CPSC 430 Programming Assignments
Symmetric Key Encryption
Implement a Stream Cipher: Due Wednesday, Feb. 2
Write a program in the programming language of your
choice (available on cs - Java, C++, Python, PHP)
that encrypts each bit of
the plaintext by XORing it with a random bit generated
by an 8-bit linear feedback shift register with a tap
sequence of 7, 3, 0 (that is, it generates
the feedback bit by XORing bits at index 7, 3, and 0).
You must use bit
operations for your implementation.
Your program should read in an 8-bit key (a string of 0s and 1s)
that is the starting point for the LFSR and an arbitrary length
string of 0s and 1s for the plaintext. The program needs to
convert the strings to numeric values to perform the bit
Implement the LFSR as a class. The constructor should take
the key as a parameter. The class must provide a method
to compute and return the next bit in the random stream
(and change the state of the register).
Implement Simplified Data Encryption Standard (SDES):
Due Friday, Feb. 4
Write a program in the language of your choice (available on cs)
to implement the SDES algorithm as described in the handout.
Implement SDES in a class that provides methods for both
encryption and decryption. The class must have the following:
- A constructor that takes
a 10-bit key as a parameter. You may choose the format for
the parameter - a string, array,
or the representation as an integer - clearly DOCUMENT!!!).
The constructor must change the parameter to an int
for internal calculations.
- Public methods to encrypt and decrypt. These
take an 8-bit plaintext (or ciphertext as appropriate)
and return a string (or array representation of a string)
as the result. This should be clearly documented so the
calling program will know how to print the result.
- It must use bitwise operations for
all internal calculations (permutations, xor). There should
be ONE generic method to perform a permutation on the
bits in an int.
Test your program with a program that asks the user for
the key and asks if the user wants to encrypt or decrypt,
then asks for the 8-bit string to encrypt or decrypt.
Print the result.
Extra Credit: Add a feature to your test program that allows
it to take a string of characters to encrypt or decrypt.
- Document your program according to
- Tar the directory with your program and send the tar
file in an email.