Abstract: A method for selective data use and/or data provision between a first and a second participant. An attack path to the first participant is determined by the first participant, which attack path has a first feasibility rating indicating the difficulty of the attack path and for which there is a security assumption about the second participant that, if not established, enables the attack path to the first participant. At least one attack path to the second participant is determined by the second participant, which attack path has a second feasibility rating indicating the difficulty of the attack path and breaches the security assumption. A risk function is determined by the first and/or the second participant. The first and/or the second participant, according to the risk value, provides data to the relevant other participant and/or uses data from the relevant other participant.

Abstract: A method for the digital signing of a message by a sender of the message. A check value based on a symmetrical key pair is ascertained using a secret key as part of a symmetrical key pair and the message. A digital signature is ascertained using a private key as part of an asymmetrical key pair and the check value. The digital signature is provided for transmission, to a method for checking a received, digitally signed message by a receiver.

Abstract: A method for the digital signing of a message by a sender of the message. A check value based on a symmetrical key pair is ascertained using a secret key as part of a symmetrical key pair and the message. A digital signature is ascertained using a private key as part of an asymmetrical key pair and the check value. The digital signature is provided for transmission, to a method for checking a received, digitally signed message by a receiver.