Lecture 13: 29th October 2019 Flashcards Preview

CS4203 Computer Security > Lecture 13: 29th October 2019 > Flashcards

Flashcards in Lecture 13: 29th October 2019 Deck (22)
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What is steganography?

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


What is image steganography?

Hiding information within image files


What results from performing image steganography?

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


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

24 bit


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

busy and dark images with more colour edges/borders


What image filetypes can you perform image steganography on?

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


What is the cover image in image steganography?

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


What is the LSB algorithm for image steganography?

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.


What is the format of pixels?

3 hex values for red, green, and blue.


What is a stego image in image steganography?

The combined message image and cover image.


What are S-Tools and WhiteNoiseStorm?

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


What is LSBn?

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


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

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


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

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


How are data inserted into pixel values in steganography?

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


What are hard edges and their effects on steganography?

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.


How does fuzziness affect the effectiveness of cover images?

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


What is the Information Loss Problem?

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


How is Data Loss Prevention related to steganography?

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


How is steganography used?

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


What is colour depth?

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.


What is a message image?

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