Key Highlights:
- Falcon-1024 outperforms Dilithium in block space efficiency, requiring 3,073 bytes for its combined public key and signature compared to Dilithium’s 5,261 bytes at Category 3.
- Blockstream identified significant deployment hurdles for Falcon-1024, including a 90 KB signing memory footprint, floating-point math complexity, and a lack of hierarchical deterministic (HD) wallet derivation.
- While Falcon serves as a potential long-term lattice option, Blockstream’s hash-based alternative, SHRINCS, reached draft BIP status in late August 2026 after live tests on the Liquid sidechain.
Blockstream Evaluates Post-Quantum Cryptography for Bitcoin
As blockchain researchers study post-quantum cryptography to prepare distributed ledgers for future computing threats, Blockstream has released research comparing leading signature schemes. In an evaluation focusing on footprint and performance, the lattice-based cryptographic scheme Falcon-1024 won on size against its primary alternative, Dilithium. Falcon-1024 requires a combined total of 3,073 bytes for its public key and signature. In comparison, Dilithium at Category 3 demands 5,261 bytes for the equivalent task. With Falcon’s footprint measuring slightly more than half that of Dilithium, it presents a substantial advantage for a blockchain where transactions continually compete for scarce block space.
In addition to storage savings, Blockstream emphasized the scheme’s rapid verification times. Because every full node on the Bitcoin network must independently validate transaction signatures, signature schemes featuring low-latency verification are essential to prevent the resource costs of node operation from escalating. However, despite these operational benefits, Blockstream highlighted that Falcon-1024 faces a comprehensive list of hurdles that preclude immediate adoption.
Implementation Challenges and Hardware Hurdles
Winning the size comparison did not give Falcon-1024 an immediate path to deployment. Blockstream outlined several key technical challenges, chief among them being memory overhead. Falcon requires approximately 90 KB of memory during the signing process, which the report classified as a high operational demand. Furthermore, the scheme’s underlying mechanics introduce implementation complexity due to its reliance on floating-point arithmetic. Implementing floating-point mathematics correctly and deterministically across different computing environments introduces significant software challenges.
From an end-user and infrastructure perspective, Falcon currently lacks native support for hierarchical deterministic (HD) key derivation, the cryptographic standard used by modern Bitcoin wallets to generate multiple addresses from a single seed phrase. Finally, the Falcon-1024 specification has not yet reached final standardization. Developing consensus-level upgrades for Bitcoin atop a moving specification presents unacceptable risks, meaning protocol architects would be targeting a standard that remains subject to potential revisions.
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The Conservative Path: Hash-Based Signatures and SHRINCS
Falcon-1024 represents only one facet of Blockstream’s broader post-quantum roadmap. In parallel, the company has actively explored more conservative alternatives focused on hash-based signatures. Blockstream’s signature proposal, known as SHRINCS, advanced to draft Bitcoin Improvement Proposal (BIP) status in late August 2026. Attaining draft BIP status formalizes the approach for public scrutiny and technical review across the open-source developer ecosystem.
Unlike purely theoretical frameworks, SHRINCS has already undergone experimental deployment in live conditions. Blockstream conducted operational trials of the technology on its Liquid sidechain, successfully executing a landmark post-quantum transaction in March 2026 to evaluate performance beyond laboratory conditions.
Why This Matters
The post-quantum security debate highlights an inevitable architectural tradeoff facing Bitcoin: transitioning to quantum-resistant cryptography will carry substantial costs in data overhead. Even compact lattice-based designs like Falcon-1024 require thousands of bytes per transaction, which will inherently impact block space, network bandwidth, and transaction fee markets.
For current Bitcoin users, the network’s legacy elliptic-curve signature model remains secure, as quantum computers capable of breaking Bitcoin signatures do not exist today. Blockstream envisions a phased transition rather than an abrupt migration. The primary burden in the near term falls on hardware and software wallet developers, who must design systems capable of handling 90 KB signing memory requirements and engineer practical workarounds for hierarchical deterministic address generation before lattice-based transactions can become accessible to mainstream users.
Frequently Asked Questions
Why is Falcon-1024 preferred over Dilithium for blockchain data?
Falcon-1024 requires 3,073 bytes for its combined public key and signature, whereas Dilithium requires 5,261 bytes at Category 3. Because block space is constrained on decentralized blockchains, Falcon’s smaller data footprint makes it significantly more efficient for transaction throughput and node verification costs.
What is preventing Falcon-1024 from being implemented on Bitcoin immediately?
Falcon-1024 faces technical limitations including a 90 KB memory requirement during signing, the mathematical complexity of floating-point arithmetic, an absence of native hierarchical deterministic (HD) key generation for wallets, and the fact that its formal cryptographic standard has not been fully finalized.
What is Blockstream’s SHRINCS proposal?
SHRINCS is Blockstream’s conservative, hash-based alternative to lattice-based signatures. It reached draft BIP status in late August 2026 for community review and was previously trialed in live network conditions on the Liquid sidechain in March 2026.
