topic 8 - steganography part 2 Flashcards
how secure is a stego object?
if an attacker believes we are sending a hidden message it is relatively easy for him/her to guess the extraction algorithm and thereby obtain the secret.
A better approach is to use the random interval method in which elements of the cover are chosen at random for hiding data.
what is a better approach to secure my stego object?
A better approach is to use the random interval method in which elements of the cover are chosen at random for hiding data.
what is secret key stegaonography?
as the ‘seed’ for the random number generator must be available to both parties in the communication.
what is the random interval method?
Use a pseudo random number generator (PRNG) to generate a sequence of random intervals.
A number is used to ‘seed’ the PRNG. This number is the stego-key (k).
The stego-key is used by the sender to generate the sequence of random intervals {k} for encrypting the secret message.
The stego-key is also used by the receiver to generate the same sequence of random intervals {k} that allows him/her to decrypt the secret message.
what does the random interval method allow?
The random intervals allow the secret message/image, m, to be distributed over the cover object, c.
The stego-key is required to determine the locations of the pixel values that contain the secret information.
what is a visual attack on steganography?
A visual attack is a means of detecting embedded information e.g. by visual inspection of the least significant bits only of a digital image.
what is a statistical attack on steganography?
The term statistical attack is used when referring to non-visual methods for determining embedding.
what is the definition of an image histogram?
Image histogram is the frequency distribution of grey-levels within a digital image.
how do we analyse an image histogram?
We can analyse an image histogram using the chi-squared statistic to obtain a probability of embedding.
what is a statistical attack on steganography?
For simple 4-bit images we can determine the chi-squared statistic by hand and use a table to see if the value obtained is significant at the 5% level.
