In da past two weeks, I have encountered at least 3 people who talk about quantum menace as if it will be the end of all existing blockchains today. So here are some facts:
Most blockchains today rely on elliptic curve signatures (like ECDSA/EdDSA). These are not post-quantum secure. A sufficiently powerful quantum computer could forge signatures and spend funds from exposed keys. This is probably where they’re coming from.
Hash functions like Keccak256 (used in Ethereum) are more resilient, even under quantum attacks. Grover’s algorithm weakens them, but doesn’t break them outright. So no, a quantum attacker doesn’t just rewrite chain history or magically “undo hashes.”
This means the real risk is key compromise, not instant consensus collapse. But note: signatures are also used in validators, bridges, multisigs, etc. so it’s not just wallets.
Blockchains are not static. They can upgrade. Ethereum alone has already coordinated massive changes (see: EIP-4844, account abstraction direction, etc.). Migration to post-quantum signatures is hard — but very doable with enough lead time.
Post-quantum cryptography isn’t hypothetical. We already have standardized schemes (like lattice-based signatures from NIST). The problem is efficiency and integration, not existence.
ZK systems are a mixed bag. Many SNARKs today rely on algebraic assumptions (pairings, discrete logs) that are not quantum-safe. Most of today’s widely used ZK opt for statistical zero-knowledge over statistical soundness… which means a quantum adversary may break soundness in terms of deriving toxic waste from a trusted setup ceremony and fake a ZK-SNARK. A strong enough quantum adversary could forge proofs in some setups. STARKs and hash-based systems are generally more post-quantum friendly.
Also, please stop quoting raw qubit numbers like it’s a countdown timer. Breaking ECC requires error-corrected (logical) qubits, not the noisy ones you see in headlines. We are not there yet. Not even close.
Now there are a lot of ways quantum computing can potentially break the blockchain. But right now it’s mostly a migration problem, not an extinction event.
As for me, I’ll only start panicking if someone figures out how to efficiently reverse hash functions. I don’t think it will happen though. But to each his own.
Ok now go, have better discussions about post-quantum cryptography in da blockchainz