I think accessing private keys of all bitcoin address is quite impossible as to access private key of even one bitcoin address will take lots of computing power and very long time may be even a lifetime period. There is some fear regarding supercomputers and quantum computers which are still a dream and yet to find actual working prototype so i don't think this is possible and will be possible even for next decades.
I didn't meant for a single Address
I meant he generate all the private keys which are possible and then search them using the addresses .
Isn't that correct