introduction: science of writing hidden messages in such a

introduction:

in the present world of communication, computer and
internet are the major media that connects different parts of the world as one
global virtual world in this modern era. so we can easily exchange lots of
information  within seconds of time , but
the confidential data that needs to be transferred should be kept confidential.
so by using steganography and cryptography 
we can secure the confidential data. but individually  steganography and cryptography provides
confidentiality  to the data but they
some vulnerability so by combining steganography with cryptography we have more
security.

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steganography is the art and science of writing
hidden messages in such a way that no one, except the sender and receiver,
suspects the existence of the message, a form of security through hiding the
message.ie., Steganography is concealed writing and is the scientific approach
of inserting the secret data within a cover media such that the unauthorized
viewers do not get an idea of any information hidden in it.

Cryptography is also known as the science of secret
writing. Cryptography is the study of mathematical techniques related to
aspects of information security such as confidentiality, entity authentication,
integrity of data and message origin authentication The goal of cryptography is
to make data unreadable by a third party.

Cryptography algorithms are divided into symmetric
(secret-key) and asymmetric (public-key) network security protocols. Symmetric
algorithms are used to encrypt and decrypt original messages (plaintext) by
using the same key. While Asymmetric algorithms uses public-key cryptosystem to
exchange key and then use faster secret key algorithms to ensure
confidentiality of stream data. In Public-key encryption algorithms, there is a
pair of keys, one key is known to the public, and is used to encrypt
information to be sent to a receiver who owns the corresponding private key.
The private and public keys are both different and need for key exchange.

Individually 
both steganography and cryptography provides security to the data but
they have some vulnerability.so by combination of  steganography and cryptography we have more
confidentiality and security.There are different techniques available in steganography
and cryptography  so can we have
different combinations of steganography.

In this paper we compare different techniques
available in steganography based on their security. And on the improved LSB
based  steganalysis combined with  RSA algorithm of cryptography.

Steganography Techniques:

Steganography
is the art of hiding the existence of data in another transmission medium to
achieve secret communication.In steganography the secrete data is embedded into
the cover image in such way that only cover image  is visible which is sent from transmitter to
receiver without scrambling. It does not replace cryptography but it can be
used to improve the security of cryptography .

COMPARISION
OF DIFFERENT TECHNIQUES IN STEGANOGRAPHY:

1)lsb-steganography:

In Least
Significant Bit (LSB) steganography 8 embed the text message in least
significant bits of digital picture. In which data is embedded by replacing the
LSB of cover carrier with the data to be send.ie first read the cover image and
text message which is to be hidden in the cover image, then convert text
message in binary. Calculate LSB of each pixels of cover image. Replace LSB of
cover image with each bit of secret message one by one so we get an image in
which data is hidden.

2)dct
–steganography:

The
hidden message is converted into binary stream of “1” and “0” are insert the
into the DCT domain of the cover image. The color-based transformation converts
the image (cover image) into 8×8 blocks of pixels. 8 Next, take larger
positive coefficients need to embed in the cover image in the low-mid frequency
range. DCT can divide the image into high, middle and low frequency components.
As the high frequency coefficients are vulnerable and less robust on the
quality of image. The main issue of this work is robustness against with high
quality of image, thus the low and mid frequency coefficients are the most
appropriate. The selected coefficients ci are modified by the corresponding bit
in the message stream. This K quantity represents the persistence factor. As
soon as the ith term of message bit s(i) is “1”, the coefficient of the image
is added with a quantity K; otherwise the same quantity is subtracted from it.

3)
DWT-Steganography

A
discrete wavelet transform (DWT) is any wavelet transform 6 for which the
wavelets are discretely sampled. This is one of the frequency domains in which
steganography can be implemented. DCT is calculated on blocks of independent
pixels, a coding error causes discontinuity between blocks resulting in
annoying blocking artifact. This drawback of DCT is eliminated using DWT
because DWT applies on entire image. DWT offers better energy compaction than
DCT without any blocking artifact. DWT splits component into numerous frequency
bands called sub bands known as

LL –
Horizontally and vertically low pass

LH –
Horizontally low pass and vertically high pass

HL –
Horizontally high pass and vertically low pass

HH –
Horizontally and vertically high pass

Since
Human eyes are much more sensitive to the low frequency part (LL sub band) we
can hide secret message in other three parts without making any alteration in
LL sub band. As other three subbands are high frequency sub-band they contain
insignificant data. Hiding secret data in these subbands doesn?t degrade image
quality that much.

S.NO

Technique

MSE

PSNR

1

LSB

 

 

2

DCT

 

 

 

 

CRYPTOGRAPHY
TECHNIQUES:

Cryptography
is the study of sending messages in cipher form so that receiver only  can able to read the message. It is performed
by converting messages into  encrypted by
using symmetric key algorithm and asymmetric key algorithm. In symmetric key
algorithm a single key is used for both encryption and decryption. In
asymmetric key algorithm  we use public
key for encryption purpose and private key for decryption purpose.

RSA algorithm:

RSA was
first described in 1977 by Ron Rivest, Adi Shamir and Leonard Adleman of the
Massachusetts Institute of Technology. RSA is one of the earliest public-key
cryptosystems and it is widely used for securing data transmission.  Here encryption key is public and decryption
key is private, it kept secret. RSA is based on factorizing two large prime
numbers. The public and the private key-generation algorithm is the most
complex part of RSA cryptography. We can consider two  prime numbers, x and y,. A modulus is
calculated by multiplying x and y. This number is used by both the public and
private keys and provides the link between them. Its length is called the key
length.