Google's Quantum Paper Correction re BCH
The paper "Securing Elliptic Curve Cryptocurrencies against Quantum Vulnerabilities: Resource Estimates and Mitigations" groups BTC and BCH together, correctly recognizing their shared history and some divergences, but fails to account for recent BCH upgrades that enable quantum-resistant wallet implementations today.
Since the 2017 fork, BCH has continued evolving its consensus system and extended the UTXO model with native token primitives ("CashTokens", activated May 2023) along with significant Script VM upgrades including native transaction introspection opcodes and big-integer arithmetic. A summary of differences: https://bitcoin.stackexchange.com/a/115856/137501
The upcoming upgrade (scheduled May 15, 2026; v29 node software already released) adds native functions and loops to the Script VM.
These capabilities enable efficient quantum-resistant vault implementations. Specifically, the "Quantumroot" design leverages CashTokens for account abstraction, allowing users to maintain a constant receiving address while using UTXO-bound tokens secured by LM-OTS signatures (RFC 8554) to authorize spends. Post-quantum transactions require only ~1.5KB per UTXO, and aggregated sweeps of 400+ addresses fit within a single 100KB transaction.
Notably, Quantumroot vaults are quantum-safe "at rest" from deployment, unlike BTC's Taproot, which exposes public keys on-chain. All required components are functional on BCH mainnet today.
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