Weak links in the blockchain: We're neglecting the foundations

Premature infatuation with blockchain overlooks security weaknesses in the platform that underlies Bitcoin digital currency.

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

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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 aspect that blockchain provides is not tamper resistance or inviolability per se; you can get those any number of ways using standard cryptography. 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. You see, the the power of the original blockchain consensus algorithm lies in its vast network, and the Bitcoin rewards for the miners that power it. Scale it down and you sacrifice inviolability.

For more in-depth analysis my report, "Blockchain: Understanding the Weak Links" reviews blockchain's special properties, provides practical advice for deploying digital ledgers, and soberly re-assesses blockchain's true disruptive potential.

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 spin-offs are barely out of the lab. Analysts and journalists are bound to be burned 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 (like permissioning) back into the original utopia, blockchain's raison d'etre is no longer clear, and it starts to look very costly for the marginal security increment.

Business journalists are supposed to be skeptical 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 that 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.

See also:

Resources

"Blockchain: Understanding the Weak Links" - This report highlights the weaknesses of Blockchain, the platform underlying Bitcoin digital currency

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