3. [10 points] When a client C accesses server S through Tor, she usually builds a circuit of three nodes: N1, N2, and N3. A connection is established as follows:

C N1 N2 N3 S

N1 is also known as the entry node or the guard node, and N3 is also known as the exit node. Visit metrics.torproject.org to answer the following questions:

(a) [3 points] Give the total amount of advertised bandwidth of relays with the Guard flag and relays with the Exit flag on 2017-01-01. Which is more? Give one reason to explain this phenomenon.

(b) [4 points] Give the median download rate of a file (in bits per second) for a 50 KiB file and a 5 MiB file to the op-hk onion server on 2017-06-01. Can you explain the difference?

(c) [3 points] What is a disadvantage of using three nodes in a Tor circuit instead of one node? What is an advantage of doing so?

(d) [3 points (bonus)] Find the list of top 10 countries by number of bridge users. Which, amongst those, is the country with the greatest ratio of bridge users com- pared to relay users on 2017-06-01? Give the ratio, and suggest why this is the case.