栅栏密码(Fence crypto)

# write by 2021/8/5
# 栅栏密码
def encrypt_fence(string, key):
   ciphertext = ""
   temp = []
   for i in range(key):
       temp.append("")
   for index, i in enumerate(string):
       temp[index % key] += i
   # print("".join(temp))
   ciphertext = "".join(temp)
   return ciphertext
def decrypt_fence(string, key):
   plaintext = ""
   length = len(string)
   min_row = length // key
   max_num = length % key
   temp = []
   index = 0
   for i in range(key):
       if i < max_num:
           temp.append(string[index:index+min_row+1])
           index += min_row + 1
       else:
           temp.append(string[index:index+min_row])
           index += min_row
   # print(temp)
   for i in range(length):
       plaintext += temp[i % key][i // key]
   return plaintext
if __name__ == '__main__':
   key_ = 4
   ciphertext_ = encrypt_fence("i will beat you this day", key_)
   plaintext_ = decrypt_fence(ciphertext_, key_)
   print(f"{plaintext_} : {ciphertext_}")