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.
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
DIFFERENCE B/WCRYPTOGRAPHY AND STEGANOGRAPHYSteganography deals with composing hidden messages so thatonly the sender and the receiver know that the message evenexists. Since, nobody except the sender and the receiver knowsthe existence of the message, it does not attract unwantedattention.Steganography is hidden writing. The message is there, butnobody notices it. Once the presence of hidden information isrevealed or even suspected, the purpose of steganography isdefeated.However, once noticed, it can be read. A common form ofsteganography is the use of JPEG files (a computer image) tohide the message.The obvious advantage of Steganography overcryptography is that messages do not attract anyattention
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 messengers 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 plansWorld War IIthe French Resistance sent some messages written on the backs of couriers using invisible ink.
Modern Steganography TechniqueLeast 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.
Image of a tree with a steganographicallyhidden image. The hidden image is revealed byremoving all but the two least significant bitsof each color component and a subsequentnormalization. The hidden image is shownbelow. Image of a cat extracted from the tree image above.
Basics of Modern SteganographyfE: steganographic function "embedding"fE-1: steganographic function "extracting"cover: cover data in which emb will be hiddenemb: message to be hiddenkey: parameter of fEstego: cover data with the hidden message
Important Requirement for Steganographic SystemSecurity of the hidden communicationsize of the payloadRobustness against malicious and unintentional attacks
Detection of Steganographic Content/CountermeasuresThe 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 images 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.