@qtip2001/

Hill Cipher

Python

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  • main.py
  • common-passwords.txt
  • passwords-v4.txt
main.py
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# Quentin Bishop
# 22 Oct 2018

def prepare_string(s, alphabet):
  s = s.upper()
  k = list(s)
  for char in k:
    if char not in alphabet:
      k.remove(char)
  return "".join(k).upper().replace(" ", "")

def c2i(c, alphabet):
  if c in alphabet:
    return alphabet.index(c)
  else:
    print("Error")

def i2c(i, alphabet):
  return alphabet[i]

def mod_inverse(a, m):
  for x in range(m):
    if (x*a)%m == 1:
      return x
  return -1

def matrix_inverse(matrix, mod):
  det = matrix[0]*matrix[3] - matrix[1]*matrix[2]
  inv = mod_inverse(det, mod)
  if inv == -1:
    #return [-1, -1, -1, -1]
    #print("Error")
    return 0
  else:
    new_mat = [None, None, None, None]
    new_mat[0] = ( inv * matrix[3]) % mod
    new_mat[2] = (-inv * matrix[2]) % mod
    new_mat[1] = (-inv * matrix[1]) % mod
    new_mat[3] = ( inv * matrix[0]) % mod
    return new_mat

def mult_2x1(matrix1, matrix2, mod):
  new_mat = [None, None]
  new_mat[0] = (matrix1[0]*matrix2[0]+matrix1[1]*matrix2[1]) % mod
  new_mat[1] = (matrix1[2]*matrix2[0]+matrix1[3]*matrix2[1]) % mod
  return new_mat

def mult_2x2(matrix1, matrix2, mod):
  new_mat = [None, None, None, None]
  new_mat[0] = (matrix1[0]*matrix2[0]+matrix1[1]*matrix2[2]) % mod
  new_mat[1] = (matrix1[0]*matrix2[1]+matrix1[1]*matrix2[3]) % mod
  new_mat[2] = (matrix1[2]*matrix2[0]+matrix1[3]*matrix2[2]) % mod
  new_mat[3] = (matrix1[2]*matrix2[1]+matrix1[3]*matrix2[3]) % mod
  return new_mat

def hill_encode(plaintext, matrix, mod, alphabet):
  if len(plaintext)%2 == 1:
    plaintext = plaintext+"X"
  encoded = []
  for x in range(0, int(len(plaintext)/2)):
    d = [c2i(plaintext[2*x], alphabet), c2i(plaintext[2*x+1], alphabet)]
    k = mult_2x1(matrix, d, mod)
    encoded.append(i2c(k[0], alphabet))
    encoded.append(i2c(k[1], alphabet))
  return "".join(encoded)

def hill_decode(ciphertext, matrix, mod, alphabet):
  inv = matrix_inverse(matrix, mod)
  if inv == 0:
    return 0
  decoded = []
  for x in range(0, int(len(ciphertext)/2)):
    d = [c2i(ciphertext[2*x], alphabet), c2i(ciphertext[2*x+1], alphabet)]
    k = mult_2x1(inv, d, mod)
    decoded.append(i2c(k[0], alphabet))
    decoded.append(i2c(k[1], alphabet))
  return "".join(decoded)

def determine_mat(plain, cipher, mod, alphabet):
  matrix = [c2i(plain[0], alphabet),c2i(plain[2], alphabet),c2i(plain[1], alphabet),c2i(plain[3], alphabet)]
  answer = [c2i(cipher[0], alphabet),c2i(cipher[2], alphabet),c2i(cipher[1], alphabet),c2i(cipher[3], alphabet)]
  mi = matrix_inverse(matrix, mod)
  if mi == 0:
    return 0
  return mult_2x2(answer, mi, mod)

alpha = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz.!?, ':"
cipher = "JYnbMGhQXyUo?OAUuCtwWFPNckxtjsANHeJ.uyCFDSMGZvuCvKJYnbMGhQXyUo?Of!'',BAI.G'd''Z.SpvHfqz:erXy'GWFHWeoTfNXZ:yqcSfteWPBPQUowF"

m = determine_mat("help", "okay", len(alpha), alpha)
#print(m)
#print(hill_decode("okay", m, len(alpha), alpha))
#print(hill_encode(cipher, [27,13,5,14],len(alpha),alpha))
print(matrix_inverse([2,5,3,20], 256))

'''alphabet = ""
for x in range(33, 94):
  alphabet = alphabet + chr(x)

users = {}
common = []

pss = open("passwords-v4.txt","r")
for line in pss.readlines():
  line = line.strip()
  (w1,w2) = line.split()
  users[w1] = w2
pss.close()

com = open("common-passwords.txt")
for line in com.readlines():
  line = line.strip()
  common.append(line.upper())
com.close()

matrices = []
best = []'''

'''for a in users:
  print(a)
  for b in common:
    if len(b) > 4:
      y = determine_mat(b,users[a],len(alphabet),alphabet)
      if y != 0:
        x = hill_decode(users[a], y, len(alphabet), alphabet)
        if x != 0:
          if x.startswith(b):
          #print(x)
            #print(x)
            if y in matrices:
              best.append(y)
              print(x)
            matrices.append(y)'''

'''for x in best:
  print(x)
  for a in users:
    print(hill_decode(users[a],x,len(alphabet), alphabet))'''


'''for b in mx:
  q = input()
  print(b)
  for a in users:
    print(hill_decode(users[a],  b,  len(alphabet), alphabet))'''

'''for a in users:
  x = hill_decode(users[a], [32, 17, 27, 13], len(alphabet),alphabet)
  print(a,x)'''