What is a Public Key?
A cryptographic key derived from your private key that can be shared publicly. Your Bitcoin address is generated from your public key.
Why It Matters
Your public key is the bridge between your private key and your Bitcoin address. It can be shared with anyone without compromising security because it's mathematically difficult to reverse (you cannot derive a private key from a public key). When someone wants to send you bitcoin, they send it to your address, which is derived from your public key. Multiple Bitcoin addresses can be derived from a single public key, and a single private key generates a matching public key. Understanding public key cryptography is essential to understanding Bitcoin's security model: you prove ownership through a private key, but you receive payments through a public address.
How It Works
Bitcoin uses elliptic curve cryptography (specifically secp256k1) to derive public keys from private keys. The mathematical operation is one-way—going from private to public is easy and deterministic, but going from public to private is mathematically infeasible. Your public key is a long string of characters. Your Bitcoin address is created by hashing your public key multiple times (SHA-256 followed by RIPEMD-160), producing a shorter, more usable address. Some address formats show the public key more directly, while others use layers of hashing. This design lets you share your address freely while keeping your private key secret.