密码学代写|CP3404 Assignment 1

本次新加坡代写是一个密码学相关的assignment

Aim: This assignment is designed to help you improve your critical thinking and
problem solving skills, as well as your information literacy skills (i.e. the ability to
select and organise information and to communicate it effectively and ethically).

1. Answer a) OR b)

a)

Using the web, find out who Kevin Mitnick was.

What did he do?

Who caught him?

Write a short summary of his activities and why he is famous.

b)

What went wrong at Sony Entertainment? Review the Fortune Magazine article Hack of
the Century and other resources and summarize what went wrong and why.

2. One-Time Pad (OTP) – An unbreakable cryptographic system

Use the Internet to search OTPs; who was behind the initial idea, when they were first used,
in what application they were found, how they are used today, etc. Then visit an online OTP
creation site (such as www.braingle.com/brainteasers/codes/onetimepad.php) and
practice creating your own ciphertext with OTP. Exchange your OTPs with other students
to see how you might try to break them. Would it be practical to use OTPs? Why or why
not? Can you find any references about its use in practical situation? Write a short
summary on your findings.

3. Cryptanalysis of Substitution Ciphers

In this question you learn a classical monoalphabetic (substitution) cryptographic system,
and are required to cryptanalysis a given cryptogram.

In substitution ciphers, a permutation of the alphabet is chosen as the cryptogram of
original alphabet. That is, every letter of the plaintext substitutes by corresponding letter in
the permuted alphabet. For example,

a b c d e f g h i j k l m n o p q r s t u v w x y z
c o d k s z r g e l u y a f m v p h i n w t b j q x

Figure 1: A possible permutation of English alphabet

is one of such permutation, in which letters a,b,c,···,y,z from the plaintext are substituted by
corresponding letters c,o,d,···,q,x respectively. Since remembering permutation is not easy,
one may employ a keyword and use a table to generate the permuted alphabet. Let
CRYPTOGRAPHY be the keyword. The permuted alphabet can be obtained as follows.

Choose a 6 × 5 table/matrix, i.e., a table with 6 rows and 5 columns.

Write down the secret keyword in cells (1,1),(1,2),···, one letter in each cell, but skip
repeated letters. Figure 2 shows how ‘CRYPTOGRAPHY’ (as a keyword) written down in
the table.

Write alphabet letters (in order) from the first available cell after keyword, but skip all
letters that are already written in the table. You will come out with Table 3.

The permuted alphabet, which will be used to generate the cryptogram, can be obtained by
simply reading the content of Table 3 in columns order (Which gives you the cryptogram
alphabeth of Figure 1).


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