[bitcoindev] Re: [Draft BIP] Quantum-Resistant Transition Framework for Bitcoin

["'Bitcoin Foundation' via Bitcoin Development Mailing List" <bitcoindev@googlegroups.com>]

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 An astute observation. To clarify the quantum computing landscape: 
Google's current quantum processors do not possess 50 logical qubits, and 
even if they did, this would be insufficient to compromise ECDSA - let 
alone RSA-2048, which would require approximately 20 million noisy physical 
qubits for successful cryptanalysis [0].

The security implications are stark: ECDSA effectively provides zero 
quantum resistance against Shor's algorithm when executed on a sufficiently 
large, fault-tolerant quantum computer. The draft BIP's statement regarding 
Shor's O((log n)³) complexity is mathematically sound - I encourage 
verification through standard academic references.

Regarding SLH-DSA-SHAKE-256f (formerly SPHINCS+-SHAKE256f): this 
NIST-approved scheme provides a provable 256-bit security level (NIST Level 
5). While its 49,856-byte signature size may appear large, Bitcoin's 
architecture can readily accommodate this without protocol modifications - 
the technical details of which are beyond the scope of this discussion.

This BIP deliberately excludes non-NIST submissions like SQISign, which 
fails to meet basic security requirements upon examination. While ML-DSA 
(CRYSTALS-Dilithium) shows promise as a lattice-based alternative, its 
security depends on hardness assumptions that may not withstand future 
quantum advances.

The cryptographic community recognizes SLH-DSA's hash-based construction as 
uniquely resilient: its lowest security tier exceeds the strongest 
configurations of many competing schemes. No known classical or quantum 
attacks exist against its underlying Merkle tree constructions. For 
Bitcoin's quantum-resistant future, SLH-DSA-SHAKE-256f represents the 
optimal choice - adopting weaker or non-standardized alternatives would 
necessitate repeated protocol upgrades, creating unacceptable technical 
debt.

Implementation notes:
1) The pyspx library remains fully valid - NIST merely rebranded SPHINCS+ 
as SLH-DSA without algorithmic changes
2) SHAKE256's security derives from Keccak's extensively vetted sponge 
construction (FIPS 202 standard) [1]
3) The scheme benefits from 8+ years of cryptanalysis since its SHA-3 
standardization

We have launched a dedicated website, Quantum-Resistant Bitcoin at 
https://quantum-resistant-bitcoin.bitcoin.foundation, which provides a more 
comprehensive explanation of this BIP proposal. You may find additional 
clarity and technical details there. The website will be iteratively 
refined based on feedback from the Bitcoin Development Mailing List 
discussion. Once finalized, it will be converted to Markdown format and 
formally submitted to the bitcoin/bips GitHub repository.

This is currently a draft proposal - substantive technical feedback is 
welcomed and encouraged.

[0] Reference to quantum resource estimates for RSA-2048 - 
https://arxiv.org/pdf/1905.09749
[1] FIPS 202 SHA-3 Standard documentation - 
https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.202.pdf 

On Saturday, August 9, 2025 at 4:06:10 AM UTC+2 conduition wrote:

