CO3326留学生代做、Computer security代写、代做Java，c/c++代写、代写Python程序

日期：2019-04-05 10:11

Computing and Information Systems/Creative

Computing

CO3326 Computer security

Coursework assignment 2 2018–19

IMPORTANT: all students have been allocated a unique set of

data to use for this coursework assignment. You can obtain this using

your Student Reference Number (SRN) from the following URL:

http://foley.gold.ac.uk/cw19/api/cw2/{srn}. For example, if your SRN is

877665544, you would obtain your data from http://foley.gold.ac.uk/cw19/api/

cw2/877665544. If you have difficulties obtaining your assignment data, please

email us at: intcomp@gold.ac.uk

This coursework assignment is designed to help you enrich your learning experience

and to encourage self-study and creativity. Chapter 9 (pages 95-103) of the

subject guide, including the suggested supplementary reading, will help you in

completing this assignment. You should read the coursework assignment very

carefully and pay particular attention to the Submission requirements.

You are expected to submit two files: a report and a results sheet. The

report counts as 60% of your coursework assignment mark, in which you are

expected to answer the questions below. The results sheet counts as 40% of your

mark, in which you are expected to summarise the results of your calculations in

a specific format. Please use the cipher text and keys provided when answering

the questions and when compiling the results sheet.

To complete the coursework assignment, it will make your life easier if you write

a program. You are welcome to use any programming language.

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Coursework assignment 2

This coursework assignment takes a practical example for the El Gamal public

key cryptosystem. The notation is similar to the one used in your subject guide

(section 9.4, pages 99 - 101). IMPORTANT: To answer the questions below,

please use the coursework 2 assignment data that you obtained using your SRN.

Question 1 Verify whether p is an actual prime (i.e. not just a probable

prime). Provide a brief explanation and include the method from your code, as

well as the runtime.

Question 2 What is the computational complexity of your primality check?

Presumably, you have a loop; how many steps does it take relative to p? Include

the code where you calculate this.

Question 3 Discuss briefly how you can go about optimising the primality

check, including a code snippet.

Question 4 Verify whether g is a generator for p. Provide a brief explanation

and include the method from your code, as well as the runtime. Hint: As p is a

16-digit prime, the definition from your subject guide is not a practical way to

verify whether g is a generator. You will have to research on how El Gamal is

implemented in practice (for example in Open SSL) – you will find that p is a

special kind of prime.

Question 5 Considering that a is Alice’s private key and b is Bob’s private

key, compute their public keys and show how they can generate the same shared

key. Include a brief explanation and the relevant code snippet.

Question 6 Decrypt the provided cipher text which has been encrypted with

the shared key that you computed in Question 5. Include a brief explanation

and the relevant code snippet.

Question 7 Suppose Alice and Bob want to generate a new set of keys. They

decide that they should use a 17-digit prime instead. How would they go on

about generating a new p and a corresponding generator g? Provide a brief

explanation and include the relevant code snippet, as well as its runtime.

Question 8 Generate a new set of private and public keys for Alice and Bob,

using the p and g you generated in Question 7. Encrypt your SRN with the

shared key. Include a brief explanation and the relevant code snippet.

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Submission requirements

REMINDER: It is important that your submitted coursework assignment is

your own individual work and, for the most part, written in your own words. You

must provide appropriate in-text citation for both paraphrase and quotation, with

a detailed reference section at the end of your coursework. Copying, plagiarism

and unaccredited and wholesale reproduction of material from books or from

any online source is unacceptable, and will be penalised (see our guide on how

to avoid plagiarism on the VLE).

You should upload two single files only. These must not be placed in a folder,

zipped, etc.

The report should be submitted as a PDF document following a strict naming

scheme: YourName_{srn}_CO3326cw2.pdf. For example, Steve Jobs with SRN

877665544 would submit SteveJobs_877665544_CO3326cw2.pdf.

The results sheet should be submitted as a JSON file with a strict

format and strict naming scheme. This summarises the results of your

calculations and will be automatically checked by an algorithm, so pay

particular attention to its format. The name of the file should be

YourName_{srn}_CO3326cw2.json; for example, Steve Jobs with SRN

877665544 would submit SteveJobs_877665544_CO3326cw2.json.

Example

You have obtained your coursework assignment data in the following format

(this is an example for illustration):

{

"srn": "877665544",

"name": "Steve Jobs",

"exercise1": {

"p": "2685735182215187",

"g": "2",

"a": "3628281929",

"b": "5915661551",

"cipherText": {

"encoded": "65462432711955",

"base64": "O4mpDEUT"

}

}

}

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For this, Steve Jobs would submit the following JSON, which reflects a correct

solution:

{

"srn": "877665544",

"name": "Steve Jobs",

"exercise1": {

"p": "2685735182215187",

"g": "2",

"a": "3628281929",

"b": "5915661551",

"x": "1611247168640770",

"y": "1057465508852156",

"k": "1133299385179611",

"cipherText": {

"encoded": "65462432711955",

"base64": "O4mpDEUT"

},

"plainText": {

"encoded": "427071729268",

"base64": "Y291bnQ=",

"text": "count"

}

},

"exercise2": {

"p": "44685735181995023",

"g": "5",

"a": "4628273483",

"b": "6915587579",

"x": "3934012106049896",

"y": "6387156331543282",

"k": "16887845058447247",

"cipherText": {

"encoded": "27261997930282270",

"base64": "YNqkhoB9Hg=="

},

"plainText": {

"encoded": "877665544",

"base64": "NFAdCA=="

}

}

}

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Explanation

The srn and name fields are self-explanatory. exercise1 is relevant for questions

1 to 6 from the report. exercise2 contains the results of questions 7 and 8. The

notation is similar to the notation used in section 9.4, pages 99 - 101, in the

subject guide: p is the prime, g is the generator, a is Alice’s private key, b is

Bob’s private key, x is Alice’s public key, y is Bob’s public key, k is the resulting

shared secret key.

In Exercise 1 the plain text has been encoded with Base64, which has been

transformed to a number. If you are using Java, there are utilities provided by

Apache or Google, among others, to do these operations. Similar libraries exist

in other programming languages. If you struggle with these operations or you

would like to double-check your results, you can use the web API calls below.

For Base64 encoding/decoding you can use the following:

http://foley.gold.ac.uk/cw19/api/cw2/encode?text=count

http://foley.gold.ac.uk/cw19/api/cw2/decode?base64=Y291bnQ=

For text encoding/decoding to/from numbers, you can use the following:

http://foley.gold.ac.uk/cw19/api/cw2/toNumber?text=Y291bnQ=

http://foley.gold.ac.uk/cw19/api/cw2/toText?number=427071729268

obviously replacing count, Y291bnQ= and 427071729268 with the text or number

you want to encode/decode.

In both the plainText and cipherText, the encoded is a number, the text is an

English dictionary word and the base64 is a Base64-encoded text. As in exercise2

you have a number to encrypt (your SRN), the text field is irrelevant.

Final note

You can use the example solution above as a template, which is a well-formed

JSON, and replace the values with your data and calculation results. As the

JSON will be evaluated by an algorithm, every quote, comma, colon, curly

brace upper/lower case is crucial. Please pay attention to these. It would

be a shame to lose a potential 40% of the total marks for this coursework

assignment because of a misplaced comma or a missing quote. There are

online tools you can use for JSON formatting and validation (for example

https://jsonformatter.curiousconcept.com), so double-check that your JSON is

syntactically correct.

[END OF COURSEWORK ASSIGNMENT 2]

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