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Can quantum computing break blockchain encryption? 

Quantum computing could pose a threat to the current public-key encryption used in blockchains, but it is not an immediate risk. Here is a breakdown of the different aspects:

1. Vulnerabilities in Current Blockchain Cryptography

  • Public-Key Cryptography (ECDSA/RSA):
    • The hardness of the problem is based on integer factorization and elliptic curvature discrete logarithms.
    • Shor’s Algorithm A quantum algorithms that can solve this problem efficiently and break ECDSA/RSA if a powerful enough quantum computer is available. This could enable attackers to deduce private keys from the public keys and compromise transaction security.
  • Hash functions (SHA-256):
    • Grover’s Algorithm : Reduces the search complexity quadratically and weakens hash function security. (e.g. SHA-256’s 256-bit is now 128-bit). Double hash outputs (e.g. SHA-512), however, can reduce this vulnerability, making it less of a concern compared with public-key weaknesses.

2. Quantum Attacks: Current Possibility

  • Qubit Requirements: Breaking 256-bit ECC requires ~1,500-4,000 logical qubits (error-corrected). Current quantum computers are far from being practical, with only 100-1,000 physical quabits and high error rates.
  • Timeline Experts estimate that large-scale quantum computers with error-correction are still decades away. However, progress is accelerating.

3. Blockchain Specific Considerations

  • Public Key Exposed:
    • Address reuse on blockchains, such as Bitcoin, exposes public key information and creates long-term risk. Single-use addresses reduce (but do not eliminate) vulnerability by delaying exposure until the broadcast of transactions.
    • Finalization of Transactions: Funds could be stolen if a quantum computer is able to derive the private key prior to a transaction being confirmed (10 mins for Bitcoin). Quantum hardware currently available cannot reach this speed.

4. Mitigation Strategies

  • Post-Quantum Cryptography (PQC):
    • It is crucial to switch over to quantum-resistant algorithms, such as hash-based or code-based encryption. NIST standardizes PQC algorithms, e.g. CRYSTALS, SPHINCS+.
    • Implementation challenges: requires hard forks, community consensus and technical and governance obstacles.
  • Proactive Upgrades Blockchains such as IOTA already use quantum resistant signatures (Winternitz OS), although trade-offs, like larger signatures, exist.

5. The conclusion of the article is:

  • Immediate risk: low, since quantum computers that can break ECDSA/RSA have not yet been developed.
  • Risk in the Long-Term: High, if Blockchains do not adopt PQC. To protect against future threats, proactive upgrades are necessary.

Quantum computing can theoretically crack blockchain encryption. However, timely adoption of quantum resistant algorithms and practices, such as avoiding address re-use, can reduce risks. To ensure long-term safety, the blockchain community should prioritize preparation.

Read : How do miners validate transactions without a central authority?