-university of Malaya-Kuala LumpurMalaysia
6
University Putra Malaysia Department of Mathematics-Faculty of Mathematics and Computer Sciencesuniversity of Kufa- Najaf- Iraq
1
Ashwakalabaichi2007@yahoo.com, 3ramlan@fsktm.upm.edu.my,4fudz@uum.edu.my,
5mohsabd@yahoo.com
1
Abstract
Blowfish is a secret-key block cipher proposed by B. Shneier. It is a Feistel
network which can iterate a simple encryption function 16 times. The block size is 8bytes and the key can be of any length up to 56-bytes.
Blowfish algorithm must dynamically compute all sub-keys and S-boxes before the
start of encryption; there is a slight overhead in the computation. This computational
overhead of sub-keys and S-box creation results in roughly the equivalence of encrypting
an additional four kilobytes of data per data file. Its large memory requirement makes it
infeasible for smart card applications. Blowfish also suffers from the defect of the weak
key problem. It means that there exists a collision of an S-box. That is, for the keydependant S-box of Blowfish (S1), there exists two different bytes of 'a' and 'a0' such
that S1(a) = S1(a0 ).
In this paper a 64- bit block cipher called blowfish dynamic S-box and a dynamic
permutation table encryption algorithm using a variable key length up to 56 bytes are
proposed. It is a Feistel network, iterating a simple encryption function 16 times and it is
inspired from 64-bits Blowfish designed to satisfy many goals such as reducing
requirements of memory as well as improving the security. The security of blowfish
dynamic S-box and the dynamic permutation table encryption algorithm (BDSDP)
increased by several techniques such as the relocation of bytes-based secret keys,
transformation of the cylinder in three different cases, permutation table -based secret
keys and the application of one of block cipher modes(CBC).
In BDSDP, Algorithm avoids a symmetric from the output of S-box by a specified
approach. The memory requirement is reduced by using the idea of cylinder as a single
3D S-box. The size of 3D S-box is 256 bytes instead of four S-boxes the size of each is
1024 bytes without compromising security. The Cryptographic strength in the context of
this paper is related to the ability of the algorithm to produce a random output. The
experimental results on five data categories show that BDSDP is better from blowfish
algorithm and compatible for any files type without restrictions on files contents.
Keywords: block cipher, Blowfish algorithm, dynamic S-box, cylinder, F-function;
relocate byte, transformation, dynamic permutation table, randomness
test
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mo