The document discusses various ways to double spend in Bitcoin, including outsourcing the double spend to miners, initiating a mining race by paying miners higher fees, and using a "feather fork" where a miner with 20% of the hash power blacklists a target address to censor transactions. It also notes criticisms of these approaches and their potential consequences.

1. Bitcoin doesn’t work in theory.
Who cares?
Arvind Narayanan
Princeton University

3. How to outsource a double spend
Joseph Bonneau

4. How to outsource a double spend
...
...
→ Miner0: 25
Attacker → A: x
...
...
→ Miner1: 25
...
...
→ Minerk: 25
×6
Attacker → B: x
...
...
→ Miner1: 25
1. pay miners to mine here
2. profit!
I’ll pay 26 for blocks
on this fork!
buy a load of mining ASICS
win a mining race
3. profit?

5. Feather fork (Andrew Miller)
I have 20% of hashpower I’m blacklisting address X
I will consider transactions with input X invalid
I won’t mine on top of blocks that include such tx’s
But if such a TX has two confirmations I’ll accept it
Whatevs
We heard you the first time
You’re just hurting yourself
Wait… shit. You might just be
To maximize your revenue you’d better blacklist X too crazy enough to really do it

11. Joseph Bonneau Ed Felten Arvind Narayanan Andrew Miller

12. Moving past spherical cows