A YouTube interview with Adam Back discussing early security curiosity (a master PIN sequence), his interest in cryptography and hash functions (birthday collision), and how those ideas plus running an anonymous remailer led to creating Hashcash as an anti-spam proof-of-work. The conversation also touches on Bitcoin’s layered understandability and Back’s satellite projects to broadcast/receive Bitcoin in space.
I have a kind of security mindset. So I'd noticed that the university had some PIN codes on some of the doors. And I realized that this code is a four digit code. But basically there was no, like, button to press enter to let you in. You know, if the code was 2, 3, 4, 5, it would let you in whether you typed 1, 2, 3, 4, 5 or whether you typed 23, 45, say. So it occurred to me there would be a kind of master code, like a single long sequence that included all permutations of four digits. So I wrote a bit of software to create this and printed out on a single sheet of paper about two thirds of a sheet. And I tested it on another door that I wasn't supposed to have access to, and it worked. I got into the room.
What was this room you got into? I've been trying to. You wanted to discover.
Well, it was a kind of research lab with some parallel computers in it that was accessible to postdocs or something.
Are we rolling, Gaz? Yeah, good to go. Okay, fantastic. Let's play some Jenga.
I'm not sure what the rules are because it's like when I played it.
As a kid, I think it was you were only supposed to use one hand or finger. And then there were certain things about, you know, not doing the easy blocks, but I literally went for one of the easiest blocks straight away. Okay, so let's jump to hash cash. Was there an aha moment during this process, or was it a long, arduous process similar to picking a lock?
I was interested in cryptography, so I happen to have been reading about hash functions and the birthday collision. It's from the phenomena that if you have a room full of people at a party or something, there's a question which is how many people need to be in the room before there's a 50, 50 chance that there are two people with the same birthday? You know, you think, well, it's got to be related to 365. That's the number of days. But actually it's a lot smaller. It's like 23 people or something counterintuitive. 23? Yeah. So it's so low. It's because people are like pulling a dice out of a bag or something. Right. So they got random birthdays, and as you get more of them, there are more potential birthdays for them to collide with. Right. So overall, it ends up being a lot less than you'd expect. So anyway, with hash functions, like, you.
Can take your time here. Oh, wow.
Okay. That's there? No, I'm not sure that one's going to go. Yeah. Ok, we've got one more left. There you go. So I was reading about hash functions in this birthday collision. The hash functions were. There are much more permutations than the number of birthdays, obviously. Right. So there's trillions and trillions of permutations. But it did occur to me that if you found such a collision almost computationally impossible at the time, particularly, you could instantly prove it to anybody. They could instantly verify this enormous amount of work. And then I was also running a remailer, which is a way to have privacy for email, and there were people spamming through it, which was a nuisance. And because it's related to anonymity, you couldn't block their IP address or email and stuff like that. Right. So I was trying to think about a way to solve this spam problem that didn't involve blocking IP addresses. So those two ideas came together and so that's where has cache came from.
Oh, that looks risque.
There you go.
Pressure's on. Okay.
When people see a finished system like hashcache, it looks kind of simple and elegant, right? You're like, ah, oh, it's pretty simple. I can understand that. And then their intuition is, you know, I could have built that. People were trying to make electronic cache systems from hashcash from after that, like 1997, 1998 and so on. But it was quite hard to do. They didn't get implemented because they weren't fully decentralizable. And, you know, as bitcoin came to adopt it done by a massive amount of computers in 10 minutes. And that's obviously a much higher amount of work.
I held my breath there.
One of the nice things about Bitcoin is it's understandable at lots of different levels. Right. You can understand it from a user level or from an economics level. It's surprisingly complex to fully appreciate all of it, including the game theory and things like that.
Obviously you're very busy with satellite projects putting bitcoin in space. Why do we need bitcoin in space?
There's a few reasons. One is because it's cool and you can.
Why do anything, right?
Yeah, sure.
No shit.
Oop.
I mean, I expect to lose there with the man that is, you know, building blocks better than most people.
And another is that you get some kind of privacy because the receiving is anonymous. Yeah, just more bitcoin.
More bitcoin, more blocks.
Sam.
