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Is Bitcoin Quantum Resistant?

As quantum computing advances, Bitcoin faces potential risks to its cryptographic foundations. Explore how superposition, Shor’s Algorithm, and post-quantum cryptography shape the future of Bitcoin security—and the steps being taken to safeguard against quantum threats.

Andrea Carnimeo

07 Dec 2024 • 8 min read

As Bitcoin's value continues to rise over the decades, so does a looming concern shared by millions of hodlers—one that even the most ardent self-custody advocates can't ignore: the threat of quantum computing. But what exactly is quantum computing, and is Bitcoin prepared to withstand it?

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Quantum resistance refers to the ability of cryptographic protocols to remain secure even when faced with powerful quantum computers capable of executing algorithms like Shor's and Grover's, which threaten conventional cryptographic methods. Bitcoin’s reliance on specific cryptographic techniques means its vulnerability to quantum attacks varies depending on the protocol in question.

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What Is Quantum Computing?

Quantum computing represents a groundbreaking evolution in computing technology, leveraging the principles of quantum mechanics to perform certain computations significantly faster than traditional computers. Unlike classical computers that process information as binary bits (0s or 1s), quantum computers utilize qubits, which can exist in superpositions of states, enabling them to handle complex calculations with remarkable efficiency.

Classical Bit VS. Qubit — Classical Bit vs Qubit

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In simple terms, superposition means that a qubit, unlike a classical bit, can be in a combination of both 0 and 1 at the same time. For instance, a qubit might be 30% in the state of "0" and 70% in the state of "1". It’s like if you were flipping a coin, and while it’s spinning, it’s both heads and tails at once—only when you catch it does it land on one outcome. This ability to be in multiple states at once gives quantum computers a huge advantage in processing complex information much faster than classical computers.

This innovation introduces a dual-edged sword for cryptographic systems like Bitcoin. While it opens up incredible opportunities for advancements in computation, it also presents potential risks to the cryptographic foundations underpinning Bitcoin's security.

Bitcoin's Quantum Weaknesses

Quantum computers pose a significant risk to Bitcoin due to their potential to undermine the cryptographic principles securing its network. Here’s a breakdown of Bitcoin’s vulnerabilities, organized by the cryptographic protocols it employs:

Public-Key Cryptography: A Core Vulnerability

Classical Algorithm vs Shor’s Quantum Algorithm

Bitcoin’s security relies heavily on the infeasibility of deriving private keys from public keys using classical computers. However, quantum computers equipped with Shor’s Algorithm could drastically reduce this computational difficulty.

Current Security: Deriving private keys requires 21282^{128}2128 operations—a scale infeasible for classical supercomputers.
Quantum Threat: Shor’s Algorithm could reduce this to 2832^{83}283 operations, bringing key derivation within reach of sufficiently advanced quantum machines.
At Risk: Public keys exposed in Bitcoin transactions become particularly vulnerable, enabling quantum attackers to forge signatures and steal funds.

Symmetric Cryptography: More Resilient but Not Immune

Bitcoin also employs symmetric cryptography, which is comparatively more resistant to quantum attacks. Algorithms like SHA-256 and SHA-256d are central to Bitcoin’s proof-of-work (algorithm used in mining) and address generation.

Current Security: Brute-force attacks on SHA-256 require 22562^{256}2256 operations, ensuring strong resistance against classical attackers.
Quantum Threat: Using Grover’s Algorithm, quantum computers could reduce the effort to 21282^{128}2128, halving the effective security strength.
Mitigation: Transitioning to stronger algorithms like SHA-512, which provides a security level of 256 bits even after Grover’s Algorithm, could offset this risk.

Elliptic Curve Cryptography (ECDSA and Schnorr Signatures)

Bitcoin's digital signatures rely on ECDSA (Elliptic Curve Digital Signature Algorithm) and, more recently, Schnorr signatures. These cryptographic methods ensure transaction authenticity but are highly vulnerable to quantum attacks.

Current Security: ECDSA’s security comes from the discrete logarithm problem, which classical computers cannot solve efficiently.
Quantum Threat: Shor’s Algorithm could efficiently solve this problem, rendering ECDSA completely insecure. Public keys exposed in Bitcoin transactions would allow attackers to derive private keys.
At Risk: Both ECDSA and Schnorr signatures would fail against quantum adversaries due to their shared elliptic curve foundation.
Mitigation: Post-quantum alternatives like lattice-based cryptography offer potential solutions, though their larger key and signature sizes could increase transaction costs and storage demands.

Lightning Network Encryption

The Lightning Network (LN), which enables fast off-chain transactions, relies on the Noise Protocol Framework for encryption.

Current Security: The framework secures communication between nodes but depends on classical cryptographic primitives, including ECDSA.
Quantum Threat: Historical communications could be retroactively decrypted by quantum attackers, exposing sensitive LN data.
Mitigation: Incorporating post-quantum cryptographic methods, such as the NewHope key exchange mechanism, could protect the Lightning Network in future upgrades.

The Gradual Threat of Quantum Computing

Quantum computers capable of breaking current cryptographic standards remain theoretical but are under active development. Progress in quantum computing capacity and reliability is expected to be incremental, meaning Bitcoin’s cryptographic security will degrade over time rather than suddenly failing. This gradual progression—from infeasible to practical attacks—provides the Bitcoin ecosystem with a critical advantage: time.

