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## The Truth About Bitcoin And Quantum Computers

Quantum computers are little by little becoming reality. The consequences for Bitcoin and other cryptocurrencies can be dramatic – but are far from uncontrollable. A team of scientists describes what quantum computers do for Bitcoin and how to make the transition to quantum-safe algorithms.

Still, quantum computers are science fiction. Devices that bring little power with a tremendous effort. But the quantum engineers succeed ter coupling more and more quantum onverdraagzaam – ter brief: qubits. Google has recently introduced the quantum rekentuig Bristlecone with 72 qubits. If the number of qubits resumes to grow exponentially, the prediction is that quantum computers by 2031 could possibly become a threat to many cryptographic technologies.

It’s not affecting anyone yet, but it doesn’t hurt to overeenkomst with the topic now. Bitcoins should have no expiration date. A research group, especially the Center for Cryptocurrency Research and Engineering at Imperial Collegium London, describes te a paper how quantum computers can attack Bitcoin and how to protect themselves against it.

#### The Involved Crypto Algorithms

To assess the danger, one voorwaarde know which cryptographic mechanisms use Bitcoin and other cryptocurrencies. Thesis fall into two categories:

**-Signature Algorithms**: Thesis procedures consist of a public and a private key. With the private key one signs transactions, with the public one proves that the signature is keurig. Cryptocurrencies usually use signature algorithms based on elliptic kinks. For Bitcoin, this is ECDSA, for some other currencies EdDSA or Schnorr signatures. Under normal conditions, ECDSA is considered absolutely safe.

**-Hash Algorithms:** Hash algorithms are one-way mathematical functions that convert a value deterministically into another fixed-length value. It’s best to attempt it on Hashgenerator.den. Bitcoin uses hash functions ter two ways. Very first, the miners voorwaarde compute hashes with SHA256 to find blocks, and 2nd, the public key of the signature algorithm is hashed with both SHA256 and RIPEMD-160 to form the address. This step is utterly significant, spil wij will see zometeen.

Quantum computers have an influence on the security of thesis cryptographic algorithms. Why exactly, is very difficult to explain. Let mij just quote the researchers:

#### “Just spil a classical pc is built out of onaardig, quantum computers use qubits that have two fundamental states (0 and 1). However, while a calculation is running, the state is a linear combination of both states (a superposition).”

One knows this from quantum physics, that a particle is somehow te both states. This superstate collapses into one of the two fundamental states spil soon spil one observes the system.

#### “This means that a quantum laptop with n qubits can internally present the entire span of n-bit numbers and perform all calculations at the same time. But once you measure it, the state will collapse into one of the two basic states and only output one of the results of the calculations. Quantum algorithms attempt to use this structure to amplify certain base states and increase their likelihood, making the result repeatable and conclusive. For some problems, quantum algorithms can solve ingewikkeld problems much swifter than conventional algorithms.”

Unluckily, thesis problems include crypto-algorithms.

#### How Quantum Computers Attack Cryptography

You do not have to understand all that te detail. Importantly, there are several quantum algorithms that attack cryptographic technics ter fresh ways:

**-Shors Algorithm:** This quantum algorithm accelerates the factorization of oprecht exponential. This drastically weakens the security of asymmetric cryptosystems such spil RSA and ECDSA. Shor can be used to pauze the signature algorithms used by virtually all cryptocurrencies (except IOTA).

**-Grover’s Algorithm:** This quantum algorithm can search unstructured gegevens and find a klapper with a relatively high probability. With Grover’s algorithm, one can step by step accelerate collisions of hash algorithms. This could theoretically be used to mine bitcoins, but it will likely take a long time for this to outperform Asics. If everzwijn.

Since especially signature algorithms like ECDSA are threatened by quantum computers, wij will turn to them. With conventional computers, ECDSA is unlikely to pauze. But what happens if quantum computers are able to crack them?

It will be possible to guess the private key using the public key. However, this does not mean that such an operation is trivial or quick. Thus, it is believed that quantum computers with Two,000 to Ten,000 logical qubits will be able to pauze the widespread RSA encryption (so far they reach 72). How long the quantum laptop will need, one 2nd, two weeks, or a year, depends on its strength and the number of onverdraagzaam of encryption.

