2 Part Question Alice has a picture-based password system, where she has each us

Question

2 Part Question Alice has a picture-based password system, where she has each user pick a set of their 20 favorite pictures, say, of cats, dogs, cars, etc. To login, a user is shown a series of pictures in pairsone on the left and one on the right. In each pair, the user has to pick the one that is in his set of favorites. If the user picks the correct 20 out of the 40 he is shown (as 20 pairs), then the system logs him in. Analyze the security of this system, including the size of the search space. Is it more secure than a standard password system?

Charlie likes Alices picture-password system of the previous exercise, but he has changed the login so that it just shows the user 40 different pictures in random order and they have to indicate which 20 of these are from their set of favorites. Is this an improvement over Alices system? Why or why not?

Explanation / Answer

Charlie likes Alice’s picture-password system of the previous exercise, but he has changed the login so that it just shows the user 40 different pictures in random order and they have to indicate which of 20 of these are from their set of favorites

Choosing one picture each from 20 pairs od pictures Charlie's system: Choosing 20 pictures from a set of 40 pictures probabilty of success in

Alice's system (let it be A)

= (number of ways of choosing a correct picture from a pair/number of pictures in a pair) ^ 20

= (1/2) ^ 20

= 1/1048576

Probabilty of success in Charlie's system (let it be B)

= (number of ways of choosing correct combination of 20 pictures from 40 pictures/ totalnumber of ways of choosing 20 od pictures)

= (1/2) ^ 20

= 1/1048576

Both are same so no improvement.

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