25% of Bitcoin at Quantum Risk: Can Post-Quantum Upgrades Save the Network?

Bitcoin’s quantum risk has emerged as a critical concern for the cryptocurrency’s long-term security, with researchers and developers exploring solutions to mitigate the threat. Approximately 25% of Bitcoin’s supply is currently exposed to quantum attacks, as these coins are tied to public keys revealed on the blockchain. A quantum computer leveraging Shor’s algorithm could theoretically derive private keys from these public keys, compromising the cryptographic foundations of Bitcoin’s digital signatures, including ECDSA and SchnorrBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1]. This vulnerability could enable both large-scale thefts and coordinated attacks that undermine trust in Bitcoin’s value, with state actors or malicious entities exploiting quantum computing to destabilize the networkBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1].

The urgency of addressing this risk has spurred proposals for integrating post-quantum (PQ) cryptography into Bitcoin’s infrastructure. One promising approach leverages the Taproot upgrade, introduced in 2021, which allows for hidden alternative spending conditions within Bitcoin UTXOs. These script paths, initially designed to enhance privacy and efficiency, can be repurposed to embed PQ signatures without disrupting existing transactionsBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1]. By adding new opcodes to Bitcoin Script, developers could enable Taproot outputs to verify PQ signatures using algorithms under evaluation for standardization. This would allow users to create outputs with dual spending paths: one using Schnorr signatures for daily transactions and another as a quantum-safe fallbackBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1].

Tim Ruffing of Blockstream Research has validated the security of this approach, demonstrating that Taproot’s hidden script paths remain trustworthy even if Schnorr and ECDSA are compromised. A two-step implementation strategy has been proposed: first, introducing PQ opcode support to allow gradual adoption, and second, activating a “kill switch” to disable vulnerable signature schemes if a quantum threat materializes. This would protect coins moved to upgraded Taproot outputs while minimizing disruption during a transition periodBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1].

The complexity of this solution lies in balancing technical feasibility with practical usability. Post-quantum signatures are significantly larger than current Bitcoin signatures, with sizes ranging 40-600 times greater. This increases storage and transaction costs, complicating key management, multisig setups, and threshold signatures. A proposed 4-year migration window by Jameson Lopp aims to incentivize users to transition to PQ outputs, treating un-updated coins as lost after the deadline. However, such measures require broad consensus and careful planning to avoid network fragmentationBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1].

Proponents argue that proactive preparation is essential, as the timeline for quantum computing breakthroughs remains uncertain. While current research focuses on algorithms like lattice-based cryptography, challenges persist in optimizing efficiency and preserving Bitcoin’s core features. By integrating PQ capabilities now, the network can adapt incrementally, allowing users to migrate at their own pace and avoid last-minute chaos. The absence of a “countdown clock” to the quantum threat underscores the need for early action, ensuring Bitcoin’s resilience in a post-quantum eraBitcoin’s Quantum Risk Is Real – One Solution Might Start With …^[1].