Steganography is the practice of concealing a file, message, image, or video within another file, message, image, or video. The concealed message is hidden in a way that prevents detection. It differs from cryptography, which encrypts a message to hide its meaning but not its existence. Modern steganography techniques include least significant bit insertion to hide messages in image files with minimal distortion. Detection of concealed messages is called steganalysis and involves visual or statistical analysis to reveal alterations caused by message embedding.

1. What is Steganography?
Greek Words:
STEGANOS – “Covered”
GRAPHIE – “Writing”
 Steganography is the art and
science of writing hidden messages
in such a way that no one apart Stegosaurus: a covered lizard
from the intended recipient knows
(but not a type of cryptography)
of the existence of the message.
 This can be achieve by concealing
the existence of information
within seemingly harmless carriers
or cover
 Carrier: text, image, video, audio,
etc.

2. Cryptography
Cryptography was concerned solely with message
confidentiality (i.e., encryption)—conversion of message
from a comprehensible form into an incomprehensible one
and back again at the other end, rendering it unreadable by
interceptors or eavesdroppers without secret knowledge
(namely the key needed for decryption of that message)
Cryptography is secret writing. Anybody can see the message,
but nobody else can read it. Usually, this is because its letters
have been re-arranged, or replaced by different letters,
according to some scheme that only the sender and receiver
know. Only those who possess a secret key can decrypt the
message into plain text

3. DIFFERENCE B/W
CRYPTOGRAPHY AND STEGANOGRAPHY
Steganography deals with composing hidden messages so that
only the sender and the receiver know that the message even
exists. Since, nobody except the sender and the receiver knows
the existence of the message, it does not attract unwanted
attention.
Steganography is hidden writing. The message is there, but
nobody notices it. Once the presence of hidden information is
revealed or even suspected, the purpose of steganography is
defeated.
However, once noticed, it can be read. A common form of
steganography is the use of JPEG files (a computer image) to
hide the message.
The obvious advantage of Steganography over
cryptography is that messages do not attract any
attention

4. History of Steganography
Steganography ancient origins can be traced back to 440 BC, from the Histories of
Herodotus
Demeratus sent a warning about a forthcoming attack to Greece by writing it on a
wooden panel and covering it in wax.
Histiaeus, who shaved the head of his most trusted slave and tattooed a message on it.
After his hair had grown the message was hidden. The purpose was to instigate a revolt
against the Persians.
Hidden messages on messenger's body — also used in ancient Greece. Herodotus tells
the story of a message tattooed on the shaved head of a slave of Histiaeus, hidden by the
hair that afterwards grew over it, and exposed by shaving the head again. The message
allegedly carried a warning to Greece about Persian invasion plans
World War II
the French Resistance sent some messages written on the backs of couriers using invisible
ink.

5. Modern Steganography Technique
Least Significant Bit Insertion: The most common and
popular method of modern day Steganography is to
make use of the LSB of a picture’s pixel information.
Thus the overall image distortion is kept to a minimum
while the message is spaced out over the pixels in the
images. This technique works best when the image file
is larger then the message file and if the image is
grayscale.

6. Image of a tree with a steganographically
hidden image. The hidden image is revealed by
removing all but the two least significant bits
of each color component and a subsequent
normalization. The hidden image is shown
below.
Image of a cat extracted from the tree image
above.

7. Basics of Modern Steganography
fE: steganographic function "embedding"
fE-1: steganographic function "extracting"
cover: cover data in which emb will be hidden
emb: message to be hidden
key: parameter of fE
stego: cover data with the hidden message

8. Important Requirement for
Steganographic System
Security of the hidden communication
size of the payload
Robustness against malicious and unintentional attacks

9. Detection of Steganographic
Content/Countermeasures
The detection of steganographically encoded packages is
called Steganalysis.
Visual Analysis tries to reveal the presence of secret
communication through inspection, either with the naked eye
or with the assistance of a computer.
Statistical (Algorithmic) Analysis reveals tiny alterations
in an image's statistical behavior caused by steganographic
embedding.
 The nominally universal methods developed to detect embedded stego-
data are generally less effective than the steganalytic methods aimed at
specific types of embedding.