Defying the Quantum Apocalypse : How QSB leverages 201 opcodes and the pre-image resistance of RIPEMD-160 to shield your Bitcoin today—no protocol changes required.

The QSB (Quantum-Safe Bitcoin): a new paper by Avihu Mordechai Levy of StarkWare proposes a way to make Cryptocurrency transactions quantum-safe today, without a single change to the existing consensus rules. No softfork, no waiting, just pure, unadulterated Cryptocurrency Script wizardry.

Today, we’re speaking about the QSB proposal. It’s brilliant, it’s expensive, and it’s a bit of a “last resort”. But in a world where Shor’s algorithm is a reality, it might be the only way to move your coins without an attacker snatching them out of the mempool.

The Disadvantages : The High Cost of Safety

As the saying goes, there’s no such thing as a free lunch in Bitcoin. QSB is “heavy,” and using it feels less like using a wallet and more like running a small mining operation.

1. The GPU Burn : Expensive Off-Chain Compute

Finding a valid QSB transaction is hard. You have to solve the “Pinning Puzzle” (~246) and then find subsets for two “Digest Rounds”.

Levy estimates the off-chain GPU cost at roughly $75 to $200 per transaction. This isn’t something you’ll use to buy a cup of coffee. It is a “last-resort measure” for moving large amounts of capital or “cold storage” funds that are at risk of being swept by a quantum attacker.

2. On-Chain Bloat : 10,000 Byte Scripts

QSB pushes the absolute limits of Bitcoin’s legacy constraints. A single QSB locking script (the scriptPubKey) is massive, coming in at approximately 9,650 bytes.

For context, a standard Bitcoin transaction is a few hundred bytes. A QSB transaction is nearly 10KB. This is “non-standard” by Bitcoin Core’s default relay rules, meaning you can’t just broadcast it to the network. You have to send it directly to a mining pool that supports “non-standard” transactions, like Marathon’s Slipstream. This adds a layer of centralization and complexity to the user experience.

3. The “FindAndDelete” Legacy Prison

To make the binomial selection work, QSB relies on a weird quirk of the original Bitcoin code called FindAndDelete. This mechanism was removed in SegWit (BIP 143) because it was inefficient and caused problems.

Because QSB needs this quirk, it cannot use SegWit or Taproot. This means :

No “SegWit discount” on fees (you pay for every byte).

Vulnerability to the old “transaction malleability” issues.

Incompatibility with modern Layer 2 solutions like the Lightning Network.

4. Complexity and UX Hurdles

The “spending procedure” for QSB is a nightmare for the average user. It requires a separate “GPU Farm” to do the heavy lifting of searching for the puzzle solution, while keeping the secret “HORS” keys on a secure, air-gapped device.

The separation of the “Search” (public data) and “Sign” (private data) is a security win, but the technical overhead of managing this architecture is a massive barrier to entry.

The “Bonus Key” Optimization : A Clever Tradeoff

Levy introduces a concept called Bonus Keys to help bridge the gap between “secure” and “usable”.

In the baseline configuration, the chances of finding a valid subset are so low that a spender might have to try 180 different pinned transactions before they get lucky. By adding “Bonus Keys”—selections that participate in the transaction identification but don’t require a full Lamport signature—the spender can find a solution in almost every attempt.

This reduces the off-chain cost dramatically, though it comes at the cost of about 20 bits of security (dropping from 2138 to 2118 second preimage resistance). For most of us, that’s a trade we’d take any day to save $100 in GPU fees.

Comparison : QSB vs. BINOHASH

How does QSB stack up against its predecessor ?

QSB is essentially a more “grown-up” version of BINOHASH. It’s slightly more expensive and complex, but it actually solves the problem it sets out to fix—the quantum threat—whereas BINOHASH left a back door open for anyone with a logical qubit.

The Verdict : A Break-Glass-In-Case-of-Emergency Shield

Is QSB the future of Bitcoin ? No. Even the author admits that protocol-level changes are the better long-term path for efficiency and user experience. We still want that quantum-safe softfork.

But is QSB a masterpiece of Bitcoin engineering ? Absolutely.

It represents the ultimate expression of Bitcoin’s resilience. It proves that even if the world’s governments and developers can’t agree on a soft fork, a single motivated Bitcoiner can still secure their wealth against the most advanced computers in existence using nothing but the original rules of the game.

If you are a “whale” sitting on a legacy address and you start hearing rumors that a CRQC has been built in a lab somewhere, QSB is your “break glass in case of emergency” tool. It’s expensive, it’s clunky, and it’s beautiful.

In a world where the very math behind our signatures might fail, QSB reminds us that as long as we have hash functions and the 201-opcode limit, we have a chance.

Stack sats, keep your nodes running, and maybe keep a few GPUs on standby. Just in case.

The Advantages : Why We Might Need This

QSB isn’t just a cool academic exercise ; it offers several massive advantages for the “paranoid” Bitcoiner.

1. No Softfork Required

This is the “killer feature.” Most quantum-safe proposals require changing the Bitcoin protocol (a softfork). As we saw with SegWit and Taproot, this can take years of social coordination and developer effort. QSB works on the Live Network today. It uses legacy script execution (pre-SegWit) and quirks like “FindAndDelete” that have been in the code since Satoshi was around.

2. True Shor-Resistance

By shifting the security burden to RIPEMD-160, QSB effectively nullifies the greatest weapon in the quantum arsenal. While an attacker with a quantum computer can break ECDSA in seconds, they are still stuck grinding hashes for QSB transactions, just like a classical attacker. It achieves approximately 118-bit second preimage resistance—a level of security that should keep your coins safe for the foreseeable future.

3. Solving the Sighash Uncertainty

One of the technical criticisms of the original BINOHASH was that the script didn’t know which “sighash flag” (like ALL or NONE) the spender was using. QSB fixes this by hardcoding the signature with SIGHASH_ALL. This ensures that every field of the transaction—inputs, outputs, and amounts—is cryptographically committed to, leaving no room for “signature reuse” attacks.