What is a private key?
A private key is the tool used to decrypt messages in an asymmetric encryption scheme. As its name suggests, this key is not made public, unlike the public key used to encrypt the message. See also asymmetric encryption and public key.
How do private keys work?
In asymmetric encryption, senders encrypt their files and messages using a public key, which can then only be decrypted using the private key. Private keys should be stored somewhere safe and hidden on the receiver’s device.
If a private key is lost or forgotten, anything encrypted using the paired public key can never be decrypted (at least not without considerable computing resources).