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solution_A4.py
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solution_A4.py
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# --------------------------
# Name: Jiayao Pang ID: 194174300
# CP460 (Fall 2019)
# Assignment 4
# --------------------------
import math
import string
import mod
import matrix
import utilities_A4
# ---------------------------------
# Q1: Modular Arithmetic Library #
# ---------------------------------
# solution is available in mod.py
# ---------------------------------
# Q2: Decimation Cipher #
# ---------------------------------
# -----------------------------------------------------------
# Parameters: plaintext (str)
# key (str,int)
# Return: ciphertext (str)
# Description: Encryption using Decimation Cipher
# key is tuple (baseString,k)
# Does not encrypt characters not in baseString
# Case of letters should be preserved
# Errors: if key has no multiplicative inverse -->
# print error msg and return empty string
# -----------------------------------------------------------
def e_decimation(plaintext, key):
# your code here
if not isinstance(key, tuple):
print('Error (e_decimation): Invalid key')
return ''
if not isinstance(key[0], str) or not isinstance(key[1], int):
print('Error (e_decimation): Invalid key')
return ''
baseString = key[0]
m = len(baseString)
k = key[1]
if not mod.has_mul_inv(k, m):
print('Error (e_decimation): Invalid key')
return ''
ciphertext = ''
for p in plaintext:
if p.lower() in baseString:
x = baseString.index(p.lower())
y = mod.residue(k * x, m)
cipherChar = baseString[y]
ciphertext += cipherChar.upper() if p.isupper() else cipherChar
else:
ciphertext += p
return ciphertext
# -----------------------------------------------------------
# Parameters: ciphertext (str)
# key (str,int)
# Return: plaintext (str)
# Description: Decryption using Decimation Cipher
# key is tuple (baseString,k)
# Does not decrypt characters not in baseString
# Case of letters should be preserved
# Errors: if key has no multiplicative inverse -->
# print error msg and return empty string
# -----------------------------------------------------------
def d_decimation(ciphertext, key):
# your code here
if not isinstance(key, tuple):
print('Error (d_decimation): Invalid key')
return ''
if not isinstance(key[0], str) or not isinstance(key[1], int):
print('Error (d_decimation): Invalid key')
return ''
baseString = key[0]
m = len(baseString)
k = key[1]
if not mod.has_mul_inv(k, m):
print('Error (d_decimation): Invalid key')
return ''
m_i_k = mod.mul_inv(k, m)
plaintext = ''
for c in ciphertext:
if c.lower() in baseString:
y = baseString.index(c.lower())
x = mod.residue(m_i_k * y, m)
plainChar = baseString[x]
plaintext += plainChar.upper() if c.isupper() else plainChar
else:
plaintext += c
return plaintext
# -----------------------------------------------------------
# Parameters: ciphertext (str)
# Return: plaintext,key
# Description: Cryptanalysis of Decimation Cipher
# -----------------------------------------------------------
def cryptanalysis_decimation(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':
plaintext = d_decimation(ciphertext, (n_s, mi))
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, (n_s, mi)
return '', ''
# ---------------------------------
# Q3: Affine Cipher #
# ---------------------------------
# -----------------------------------------------------------
# Parameters: plaintext (str)
# key (str,[int,int])
# Return: ciphertext (str)
# Description: Encryption using Affine Cipher
# key is tuple (baseString,[alpha,beta])
# Does not encrypt characters not in baseString
# Case of letters should be preserved
# Errors: if key can not be used for decryption
# print error msg and return empty string
# -----------------------------------------------------------
def e_affine(plaintext, key):
# your code here
if not isinstance(key, tuple):
print('Error (e_affine): Invalid key')
return ''
if not isinstance(key[0], str) or not isinstance(key[1], list):
print('Error (e_affine): Invalid key')
return ''
if not isinstance(key[1][0], int) or not isinstance(key[1][1], int):
