Department of Computing
COMP347 Advanced Computer Networks
Assignment 2, Semester 2 2019
Due: Tuesday 29th October, 2019, 5 pm
Marks: 60
Value: 15%
Topics
TCP
Security
Submission
Submit on line via Turnitin link on COMP347 iLearn page.
Please do not double space lines.
Assignments will be marked and returned online. There are no hardcopy
submissions for written assignments.
1.Security and Applications (20 marks)
Authentication has long been a problem for transactions. How do you know if
someone presenting a card really is the owner of that card? Simple methods include
matching a signature to a previously signed one on the back or entering a PIN.
Now with PayWave, only authentication by possession (of the card) is required. 



Currently, there are a number of initiatives to use mobile devices for the
functionality of payment. This raises the question of how safe are the devices and
what mechanisms are built in to prevent fraud. A number of platform vendors have
introduced electronic card payments to their devices. For example Apple
introduced ApplePay in iPhone and Apple Watch.
With reference to the techniques in the security lectures, examine how various
vendors approach secure payments. Is it easy to use for legitimate users while
difficult to crack for attackers? Does it provide confidentiality, integrity,
authentication, anti-replay, and non-repudiation? In what ways might these
transactions be compromised and how are they counteracted? 



You should start with a general description of Apple Pay and another (Android-
based) service, an overview of how it works, and what encryption is used. Where is
encryption applied? Examine the authentication functions. What protocols are
used? Then evaluate it with reference to the previous paragraph. How do the
different vendor’s offerings compare? Where are they the same or similar, and how
do they differ?



Here are a few web links you can start with, but you should also find your own:
GooglePay API
Google Android PaymentsClient API
ApplePay API
AppleInsider article on PayPal's doubts about ApplePay's security
AppleInsider's article on the ApplePay and NFC patent
PayPal's Braintree Blog on ApplePay
Some background to iOS security although it predates Apple Pay:
Apple iOS Security Guide
2. TCP (40 marks)
Host A and B are communicating over a TCP connection, and Host B has already
received from A all bytes up to byte 126. Suppose Host A then sends two segments
to Host B back-to-back. The first and second segments contain 80 and 40 bytes of
data, respectively. In the first segment, the sequence number is 127, the source port
number is 3024, and the destination port number is 80. Host B sends an
acknowledgement whenever it receives a segment from Host A.
a. [5 marks] In the second segment sent from Host A to B, what are the sequence
number, source port number, and destination port number?
b. [5 marks] If the first segment arrives before the second segment, in the
acknowledgement of the first arriving segment, what is the acknowledgement
number, the source port number, and the destination port number?
c. [5 marks] If the second segment arrives before the first segment, in the
acknowledgement of the first arriving segment, what is the acknowledgement
number?
d. [10 marks] Suppose the two segments sent by A arrive in order at B. B sends
acknowledgements for both segments, but the first acknowledgement is lost and
the second acknowledgement arrives after the first timeout interval. Draw a
timing diagram showing these segments and all other segments and
acknowledgements sent (you can assume no other segment loss). For each
segment in your diagram, provide the sequence number and the number of
bytes of data; for each acknowledgement that you add, show the
acknowledgement number.
e. [5 marks] As we have seen, the Internet layer of TCP/IP has two protocols –
IPv4 and IPv6. The transport layer provides two main protocols TCP and UDP
(along with some special-purpose, minor protocols). But these are for very
different reasons. Why are the Internet and Transport layers very different in
providing two protocols?
f. [5 marks] Since UDP does very little that is different from IP, why do we even
have a transport layer such as UDP?
g. [5 marks] Describe how DDoS attacks may be mounted against TCP and UDP
services. In what way will being connection oriented be different for TCP and
UDP?
Assessment
For all questions in this assignment not only content but also presentation
will affect your mark. You will lose marks (and not necessarily only a small
portion) if there are problems with the presentation, particularly with clarity.
This means that your answers to each question should be a coherent
statement and that the spelling and grammar of your submission will be
taken into account in assessing its presentation.
For full marks, your answers should all be clear, coherent and correct.
The standards of marking described in the unit outline L.O. 1-4 will be
applied to this assignment as relevant to the assignment topics.
In addition, the following particular standards will be applied in marking
this assignment:
Correctness of approach
Incorrect answers with the correct logic or approach will receive no more
than a pass for the individual question.
Correct answers within correct logic or approach will receive no more than
pass for the individual question.
Incorrect answers with no explanation of the approach taken or with the
incorrect approach will receive a fail grade for the individual question.
The questions will be marked individually, the marks totalled, and a final
grade assigned that is no more than indicated by the total marks, and no
more than allowed by the standards specified above and in the unit outline.
Clarity
Multi-paragraph answers should be structured into sections and subsections
with appropriate headings and subheadings.
Ambiguous or poorly worded answers will receive a grade no more than a
pass for the individual question.
Minor issues of clarity will receive a grade no more than credit for the
individual question.
Spelling and grammar
Assignment submissions with more than 4 spelling or grammatical errors
will not achieve a grade higher than distinction; submissions with more than
8 such errors will not achieve a grade higher than credit.
Bibliography Guidelines
In your bibliography be careful to identify the source of all material that you
use and to clearly identify any quotations that you make. (See the section on
plagiarism, below.) Here is an example of a quotation using the Harvard
method of citation: 

“In this assignment, you must be particularly careful to avoid plagiarizing
your articles or any other sources of information.” (Shankaran, 2005)
And here is an example of a bibliography entry:
Shankaran, R. “Comp247 Assignment 2” 2005. [available online http://
www.comp.mq.edu.au/units/comp247/assigns/ass2.pdf; accessed May
2005].
Any quotations that are not properly identified will be considered as
plagiarism and will attract a penalty. For more information on how to write
bibliographies, you can find resources on the Internet such as How to Write a
Bibliography (an introduction) or Bibliography Guides (a detailed description
of the APA style). However, we do not require a strict adherence to any
particular bibliography style provided that you include the key information
such as authors, article title, date of publication and title of publication, and
provided that your citations are clear.
Originality
All material must be in your own work and expressed in your own words.
Plagiarism
You should be well aware by now of the University's plagiarism policy. In this
assignment, you must be particularly careful to avoid plagiarising your articles or
any other sources of information. If you wish to directly quote any portion of
another document, you must enclose your quotation in quotation marks and
immediately following the quotation you must identify your source. It is important
that you do not attempt to write your essay by pasting together pieces of text that
you find on the Internet. You need to write your own words and phrases that
express your own ideas. You must also list all sources used in your answer/essay in
a bibliography at the end of the answer/essay.