Crypto glossary
Public key
A public key is the shareable half of a cryptographic key pair, used to derive wallet addresses and to verify that the owner signed a transaction.
Every crypto wallet is built on a key pair. The private key is secret; the public key is mathematically derived from it, but the reverse calculation is practically impossible. That one-way link is what makes it safe to share the public key.
When you sign a transaction with your private key, the network uses the public key to check the signature without ever seeing the secret. Wallet addresses are usually a shortened, hashed form of the public key, which is why people share an address rather than the raw key.
Bitcoin and Ethereum use elliptic curve cryptography on the secp256k1 curve. Researchers warn that a sufficiently powerful quantum computer could one day derive private keys from exposed public keys, which is why post-quantum upgrades are being discussed.
Example
When a merchant gives you a Bitcoin address starting with bc1, that string is derived from their public key; you can send funds to it, but only their private key can move them afterwards.
