stronaut on a mission somewhere in the Solar System (meaning several light-hours away). We may conceive of the system represented by the two envelopes altogether forming the entangled superposition IB) = (|cat) A |dog) B + |dog) A |cat) B) where only the qubit (X = A, B) is accessible and measurable by Alice (A) or Bob (B). The outcome of either measurement is equally likely to be cat or dog. Alice may wait until Bob receives his envelope to open hers, or alternatively she may decide to do it beforehand, hours ahead or just a few minutes before. Opening her envelope, Alice finds the dog! Then she gets the instant knowledge that Bob will find, or has already found, the cat. And this despite the need for the information to propagate for several hours through space. It may well be that Alice and Bob perform their openings at the same universal time. They both instantly know who has the cat and who has the dog, without exchanging information. This is an illustration of the principle of nonlocality of the combined system. But it took Bob's envelope to travel at (somewhere under) the speed of light to reach him, therefore, putting physical limit to the information flow from Alice to Bob, which is consistent with relativity. Classical and quantum cryptography magic. This is where quantum error correction (Chapter 24) may come to the rescue, but as an additional burden to an approach otherwise presumed to be fairly straightforward in implementation. It is important to recall here that error-correction in the quantum domain requires fully operational quantum-gate circuits with qubit dimensions of seven to nine in the quantum channel (as applicable to BB84, B92). Other techniques have been proposed to purify, distil, or swap EPR pairs, making it possible to expand the channel reach in the presence of quantum noise. Such considerations illustrate that it is theoretically possible to implement both local and nonlocal QKD algorithms at global scales, but at the expense of increased complexity in quantum processing and gate ci