A user for a secure internet service has a 20 digit key phrase. The key phrase is known by the user only and each digit in the key phrase has a value 0-9. When the user attempts to log onto the secure service he/she is asked for 3 random digits from the keyphrase, for example digit 1, digit 2 and digit 3. After they have entered the 3 numbers correctly they are logged into the secure service.
Now there is a keylogger, which observes the data being input, it logs the digit numbers and their values. It will do this each time the same user attempts the enter the secure site.
So how many observations would the keylogger have to make before it has a 50% sucess rate of logging into the secure service?
1[11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11][11]
1does the keylogger know which 3 digits are asked each time?normally keylogger shouldn't be able to do that
