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.

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.