Key Takeaways
Quantum computers could spark extraordinary technological developments but could also weaken most of our digital security infrastructure.
In theory, quantum computers might one day be able to break the cryptographic systems that protect cryptocurrencies and other important digital systems.
For now, quantum computers aren’t strong enough to crack Bitcoin wallets or affect mining, so current blockchains remain safe.
Many in the crypto world are already working on new security measures to stay ahead of potential quantum threats in the future.
Introduction
Quantum computers are powerful machines that use the principles of quantum mechanics to solve certain problems far more efficiently than conventional computers. While these machines remain mostly experimental, their eventual development could present new challenges to current digital security, including the cryptography used by Bitcoin and other cryptocurrencies.
This article explains how quantum computers differ from classical computers, the risks they pose to cryptocurrencies and digital infrastructure, and ongoing efforts to mitigate these future threats.
Asymmetric Cryptography and Internet Security
Asymmetric cryptography (also known as public-key cryptography or PKC) is a critical component of the cryptocurrency ecosystem and much of the Internet.
PKC uses a pair of keys: a private key, which must be kept secret, and a public key, which can be shared with others. In cryptocurrencies, users sign transactions with private keys, and anyone can verify the authenticity using the associated public key.
A PKC system relies on algorithms for generating key pairs. A good algorithm should generate keys in a way that makes it incredibly difficult to calculate the private key from the public key, but very easy to calculate the public key from the private key.
In other words, the PKC system depends on mathematical functions known as "trapdoor functions." These are easy to perform in one direction (for example, generating a public key from a private key), but computationally infeasible in the reverse direction (such as deriving a private key from a public key).
If you’d like to read more on the subject, check out Symmetric vs. Asymmetric Encryption.
Can Quantum Computers Break Crypto Wallets?
In theory, yes. Realistically, not yet. Modern algorithms used in crypto and internet security have robust trapdoor functions that aren’t “solvable” in a timeframe that would be feasible for any existing computer. It would take immense amounts of time for even the most powerful of machines to perform these computations (more on this below).
However, this might change in the future with the development of quantum computers. To understand why quantum computers are so powerful, let’s examine how regular computers work first.
Classical Computers
Classical computers process information using binary digits, or bits, which can be either 0 or 1. Complex computations are performed by breaking large problems into smaller tasks, and while modern systems can run certain operations in parallel, each bit still exists only in a state of either 0 or 1 (off or on).
Let’s look at guessing a cryptographic key as an example. For a 4-bit key, there are 16 possible combinations. A classical computer would need to try each combination one by one, as shown in the table below.
However, as the key length grows, the number of possible combinations grows exponentially. In the example above, adding an extra bit to increase the key length to 5 bits would result in 32 possible combinations. Increasing it to 6 bits would result in 64 possible combinations. At 256 bits, the number of possible combinations is close to the estimated number of atoms in the observable universe.
Notably, the speed of classical computers increases linearly, so exponential growth in keyspace far outpaces improvements in hardware. It’s estimated that it would take at least a thousand years for a classical computing system to guess a 55-bit key (roughly 36 quadrillion possible combinations).
For reference, the minimum recommended size for a seed used in Bitcoin is 128 bits, with many wallet implementations using 256 bits, making brute-force attacks by classical computers practically impossible.
Quantum Computers
Quantum computers use quantum bits, or qubits, which—unlike classical bits—can exist in a superposition of 0 and 1 simultaneously. This unique property, as well as quantum entanglement, allows quantum computers to process certain kinds of problems much more efficiently than classical machines.
Two of the most relevant quantum algorithms for cryptography are:
Shor’s Algorithm: Enables efficient factorization of large numbers and calculation of discrete logarithms, which could eventually compromise public-key cryptosystems like RSA and elliptic-curve cryptography (ECC), widely used in blockchain technology.
Grover’s Algorithm: Provides a quadratic speedup for searching and brute-forcing symmetric keys or hash values, but is less of a risk because its effects can be mitigated by simply doubling key sizes.
However, it’s important to correct a common misconception: quantum computers do not “try every combination at once.” Instead, they use interference and superposition to solve certain structured problems faster, but not all types of problems benefit equally from quantum speedups.
Currently, large-scale, fault-tolerant quantum computers required to threaten blockchain cryptography do not exist and are likely years or even decades away, according to most experts.
Quantum-Resistant Cryptography
The potential for quantum computers to break modern cryptography has driven significant research into new forms of “post-quantum” or quantum-resistant cryptography. These are cryptographic methods believed to be secure even in the presence of capable quantum adversaries.
Several types of post-quantum cryptography are being investigated, including:
Lattice-based cryptography
Hash-based cryptography
Multivariate polynomial cryptography
Code-based cryptography
International standardization bodies, like NIST, are actively working to identify and endorse these quantum-resistant algorithms so they can be widely deployed before large-scale quantum computers become a reality.
For symmetric cryptography, Grover’s algorithm halves the effective strength of keys. This means that, for example, AES-256 would provide 128 bits of security against a quantum attacker—still considered strong. Therefore, simply using longer keys can maintain security for symmetric encryption.
Another area of research is quantum key distribution (QKD), which can detect eavesdropping on key exchanges using quantum properties, although it is a separate field from blockchain cryptography and presents its own deployment challenges.
Quantum Computers and Bitcoin Mining
Bitcoin mining relies on solving cryptographic hash puzzles (using functions like SHA-256). Quantum computers can apply Grover’s algorithm for a quadratic speedup in searching for valid hashes. However, this is not nearly as powerful as the exponential speedup Shor's algorithm provides against public-key systems.
As a result, simply increasing the difficulty or length of hash functions could counteract quantum improvements in mining. Moreover, most researchers agree that quantum computing does not pose an imminent existential threat to Bitcoin mining.
It’s also worth noting that the effectiveness of quantum computers for mining is theoretical and, in practice, faces many real-world engineering challenges.
Transitioning to Quantum-Resistant Blockchains
Moving crypto networks to quantum-resistant algorithms will be a substantial effort. Updating protocols, wallets, and infrastructure will require global coordination and active user participation. Ensuring a smooth migration—possibly including hard or soft forks—will be technically and logistically complex but is considered essential for long-term security.
Importantly, public keys on the Bitcoin blockchain are only exposed after coins are spent from an address. Unspent addresses, therefore, are less immediately vulnerable to quantum attacks.
Closing Thoughts
Quantum computing is an active field with the potential to disrupt current digital security standards, including public-key cryptography systems used in Bitcoin and other cryptocurrencies. Still, practical quantum computers capable of breaking modern blockchains do not yet exist and are likely still years, if not decades, away.
The cryptocurrency industry and broader digital security communities are preparing for these future risks by developing and standardizing quantum-resistant algorithms. Although quantum computers do not currently pose an urgent risk to assets like Bitcoin, it’s worth keeping track of recent developments in the field.
Further Reading
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