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. Share it freely. The math protects you. You cannot derive a private key from a public key, no matter how much computing power you throw at it.
When someone wants to send you bitcoin, they send it to your address. Your address is derived from your public key. Multiple addresses can come from one public key. Understanding this matters because it's how Bitcoin's security model works: you prove ownership with a private key but receive payments through a public address.
How It Works
Bitcoin uses elliptic curve cryptography. Specifically the secp256k1 curve. The math runs one direction only. Private to public: fast and deterministic. Public to private: mathematically infeasible with current or foreseeable technology.
Your public key is a long string of characters. To get your Bitcoin address, the wallet hashes the public key (SHA-256 followed by RIPEMD-160) to produce a shorter, more usable string. Some address formats show the public key more directly. Others use additional layers of hashing. The design lets you share your address freely while keeping the underlying private key completely secret from anyone who can see your address on the blockchain, no matter how much computing power they apply to the problem of working backward from public information.
The practical flow looks like this. You create a wallet on your phone. The wallet generates a private key from a random source. That private key produces a public key via elliptic curve math. The public key gets hashed into your Bitcoin address. You share the address. Someone sends bitcoin to it. To spend, your wallet signs the transaction with the private key. Nodes across the network use your public key to verify the signature, which means anyone can confirm the spend is authorized without ever seeing the private key itself.