Practical Cryptology - Hill Cipher
Cryptanalysis Programming Lab
Option 1 (100 points) Write a program that reads two strings -
ciphertext and
the partial plaintext and finds the key matrix and the complete plaintext using the
known plaintext cryptanalysis technique that we learned in class and the decryption
part of your Part 1 program.
You can assume that the ciphertext was obtained by encrypting plaintext
using Hill Cipher with 2X2 matrix.
You can assume that the ciphertext
is
a string of UPPER CASE letters and the plaintext is the string of LOWER
CASE letters.
You can assume that there are no other characters in the
input strings.
Simplification: you can assume that the maximal length of the known
plaintext is 10 character. This simplification will result in 5 points
reduction.
Your program must print the following:
- Matrix B
for each two pairs that you are trying at the current moment and the
determinant
of B.
- The message that tells if you continue to the next pair (since the
determinant was not relatively prime with 26) or this pair is good for the
following step
- The final printout should include:
- the matrix B that gave you a
successful determinant (relatively prime with 26),
- the determinant of B,
- the
inverse of B
- the final key matrix A.
- The final plaintext(use Part 1 decryption)
All these intermediate prints and final output will help you to test your
program.
Also, pay attention, it could be the situation that the plaintext
input is
not sufficient to find the key matrix (for example, if the plaintext is MONDAY
and ciphertext is SELUKE).
Your program must print the
appropriate message in this case. You can test your program for this case
on MONDAY and SELUKE as plaintext and ciphertext.
Due Day: Frfiday, October 27