Steganography with Digital Images By Karl Schramm

Generic Stegosystem Cover Data Key Stego Data Embedding Algorithm Secret Message

Embedding Guidelines Alteration must be invisible Don’t alter the header The message must be contained in the cover data Use error-correcting code if possible Don’t reuse the cover data

LSB Modification Hide data by altering the LSB of a pixel Choose pixels pseudo-randomly Works with both true color and color index modes Blue 220 Blue 221

JPEG Algorithms Modify discrete cosine transform (DCT) coefficients Choose either larger coefficient values or coefficients in a particular range Attack at dawn!

Patchwork Choose random pixel pairs Let d = p1 – p2 Encode information with values: d < 0 == 0 d > 0 == 1 Swap the pixels if necessary If d == 0, choose a new pair

Steganalysis Traffic analysis Detection Brute force Manipulation