Private Key

From DBWiki

A private key is used when creating a digital signature. A private key is much like a driver's license or passport in that it should only be used by the person to which it is issued.

A private key works with a public key to create a digital signature that is incredibly difficult to forge and thus provides a very reliable means of validating a person's identity online. There is absolutely no reason for anybody to need your private key, so guard it closely... if someone were to steal it, they could forge your digital signature and impersonate your identity online.