# What is QRL?

> A plain-English introduction to the Quantum Resistant Ledger — the two chains, why it exists, and how to engage with it.

QRL — the Quantum Resistant Ledger — is a blockchain built from the start to survive the arrival of cryptographically-relevant quantum computers. Most existing cryptocurrencies sign transactions with elliptic-curve cryptography (ECDSA), which a sufficiently powerful quantum computer can break using Shor's algorithm. QRL replaces that with signature schemes that have no known quantum attack.

In practice, that single design decision shapes everything else about the project.

## Two chains, one ecosystem

Today QRL is actually two chains running in parallel:

- **QRL Legacy** — the original mainnet, running since 2018. It uses Proof-of-Work consensus and XMSS one-time signatures. Mining rewards still flow, balances are intact, and the chain is fully indexed in Quantascan under the `/qrl-legacy/` URL prefix. Browse it via [blocks](/qrl-legacy/blocks) or [transactions](/qrl-legacy/transactions).

- **QRL 2.0** — the new EVM-compatible chain, running Proof-of-Stake consensus. It uses `qrysm` (QRL's fork of Ethereum's Prysm consensus client) paired with `gqrl` execution. Signatures here are ML-DSA-87 (a NIST-standardised post-quantum signature scheme). It currently runs as `testnetv2`; mainnet is the eventual destination.

Both chains are first-class on Quantascan. The chain switcher in the header lets you flip between them; URLs are stable and chain-prefixed.

## What makes it "quantum-resistant"

Two ingredients matter:

1. **Signature scheme**. Bitcoin and Ethereum use ECDSA. A capable quantum computer could derive a private key from a public key, letting an attacker spend any wallet whose public key has been revealed (every wallet that has spent at least once). QRL Legacy uses **XMSS**, a hash-based signature that does not depend on number-theoretic hardness. QRL 2.0 uses **ML-DSA-87** (Dilithium), part of NIST's post-quantum standards.

2. **Hash functions**. Hash-based primitives like SHA-256 are weakened by Grover's algorithm, but only by a square-root factor. Doubling the hash output (256 → 512 bits) restores the original security margin. QRL's hashing choices reflect that.

The signature scheme is the meaningful change. Hash functions just need more bits. For the deeper why — Shor's algorithm, "harvest now, decrypt later", and the 2024 NIST post-quantum standards — see [why quantum-resistance matters](/learn/quantum-resistance-explained).

## How to engage

You probably want one of these:

- **Check a wallet or transaction**. Paste an address or transaction hash into the search bar at the top of any Quantascan page.
- **Buy or hold QRL**. See [where to buy QRL](/exchanges) for exchanges and on-ramps, and the [ecosystem directory](/ecosystem) for wallets and tooling.
- **Read analytics**. The [network page](/network) summarises chain activity; the [richlist](/richlist) ranks holders by balance; the [supply page](/supply) covers tokenomics.
- **Track validators**. On QRL 2.0, see the [validators page](/validators) for leaderboards and decentralisation metrics.
- **Run a node or validator**. Out of scope for this site — start at the foundation's [official documentation](https://theqrl.org).

## Why this project exists

Quantum computers capable of breaking ECDSA do not exist today. Estimates for when they will exist range from "decade-plus" to "never", depending on who you ask. The QRL bet is that the cost of preparing now is small, the cost of being unprepared is catastrophic, and the design choices that make a chain quantum-resistant force a sharper focus on signature efficiency anyway.

You don't have to share that bet to find the resulting chain interesting. The cryptography is unusual, the consensus is moving from PoW to PoS, and the two-chain transition is rare enough on its own to be worth watching.