Certificate Authority (CA)

A Certificate Authority (CA) is an organization that issues digital certificates, which are electronic documents that Web sites use to prove their identity. CAs are trusted third parties that help establish a level of trust between two parties that want to carry out a transaction. They can be government institutions or private organizations like Verisign  or Thawte .

CAs are essential for asymmetric encryption which uses two different keys, a public key and a private key, to encrypt and decrypt communications. CAs issue public key certificates to Web sites and other organizations, which certify that the public key contained in the certificate belongs to that particular Web site/organization. Users can then use this certified public key to encrypt data and carry out transactions with the Web site. Public key certificates can also be used to protect against phishing attacks, since a user can look at a site's certificate to make sure they are at the correct Web site for an organization.

CAs assure users that the Web site/organization they are dealing with is who they claim to be, so it is important for CAs to verify the identity of entities that apply for digital certificates. This verification is done through government references, notaries, payment infrastructure and third-party databases.