Abstract: A blockchain system according to an embodiment of the present disclosure includes a generation logic, a mining logic, and a change logic. The generation logic generates a cipher-type transaction including a transaction number, a transaction type, an index, a signature for the index, an address of a sender, a cipher text, metadata, a first signature value, and a second signature value. The mining logic generates a block based on a hash function for the cipher-type transaction. The change logic receives the change transaction generated by a user based on the change plain text, and changes the transaction after verification of the change transaction is completed.