# Wallets, addresses and keys

> What a private key, public key, address and wallet actually are — and what makes QRL's keys different.

Owning coins on a blockchain means controlling a **key**. This guide explains the handful of terms behind that — private key, public key, address and wallet — and what QRL does differently.

## The chain of derivation

These four things form a one-way chain, each derived from the one before:

```
private key  →  public key  →  address
   (secret)      (shareable)    (shareable, short)
```

- **Private key** — the secret. Whoever has it can sign transactions and move the funds. Guard it like cash.
- **Public key** — mathematically derived from the private key. It can be shared, and it's what the network uses to *verify* your signatures.
- **Address** — a short, hashed form of the public key that you give to others to receive funds. On QRL, addresses start with `Q`.
- **Wallet** — the software that stores your keys and assembles signed transactions. The wallet is not the money; the **keys** are.

The derivation only runs one way: you can compute the address from the key, never the key from the address. (At least, not without breaking the underlying cryptography — which for ECDSA is exactly what a [quantum computer could do](/learn/how-quantum-computers-break-crypto), and what QRL is built to prevent.)

## What QRL does differently

On most chains, the public key → address step uses ECDSA. QRL replaces the signature scheme with a quantum-resistant one:

- **QRL Legacy** uses [XMSS](/learn/xmss-explained), and its addresses are 79 characters.
- **QRL 2.0** uses [ML-DSA-87](/learn/ml-dsa-87-explained), and its addresses are 41 characters.

Both start with `Q`, so you tell them apart by length — see [QRL address formats](/learn/qrl-address-formats).

## The one-time-key rule (QRL Legacy)

There's one extra wrinkle unique to QRL Legacy. Because XMSS is built from [one-time signatures](/learn/one-time-signatures-and-ots-keys), the wallet must **track which signing keys it has already used** — the OTS index — and never reuse one. Good QRL Legacy wallets handle this for you, but it's why restoring an old backup needs care.

QRL 2.0's ML-DSA-87 is **stateless**: there's no index to track, and you can sign as often as you like with the same key.

## Keeping keys safe

The golden rule never changes: **whoever holds the private key holds the funds.** There is no support line that can reverse a theft or recover a lost key. Back up your wallet's recovery material, store it offline, and treat it as the single most important thing to protect.

## Where to go next

- [QRL address formats](/learn/qrl-address-formats) — the 79- vs 41-character split.
- [One-time signatures and OTS keys](/learn/one-time-signatures-and-ots-keys) — the XMSS index rule.
- [Reading an address page](/learn/reading-an-address-page) — what the explorer shows for an address.