In cryptography, the digital certificate is signed by which type of key?

In cryptography, a digital certificate is signed using a private key. The digital certificate itself serves as a means to bind a public key to an entity, such as a person or organization. When a certificate authority (CA) creates a digital certificate, it uses its private key to sign the certificate. This process ensures that the certificate can be trusted and is authentic, as it can be verified by anyone using the corresponding public key of the CA to verify the signature.

The private key is kept secret and is only known by the certificate authority, which helps maintain the security and integrity of the certification process. When users receive a digital certificate, they can validate the identity of the holder by checking the signature with the CA's public key, ensuring that the certificate has not been tampered with and is from a legitimate source.

The other options, such as a public key, user key, or session key, do not serve the purpose of signing a digital certificate. The public key is used to verify the certificate, while user keys and session keys pertain to different cryptographic functions and are not utilized for the signing of digital certificates.