Question

Please write functions to decrypt both the shift (Caesar) and linear ciphers.

Also, answer the questions in Python and show how it typed and ran inside the client. The def is what to start with

1) Write a function called decrypt that accepts three numbers (c, m, and k) and returns the corresponding plaintext (p) value as a number. You can assume the modulus (n) is 256. You will need to compute the multiplicative inverse of m mod 256 to decipher c.

# Problem 1: Decrypt a single value
def decrypt(c, m, k):

2) Write a function called decryptstring that accepts a ciphertext byte string, a multiplier (m), and shift amount (k). It returns an array of integers containing the decrypted values. For example, decryptstring(b'\xa7J##\x80', 31, 15) should return [104, 101, 108, 108, 111].

# Problem 2: Decrypt a byte string into an array of ints
def decryptstring(ciphertext, m, k):

3)Finally, write a function called lineardecipher that accepts a ciphertext byte string, a multiplier (m), and a shift amount (k). It returns the corresponding plaintext byte string.

# Problem 3: Decrypt a byte string, returning a byte string
def lineardecipher(ciphertext, m, k):

Answer 1

PYTHON PROGRAM:

def decrypt(c, m, k):
ciphertext = c * m
plaintext = (ciphertext**k)%256
return plaintext

def decryptstring(ciphertext, m, k):
list = []
for i in range(0, len(ciphertext)):
list[i] = decrypt(ciphertext[i], m, k)
return list

def lineardecipher(ciphertext, m, k):
text = "";
for i in range(0, len(ciphertext)):
text += decrypt(ciphertext[i], m, k)
return text