In a Public Key Infrastructure (PKI), which certificate authority level is the topmost?

The topmost level in a Public Key Infrastructure (PKI) is the Root CA. This authority is crucial because it serves as the foundation upon which other certificates are built. The Root CA issues certificates to Intermediate CAs and can directly issue certificates to end entities, such as users or devices.

The security of the entire PKI relies heavily on the Root CA, as it holds the ultimate trust; if the Root CA is compromised, the entire hierarchy can be affected. Its private key must be safeguarded with utmost care because it is used to sign the public keys of Intermediate CAs and other certificates.

Other certificate authorities, such as Intermediate CAs and Subordinate CAs, operate beneath the Root CA in the hierarchy. They can issue certificates for various purposes but do so under the trust established by the Root CA. These layers help create a more scalable and manageable PKI, while also allowing for better delegation of responsibilities within the infrastructure.