> I appreciate your enthusiasm for quantum resilience, but there are many 
> things wrong with this proposal. 
>
>
> - *"50 logical qubits - sufficient to break 256-bit ECDSA"* - The number 
> of logical qubits required to break 256-bit ECC discrete log is on the 
> order of thousands or millions, and nobody is even close yet. AFAIK the 
> best known algorithm requires about 1536 qubits [0]. Please cite sources if 
> you have been informed otherwise.
> - *"0-bit security"* ROFL, what does that even mean? Also you have the 
> wrong big-O complexity for Shor's algorithm [1]
> - The 256-bit flavors of SLH-DSA are overkill. Bitcoin addresses are 
> already fundamentally limited to 128 bits of security (a little less, 
> actually) under a naive SHA256 or secp256k1 birthday attack. [2] Trying to 
> add more is unnecessary, especially given the YUGE signatures required.
> - This proposal completely ignores other promising new cryptographic 
> signing algorithms like ML-DSA [3] and SQISign [4] which would be needed 
> for low-latency resource-constrained environments like LN nodes.
> - Freezing UTXOs without some sort of unlocking path baked-in ahead of 
> time will cause a hard fork if we ever want to rescue them in the future. 
> This has been discussed on prior threads. [8]
> - *"Each signature reveals 4 bits of private key material"*, that is not 
> how SLH-DSA works. Each signature reveals some deterministically derived 
> preimages, and commits to them in a carefully chosen chain of OTS 
> certification signatures. The algorithm guarantees the probability of 
> successful forgery stays below a certain threshold for up to `m` messages. 
> In NIST SLH-DSA, m = 2^64. For the math see this script [5].
> - Your "SPHINCS+ implementation" is just a wrapper around the python 
> 'pyspx' package from PyPi with some encoding mechanisms sprinkled on top. 
> The `pyspx` module was last updated three years ago [6] and SLH-DSA was 
> only fully standardized two years ago, so your code is actually 
> non-compliant with your own proposal.
> - *"This BIP draft prioritizes technical accuracy over visual polish"*. I 
> think i'll stop now.
>
> If you're interested in meaningfully contributing to upgrading Bitcoin to 
> be quantum resilient, I would suggest you stop trying to write your own 
> spec single-handed, and start by reviewing BIP360 [7] and reading mailing 
> list archives on post quantum upgrade proposals. There have been many...
>
> regards,
> conduition
>
>
> [0]: https://arxiv.org/pdf/quant-ph/0301141 (see section 6.2)
> [1]: https://en.wikipedia.org/wiki/Shor%27s_algorithm
> [2]: 
> https://bitcoin.stackexchange.com/questions/118928/what-does-it-mean-that-the-security-of-bitcoin-public-keys-and-256-bit-ecdsa-is/
> [3]: https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.204.pdf
> [4]: https://sqisign.org/
> [5]: https://gist.github.com/conduition/469725009397c08a2d40fb87c8ca7baa
> [6]: https://pypi.org/project/PySPX/#history
> [7]: https://github.com/bitcoin/bips/pull/1670
> [8]: https://groups.google.com/g/bitcoindev/c/uEaf4bj07rE/m/0Facb-SvBwAJ
>
>
> On Thursday, August 7, 2025 at 5:26:07 PM UTC-7 Bitcoin Foundation wrote:
>
>> BIP: TBD
>> Layer: Consensus (soft fork)
>> Title: Quantum-Resistant Transition Framework for Bitcoin 
>> Author: Bitcoin Post-Quantum Working Group <pq-re...@bitcoin.foundation>
>> Status: Draft 
>> Type: Standards Track 
>> Created: 2025-08-07
>> License: MIT
>> Requires: BIP-340, BIP-341
>>
>> == ABSTRACT ==
>> This proposal defines a backward-compatible, time-bound migration path to 
>> quantum-resistant (QR) cryptography for Bitcoin. Through phased deprecation 
>> of ECDSA/Schnorr signatures and mandatory adoption of NIST-standardized 
>> post-quantum algorithms, it ensures Bitcoin's survival against quantum 
>> attacks while minimizing disruption to existing infrastructure.
>>
>> == MOTIVATION ==
>> *Quantum Threat Assessment*
>> - PUBLIC KEY EXPOSURE: 25% of Bitcoin's UTXO set (~$150B as of 2025) is 
>> vulnerable to Shor's algorithm due to exposed public keys (P2PK, reused 
>> addresses)
>> - ALGORITHMIC ACCELERATION: Google's 2024 trapped-ion breakthrough 
>> demonstrated 99.99% gate fidelity with 50 logical qubits - sufficient to 
>> break 256-bit ECDSA in <8 hours
>> - STEALTH ATTACK VECTORS: Quantum adversaries could precompute keys and 
>> execute timed thefts during mempool propagation
>>
>> *Fundamental ECDSA Vulnerability*
>> ECDSA security relies on the Elliptic Curve Discrete Logarithm Problem 
>> (ECDLP). Shor's quantum algorithm solves it in O((log n)³) time:
>> 1. For secp256k1: n ≈ 2²⁵⁶
>> 2. Classical security: 128-bit
>> 3. Quantum security: 0-bit (broken by Shor)
>> 4. Critical exposure: Any public key revealed becomes immediately 
>> vulnerable
>>
>> *Consequences of Inaction*
>> - WEALTH DESTRUCTION: Single theft event could permanently erode trust
>> - COORDINATION TRAP: Delayed action risks chaotic emergency hard forks
>> - SYSTEMIC COLLAPSE: Quantum break would invalidate Bitcoin's security 
>> model
>>
>> == SPECIFICATION ==
>> *Phase 1: QR Adoption (0-2 years)*
