# What is post-quantum cryptography?

Post-quantum cryptography is cryptography built to stay secure against quantum computers, which could break the elliptic curves and RSA that most wallets and websites rely on today.

Also called quantum-safe cryptography, quantum-resistant cryptography or PQC.

## What a quantum computer would break

Shor’s algorithm would let a large quantum computer recover a private key from its public key, for elliptic-curve signatures such as ECDSA and Schnorr and for RSA alike. Hash functions only lose part of their margin, so cryptography built on hashes stays standing.

## The new standards

In August 2024 NIST published its first three post-quantum standards. FIPS 203 (ML-KEM) and FIPS 204 (ML-DSA) are built on lattices, and FIPS 205 (SLH-DSA) is built on hash functions alone.

## Hashes or lattices

Lattice schemes are smaller and faster, and they rest on newer mathematical assumptions. Justin Drake has argued for going all in on hash-based cryptography and avoiding structured assumptions from curves, lattices and isogenies alike.

## In Redacted

Redacted’s bunker mode uses hash-based building blocks only, with SHA-256 for notes and proofs, STARKs that need no trusted setup and SLH-DSA for signatures. It uses no curves and no lattices.

More: [Bunker mode](https://redacted.gg/docs/using-redacted/bunker-mode.md)

## Related terms

- [Hash function](https://redacted.gg/glossary/hash-function.md): A hash function turns any input into a short fingerprint of fixed size. The same input always gives the same fingerprint, and nobody can work back from it or find two inputs that share one.
- [SLH-DSA](https://redacted.gg/glossary/slh-dsa.md): SLH-DSA is the hash-based signature standard NIST published in 2024 as FIPS 205. It is based on SPHINCS+, and its security rests only on hash functions.
- [STARK](https://redacted.gg/glossary/stark.md): A STARK is a zero-knowledge proof built from hash functions alone. It needs no trusted setup and no elliptic curves, so it is expected to hold up against quantum computers.
- [ECDSA](https://redacted.gg/glossary/ecdsa.md): ECDSA is the elliptic-curve signature scheme behind most Bitcoin and Ethereum wallets. It proves you hold a private key without showing it, and its security rests on the math of the secp256k1 curve.
- [Bunker mode](https://redacted.gg/glossary/bunker-mode.md): Bunker mode is Justin Drake’s name for a calm, controlled move of crypto to addresses whose public keys are still hidden behind a hash, in case elliptic curves break sooner than expected.

Sources: [NIST releases first 3 finalized post-quantum encryption standards, August 2024](https://www.nist.gov/news-events/news/2024/08/nist-releases-first-3-finalized-post-quantum-encryption-standards)
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Page: https://redacted.gg/glossary/post-quantum-cryptography/