docs: def decrypt_cbc_cts(self, data, init_vector):
      """
      Return an iterator that decrypts `data` using the Cipher-Block Chaining
      with Ciphertext Stealing (CBC-CTS) mode of operation.
      
      CBC-CTS mode can only operate on `data` that is greater than 8 bytes in
      length.
      
      Each iteration, except the last, always returns a block-sized :obj:`bytes`
      object (i.e. 8 bytes). The last iteration may return a :obj:`bytes` object
      with a length less than the block-size, if `data` is not a multiple of the
      block-size in length.
      
      `data` should be a :obj:`bytes`-like object that is greater than 8 bytes in
      length.
      If it is not, a :exc:`ValueError` exception is raised.
      
      `init_vector` is the initialization vector and should be a
      :obj:`bytes`-like object with exactly 8 bytes.
      If it is not, a :exc:`ValueError` exception is raised.
      """
      data_len = len(data)
      if data_len <= 8:
        raise ValueError("data is not greater than 8 bytes in length")
      
      S1, S2, S3, S4 = self.S
      P = self.P
      
      u4_1_pack = self._u4_1_pack
      u1_4_unpack = self._u1_4_unpack
      u4_2_pack = self._u4_2_pack
      u4_2_unpack = self._u4_2_unpack
      decrypt = self._decrypt
      
      try:
        prev_cipher_L, prev_cipher_R = u4_2_unpack(init_vector)
      except struct_error:
        raise ValueError("initialization vector is not 8 bytes in length")
        
      extra_bytes = data_len % 8
      last_block_stop_i = data_len - extra_bytes
      last_block_start_i = last_block_stop_i - 8
      
      for cipher_L, cipher_R in self._u4_2_iter_unpack(
        data[0:last_block_start_i]
      ):
        L, R = decrypt(
          cipher_L, cipher_R,
          P, S1, S2, S3, S4,
          u4_1_pack, u1_4_unpack
        )
        yield u4_2_pack(L ^ prev_cipher_L, R ^ prev_cipher_R)
        prev_cipher_L = cipher_L
        prev_cipher_R = cipher_R
      
      cipher_L, cipher_R = u4_2_unpack(data[last_block_start_i:last_block_stop_i])
      L, R = decrypt(
        cipher_L, cipher_R,
        P, S1, S2, S3, S4,
        u4_1_pack, u1_4_unpack
      )
      
      C_L, C_R = u4_2_unpack(data[last_block_stop_i:] + bytes(8 - extra_bytes))
      
      Xn = u4_2_pack(L ^ C_L, R ^ C_R)
      
      E_L, E_R = u4_2_unpack(data[last_block_stop_i:] + Xn[extra_bytes:])
      L, R = decrypt(
        E_L, E_R,
        P, S1, S2, S3, S4,
        u4_1_pack, u1_4_unpack
      )
      yield u4_2_pack(L ^ prev_cipher_L, R ^ prev_cipher_R)
       
      yield Xn[:extra_bytes]