possible to use up ALL wallet address combinations?

[netrin]

If every particle in the known universe could create a billion addresses a second for the entire age of the universe, they would generate about one-quintillionth of the possible addresses.

Sorry JoelKatz. I know you mean to say "It's highly unlikely" (TM), but you're way overestimating the address space which is numerous orders of magnitude LESS than the number of atoms in the universe (what I think you mean by particle), so if every atom generated just ONE address, the vast majority of them would be expected to collide with others. In fact, unique values would be exceedingly rare.

Is it possible that some individual on the planet has a unique birthday?

The size of the 160 bit SHA-1 key space is in the same order of magnitude as the number of atoms in the Earth (~10^50)

This estimate is accurate to about one order of magnitude. If every atom of the Earth generated ONE address, then the chance of collision approaches 100% and only about half of all addresses would be expected to be unique.

[JoelKatz]

If every particle in the known universe could create a billion addresses a second for the entire age of the universe, they would generate about one-quintillionth of the possible addresses.

Sorry JoelKatz. I know you mean to say "It's highly unlikely" (TM), but you're way overestimating the address space which is numerous orders of magnitude LESS than the number of atoms in the universe (what I think you mean by particle), so if every atom generated just ONE address, the vast majority of them would be expected to collide with others. In fact, unique values would be exceedingly rare.

Ack! You're right. I confused powers of 10 with powers of 2.

In any event, creating a 160-bit hash collision is vastly easier than anything that would constitute an attack on bitcoin, and nobody's even close to doing that yet. And even if they did, we'd just respond by using the full 256-bit public key.

[netrin]

In any event, creating a 160-bit hash collision is vastly easier than anything that would constitute an attack on bitcoin, and nobody's even close to doing that yet. And even if they did, we'd just respond by using the full 256-bit public key.

Right. It's telling that we are arguing about the number of atoms in the universe, etc. A collision is simply not something we should be worrying about before disruptive technology such as quantum computing or the invalidation of mathematical theories established before Christ (Euclid 300 BCE).

In order for brute forcing a collision to be more profitable than generating a block, then the current target divided by the number of money-holding addresses (10M?) must be less than one, but it's currently something like 1594393648759678455702984006915721031668773442824246741.