def d_hill(ciphertext, key):
# your code here
if len(ciphertext) == 0:
print('Error(d_hill): invalid ciphertext')
return ''
new_key = ''
if len(key) > 4:
new_key += key[:4]
elif len(key) == 4:
new_key += key
else:
new_key += key
counter = 0
while len(new_key) < 4:
new_key += key[counter]
counter += 1
baseString = utilities_A4.get_lower()
key_matrix = matrix.new_matrix(2, 2, 0)
count = 0
for i in range(2):
for j in range(2):
key_matrix[i][j] = baseString.index(new_key[count].lower())
count += 1
if mod.gcd(matrix.det(key_matrix), 26) != 1:
print('Error(d_hill): key is not invertible')
return ''
inverse_key_matrix = matrix.inverse(key_matrix, 26)
plaintext = ''
non_alpha = utilities_A4.get_nonalpha(ciphertext)
blocks = utilities_A4.text_to_blocks(
utilities_A4.remove_nonalpha(ciphertext), 2)
for block in blocks:
block_m = matrix.new_matrix(2, 1, 0)
block_m[0][0] = baseString.index(block[0].lower())
block_m[1][0] = baseString.index(block[1].lower())
result_m = matrix.matrix_mod(matrix.mul(inverse_key_matrix, block_m),
26)
plaintext += baseString[result_m[0][0]].lower()
plaintext += baseString[result_m[1][0]].lower()
plaintext = utilities_A4.insert_nonalpha(plaintext, non_alpha)
while plaintext[-1] == 'q':
plaintext = plaintext[:-1]
return plaintext
def test_q3():
print("-------------------------------------------")
print("Testing Q3: Affine Cipher")
print()
alphabet = utilities_A4.get_lower()
baseStr = alphabet
k = [5, 8]
plaintext = 'AFFINE CIPHER'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
ciphertext = solution_A4.e_affine(plaintext, key)
print('ciphertext= ', ciphertext)
plaintext2 = solution_A4.d_affine(ciphertext, key)
print('plaintext2= ', plaintext2)
print()
baseStr = alphabet + ' ?!'
k = [45, 3]
plaintext = 'Is mission accomplished?'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
ciphertext = solution_A4.e_affine(plaintext, key)
print('ciphertext= ', ciphertext)
plaintext2 = solution_A4.d_affine(ciphertext, key)
print('plaintext2= ', plaintext2)
print()
baseStr = alphabet + ' ?!.'
k = [10, 19]
plaintext = 'Plan B ... initiated'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
print('ciphertext= ', end='')
solution_A4.e_affine(plaintext, key)
print('plaintext2= ', end='')
solution_A4.d_affine(plaintext, key)
print()
print('Testing cryptanalysis:')
plaintext = 'There are two kinds of cryptography in this world: cryptography that will stop your kid sister '
plaintext += 'from reading your files, and cryptography that will stop major governments from reading your files.'
baseString = utilities_A4.get_baseString()[:26]
key = (baseString, [3, 9])
ciphertext = solution_A4.e_affine(plaintext, key)
plaintext, key = solution_A4.cryptanalysis_affine(ciphertext)
if plaintext != '':
print('Key found = ', key)
print('plaintext = ', plaintext)
print()
baseString = utilities_A4.get_baseString()[:27]
key = (baseString, [17, 11])
ciphertext = solution_A4.e_affine(plaintext, key)
plaintext, key = solution_A4.cryptanalysis_affine(ciphertext)
if plaintext != '':
print('Key found = ', key)
print('plaintext = ', plaintext)
print("-------------------------------------------")
print()
return
def test_q2():
print("-------------------------------------------")
print("Testing Q2: Decimation Cipher")
print()
alphabet = utilities_A4.get_lower()
baseStr = alphabet
k = 5
plaintext = 'Strike in progress'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
ciphertext = solution_A4.e_decimation(plaintext, key)
print('ciphertext= ', ciphertext)
plaintext2 = solution_A4.d_decimation(ciphertext, key)
print('plaintext2= ', plaintext2)
print()
baseStr = alphabet + ' ?!'
k = 46
plaintext = 'Is mission accomplished?'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
ciphertext = solution_A4.e_decimation(plaintext, key)
print('ciphertext= ', ciphertext)
plaintext2 = solution_A4.d_decimation(ciphertext, key)
print('plaintext2= ', plaintext2)
print()
baseStr = alphabet + ' ?!.'
k = 10
plaintext = 'Plan B ... initiated'
key = (baseStr, k)
print('key = ', key)
print('plaintext = ', plaintext)
print('ciphertext= ', end='')
solution_A4.e_decimation(plaintext, key)
print('plaintext2= ', end='')
solution_A4.d_decimation(plaintext, key)
print()
print('Testing cryptanalysis:')
ciphertext = 'Mrhoyu on xhsehumm'
plaintext, key = solution_A4.cryptanalysis_decimation(ciphertext)
if plaintext != '':
print('Key found = ', key)
print('plaintext = ', plaintext)
print()
plaintext = 'There are two kinds of cryptography in this world: cryptography that will stop your kid sister '
plaintext += 'from reading your files, and cryptography that will stop major governments from reading your files.'
baseString = utilities_A4.get_baseString()[:35]
key = (baseString, 33)
ciphertext = solution_A4.e_decimation(plaintext, key)
plaintext, key = solution_A4.cryptanalysis_decimation(ciphertext)
if plaintext != '':
print('Key found = ', key)
print('plaintext = ', plaintext)
print("-------------------------------------------")
print()
return