On a particular system all passwords are 8 characters and th

On a particular system, all passwords are 8 characters and there are 128 possible choices for each character. There is a password file containing the hashes of 2 10 passwords. Trudy has a dictionary of 2 30 passwords, and the probability that a randomly selected password is in her dictionary is 1 / 4. Work is measured in terms of the number of hashes computed.

a.Suppose that Trudy wants to recover Alice’s password. Using the dictionary, what is the

expected work to crack this particular password?

b. What is the probability that at least one of the passwords in the password file is in Trudy’s

dictionary

Solution

a)

1/4 * 230 = 57.5

b)

210 / 230 = 0.9130