The main difference between private keys and public keys lies in their usage and confidentiality:

1. **Confidentiality* Private keys must be kept secret and should never be shared with anyone else. They are used to sign transactions or decrypt messages, and if someone else gains access to your private key, they can potentially access your data or assets.

2. **Usage* Public keys, on the other hand, are meant to be shared widely. They are derived from private keys and are used to verify digital signatures or encrypt messages. Public keys allow others to interact with you securely, but they cannot be used to determine your private key.

In summary, private keys are kept secret and used for signing or decrypting, while public keys are shared and used for verification or encryption.