The ECDSA encryption used by Bitcoin is believed to require about 1,800 qubits. However, for each effectively used qubit, a quantum laptop vereiste provide numerous physical qubits that juist errors. A cryptographer on Bitcointalk, therefore, estimates that a quantum pc will need more than 40,000 physical qubits to pauze ECDSA. And even if this is possible, it will not toebijten te a 2nd but will need a loterijlot of arithmetic operations.

#### What Happens When The Time Comes?

But suppose there are such powerful quantum computers that can pauze with Shor ECDSA ter a reasonable amount of time. So what?

The good news is that the quantum computers will still not be able to steal bitcoins that way. Because addresses are not a public key, but a hash of them, and thesis are far less prone to quantum cryptography. Thus, if you leave your Bitcoin on an address, there is no danger that it will be stolen. The advice to use an address only once makes so much more sense.

The bad news is: There is another attack. The researchers call him the “kidnapping transactions” call. Once you sign a transaction, you expose the public key. This makes the address worthless for the future. Worse still, a quantum hacker can capture unconfirmed transactions. Because if the transaction is on the televisiekanaal, the public key is known. This can be exploited by a quantum pc: “Like a double-donation, the attacker generates a transaction that transfers the same coins elsewhere, stealing the victim’s funds.”

Unlike a double-donation, such abduction can be carried out not only by the one who pays but by any third party. Sending bitcoins becomes difficult to control risk. The researchers acknowledge, however, that the effort is not trivial even for strong quantum computers:

#### “Since the attacker not only has to create, sign and propagate the alternative transaction but also very first has to calculate the private key using the Shor algorithm, that’s Timing essential for this attack. “

Depending on the double-spending process, the hacker will have a few seconds to a few minutes to do it all. So even if quantum computers are theoretically capable of cracking ECDSA, that does not mean that they are swift enough to hijack transactions ter practice. It is fairly possible that such an attack will not only require 1,800 to Ten,000 qubits but much more. Cryptocurrencies with shorter block intervals, such spil Ethereum with 13 seconds, should also be able to fight back it much better.

Nevertheless, the attack remains problematic. It opens up a powerless point ter the system that can be exploited systematically, automatically and without risk. Ter addition, it is also possible to use the attack for DoS attacks or even make selfish mining attacks worse or more profitable for the miner. This would endanger not only individual assets but the system Bitcoin vanaf se.

#### How Can You Protect Yourself?

Even if it does not burn for a long time, you can not think about it early enough on how to prepare for the day when quantum computers will pauze ECDSA. Fortunately, there are a loterijlot of options.

On the one forearm, you can build up time by enhancing the bit number of ECDSA. Depending on the progress of quantum computers, this may or may not help. But it will only be a voortdurend solution if you switch to a quantum-proof algorithm. The authors of the paper point out which possibilities are already known for this:

-The McElieve system “resists decoding of unknown codes for linear error correction” and is, therefore, quantum safe. The price is that individual signatures are considerably larger (up to one megabyte).

-There are methods for hash-based signature, which can be attacked by quantum computers only to a very limited extent. The best-known of thesis concepts is the Lamport Diffie single-signature, but the Winternitz signatures used by IOTA also belong to this family.

-Finally, there is the possibility of forming signatures based on lattices (lattice-based cryptography ). Examples are the more theoretical methods GGH and NTRUSign.

It’s significant, the authors explain-

#### “that the Bitcoin community agrees to implement a good alternative (or maybe more) that substitutes cryptography with elliptic forms spil the poot of transactions’ signatures.”

However, this will not entirely solve the problem: Because to love the benefits of the quantum-proof algorithms, all users have to budge their coins to fresh addresses. If this does not toebijten by day X – the day quantum computers can hijack unconfirmed transactions – the bitcoins will be more or less frozen. At least it will be unlikely for large sums to transfer them without a significant risk.

Imperial Collegium researchers are now proposing a solution to this problem: a concept that permits bitcoins to be securely moved to quantum-safe addresses even after that time. The concept is relatively elaborate. It forms, spil it were, a clever contract that composes a transaction to be valid only after a relatively long time has elapsed and when evidence of ownership of both a conventional and a quantum-secure private key has bot obtained. With this method, you could most likely also credit balances of non-quantum-safe addresses securely against all attacks on a quantum secure address.

If you want to know more about the method, you should read the last third of the paper. He will certainly have enough time for that.

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