In a communications system supporting the exchange of messages, a method for authenticating messages, comprising: having a message sender send a message to be authenticated to a signature generator entity in the communications system; having the signature generator entity generate a signature with respect to the received message, the signature being dependent on the message sender; having the signature generator entity send back to the message sender an authenticated message, the authenticated message including the generated signature; having the message sender forward the authenticated message to a message recipient; having the message recipient send the received message to a signature verifier entity in the communications system; having the signature verifier entity verify the validity of the signature, and notifying the message recipient of an outcome of the validity verification.