Improved LSB Based Image Steganography-Paper (Aparna S & Shinija B)
Improved LSB Based Image Steganography-Paper (Aparna S & Shinija B)
Improved LSB Based Image Steganography-Paper (Aparna S & Shinija B)
Aparna S
Shinija B
Information Technology
Govt. Engg. College
Trivandrum
Information Technology
Govt. Engg. College
Trivandrum
Abstract
Steganography is a technique used for transmission
of secret message. Here the existence of message is
unknown. The secret message can be embedded within
a digital medium like audio, video, image or text.
Image steganography uses image as the cover object. The most commonly used Image Steganography
technique is LSB Insertion. This paper intends to give
an overview about how to enhance the security of the
techniques by using a suitable cryptographic algorithm,
i.e. , how cryptography can be used to supplement
steganography.
Introduction
1.1
Cryptography
1.2
Steganography
Steganography is the art or practice of concealing a file, message, image, or video within another file,
message, image, or video. The word steganography
combines the Ancient Greek words steganos, meaning covered, concealed, or protected, and graphein
meaning writing. Here the existence of mesage is
unknown. The object in which the secret message is
hidden is called the cover object and the object obtained as the output of steganography is called stego
object.In image steganography, image is used as the
medium for the transmission of secret message.
2.1
Image
2.2
Image Domain
2.2.1
LSB Insertion
3.1
3.1.1
RSA Algorithm
Introduction
RSA is one of the first practicable public-key cryptosystems and is widely used for secure data transmission. In such a cryptosystem, the encryption key
is public and differs from the decryption key which is
kept secret. In RSA, this asymmetry is based on the
practical difficulty of factoring the product of two large
prime numbers, the factoring problem. RSA stands for
Ron Rivest, Adi Shamir and Leonard Adleman, who
first publicly described the algorithm in 1977. Clifford
Cocks, an English mathematician, had developed an
equivalent system in 1973, but it was not declassified
until 1997 [6]
Suppose, Alice wish to send a secret message to
Bob.Alice will first encrypt the secret message using
Bobs public key and send it to Bob.Bob can decrypt
the message using his private key.
3.1.2
Operation
Key Generation
RSA involves two type of keys: public key and
private key. Public key is made public.The secret message encrypted by a public key can be
decrypted only using the corresponding private
key.The keys are generated as follows:
1. Choose two very large random prime numbers ,say p and q
2. Compute the product n=p.q
3. Compute f(n)=(p-1)(q-1)
4. Choose a random number e such that
1hehf (n) and GCD(e,f(n))=1
(e,n) is the public key.
5. Compute d such that (d*e) mod f(n)=1
(d,n) is the private key.
Encryption
Encryption is done using the public key (e,n).
Suppose the secret message be M.Then
C=Me mod n is the cipher text where M h n
Decryption
Decryption is done using the private key(d,n).
Suppose the cipher text is C.Then
M=Cd mod n is the plain text.
3.2
Encoding
3.3
Decoding
The security of image steganography system is enhanced and iproved using a cryptographic algorithm
like RSA Algorithm.Here, even if a third person comes
to know about the existence of secret data in an image and retrieve the seret data, he will get only the
encrypted message which is meaningless, thereby enhancing security of image steganography.So steganography is not intended to replace cryptography,but
rather to supplement it.
References
[1] Liddell and Scotts Greek-English Lexicon, Oxford
University Press , 1984.
[2] Rivest,Ronald L(1990), Cryptology In J.Van
Leeuwen Handbook of Theoritial Computer Science, 1. Elsevier.
[3] Johnson N.F.,Jajodia S. Exploring Steganography: Seeing the Unseen Computer Journal,
February 1998
[4] Reference
guide:Graphics
Technical
Options
and
Decisions
http://www.devx.com/projectcool/Article/19997
[5] Owens M. A discussion of covert channels and
steganography SANS Institute, 2002
[6] Smart, Nigel Dr Clifford Cocks CB Bristol University, 2008.