Blockchain with transaction cancellation

A blockchain management device comprising:

• a communication interface arranged to receive transactions for recording in a blockchain, and
• a processor circuit configured to:
• apply a symmetric hash function over multiple transactions received over the communication interface thus obtaining a hash value, the symmetric hash function being arranged to produce a same hash value for the multiple transactions independent from an order in which the multiple transactions are arranged,
• generate a consensus proof over at least the hash value,
• assemble a new block for inclusion in the blockchain, the new block comprising at least the multiple transactions, the consensus proof, and a reference to a preceding block on the blockchain, and
• distribute the new block to at least one further blockchain management device over the communication interface;
• wherein the processor circuit is arranged to:
• determine that a transaction received over the communication interface is a cancellation request which requests cancellation of a transaction recorded in a block of the blockchain, said transaction being identified in the cancellation request,
• determine from the cancellation request a prior block on the blockchain which comprises the transaction which is to be cancelled, and
• generate from the prior block a replacement block, said replacement block comprising the consensus proof and the multiple transactions from the prior block, wherein the ordering of the multiple transactions in the replacement block differs from the ordering of the multiple transactions in the prior block indicating the cancellation of the transaction identified in the cancellation request;
• wherein the processor circuit is further arranged to:
• include in the new block a cancellation transaction indicating the replacement of the prior block with the replacement block, and
• distribute the replacement block to the at least one further blockchain management device over the communication interface.