Certificate Authority in the Digital world refers to the entity that issues Digital certificates for the key holders in Cryptography Encryption. This certificate is given to the public key holders, who becomes a part of the Public Key Infrastructure (PKI), in order to establish a communication channel with the one person or entity who is in possession of the private key (The Subject). This communication channel is called a Secured Socket Layer (SSL) Handshake. SSL certificate can be either single domain, multi domain or SAN SSL Certificate, wildcard certificate. A website should have an SSL cert as per its requirement. All SSL certs offer the same level of 256-bit encryption.
The system belongs to the private key holders who provide the public key to the individuals they need to communicate with. The certificate is proof that the key has been given to them and the digital signature further validates the certificate which can be used to keep a count of numbers of the public key holders. This way, no unusual activities will go unaccounted for. The Digital Certificate works as an identity card which can be effective to keep hackers outside of your system.
The certificate authority is a third party that is trusted by both the private and public key holders. To understand this communication, the most understandable example you can take is your web browser. Whenever you use your browser for internet search and surfing on the world wide web, this Digital Certificate is used to establish a secure connection between the websites and your device or network. The identity of the issuing authority is also disclosed in the certificate, making it a transparent system all the way.
Other information that a digital certificate contains includes a public key, the expiration date, etc. To get this certificate, one needs to file a request to the registration authority along with the general information which is needed to be verified in order for them to obtain the certificate.
This certificate system is a step closer to put human emotions like trust into an altogether technical world of machines and the credit should be given to the CA because it is the only link in the process that both parties trust and through it they trust each other.
But the responsibility on the shoulders of CAs is a huge one because billions of certificates are issued every year, which is needed to protect sensitive information of billions of people which in no circumstances should be leaked or go into the wrong hands. To ensure that, it is necessary for all the CAs to meet certain criteria before they can be accepted as a trusted party.