What is signing with private key?
Regarding this, what is private key in digital signature?
One key in the pair which can be shared with everyone is called the public key. The other key in the pair which is kept secret and is only known by the owner is called the private key. Either of the keys can be used to encrypt a message; the opposite key from the one used to encrypt the message is used for decryption.
Likewise, what does it mean to sign a key? SIgning a key is effectively a way of saying that you trust the key is correct and associated with a particular individual or identity (thanks @Bruno). People who trust you may then choose to trust it based on the fact that you have signed it. Signing means you digitally sign the key certificate.
In this way, which algorithm is used to sign the digest with the private key?
Generally the signing of the hash only applies to the key exchange to ensure that everything was received and sent correctly by both parties. Generally each individual message is verified using an HMAC algorithm.
How do private keys work?
Private Key. The private key is a secret key that is used to decrypt the message and the party knows it that exchange message. In the traditional method, a secret key is shared within communicators to enable encryption and decryption the message, but if the key is lost, the system becomes void.