Public Key vs. Private Key

People say "key" like it's one thing, so what actually separates the public one from the private one? Picture a mailbox: the address on the front is public, and anyone can drop mail into it, but only the matching physical key can open the box and take mail out. A private key works like that physical key — it authorizes taking action. A public key, or the address derived from it, works like the mailbox address — meant to be shared so others know where to send something.

Private Key

• Spending Authorization: the private key is the secret credential that proves you can move funds.
• Must Stay Secret: anyone else who gets it can act as if they were you.
• Full Compromise: if it leaks, everything it protects is exposed along with it.

Public Key

• Derived Address: the public key, or the address built from it, is mathematically generated from the private key.
• Safe to Share: publishing it doesn't reveal the private key it came from.
• Receiving Only: it's used to receive funds, not to authorize sending them.

The distinction is simple once stated plainly: the private key authorizes, the public key receives, and only one of the two needs to stay secret. Read more in Key Security.