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Weak links in the Blockchain

One of the silliest things I've read yet about blockchain came out in Business Insider Australia last week. They said that the blockchain “in effect” lets the crowd police the monetary system.

In the rush to make bigger and grander claims for the disruptive potential of blockchain, too many commentators are neglecting the foundations. If they think blockchain is important, then it’s all the more important they understand what it does well, and what it just doesn’t do at all.

Blockchain has one very clever, very innovative trick: it polices the order of special events (namely Bitcoin spends) without needing a central authority. The main “security” that blockchain provides is nottamper resistance or inviolability per se -- you can get that any number of ways using standard cryptography -- but rather it’s the process for a big network of nodes to reach agreement on the state of a distributed ledger, especially the order of updates to the ledger.

To say blockchain is “more secure” is a non sequitur. Security claims need context.

  • If what matters is agreeing ‘democratically’ on the order of events in a decentralised public ledger, without any central authority, then blockchain makes sense.
  • But if you don't care about the order of events, then blockchain is probably irrelevant or, at best, heavily over-engineered.
  • And if you do care about the order of events (like stock transactions) but you have some central authority in your system (like a stock exchange), then blockchain is not only over-engineered, but its much-admired maths is compromised by efforts to scale it down, into private chains and the like, for the power of the original blockchain consensus algorithm lies in its vast network, and the Bitcoin rewards for the miners that power it.

A great thing about blockchain is the innovation it has inspired. But let’s remember that the blockchain (the one underpinning Bitcoin) has been around for just seven years, and its spinoffs are barely out of the lab. Analysts and journalists are bound to be burnt if they over-reach at this early stage.

The initiatives to build smaller, private or special purpose distributed ledgers, to get away from Bitcoin and payments, detract from the original innovation, in two important ways. Firstly, even if they replace the Bitcoin incentive for running the network (i.e. mining or “proof of work”) with some other economic model (like “proof of stake”), they compromise the tamper resistance of blockchain by shrinking the pool. And secondly, as soon as you fold some command and control back into the original utopia, blockchain’s raison d'etre is no longer clear, and its construction looks over-engineered.

Business journalists are supposed to be sceptical about technology, but many have apparently taken leave of their critical faculties, even talking up blockchain as a "trust machine". You don’t need to be a cryptographer to understand the essence of blockchain, you just have to be cautious with magic words like “open” and “decentralised”, and the old saw "trust". What do they really mean? Blockchain does things that not all applications really need, and it doesn't do what many apps do need, like access control and confidentiality.

Didn't we learn from PKI that technology doesn't confer trust? It's been claimed that putting land titles on the blockchain will prevent government corruption. To which I say, please heed Bruce Schneier, who said only amateurs hack computers; professional criminals hack people.

Posted in Security, Payments, Innovation, Blockchain, Trust

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