> Programmable blockchains allow generalized applications requiring decentralized trust. Yeah, they don't really though. They allow a few extremely specific ap

> Programmable blockchains allow generalized applications requiring decentralized trust. Yeah, they don't really though. They allow a few extremely specific applications requiring decentralized trust. The trust guarantees only hold if no single party can, even momentarily, control more hashing power than was collectively used to generate the last X blocks, where X is number of updates made since the data you want to tamper with was inserted. To put it in concrete terms, pretend we have a blockchain for publishing PGP keys, and that your public key is 10 blocks down in the chain. If I want to maliciously replace your key with one of my own then all I need to do is rent a few dozen servers off of AWS for a day or two and use them to generate a modified chain that has my key instead of yours in the 11th block down and then rehash all ten blocks spending slightly more compute power each time than the original committers did. The network will recognize my fork as the authoritative one because it's got more proof of work. That's expensive, but it's certainly not infeasible. This trust mechanism works out for cryptocurrencies because their only value is monetary. That means that people are incentivized to set up mining rigs to spend a lot of real resources on mining because they automatically get compensated. It also means that there's a bounded maximum amount of effort that a rational actor will spend to tamper with the chain, because there's a finite limit on the available profit to be gained. Neither of these are true for PGP keys. Publishing a secure update to a PGP key database is not, in and of itself, a profit generating enterprise, meaning fewer miners and far less resources spent per mining rig. And the potential upside of successfully tampering with the right key is enormous. The actual mechanism which produces the security guarantees in blockchains isn't cryptographic, it's economic. Tampering with a cryptocurrency's blockchain isn't actually impossible, or even difficult, it's just by definition more expensive than it's worth. When you try and move to an application other than financial assets the economics break down, the security guarantees go out the window, and all you're left with is an extremely inefficient git clone.