def cryptanalysis_affine(ciphertext):
# your code here
baseString = utilities_A4.get_baseString()
length = len(baseString)
dictList = utilities_A4.load_dictionary('engmix.txt')
sub_baseString = []
for j in range(25, length):
sub_baseString.append(baseString[:j + 1])
attempts = 0
for n_s in sub_baseString:
m_i_table = mod.mul_inv_table(len(n_s))
for mi in m_i_table[0]:
if m_i_table[1][mi] != 'NA':
for beta in range(len(n_s)):
k = [mi, beta]
key = (n_s, k)
plaintext = d_affine(ciphertext, key)
attempts += 1
if len(utilities_A4.remove_nonalpha(
plaintext)) < len(plaintext) / 2:
continue
if utilities_A4.is_plaintext(plaintext, dictList, 0.90):
print('key found after ' + str(attempts) + ' attempts')
return plaintext, key
return '', ''
def cryptanalysis_decimation(ciphertext):
text = utilities_A4.get_baseString()
text_len = len(text)
# num = [3,5,7,9,11,15,17,19,21,23,25]
# pas = []
attempts = 0
for x in range(26, len(text)):
testing_text = text[:x]
testing_len = len(testing_text)
for y in range(1,testing_len):
inv = mod.mul_inv(y,testing_len)
if inv != 'NA':
check = d_decimation(ciphertext,(testing_text,y))
attempts+=1
is_plain = utilities_A4.is_plaintext(check, utilities_A4.load_dictionary('engmix.txt'), 0.9)
if is_plain:
print("Key found after ", attempts, "attempts")
return check, (testing_text,y)
def cryptanalysis_decimation(ciphertext):
plaintext = ''
baseString = utilities_A4.get_baseString()
dictList = utilities_A4.load_dictionary('engmix.txt')
count = 0
for i in range(0, len(baseString) - 26 + 1):
base = baseString[:26 + i]
table = mod.mul_inv_table(26 + i)
for x in table[1]:
if x != 'NA':
key = (base, table[0][x])
plaintext = d_decimation(ciphertext, key)
count += 1
if utilities_A4.is_plaintext(plaintext.lower(), dictList, 0.9):
print("Key found after:", count, "attemps")
return plaintext, key[1]
return '', ''
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