I wondered how Mike kept the keys erased. He was stopped by US department maybe the US state has access to private keys. It's just my thought. Maybe someone has better information
Here ya go
Do you keep a copy of the private key? Who has had access to the private keys?
A. I did not keep the private keys, and I am the only person who has ever had control over the private keys. I have either inserted the private keys into the coins myself, or have directly supervised others doing the same. On the series 1 coins, the hologram manufacturer pre-printed the addresses onto the hologram labels, but they were only given the 8 characters you see, not the private keys themselves.