It's not impossible, it just really compromises security. For example all legal encryption could use a master key, or both hardware and software could be subver

It's not impossible, it just really compromises security. For example all legal encryption could use a master key, or both hardware and software could be subverted to make truly secure processes impossible. These things are a Bad Thing but perfectly possible, they just preclude anything being reasonably secure. The drafters of the bill clearly don't fully understand or care about those issues though, and if they did they'd probably see it as an acceptable compromise to security in order to enable government to see all communications.