Description
1 Project Description
In this project, you will need to implement one-time pad encryption, including encryption function Enc,
decryption function Dec, and key generation function KeyGen. More specifically,
– For the encryption function, given a plaintext m and a secret key sk, your program need to compute
a ciphertext of this plaintext c ← m ⊕ sk, print it in the terminal, and write this ciphertext to a file.
– For the decryption function, given a ciphertext c and a secret key sk, your program need to output the
plaintext of this ciphertext m ← c ⊕ sk, print it in the terminal, and write this plaintext to a file.
– For the key generation function, given a security parameter λ, your program need to output a secret
key sk, where the length of sk is λ. In addition, you also need to write this secret key to a file.
2 Basic Requirements
Programming Language: You can use either C/C++, Python or Java. If you choose to use C/C++,
CMake is recommended. You can choose any IDE you like, but the code you submit must allow me (or the
grader) to compile and run from the terminal in Linux.
Program Directory: Please name your project folder as otp m123456, where otp is the name of this
project and m123456 is your UCID. The recommended directories of your program should be organized as
follows:
./ otp_m123456 / src
./ otp_m123456 / build
./ otp_m123456 / data
./ otp_m123456 / Readme . txt
Normally, folder src should include all the source files and your own header files, e.g., .cpp and .h files.
All the object files and executable files, e.g., .o files, should be under folder build. Folder data has all the
given files and data, and also includes all the files and results generated by the program. In Readme.txt
file, you should write a description of your code, show which language and version you use, and illustrate
how to compile, run and use your code.
3 Project Details
For ease of implementation, assume the security parameter (i.e., the length of the secret key) λ is fixed
for encryption and decryption, and it is 32 bits. The (default) secret key is
sk = 01010101101010101111000000001111
it should be stored in “../data/key.txt”.
2
A (default) plaintext is bear, and is stored in file “../data/plaintext.txt”. Each character in plaintext can be represented as an ASCII code (e.g., b ↔ 98), which can be further represented with 8 bits
(e.g., 98 ↔ 01100010).
1. Encryption Function:
(a) Read a secret key sk from file “../data/key.txt”, and read a plaintext m from
file “../data/plaintext.txt”;
(b) Represent plaintext m in binary, if its length is the same as the length of secret key sk, compute its
ciphertext using one-time pad, print the ciphertext in the terminal, and write this ciphertext (in binary)
to a file “../data/ciphertext.txt”;
(c) If the length of a plaintext is different from the length of secret key, return and display an error message
in the terminal (e.g.,“error: length is incorrect!”), and file “../data/ciphertext.txt” should
be an empty file in this case;
(d) Your encryption function should be able to encrypt any plaintext with four characters, e.g., eecs, cats,
bike, rice, etc.
2. Decryption Function:
(a) Read a secret key sk from file “../data/key.txt” and a ciphertext c from
file “../data/ciphertext.txt”;
(b) Decrypt this ciphertext c, output its plaintext, and write this plaintext (as a string, e.g., bear) to file
“../data/result.txt”. Similar as the encryption function, if the length of secret key is different from
the length of ciphertext, return and display an error message.
3. Key Generation Function:
(a) Given a security parameter λ as a command-line argument, where 1 ≤ λ ≤ 128, write a function to
randomly generate a secret key with λ bits, print this secret key in the terminal, and write this secret
key to file “../data/newkey.txt”.
4. (CS 6058 Only) Distribution of Keys:
(a) Given a security parameter λ = 3, repeat your key generation function for at least 5000 times. Record
all the unique 3-bit keys you program generated, calculate the frequency of each one, and prove that
those keys are (almost) uniformly distributed. You should have a function to automatically collect
this frequency distribution. In addition, you also need to evaluate the average running time of your
encryption function with λ = 128.
(b) You need to submit one-page report (in pdf) to explain and show your results in terms of key distribution
and encryption time. In your report, you should describe details of your implementation, such as OS,
programming language, crypto libraries, encryption parameters, etc. You can use tables, figures or
screenshots to help you present your results in your report. Please put this report under your project
folder and submit it together with your code.
4 Evaluation
Your project will be evaluated in three aspects.
1. Correctness of Functions (75%): Your program should be able to correctly run all the functions
described in this project. If for some reason, your code cannot be compiled but the logic of your code
is correct, you will still get partial credits.
3
2. Comments and Descriptions (15%): Write comments and explain each function in your code, such
as inputs, outputs, etc. You may need some of the functions in other projects. Detailed comments on
each function can save your time in other projects. In addition, please clearly explain how to compile
and run your code in Readme.txt.
3. Coding Style (10%): A good coding style is always important, especially for large projects. Please
keep each function simple, try to avoid long functions, and create multiple .h and .cpp files if needed.
For example, it is not a good idea to put everything in the main function.
5 Examples
This section provides some examples, which can help you understand the functions of your project.
Example 1: The following command calls the encryption function
otp enc ../ data / key . txt ../ data / plaintext . txt ../ data / ciphertext . txt
where otp is the name of your executable file, enc is argument for encryption function, ../data/key.txt is
the key file, ../data/plaintext.txt is the plaintext file, and ../data/ciphertext.txt is the ciphertext
file. Note that, depending on where your executable file is, the paths of your input and output files might
be different.
Example 2: The following command calls the decryption function
otp dec ../ data / key . txt ../ data / ciphertext . txt ../ data / result . txt
where the decryption of a ciphertext will be written to file ../data/result.txt.
Example 3: The following command calls the key generation function
otp keygen 100 ../ data / newkey . txt
where 100 is the length of a new key and this new key will be written to file ../data/newkey.txt.
