Lecture 13: 29th October 2019

Question 1

What is steganography?

Answer 1

How to hide information within other information, literally in Greek “covered writing”

Question 2

What is image steganography?

Answer 2

Hiding information within image files

Question 3

What results from performing image steganography?

Answer 3

A stego image hiding the message image and cover/background image.

Question 4

What minimum bitrate should images use to prevent an observable loss of distinction?

Answer 4

24 bit

Question 5

What sorts of background images should you use to reduce the perceptibility of image steganography?

Answer 5

busy and dark images with more colour edges/borders

Question 6

What image filetypes can you perform image steganography on?

Answer 6

Filetypes with lossless compression of images. So not JPEG as its compression is lossy but can use lossless filetypes like GIF and BMP.

Question 7

What is the cover image in image steganography?

Answer 7

The image in which the information - message - is hidden.

Question 8

What is the LSB algorithm for image steganography?

Answer 8

Insert bits from the message into the least significant bits of the RBG colour values of each pixel. Choose which colour or colours to put them into depending on the pixel’s colour - to be imperceptible.

Question 9

What is the format of pixels?

Answer 9

3 hex values for red, green, and blue.

Question 10

What is a stego image in image steganography?

Answer 10

The combined message image and cover image.

Question 11

What are S-Tools and WhiteNoiseStorm?

Answer 11

Two tools that perform image steganography. WhiteNoiseStorm adds a blue tint and blur. S-Tools adds a yellow tint but less fuzziness than WNS.

Question 12

What is LSBn?

Answer 12

Variants of the LSB algorithm in which you put the message bits into the n least significant bits of pixel values.

Question 13

How does the number of bits per pixel change the perceptibility of image steganography?

Answer 13

Lower no bits per pixel = higher proportion message data : cover data = higher perceptibility of difference

Question 14

How many bits need to be included in a pixel in a steganography operation to give a perceptible difference?

Answer 14

~4/5, i.e. LSB4 or LSB5

Question 15

How are data inserted into pixel values in steganography?

Answer 15

Insert each bit of the message data into pixels left to right then top to bottom into the least significant bits of the R/G/B values of pixels where they won’t change the pixel too much

Question 16

What are hard edges and their effects on steganography?

Answer 16

When there are straight and narrow borders between very different colours (pixel values). They are difficult to perform image steganography with and become fuzzy in the resulting stego images.

Question 17

How does fuzziness affect the effectiveness of cover images?

Answer 17

They are good cover images since any added fuzziness after image steganography will be less perceptible.

Question 18

What is the Information Loss Problem?

Answer 18

Trying how to computationally detect and decipher steganography. It is not yet possible as human intervention is required.

Question 19

How is Data Loss Prevention related to steganography?

Answer 19

Steganography is used by companies and organisations to preserve critical and sensitive information and allow their recovery in case of data loss

Question 20

How is steganography used?

Answer 20

For secure and private communications of sensitive info by companies and terrorists, data loss prevention

Question 21

What is colour depth?

Answer 21

Colour depth, also known as bit depth, is either the number of bits used to indicate the overall colour of a single pixel or the number of bits used for each colour component of a single pixel.

Question 22

What is a message image?

Answer 22

The message image concealed in another (cover) image in image steganography.