Intermediate Certificates

What is an Intermediate Certificate?

An intermediate certificate, also known as an "Intermediate CA Certificate," is a type of electronic certificate (digital certificate) issued by a Certification Authority (CA) to verify its own authenticity. A Certification Authority is a trusted third party that issues electronic certificates used for identity verification on the internet.

Certification Authorities can be broadly divided into two types: Root Certification Authorities and Intermediate Certification Authorities.

• A Root Certification Authority is the top-level authority that validates its own authenticity and can issue certificates to other Certification Authorities.
• An Intermediate Certification Authority cannot prove its own validity and requires certification from a higher-level Certification Authority. The electronic certificate issued by the higher authority to the Intermediate CA is called an Intermediate Certificate.

When performing SSL communications, websites (or web servers) must obtain an SSL server certificate from a Certification Authority in advance and send it to the client (communication partner). Additionally, the CA's certificates must also be sent together. As such, when obtaining an SSL server certificate, the Root Certificate and Intermediate Certificate provided by the CA must also be installed on the web server.

Clients verify the hierarchical structure of these certificates and validate the Root Certificate to confirm the authenticity of the SSL server certificate. Most clients that support SSL communication already have Root Certificates pre-installed. The authenticity of a Root Certificate is determined by comparing the pre-installed Root Certificate with the one received from the web server.