Method for authenticating a multicast message, with the following steps: (a) Calculation of an initialisation hash chain by a transmitter based on an anchor value of the transmitter and distribution of the last chain element of the initialisation hash chain as an initialisation function value to at least one receiver in an initialisation phase, wherein the at least one receiver is a field device; (b) Receipt of a multicast message (MC-N) by a receiver, which stores the received multicast message (MC-N); (c) Receipt of an authentication key release message from the transmitter by the receiver, wherein the authentication key release message contains a cryptographic authentication key released by the transmitter for the authentication of the stored multicast message (MC-N); (d) Calculation of a cryptographic function value h for the cryptographic authentication key contained in the authentication key release message by means of a predetermined cryptographic function by the receiver; (e) Comparison of the cryptographic function value h of the authentication key calculated by the receiver with the initialisation function value previously distributed by the transmitter to receivers in the initialisation phase for checking the validity of the cryptographic authentication key contained in the authentication key release message; and f) Authentication by the receiver of the multicast message (MC-N) originating from the transmitter stored in the receiver on the basis of the cryptographic authentication key recognised as valid; wherein in the initialisation phase the transmitter signs the initialisation function value (h n) with a private cryptographic key (K priv) and distributes it to receivers, which each verify the signature of the received initialisation function value (h n) by means of a public key (K pub), wherein, after successful verification of the signature, the initialisation function value (h n) is stored by the receiver for subsequent checking of the validity of the cryptographic key contained in an authentication key release message; wherein the cryptographic authentication key contained in the authentication key release message is a hash value which is formed by the chain element (h n-1) of the message protection hash chain preceding the hash value (h n) contained in the last preceding authentication key release message until such time as the anchor value of the message protection hash chain is reached; wherein the initialisation hash chain calculated in the initialisation phase by the transmitter on the basis of the anchor value of the transmitter is calculated by means of a hash function, the chain elements of which are provided for initialisation of further hash chains, especially of the message protection hash chain; wherein different multicast message types (MC-N-TYP) are provided, wherein the transmitter for each multicast message type, based in each case on an anchor value, calculates an associated message type hash chain by means of a predetermined hash function for the respective multicast message type (MC-N-TYP); wherein the different message type hash chains are calculated in each case on the basis of an anchor value provided by the initialisation hash chain, wherein the anchor value is formed by a chain element of the initialisation hash chain. (a) Calculation of an initialisation hash chain by a transmitter based on an anchor value of the transmitter and distribution of the last chain element of the initialisation hash chain as an initialisation function value to at least one receiver in an initialisation phase, wherein the at least one receiver is a field device; (b) Receipt of a multicast message (MC-N) by a receiver, which stores the received multicast message (MC-N); (c) Receipt of an authentication key release message from the transmitter by the receiver, wherein the authentication key release message contains a cryptographic authentication key released by the transmitter for the authentication of the stored multicast message (MC-N); (d) Calculation of a cryptographic function value h for the cryptographic authentication key contained in the authentication key release message by means of a predetermined cryptographic function by the receiver; (e) Comparison of the cryptographic function value h of the authentication key calculated by the receiver with the initialisation function value previously distributed by the transmitter to receivers in the initialisation phase for checking the validity of the cryptographic authentication key contained in the authentication key release message; and f) Authentication by the receiver of the multicast message (MC-N) originating from the transmitter stored in the receiver on the basis of the cryptographic authentication key recognised as valid;