The Role of Post-Quantum Cryptography

Post-quantum cryptography (PQC) refers to cryptographic algorithms designed to be secure against both classical and quantum computing attacks. Examples include lattice-based cryptography, hash-based signatures, and code-based cryptography. These methods typically come with trade-offs, such as increased computational requirements, larger key sizes, or longer signature lengths.

Bitcoin developers and researchers are monitoring advances in quantum computing and post-quantum cryptography. By adopting PQC algorithms when necessary, Bitcoin can maintain its security without compromising its current space and computational efficiency.

Preparing for the Future

Candidates of NIST’s PQC Standardization

The Bitcoin network’s strength lies in its adaptability. If quantum computing achieves breakthroughs, Bitcoin can implement upgrades through soft forks, transitioning to quantum-resistant cryptographic algorithms. The key is maintaining vigilance and fostering a collaborative effort among developers, researchers, and the broader Bitcoin community to ensure the protocol evolves in step with emerging threats.

Bitcoin’s long-term resilience depends not only on its current cryptographic standards but also on its ability to adopt quantum-resistant solutions when the need arises. The ongoing research into PQC ensures that Bitcoin remains prepared for a quantum-powered future.

QuBit SegWit: A Quantum-Resistant Hybrid Output Type for Bitcoin

Surmount Systems Bitcoin Quantum Security

While current cryptographic techniques like Elliptic Curve Cryptography (ECC) are secure against classical computers, they might not stand up to a Cryptographically Relevant Quantum Computer (CRQC). Was presented recently a new improvement designed to strengthen Bitcoin's defenses against potential quantum attacks.

This BIP, titled "QuBit – P2QRH Spending Rules", was authored by Hunter Beast, a cryptographic researcher from Surmount Systems, a Bitcoin Initiative for Quantum Security, with a strong background in post-quantum algorithms. The proposal has been reviewed and critiqued by prominent Bitcoin Core developers, including Jon Atack and Jameson Lopp, both known for their contributions to Bitcoin's security. The peer review process ensures the robustness of the BIP and its alignment with Bitcoin's decentralized ethos.

Here’s a simplified breakdown of its key ideas:

New Address Format: P2QRH uses a SegWit version 3 output type with addresses that start with bc1r. These are specifically designed to avoid exposing public keys on the blockchain, minimizing vulnerabilities to quantum attacks.
Hybrid Cryptography: By blending classical and post-quantum algorithms like FALCON (a NIST-approved signature scheme), the proposal ensures that even if one system is broken, the other can still provide security.
No Hard Forks Needed: Unlike some other proposals, BIP-TBD works within Bitcoin's existing structure, avoiding disruptive changes like increasing block size.
Quantum Emergency Readiness: It includes provisions like the Canary Address—a specific early Bitcoin address that could signal if current cryptography is broken.

Why Is QuBit SegWit Important?

Quantum computers aren’t an immediate threat but could become one in the future. Addressing these risks proactively ensures Bitcoin remains secure for decades to come. QuBit SegWit reflects a forward-thinking approach, preparing the network for the eventuality of quantum advancements without compromising its current functionality.

Satoshi On Quantum Computing

Before Satoshi Nakamoto disappearance, back in 2010 on the BitcoinTalk forum, a user once asked about the potential for SHA-256 collisions. Satoshi responded with characteristic pragmatism:

“If SHA-256 became completely broken, I think we could come to some agreement about what the honest blockchain was before the trouble started, lock that in, and continue from there with a new hash function.”

Bottom Line

While quantum computing looms as a potential disruptor to Bitcoin’s cryptographic foundations, the network’s resilience lies in its adaptability. Through proactive research, innovative proposals like QuBit SegWit, and the adoption of post-quantum cryptography, Bitcoin can evolve to withstand the quantum era, ensuring its security and longevity for decades to come.

Frequently Asked Questions (FAQ)

What is quantum computing and how does it differ from classical computing?

Quantum computing leverages the principles of quantum mechanics, allowing it to perform certain computations much faster than classical computers by using qubits that can exist in multiple states simultaneously. Unlike classical computing, where bits are strictly 0 or 1, quantum bits (qubits) can be in a superposition of states, such as 30% in state 0 and 70% in state 1.

How does quantum computing affect Bitcoin's security?

Quantum computing poses a significant threat to Bitcoin’s security because it could potentially break the cryptographic protocols, like those based on public-key cryptography, that currently protect Bitcoin transactions. Algorithms such as Shor’s could efficiently factor large numbers and solve the discrete logarithm problem, which underpins Bitcoin’s cryptographic security.

What are the solutions for making Bitcoin quantum-resistant?

To make Bitcoin quantum-resistant, the network could transition to using post-quantum cryptographic algorithms, such as lattice-based cryptography or hash-based signatures. These alternatives are designed to be secure against quantum attacks and could be integrated into Bitcoin’s protocols without requiring a hard fork.

How does the concept of superposition relate to quantum computing?

Superposition is a fundamental principle in quantum computing where a qubit can be in multiple states simultaneously. For example, a qubit might be 30% in state 0 and 70% in state 1. This allows quantum computers to process a vast amount of information at once, making them significantly more powerful than classical computers for certain types of calculations.

Why was Albert Einstein uncomfortable with quantum mechanics?

Albert Einstein was uneasy with quantum mechanics because it introduced a level of randomness and uncertainty that seemed to contradict the deterministic view of the universe he championed. His famous statement, "God does not play dice with the universe," reflects his discomfort with the probabilistic nature of quantum events.