- Using StarkWare’s Quantum-Safe Bitcoin (QSB) technique, the first quantum-safe Bitcoin transaction has been verified on the mainnet.
- Without the need for a soft fork, QSB defends Bitcoin against hypothetical quantum assaults via hash-based security and signature grinding.
- The QSB transaction was mined using MARA Slipstream, underscoring the necessity of miner support due to the nonstandard nature of QSB transactions.
Bitcoin’s quantum-security debate has moved from research into live experimentation, with two developments putting practical solutions in the spotlight.
StarkWare’s Quantum-Safe Bitcoin (QSB) scheme has successfully completed its first transaction on Bitcoin mainnet, while Blockstream researchers have published a Bitcoin Improvement Proposal (BIP) for SHRINCS, a new hash-based post-quantum signature scheme.
The QSB transaction was mined through MARA Slipstream, using a technique called signature grinding. Unlike a traditional Bitcoin transaction, QSB does not require a soft fork or changes to Bitcoin’s base protocol. Instead, it gives individual holders a way to move coins into outputs protected by hash-based security.
BTC’s QSB Uses Hash-based Security To Block Quantum Attacks
Bitcoin currently relies on elliptic-curve cryptography for signatures. A sufficiently powerful quantum computer running Shor’s algorithm could potentially derive private keys from exposed public keys, creating a risk of large-scale theft.
QSB takes a different approach. It uses brute-force computation to find a transaction hash that functions as a valid signature, replacing reliance on elliptic-curve keys with the difficulty of reversing cryptographic hashes.
The first QSB transaction was disclosed by StarkWare on August 26, more than four months after researcher Avihu Levy published the original proposal. StarkWare engineer Tomer Giladi helped complete the implementation for live-network use.
However, QSB comes with an important limitation: its transactions are nonstandard and cannot normally pass through Bitcoin’s mempool. That makes miner support, such as MARA Slipstream, essential.
QSB Isn’t For Everyday Bitcoin Transactions Yet
Quantum protection currently comes at a significant cost. StarkWare says generating a QSB transaction can cost several hundred dollars, compared with roughly 33 cents for a standard Bitcoin transaction.
That makes QSB more of an emergency hedge than a practical replacement for everyday Bitcoin transactions. It could appeal to holders who believe the quantum threat is becoming urgent enough to justify paying a substantial premium.
QSB also cannot protect an address whose public key has already been exposed. A quantum attacker could potentially use that information to race the protective transaction.
SHRINCS Takes A Different Route
While QSB works without changing Bitcoin’s consensus rules, Blockstream’s SHRINCS proposal takes the more conventional route of introducing a post-quantum signature scheme through a protocol upgrade.
Today, we’re publishing BIP SHRINCS, the first concrete proposal for a post-quantum signature scheme designed specifically for Bitcoin.
The BIP draft turns what began as a rough idea into exact algorithms with an executable reference implementation.
This is an important… pic.twitter.com/7xGri2ggtP— Jonas Nick (@n1ckler) August 26, 2026
Blockstream Research’s Jonas Nick described SHRINCS as the first concrete post-quantum signature proposal designed specifically for Bitcoin, while noting that further security analysis, Bitcoin Script integration and wallet testing are still needed.
SHRINCS is hash-based and designed specifically around Bitcoin’s constraints. Its smallest signatures are 548 bytes, plus a 48-byte public key, making them considerably larger than Bitcoin’s 64-byte Schnorr signatures. However, SegWit reduces the block-space impact of witness data.
Blockstream estimates Bitcoin could process around 3 transactions per second with SHRINCS, compared with much lower throughput using larger NIST-approved post-quantum schemes.
SHRINCS Still Has A Major Catch
The SHRINCS BIP openly acknowledges that its security proof remains unfinished. The scheme has also not received the same level of cryptanalysis as established post-quantum standards.
Another challenge is statefulness. SHRINCS uses one-time keys that must be tracked by the signing device. Losing that state can require a much larger recovery transaction, while incompatible implementations could potentially create fund-loss risks.
Blockstream is also exploring SHRIMPS, lattice-based signatures and zero-knowledge proof aggregation as possible pieces of a broader quantum-resistance strategy.
Bitcoin’s Quantum Debate Is Just Beginning
QSB, SHRINCS, BIP-360 and BIP-361 represent different answers to the same problem.
QSB offers an immediate, user-controlled defense without a soft fork. SHRINCS aims to provide a native protocol-level solution, but requires further testing and governance. BIP-360 proposes removing exposed key paths through Pay-to-Merkle-Root outputs, while BIP-361 adds an enforcement mechanism for migrating vulnerable coins.
The common challenge is no longer simply finding quantum-resistant cryptography. Bitcoin must also decide which approach it can trust, implement and activate before sufficiently powerful quantum computers arrive.
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