INTRODUCTION:
Information
hiding in digital images has drawn much attention in recent years. Secret
message encrypted and embedded in digital cover media. The redundancy of
digital media, as well as characteristics of the human visual system, makes it
possible to hide secret messages. Two competing aspects are considered while
designing information hiding scheme
1) Hiding
capacity and
Hiding
capacity means maximum payload. Imperceptibility means keeping undetectable. A
least significant bits (LSB) substitution method is widely used for hiding data
in digital images. This method widely used because of large capacity and easy
implementation. Cryptography was created as a technique for securing the
secrecy of communication and many different methods have been developed to
encrypt and decrypt data in order to keep the message secret. Unfortunately it
is sometimes not enough to keep the contents of a message secret, it may also
be necessary to keep the existence of the message secret. The technique used to
implement is called steganography. It is the art and science of invisible
communication. The advantage of steganography over cryptography alone is that
messages do not attract attention to themselves, to messengers, or to
recipients. Steganographic messages are often first encrypted by some traditional
means, and then a cover text is modified in some way to contain the encrypted
message, resulting in stego text. This is a technique to embed additional
message into some distortion-unacceptable cover media, such as military or
medical images, with a reversible manner so that the original cover content can
be perfectly restored after extraction of the hidden message.
IMAGE into IMAGE Steganography:
In this
method we hide binary image into grayscale or color image. In this method our
aim is to hide secrete binary image into grayscale or color image.
first step
is to encrypt secrete image with secrete key. This can be achieved with the
help of xor function. XORing of secret message and generated key stream will
complete the encryption process.
LSB (Least significant bit) substitution:
Least
significant bit (LSB) insertion is a common, simple approach to embedding
information in a cover image. The least significant bit (in other words, the
8th bit) of some or all of the bytes inside an image is changed to a bit of the
secret message. When using a 24-bit image, a bit of each of the red, green and
blue color components can be used, since they are each represented by a byte.
In other words, one can store 3 bits in each pixel. An 800 × 600 pixel image,
can thus store a total amount of 1,440,000 bits or 180,000 bytes of embedded
data. This Principle involved in this method is to replace all LSB bits of
pixels of the cover image with secret bits. This method embeds the fixed length
secret bits in the same fixed length LSBs of pixels. Although this technique is
simple, it generally causes noticeable distortion when the number of embedded
bits for each pixel exceeds three.
Image Transmitter Image Receiver
From
extraction we will get only encrypted message but to identify secret message
decryption process is used, for decryption of secret message we require same
key stream that we have used at transmitter for encryption of message. After
decryption process user will get information from secret message.
TEXT into IMAGE Steganography:
In text
steganography we first convert text from text to binary then we encrypt that
binary stream with secrete key and then we hide that encrypted binary stream to
LSBs of the cover image with the help of LSB substitution method. At receiver
side we do exactly opposite process for getting original text back.
Text Transmitter Text Receiver
Result Analysis and Discussion:
Following
results are obtained for Lena Image with the devi image. The terms in table are
EC = Embedding capacity, NBE = Number of bits embedded, PSNR = Peak signal to
noise ratio.
Cover Image Secrete image
Results for
Lena image with Devi Image:
Following results are obtained by embedding bits from LSB to MSB i.e from bit 1 to bit 8
MATLAB Implementation:
Transmitter Side:
Receiver Side:
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