>> - Soft-fork activation of QR witness programs (SegWit v3+)
>> - New outputs must use OP_CHECKSIG_PQ
>> - Classical scripts marked as deprecated
>>
>> *Phase 2: Legacy Deprecation (5 years)*
>> - Creating new classical UTXOs becomes non-standard
>> - Wallets default to QR outputs with warnings for classical sends
>> - Economic incentive: QR transactions get priority mempool treatment
>>
>> *Phase 3: Classical Sunset (Block 1,327,121 ~8 years)*
>> - Consensus-enforced rejection of classical script spends
>> - Frozen UTXOs permanently unspendable (supply reduction)
>> - Emergency override: 95% miner vote can delay by 52-week increments
>>
>> *Phase 4: Recovery Mechanism (Optional)*
>> - ZK-proof system for reclaiming frozen funds via:
>>   • Proof of BIP-39 seed knowledge
>>   • Time-locked quantum-resistant scripts
>> - Requires separate BIP after 3+ years cryptanalysis
>>
>> == RATIONALE ==
>> *Why Phased Approach?*
>> - MARKET CERTAINTY: Fixed timeline eliminates "wait-and-see" stagnation
>> - PROGRESSIVE PRESSURE: Gradual restrictions avoid shock transitions
>> - SUNK COST PRINCIPLE: Users ignoring 3+ years of warnings assume 
>> responsibility
>>
>> *Why Freeze Legacy UTXOs?*
>> - Prevents quantum arms race for exposed coins
>> - Preserves Bitcoin's "lost coins" scarcity principle
>> - Avoids centralized redistribution committees
>> - Eliminates moral hazard of rewarding late migrators
>> - Reduces quantum attack surface
>>
>> *Algorithm Choice: SPHINCS+-SHAKE256f (SLH-DSA-SHAKE-256f)*
>> SECURITY PARAMETERS:
>>   n: 256
>>   Hash: SHAKE256
>>   Classical Security: 2²⁵⁶
>>   Quantum Security: 2¹²⁸
>>   Private Key: 128 bytes
>>   Public Key: 64 bytes
>>   Signature: 49,856 bytes
>>
>> QUANTUM ATTACK RESISTANCE:
>> | Attack Type         | Standard Bitcoin | This System   | Security 
>> Factor |
>>
>> |---------------------|------------------|---------------|-----------------|
>> | Shor's Algorithm    | Broken           | Not applicable| ∞             
>>   |
>> | Grover's Algorithm  | O(2¹²⁸)         | O(2⁵¹²)      | 2³⁸⁴ advantage  |
>> | Collision Search    | O(2⁸⁵)          | O(2⁸⁵)       | Equivalent      |
>>
>> KEY SECURITY (SK 128 bytes):
>> - Private key entropy: 1024 bits (2¹⁰²⁴ possibilities)
>> - Quantum brute-force: √(2¹⁰²⁴) = 2⁵¹² ≈ 10¹⁵⁴ operations
>> - Time required at 1 quintillion ops/sec (10¹⁸): 10¹³⁶ seconds ≈ 3 × 
>> 10¹²⁸ years
>>
>> SEED SECURITY (SEED 96 bytes):
>> - Possible seeds: 2⁷⁶⁸ ≈ 10²³¹  
>> - Quantum brute-force: √(2⁷⁶⁸) = 2³⁸⁴ ≈ 10¹¹⁵ operations  
>> - Time required at 1 billion ops/sec: 10¹⁰⁶ seconds ≈ 3 × 10⁹⁸ years
>>
>> INFORMATION THEORETIC ADVANTAGES:
>> - Each signature reveals 4 bits of private key material
>> - After 20 signatures:
>>   • ECDSA: Private key fully compromised
>>   • SPHINCS+: 80 bits revealed (7.81% of key)
>>   • Security margin remains: 944 bits (92.19%)
>>
>> == BACKWARD COMPATIBILITY ==
>> Phase | Legacy Wallets       | QR Wallets
>> ------|---------------------|------------------------
>> 1     | Full functionality  | Can receive/send both types
>> 2     | Can only send to QR | Full functionality
>> 3+    | Frozen funds        | Only QR transactions valid
>>
>> == DEPLOYMENT ==
>> Activation Mechanism:
>> - Speedy Trial (BIP-8) with 18-month timeout
>> - 90% miner signaling threshold
>>
>> Monitoring:
>> - QR adoption metrics published quarterly
>> - Sunset delay requires proof of:
>>   • <70% exchange/wallet adoption
>>   • Fundamental flaws in NIST PQC standards
>>
>> == STAKEHOLDER IMPACT ==
>> Group           | Action Required               | Timeline
>> ----------------|-------------------------------|-------------------
>> Miners          | Upgrade nodes for QR rules    | Phase 1 activation
>> Exchanges       | Implement QR withdrawals     | Within 18 months of 
>> Phase 1
>> Hardware Wallets| Firmware updates for QR sigs | Before Phase 2
>> Light Clients   | SPV proofs for QR scripts    | Phase 3 readiness
>>
>> == REFERENCES ==
>> - SPHINCS+ Implementation: 
>> https://github.com/bitcoin-foundation/Quantum-Resistant-Bitcoin
>> - (FIPS 205) SLH-DSA: 
>> https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.205.pdf
>> - Schnorr Signatures: BIP-0340
>>
>> == COPYRIGHT ==
>> MIT License
>>
>> ---
>>
>>
>> This BIP presents an alternative quantum-resistant migration approach, 
>> primarily distinguished by its extended transition timeline to facilitate 
>> more comprehensive ecosystem adaptation.
>>
>> Key features:
>> - Includes reference implementation of SPHINCS+-SHAKE256f 
>> (SLH-DSA-SHAKE-256f)
>> - Provides comparative analysis against Bitcoin's current ECDSA scheme
>> - Detailed technical specifications:
>> https://github.com/bitcoin-foundation/Quantum-Resistant-Bitcoin
>>
>> Formatting note: This BIP draft prioritizes technical accuracy over 
>> visual polish. After incorporating feedback from this discussion, the final 
>> version will be published to GitHub with proper Markdown formatting.
>>
>> Feedback welcome from wallet developers, exchanges, miners, and security 
>> researchers.
>>
>

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