Steganography & Digital Watermarfking Jagdish S. Gangolly State University of New York at Albany 9/17/2018 Acc 661 (Spring 2002)

Steganography vs. Cryptography Objectives: Cryptography: To hide information (its meaning) by encrypting. It enables checking for authenticity of source, non-repudiation by receiver, and protect integrity of the message in transit. Steganography: To hide information by “finger-printing” in order to prevent illicit copying of documents, or to pass private messages without detection. 9/17/2018 Acc 661 (Spring 2002)

Steganography I "Steganography is the art and science of communicating in a way which hides the existence of the communication. In contrast to cryptography, where the enemy is allowed to detect, intercept and modify messages without being able to violate certain security premises guaranteed by a cryptosystem, the goal of steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second secret message present" [Markus Kuhn 1995-07-03]. 9/17/2018 Acc 661 (Spring 2002)

Steganography II wax covered tablets: Herodotus’ Histories Tattoos on shaved heads Invisible inks Inks that react to chemicals Null ciphers: News Eight Weather: Tonight increasing snow. Unexpected precipitation smothers eastern towns. Be extremely cautious and use snowtires especially heading east. The highways are knowingly slippery. Highway evacuation is suspected. Police report emergency situations in downtown ending near Tuesday. Newt is upset because he thinks he is President. Source: http://www.jjtc.com/stegdoc/sec202.html 9/17/2018 Acc 661 (Spring 2002)

Steganography III An Example: Hide and Seek 5.0 Uses the Least Significant Bit of each pixel to encode characters, 8 pixels per character and spreads the data throughout the GIF in a somewhat randomly. Max size: 1024 x 768 pixels Maximum message size: (320x480)/8 = 19200 Message: Steganography is the art and science of communicating in a way which hides the existence of the communication. In contrast to cryptography, where the "enemy" is allowed to detect, intercept and modify messages without being able to violate certain security premises guaranteed by a cryptosystem, the goal of steganography is to hide messages inside other "harmless" messages in a way that does not allow any "enemy" to even detect that there is a second secret message present [Markus Kuhn 1995-07-03]. 9/17/2018 Acc 661 (Spring 2002)

Steganography IV Maximum display used: 320 x 480 pixels Original: 222 x 282 pixels and 256 shades of gray Resulting image: forced to 320 x 480 pixels Source: http://www.jjtc.com/stegdoc/sec309.html 9/17/2018 Acc 661 (Spring 2002)

Steganography V 9/17/2018 Acc 661 (Spring 2002)

Steganography VI 9/17/2018 Acc 661 (Spring 2002)

Steganography IV Method: Each pixel is represented as a byte (8-bits). Gray-scale images are very good because the shades gradually change from byte to byte. A similar image with 16 shades of gray (four-bit color) may look very close to one with 256 shades of gray but the palette has less variations with which to work. The subtleties permit data to be stored without the human eye catching the changes. A message may be plain-text, ciphertext, other images or any thing that can be embedded in the least significant bits (LSB) of an image. 9/17/2018 Acc 661 (Spring 2002)