Announcing a developer preview of Quantumroot: a new kind of vault offering full 256-bit classical, 128-bit quantum security strength, without relying on new cryptography – it uses only the mining-proven SHA256 algorithm.
Quantumroot is an ultra-efficient, post-quantum vault for Bitcoin Cash. It’s optimized for business and savings use cases:
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With cross-input aggregation via introspection, sweep transactions are 15% smaller per additional input than today’s single-signature, “Pay-to-Public-Key Hash” (P2PKH) wallets, with fixed overhead “paid off” after 8 UTXOs.
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Post-quantum spends cost ~1.3KB per UTXO for typical two-input, single-signature transactions.
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With both CashToken-based cross-address aggregation and introspection-based cross-input aggregation, post-quantum sweeps of 400+ unique addresses or 800+ inputs fit in a single transaction (100KB).
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While SLH‑DSA‑SHA2‑128s (SPHINCS+) signatures weigh in at 7,856 bytes, CashToken-based delegation and Bitcoin Cash’s UTXO model allow Quantumroot to use LM-OTS signatures (RFC 8554) – improving quantum security, while also reducing signature sizes (2,180 bytes) and preventing on-chain privacy leaks.
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Quantumroot can support quantum multi-signature (30+ signers), cross-vault signature aggregation (each signature used by multiple, multi-signature vaults), sweep-free vault upgrades and key rotations, threshold and fallback conditions, time-delayed withdrawals, percentage or amount-based pre-authorizations, inheritance and business-continuity configurations, destination-based withdrawal rules, and more.
Most importantly, Quantumroot is quantum safe “at rest” from day 1, even if quantum attackers suddenly steal all Taproot-held BTC.
On “Q-Day”, Quantumroot wallets can smoothly continue operation – or even reduce their post-quantum transaction sizes by retiring pre-quantum signing.
Following Bitcoin Cash’s 2025 upgrade, all Quantumroot components are possible on BCH mainnet – today.
This developer preview combines these components with 10-100× transaction size reductions and code simplifications made possible by several 2026 Cash Improvement Proposals (CHIPs): Loops, Functions, P2S, and Bitwise.
I plan to continue verification, complete security audits of specific Quantumroot CashAssembly templates, and provide an open source implementation for wallets to integrate via Libauth, targeting Bitcoin Cash’s May 2026 Upgrade.
The full explanation, code, and demo can be found on my blog:
