Abstract:
Cryptography is the science of securing data. It makes us easy to store sensitive data
and transmit across insecure networks. Modern cryptography is applied in smart
cards, computer passwords, and electronic commerce.
Data Encryption Standard (DES) was a popular symmetric-key (64-bit) block cipher
in USA from 1970’s. It was broken in 1999 by making the key length insecure with
the improved computer speed. Later AES (Advanced Encryption Standard) was
introduced to replace DES. Both key expansion and encryption algorithms of AES
depend on S-boxes and calculations are done on the finite field GF (28). AES uses
substitution-permutation and 128 block size while DES uses a balanced fiestel
structure and 64 block size. DES has already broken but AES is still in use and is not
completely broken. Today, key attacks for AES are steadily in progress. Since AES
has theoretically broken by some key attacks, it is already at a risk of practical
breakthrough. Algebraic attacks and related- key attacks are two of the main key
attacks. The objective of the algebraic attack is recovering the key by solving system
of multivariate polynomial equations over a Galois field. Related-key attacks use
multiple pairs of plaintexts and encrypt each of them using two keys. As a result, the
encryption key can be recovered.
In this paper, we are going to combine AES algorithm with DNA cryptography which
is a branch of Nano-cryptography to enhance the security of AES. We propose an
improved algorithm to provide security against key attacks. In the algorithm we use
masking techniques and DNA cryptosystem concepts based on the Vigenere cipher.
DNA cryptography concepts help to avoid the weaknesses of Vigenere cipher and
provide both computational and biological security.
