In overview, a computer-implemented method of transmitting data in a data stream from a first device to a second device is disclosed. The data stream is encrypted before transmission from the first device to the second device, and a location of the data in the data stream is indicated to the second device. The location may be a pre-shared location between the first and second devices, or the first device may transmit the location of the data to the second device. The second device decrypts the encrypted data stream, identifies the data in the data stream based on the location, and encrypts the identified data in the data stream.