So not impossible, you _just_ have to guess the owners private key?
Presumably you could in theory brute force that in a million years or whatever. Also if there were an example of data encrypted with that key (is there in the block chain by virtue of the protocol?) then if the private key system were broken - eg by advance in quantum computing or a weakness found in the crypto used - then perhaps it would then be feasible.
The corollary of this appears to be that you'd then be able to take anyone's bitcoins?
Presumably you could in theory brute force that in a million years or whatever. Also if there were an example of data encrypted with that key (is there in the block chain by virtue of the protocol?) then if the private key system were broken - eg by advance in quantum computing or a weakness found in the crypto used - then perhaps it would then be feasible.
The corollary of this appears to be that you'd then be able to take anyone's bitcoins?