18-05-2012, 01:17 PM
An approach in improving transposition cipher system
transphocition cyber system.pdf (Size: 351.94 KB / Downloads: 74)
Introduction
With the growth of Internet,
hackers and spies make big issues
for army forces, organizations and
companies. Transposition ciphers are
still the most important kernel
techniques in the construction of
modern symmetric encryption
algorithms. We will clearly see
combinations of substitution and
transposition ciphers in two important
modern symmetric encryption
algorithms: DES and AES
(Mao Hewlett W-Packard, 2003).
DES is not very secure because of
the limitation of the space of the key
is 56 bits. On the other hand AES is a
new cipher.
Rotor machines
In the 1920s, various mechanical encryption devices
were invented to automate the process of encryption.
Most were based on the concept of a rotor, a mechanical
wheel wired to perform a general substitution.
Block cipher
In a block cipher, the bit-string is divided into blocks
of a given size and the encryption algorithm acts on that
block to produce a cryptogram block that, for most
symmetric ciphers, has the same size.
Block ciphers have many applications. They can be
used to provide confidentiality, data integrity, or user
authentication, and even be used to provide the key
stream generator for stream ciphers. With stream ciphers,
it is very difficult to give a precise assessment of their
security.
Conclusion
Although the classical transposition cipher is not
secure when it is used to encrypt unpadded messages,
this and other stream ciphers can be made as secure as
most block ciphers by using two functions, one (F(x)) for
producing the 7 extra bits of padding to each byte to
diffuse the language characteristics and the second
function (Y(j)) for positioning the bits in the binary tree to
use its in-order tour in the encryption and decryption
process that will make it as secure as 256-bit AES cipher
system. This method can resolve all the limits of the
classical transposition cipher.