It scarcely qualifies as easy, but scientists have found a factorization method that may one day spoil the RSA cryptosystem. This method assumes that, one day, physicists will be able to build a quantum computer—a computer that, unlike the computers of today, would work not according to the digital logic we are used to, but would rely on quantum mechanical principles to carry out a huge number of operations simultaneously, that is, in parallel. The laws of quantum physics would make these computers behave very differently from classical ones. A circuit in a classical computer is either on or off, representing a bit of data that is either 1 or 0. But in a quantum computer, the particles can exist in many states at once; or in the language used by view of some physicists, they exist in many different universes. In effect, all those computers in the parallel universes could be put to work factoring large numbers very quickly—a boon for codebreakers.

The catch is that it will be formidably difficult to make a quantum computer. At present, no one knows how to control large numbers of subatomic particles with sufficient precision. According to even the most optimistic estimates, quantum computers are still decades away.

But supposing a quantum computer does someday become a reality, does that mean that no secrets will ever be safe again? Hardly. Other public-key algorithms use different “one-way functions” that are not known to be reversible by a quantum computer. Presumably one of these would step into the breach if RSA lost its luster. But more fundamentally, if physicists learn to control quantum states well enough to build a computer, they will also be able to control them well enough to create a new kind of cryptosystem. This “quantum cryptography” has already been demonstrated in principle. Thanks to the Heisenberg Uncertainty Principle, which says that just observing a particle alters its state, any eavesdropper reading a specially quantum-encrypted message would alter the message, thereby alerting both sender and receiver that the message had been tampered with.

Whatever the future may bring, cryptography has moved past the era of clever gadgets, into an era when the security of encoded messages will be protected by the most fundamental principles in science—either the structure of our number system or the subatomic architecture of our universe. The more we can learn to decode nature’s secrets, it seems, the better we will be able to guard our own.