Patent ID: 8787569

Claim:
A method for securing communication of components inside a self-service automat that are connected to each other by a bus system, with a transmitter and a receiver, comprising: exchanging data as tuples (C, A, R, N, Z) between the transmitter and the receiver on a transport layer of the bus system, wherein C are message data M encrypted with an encryption key, A are message data M authenticated with an authentication key, R represents a participant role of a component on the bus system of active or passive participants, N represents a message counter, and Z represents a session counter, determining while transmitting from the transmitter to the receiver, whether Z is less than a maximum session number Z max ; determining whether N is less than a maximum message number N max ; comparing a tuple ({circumflex over (Z)},{circumflex over (N)}) to a tuple ( Z , N ), wherein {circumflex over (Z)} is a session number for Δ-last messages, {circumflex over (N)} is a message number for Δ-last messages, {circumflex over (Z)} is a last session counter, and N is a last message counter; generating, based on the comparing, an error if more than Δ messages have been lost: decrypting message data, based on the comparing, if not more than Δ messages have been lost; upon decrypting the message data, authenticating the message data; decrypting the message data based on a K dec R and C, wherein K dec R is a result of a key generation procedure using a common key K; comparing A to an authentication value A′ at the receiver, wherein A′ is determined based on K ver R , N, the decrypted message data, and |C|, wherein K ver R is a result of a key generation procedure using a common key K; and authenticating the decrypted message data, based on the comparing of A to A′, if A is equal to A′.