How A Bigger Blockchain Is Less Secure And Why Block Size Ain’t Gonna Increase Any Time Soon

Just last night, our good friends over at Qntra posted Gavin Andresen Proposes Scalability Roadmap and Hardfork. I enjoyed the article and took it upon myself to call out Teh Lead Derp of Teh Bitcoin Fundation scammers on my second favouritei channel for doing so, Twitter:

https://twitter.com/pete_d/status/519364709451968512

When Andresen finally rolled out of bed and read his Notifications this morning, he chimed in on the comments section of Qntra’s article, saying:

Gavin Andresen says:
Nobody is proposing an infinite block size.

This is lulzy first and intentionally malicious second. Why lulzy? Because that’s exactly what Gavin is proposing. Why intentionally malicious? What’s so bad about the USG’s proposal to make the block size bigger because “it’s good for Bitcoin and just as safe” when in fact the opposite is true on both counts? Well, let’s pick apart their naïve little argument and explore its entrails. Therein we will find truth. Let’s let MP kick it off:

Consider the simple problem of a blockchain with infinite block size and zero block reward. Is its security then zero ? Consider the reverse problem, of a blockchain with zero block size. Is its security then infinite ? Consider a finite block size and infinite block reward (disregarding 2ndary effects). Is the security also infinite ? Consider the case of oil supply halving. Does price double or explode ? So that’s what it is. The only way Bitcoin has a future is through the block size remaining limited. Bitcoin is not here to serve the poor. Fuck them. That’s what Bitcoin means.

In essence, the security of the Bitcoin network is ensured by mining as represented by the hashrate. The more petahashes the network maintains, the more secure the network is to attacks, that is, the more costly attacks become.ii Think of the hashrate as the height of the walls around a fortified city. When Bitcoin first started out, its walls were small enough that a 5-year-old could walk over them. That is, it would’ve cost a trivial amount of computing power, and therefore money, to take over the network. Today, of course, the walls of the Bitcoin network are Babylonesque and the cost of taking over the network can no longer be calculated in worthless government trademarks.

However, in this consideration of security as wall height, we must also take into account the size of the area we’re protecting, which, in Bitcoin terms, is what the Blockchain amounts to. Clearly, a city the size of Tokyo (6,993 sq km) would be vastly more expensive to build continuous fortified walls around than Singapore (479 sq km), at a given height. And we can’t ignore the concave non-linearities at work here either. Just imagine the difference in the size of the base of a wall when comparing a 30 metre wall vs. a 5 metre wall.iii Just think how hard it was to build a wall that could keep the Mongolians out of China.

Building taller walls, that is, making the city more secure against mauraders and would-be invaders, isn’t just a little bit more expensive for larger cities, it’s a lot more expensive. As the city grows, there’s an undeniable cost to breaking down some of the exterior walls and rebuilding them to encompass a larger land area. That’s a cost borne by those who build the walls. If an additional cost can’t be borne by the builders, nor additional taxes levied on the citizens, and the expansion in the city’s footprint is to increase regardless, then bricks and stones from the tops of walls in other parts of the city must be reused to build the new walls, resulting in shorter walls all the way around. Thus, as shorter walls are easier to attack, the city has grown at the expense of security.

To bring this into relevant (Bitcoin) terms, the size of the city is the Blockchain and the height of its walls is the network’s hashrate. As such, the larger the Blockchain, the more hashpower is required to maintain the same level of security. Larger things are inherently more fragile and are therefore exponentially more resource intensive to protect from the forces of nature. This is why Mircea Popescu and the rest of The Bitcoin Lordship will roll over in their fucking graves before letting Gavin increase the block size. Mark MP‘s words here:

The problem with Gavin’s idiocy is that roughly speaking, the square of the block size and the total network hash are on opposite sides of an equality, which describes total network security. So basically, he’s proposing significant downstepping of current blockchain security. Neither of these are getting merged into bitcoin, Whatever Gavin says or whatever forks happen. If indeed they’re stupid enough to fork it, I will sink their fork on the open market. And if that’s the path they wish to use to introduce faux Bitcoin-lite for the US domestic market, that’s fine, but it won’t go over any better than an attempt from scratch. “We” know what bitcoin is and why we’re using it.

With Bitcoin’s Blockchain, now well over 20 GBiv the task faced in securing its perimeter is growing, which is why ASICs came just in the nick of time to protect Bitcoin from Andresen et al. Hashes were our salvation and they weren’t a moment too soon.

The biggest challenge ahead isn’t “bringing Bitcoin to the people” or some such nonsense, it’s in maintaining a sufficient number of nodes to relay and verify transactions. This is challenging issue that has yet to be fully addressed.v

But hey, we need something to do in 2015 once all the derps are dead, y’know?

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  1. This blog is #1.↩
  2. While there are various types of possible attacks, the most significant is the “51% attack,” wherein a pool of mining power gains the ability to double-spend bitcoins.↩
  3. Or just look at the size of the base of the Burj Khalifa vs. your average 15-story apartment building.↩
  4. And nearly triple what it was a year ago.↩
  5. And it’s one that further affirms the need to keep blocks small.↩