May 2018
网络安全代考 The server listens on TCP port 25 for incoming connection requests. The user end of the connection is on a TCP port number above 1023.
1.This question is about basic Network Security Terminology and Mix Net-works.
a.Which are the three main security properties? Give a brief description of each property. Also, for each property, name a network security attack that breaches it and explain why.[15 marks]
b.This sub-question is about Mix Networks.
A sender A wants to send a message M to a receiver B over a chain of 4 Mixes that A chooses among the 6 Mixes mix1,…, mix6 available in the Mix Network.
i.Specify the cryptographic details of how A would prepare the message M to be sent to B over the chain of 4 Mixes, and how each Mix in the chain manipulates the message until it reaches B. 网络安全代考
(There is no need to describe the internal functionalities of the Mix,but simply describe how the Mix would process the message in the input and what the message that it forwards would look like.)[12 marks]
ii.Consider the sequence of Mixes you have chosen in question 1.b.i and describe the cryptographic details of how the fifirst Mix in the sequence can return a receipt Y for the message received from sender A.[5 marks]
iii. Describe the cryptographic details of how the recipient B can respond to the message M of the anonymous sender A with a return message N.[18 marks]
2.This question is about Firewalls and Scanning. 网络安全代考
a.This subquestion is about Firewalls.
i.SMTP (Simple Mail Transfer Protocol) is the standard protocol for transferring mail between hosts over TCP. A TCP connection is set up between a user agent and a server program. The server listens on TCP port 25 for incoming connection requests. The user end of the connection is on a TCP port number above 1023. Suppose you wish to build a packet fifilter rule set allowing inbound and outbound SMTP traffiffiffic. You generate the following ruleset (where Internal means an IP address in the internal network, and External means an IP address of a remote host):
ii.Your host in this example has IP address 172.16.1.1. Someone tries to send e-mail from a remote host with IP address 192.168.3.4. If successful, this generates an SMTP dialogue between the remote user and the SMTP server on your host consisting of SMTP commands and mail. Additionally, assume that a user on your host tries to send e-mail to the SMTP server on the remote system. Four typical packets for this scenario are as shown:
Indicate which packets are permitted or denied and which rule is used in each case.[8 marks]
iii. Someone from the outside world (10.1.2.3) attempts to open a connection from port 5150 on a remote host to the Web proxy server on port 8080 on one of your local hosts (172.16.3.4), in order to carry out an attack. Typical packets are as follows:
Will the attack succeed? Give details.[5 marks]
iv.Are there any changes you would make to the original rule set in light of your reply to the previous question?[7 marks]
b.What is the main difffference between a TCP connect scan and a SYN scan?[10 marks]
c.What are the three main techniques for port scanning? For each of them, give at least one advantage and one disadvantage.[15 marks]
3.This question is about Security Protocols, Web Security and Email Security. 网络安全代考
a.The IPSEC protocol suite provides three sub-protocols for the security of data transmission. Security policies in this suite are determined by the interaction of two specifific databases.
List each of the sub-protocols and databases, and brieflfly explain their role in IP security.[10 marks]
b.Describe the stages of transmission of an outbound IP packet using the IPSEC suite, including the querying of the related databases.[10 marks]
c.In terms of an IP datagram, explain the benefifit of ESP transport mode over AH transport mode.[5 marks]
d.What is HTTPS?[5 marks]
e.What is a cookie? How are cookies related to privacy?[10 marks]
f.Describe the steps for PGP authentication.[10 marks]
4.This question is about Linux File Access Specifification, Scripting and DNS.
a.Describe the structure of the Linux fifile access specifification. Describe the purpose, and application on this structure, of the bits which alter the standard meaning of the elements of the fifile access specifification.[10 marks]
b.What is the “shellshock” vulnerability? Give an example of a script that would show the vulnerability and explain how it works.[15 marks]
c.What is DNS, what is its motivation and what is its purpose? Explain,using diagrams, what happens when a computer wishes to access a URL whose IP address it does not know, and neither does the local nameserver. Also explain what happens when, after this, another computer wishes to access the same URL, does not know the corresponding IP address, and uses the same local nameserver.[15 marks] 网络安全代考
d.What problem is caused by the fact that DNS is stateless? Explain how a DNS poisoning query ID attack works.[5 marks]
e.Explain how bailiwick checking protects against some classes of DNS attacks. How did Dan Kaminsky’s attack get around bailiwick checking?[5 marks]
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