print('Error (e_affine): Invalid key')
return ''
baseString = key[0]
m = len(baseString)
alpha = key[1][0]
beta = key[1][1]
if not mod.has_mul_inv(alpha, m):
print('Error (e_affine): Invalid key')
return ''
ciphertext = ''
for p in plaintext:
if p.lower() in baseString:
x = baseString.index(p.lower())
y = mod.residue(alpha * x + beta, m)
cipherChar = baseString[y]
ciphertext += cipherChar.upper() if p.isupper() else cipherChar
else:
ciphertext += p
return ciphertext
# -----------------------------------------------------------
# Parameters: ciphertext (str)
# key (str,[int,int])
# Return: plaintext (str)
# Description: Decryption using Affine Cipher
# key is tuple (baseString,[alpha,beta])
# Does not decrypt characters not in baseString
# Case of letters should be preserved
# Errors: if key can not be used for decryption
# print error msg and return empty string
# -----------------------------------------------------------
def d_affine(ciphertext, key):
# your code here
if not isinstance(key, tuple):
print('Error (e_affine): Invalid key')
return ''
if not isinstance(key[0], str) or not isinstance(key[1], list):
print('Error (e_affine): Invalid key')
return ''
if not isinstance(key[1][0], int) or not isinstance(key[1][1], int):
print('Error (e_affine): Invalid key')
return ''
baseString = key[0]
m = len(baseString)
alpha = key[1][0]
beta = key[1][1]
if not mod.has_mul_inv(alpha, m):
print('Error (e_affine): Invalid key')
return ''
m_i_alpha = mod.mul_inv(alpha, m)
plaintext = ''
for c in ciphertext:
if c.lower() in baseString:
y = baseString.index(c.lower())
x = mod.residue((y - beta) * m_i_alpha, m)
plainChar = baseString[x]
plaintext += plainChar.upper() if c.isupper() else plainChar
else:
plaintext += c
return plaintext
# -----------------------------------------------------------
# Parameters: ciphertext (str)
# Return: plaintext,key
# Description: Cryptanalysis of Affine Cipher
# -----------------------------------------------------------
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 '', ''
# ---------------------------------
# Q4: Matrix Library #
# ---------------------------------
# solution is available in matrix.py
# ---------------------------------
# Q5: Hill Cipher #
# ---------------------------------
# -----------------------------------------------------------
# Parameters: plaintext (str)
# key (str)
# Return: ciphertext (str)
# Description: Encryption using Hill Cipher, 2x2 (mod 26)
# key is a string consisting of 4 characters
# if key is too short, make it a running key
# if key is too long, use first 4 characters
# Encrypts only alphabet
# Case of characters can be ignored --> cipher is upper case
# If necessary pad with 'Q'
# Errors: if key is not inveritble or if plaintext is empty
# print error msg and return empty string
# -----------------------------------------------------------
def e_hill(plaintext, key):
# your code here
if len(plaintext) == 0:
print('Error(e_hill): invalid plaintext')
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(e_hill): key is not invertible')
return ''
ciphertext = ''
non_alpha = utilities_A4.get_nonalpha(plaintext)
blocks = utilities_A4.text_to_blocks(utilities_A4.remove_nonalpha(plaintext), 2)
while len(blocks[-1]) != 2:
blocks[-1] += 'Q'
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(key_matrix, block_m), 26)
ciphertext += baseString[result_m[0][0]].upper()
ciphertext += baseString[result_m[1][0]].upper()
ciphertext = utilities_A4.insert_nonalpha(ciphertext, non_alpha)
return ciphertext
# -----------------------------------------------------------
# Parameters: ciphertext (str)
# key (str)
# Return: plaintext (str)
# Description: Decryption using Hill Cipher, 2x2 (mod 26)
# key is a string consisting of 4 characters
# if key is too short, make it a running key
# if key is too long, use first 4 characters
# Decrypts only alphabet
# Case of characters can be ignored --> plain is lower case
# Remove padding of q's
# Errors: if key is not inveritble or if ciphertext is empty
# print error msg and return empty string
# -----------------------------------------------------------
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