PLZ ANSWER EVERY QUESTION IN FULL THX WILL GIVE THUMBS UP IF EVERY QUESTION IS ANSWERED CORRECTLY IN FULL THX SO MUCH

1. (25 pts) Consider an intrusion detection system with the following properties. Attack traffic is 0.1 %. The intrusion detection system is 99 % accurate. That is 99 % of the attacks raise an alarm. Assume that a valid packet causes an alarm 1 % of the time. Answer the following questions based on this information. (a) What is the probability that an alarm will be raised for a packet? (b) What is the probability that an alarm corresponds to an attack? (c) What is the probability that an alarm corresponds to a valid packet? 2. (25 pts) A rapidly-growing online crime is phishing, in which victims are lured by an e-mail to log on to a website that appears genuine but that actually steals their passwords. You have been hired by a bank to help them harden their online banking service against phishing attacks. Explain briefly the strengths and weaknesses of the following three possible countermeasures: (a) SSL/TLS client certificates issued to each customer (b) Displaying a unique picture to each customer during the login process: (c) Requiring that large payments, or payments to new recipients, be authorised by telephone or SMS as well as online. 3. (25 pts) VerySafe Ltd offers two vaults with electronic locks. They open only after the correct decimal code has been entered. The VS100,a low-cost civilian model, expects a 6-digit code. After all six digits have been entered, it will either open or will signal that the code was wrong and ask for another try. The VS110, a far more expensive government version, expects a 40-digit code. Users of a beta-test version of the VS110 complained about the difficulty of entering such a long code correctly. The manufacturer therefore made a last-minute modification. After every five digits, the VS110 now either confirms that the code has been entered correctly so far, or it asks for the previous five digits again. Compare the security of the VS100 and VS110. 4. (25 pts) Alice wants to attack Bob's computer via the Internet, by sending IP packets to it, directly from her own computer. She does not want Bob to find out the IP address of her computer. (a) Is this easier to achieve for Alice with TCP or UDP based application protocols? Explain briefly. (b) For the more difficult protocol, explain one technique that Alice could try to overcome this obstacle and one countermeasure that Bob could implement in his computer