Address space

This morning, I found myself thinking about address space. I'm learning about Bitcoin and other cryptocurrencies and it suddenly dawned on me that each coin has something called "address space". Address space is like the number of addresses that can be used for a particular purpose. Like a phone number, a Dewey Decimal, or a street address.

Consider Internet Protocol v 4, IPv4, for short. It was first deployed in 1983 and is a 32-bit address. That means it has 2 to the 32nd power of space, and 4,294,967,296 addresses are possible with this system. As some of you are probably aware, we have run out of address space for the IPv4. This has been augmented somewhat with private IP addresses for private networks, but the public addresses are effectively used up.

Long ago, in anticipation of the exhaustion of IPv4 addresses, engineers built IPv6. This is a 128-bit address protocol and provides for 7.9*10^28 times as many addresses as IPv4. The total number of available addresses is calculated to be 2^128, or 3.4 x 10^38. This is far more than enough for every person whoever lived to have multiple addresses for all of their devices.

All of you have a hard drive in your computer, some non-volatile storage device that will retain the information on it, even when the computer is turned off. Most of you are using NTFS for Windows and HFS+ for Mac. The maximum addressing space for Windows NTFS is about 16 exabytes (EiB). HFS+ allows for a maximum volume size of 8 EiB. An exabyte is one billion gigabytes.

Then there is ZFS, the Zettabyte File System. This is the file system for the next 30 years, as some have put it. The maximum file size is 16 EiB alone. The maximum volume size is 2^128 bytes. To put this in perspective, I read in a forum long ago, that to fully populate ZFS, every single atom in the earth would have to be used as an address space.

So this morning, I'm thinking about Bitcoin addressing. I remember looking at a Bitcoin app for my phone and I noted that it recommended creating a new address for every transaction. Hmm. Interesting. So what is the address space for Bitcoin? 2^160. That means we're never going to run out of addresses for the foreseeable future. You can basically throw away an address once you've moved your coins somewhere else, to another address.

All of this is recorded on the blockchain and the movement of funds can be tracked. But the addresses themselves are not really associated with an identity unless we want them to be.

While researching this article, I found an interesting discussion on the topic and someone pointed out that:

And if you're thinking what I think you're thinking, remember that you don't actually have to find their private key to claim someone else's bitcoins. All you have to do is find any one of the roughly 2^96 private keys whose corresponding public key hashes to that address.

But the actual number of addresses in use is a tiny fraction of the total available space, and the odds of you hitting upon an address that is actually in use, are astronomical. Smaller so, are the odds of hitting upon an address with real money in it.

I find it amazing that there is so much "imaginary space" in crypto currency. It's a huge pool of information and space to work with. And we're just getting started.