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(e.g. payments), as the blockchain increases in sizewith each block. It is therefore difficult for many new users to join a blockchain at short notice.With the current broadband and storage capacities, participation is therefore difficult, especially for private individuals, or involves great demands on the technical infrastructure. Ultimately, this also limits the lifetimeof a blockchain if the expansion ofmemory andnetworkspeed is laggingbehind the resource requirementsofablockchain, and thus successive nodeswill disappear, since for instance the expensive hardware is no longer affordable. Concerning the transactions, there are two noticeable features in particular: on theonehand, the actual transactionmust alsobe signedand synchronised,which is why a blockchain has a significantly lower performance about the speed of the transactionscompared toaclassicdatabase,whichonlystores thefinal state andnot the entire transaction history as does a blockchain. It should bementioned, how- ever, that the difficulty of capacity and confirmation delays is an increasingly less weighty argument against the blockchain,mainly due to the lighting network.4On theotherhand, revising transactions isvirtually impossible—the stabilitypostulated above as an advantage is thus also a weakness. This applies in particular to public-permissionless blockchains (see the following subchapter, in particular, Table 1); in blockchainswith a restricted consensus, thismay be possible because the group of validators is clearly defined and they can decide on a rollback by majority vote (Baumann et al. 2017). The above-mentioned advantageous trans- parencyensures, especially in the caseofpublic blockchains, that everyonecanuse the public key to view the transaction history—i.e. income, expenses and prices— via an explorer, which is not desirable for every potential participant and is therefore disadvantageous at the same time. This is particularly relevant for auto- mated big data analyses, for example, regarding systematics of transaction flows. An additional problem is access to the blockchain: if a user loses the private key required forvalidation,healso loses irretrievableaccess tohiswallet and thus to the blockchain (Dasu et al. 2018). While this problemmainly affects individual par- ticipants, another problem arises on a collective level: if the actors involved in a blockchain do not have a consensus on the future of a blockchain project since the majority decision process can sometimes be difficult for actors unknown to each otherdue toa lackof trust (which iswhymajorityvoting isbothanadvantageanda disadvantage), it can lead to the so-called forks, i.e. to splits and thus fragmentation of one and the sameblockchain. This can lead to uncertainty amongusers, as they may then no longer knowwhich blockchain is the one with the more promising future. Another difficulty can be the integration of a blockchain into existing IT 4This is a protocol that allows scaling, especially of theBitcoinblockchain, although the idea also seems to be applicable to other blockchains: here, the concept is that after a start signal, the so-called funding transaction, transactionsmadewithinachannel, arenot stored in theblockchain. This results in a relief and thus potential scalability. After each payment, the current account balance is temporarily stored in the so-called commitment transaction andall transactions areonly written to the blockchainwhen one of the participants closes the channelwith afinalising signal, the so-called settlement transaction (Sixt 2017). Blockchain as an Approach for Secure Data… 109