Photo 1: Photograph of a chip constructed by D-Wave Systems Inc., mounted and wire-bonded ter a sample holder. The D-Wave processor is designed to use 128 superconducting logic elements that exhibit controllable and tunable coupling to perform operations.
Quantum computers are making an increasingly rapid transition from chalkboard fantasy to commercial reality. A few months ago, wij discovered from the Snowden leaks that the NSA is attempting to construct the world’s very first useful quantum rekentuig. D-Wave, a company interested te developing quantum rekentuig hardware for commercial use, has sold several prototypes, one to Google, of a quantum-machine that, while not a total rekentuig, may be capable of solving certain classes of problems much swifter than conventional rekentuig hardware.
Ter order to understand why this is significant, you have to understand what a quantum rekentuig is. Thesis machines, only a few very trivial prototypes of which have everzwijn bot built, are systems that permit certain kinds of mathematical problems to be solved enormously quicker than regular computers.
Photo Two: The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers.
Te pc science, there’s a critically significant idea called “computational complexity.” The key insight of computational complexity is that, if you have a rekentuig solving a problem, doubling the speed of a rekentuig doesn’t permit you to solve problems that are twice spil hard ter the same amount of time. Some problems become more complicated with extra gegevens points, at a rate greater than 1:1. Some problems, te fact, become exponentially more ingewikkeld spil you increase the size of the gegevens set you’re working on (an example is the problem of finding the shortest route among a set of points on a opbergmap, which becomes intractable with only a few hundred points). Quantum computers, by exploiting the capability of subatomic particles to be ter more than one state at the same time, can investigate numerous possible solutions at one, making some previously intractable problems solvable.
This has profound implications for cryptographic algorithms, which rely on the fact that the mathematical problems that need to be solved to pauze them would take billions of years to solve using conventional computers. Many of the cryptographic algorithms presently ter use (including staples like RSA) have known quantum algorithms that quickly crack them. Wij don’t have computers capable of running those algorithms yet, but once wij do, anyone still using those cryptographic schemes will find themselves vulnerable.
For a long time, it wasgoed believed that elliptic curve cryptography, the cryptosystem that provides digital signatures for Bitcoin, might be immune to quantum attacks. Unluckily, wij now know that this is not the case: a quantum algorithm has bot found that permits private keys to be quickly computed from known public keys.
At very first glance, this might show up to be a death deep-throat for Bitcoin – spil soon spil your public key is known, any attacker with a quantum laptop could deduce your private key, and transfer your Bitcoins to themselves. However, the situation is not fairly spil grim spil it might very first show up:
When you send a transaction to the Bitcoin network, the recipient of a transaction is concealed behind a hash: only the hash of their public key is actually disclosed to the network. This is because cryptographic hash functions are immune to quantum attacks. This means that attackers can’t simply go sniffing around robbing every wallet that Bitcoins are everzwijn sent to. They have to wait for a transaction to be made from a wallet (an operation that discloses the public key ter total). That means that wallets are still secure, provided they’re one-time-use-only. Spil soon spil you spend money from your Bitcoin wallet, you would have to instantly also transfer the remainder to a fresh, secret wallet, and repeat for each subsequent transaction. This process could be automated (and brain wallets could still be used, by generating your key pairs by hashing together your passphrase with a nonce that increments with each transaction to generate a fresh one-time-wallet). This is, however, at least a little inconvenient. Any publicly posted Bitcoin wallet would have to be updated each time the user attempted to empty it, and the idea of an offline Bitcoin addressbook becomes unlikely. Still, under thesis conditions, Bitcoin would most likely remain useable.
There may be other solutions, spil well. Wij are aware of several cryptographic schemes that are most likely not vulnerable to quantum attacks, and if wij had sufficient warning that Bitcoin wasgoed about to become vulnerable, wij can imagine creating a “Bitcoin 2” using a mature version of one of thesis schemes, and using proof-of-burn to transfer Bitcoin holdings into the fresh money. However, this is a ways off, and may not be practical at all, depending on the details of how quantum computers succesnummer the market.
If wij’re fortunate, wij will have enough warning for people to switch overheen to one-time-use wallet software, and generally prepare for the quantum apocalypse well enough to avoid major economic fallout. If wij’re unlucky, quantum computers will arrive ter a petite number of malicious forearms before wij’ve truly had enough time to decently evaluate the threat, and the resulting fright selling will crash the market, causing fine wailing and gnashing of teeth. Time will tell which script is more likely, but it’s very likely worthwhile for the Bitcoin developer community to start creating the contraptions wij’ll need sooner, rather than straks.