Complexities of Brute-Force Attacks 1. The passcode to access a tablet PC has 5 characters. Each character can be any of lower or upper case letters, a digit from 0 through 9, or one of 10 symbols. In a brute-force attack to guess the passcode, how many passcodes does an attacker have to try in the worst case? 2. Alice sends Bob an encrypted document. Characters in the original document include upper or lower case letters, numbers (0-9), 10 unique symbols, and the space. Her encryption scheme is substitution, i.e., replacing each occurrence of a character in the original document with any one of the upper or lower case letters in the alphabet, 10 digits, 10 symbols, and the space. Eve intercepts the ciphertext. In a brute-force attack, how many trials does Even have to perform to decrypt the ciphertext in the worst case? 3. Eve attempts to write a script to guess the password to Alices email account in a brute-force fashion. Suppose Alices password has 8 characters, consisting of lower/upper case letters, digits 0-9, and 10 symbols. The total network time for each password submission takes 2 seconds. Under each of the following conditions, how long does it take for Eve to successfully break into Alices account in the worst case? (a) The server allows at most 5 login attempts within one minute. (b) The server allows at most 15 login attempts within 30 minutes.