A renewed debate over quantum computing's threat to Bitcoin has emerged after StarkWare CEO Eli Ben-Sasson warned that the network needs stronger security against future quantum attacks. Blockstream co-founder Adam Back pushed back on the forecast, pointing to existing research and engineering work aimed at protecting the network and its users. The disagreement centers on how urgently Bitcoin must move to new signature schemes and what countermeasures are already in progress.

Ben-Sasson Warns of Quantum Risk

Ben-Sasson made his remarks in an interview with journalist Pete Rizzo. He said Bitcoin needs an upgrade before sufficiently powerful quantum computers can break its current transaction signatures, and he warned that failing to act could damage confidence in Bitcoin and cause its market value to fall.

Back, whose company Blockstream has tested hash-based signatures on the Liquid sidechain, rejected predictions that quantum computing would inevitably cause Bitcoin to collapse. In a post on X on November 4, 2026, he wrote:

c'mon guys, don't be silly and alarmist. Eli knows about hashes based signatures – his company implements STARKS (hash based signatures of execution), and a potential way to batch verify hash besed sigs. he also knows about SHRINCS, "find a quantum fix", there is a draft BIP even — Adam Back (@adam3us) November 4, 2026

The exchange followed a separate debate over present-day threats, including warnings about AI-assisted hackers. Swan Bitcoin founder Cory Klippstein recently argued that attacks using artificial intelligence pose a nearer danger than quantum machines.

Signatures Versus Hashing

Bitcoin uses digital signatures to confirm ownership and a separate hashing system to secure mining. Researchers say a sufficiently advanced quantum computer could break current signatures through Shor's algorithm, revealing private keys from exposed public keys. Public keys generally become visible on the blockchain once funds are spent from an address, which is central to how researchers assess which coins would be at risk.

Back said the same threat does not extend directly to Bitcoin's SHA-256 hashing, which secures the mining process. Grover's algorithm could make some searches faster, but it offers a smaller advantage, leaving hashing less exposed in current assessments. The timing of any computer powerful enough to attack Bitcoin remains uncertain, and no quantum computer has yet demonstrated such an attack against the network.

SHRINCS Testing Continues

Researchers are developing SHRINCS, a hash-based signature method designed to resist quantum attacks while limiting transaction size. Blockstream demonstrated quantum-resistant SHRINCS signatures on the Liquid sidechain in March 2026. A subsequent technical draft described signatures starting at 548 bytes, compared with the 64-byte Schnorr signatures Bitcoin currently uses. The draft remains under review, with further proofs and testing required. Hash-based constructions are an established branch of post-quantum cryptography: the U.S. National Institute of Standards and Technology included one, SLH-DSA, among its 2024 post-quantum signature standards for conventional systems.

The SHRINCS work addresses a different problem from recent thefts affecting older versions of BTCPay Server software, which involved conventional security failures rather than quantum machines.

Network Tradeoffs Weigh on Any Upgrade

Larger signatures could reduce the number of transactions that fit into each block, increasing fees for users. Developers are studying ways to manage that cost.

Quantum protection has not been activated on Bitcoin's main network. SHRINCS currently exists as an unnumbered draft specification, and any change to Bitcoin's transaction rules would require its own proposal and broad support from the network's participants. Bitcoin's upgrade history shows how long that process can take — the Taproot soft fork, proposed in 2018, activated in November 2021 — so a natural milestone to watch is whether the SHRINCS draft advances from unnumbered specification toward a formal proposal.

Elsewhere in the industry, Solflare tightened software access after recent security incidents, reflecting separate work on threats that exist today rather than those projected for the future.