A method for transmitting and analyzing at least one data stream comprising encrypted data packets, wherein the data stream is formed data stream-individually and encrypted data stream-individually by a transmitter according to a network protocol for encrypting and transmitting data streams, and information on the type of data packet is indicated in the network protocol for the key data packets, wherein a) the transmitter inserts data packets formed as key data packets into each formed and encrypted data stream, by means of which the data stream-individual key information for the respective data stream is transmitted to a data receiver corresponding to the network protocol via a network, b) in a monitoring unit which is connected to the network, the data stream is received and at least one key data packet in the respective data stream comprising key data packets is searched, and the data stream-individual key information is determined and transmitted to a decryption unit, c) using the data stream-individual key information, the associated encrypted data stream is decrypted by the decryption unit for diagnosis and/or analysis of the data stream, wherein either the type of data packet is defined or provided in the network protocol for the key data packets such that the key data packets are discarded by the data receiver corresponding to the network protocol if the data stream is received according to the network protocol or the key data packet is represented by a data packet which has the key information inserted into its header or extended header, the header information being formed such that the key information is discarded by the data receiver corresponding to the network protocol if the data stream is received according to the network protocol, wherein, by discarding the key data packets or the key information, it is ensured that the key information cannot be read by the data receiver corresponding to the network protocol. a) the transmitter inserts data packets formed as key data packets into each formed and encrypted data stream, by means of which the data stream-individual key information for the respective data stream is transmitted to a data receiver corresponding to the network protocol via a network, b) in a monitoring unit which is connected to the network, the data stream is received and at least one key data packet in the respective data stream comprising key data packets is searched, and the data stream-individual key information is determined and transmitted to a decryption unit, c) using the data stream-individual key information, the associated encrypted data stream is decrypted by the decryption unit for diagnosis and/or analysis of the data stream, wherein either the type of data packet is defined or provided in the network protocol for the key data packets such that the key data packets are discarded by the data receiver corresponding to the network protocol if the data stream is received according to the network protocol or the key data packet is represented by a data packet which has the key information inserted into its header or extended header, the header information being formed such that the key information is discarded by the data receiver corresponding to the network protocol if the data stream is received according to the network protocol, wherein, by discarding the key data packets or the key information, it is ensured that the key information cannot be read by the data receiver corresponding to the network protocol.