PKI stands for Public Key Infrastructure. The X.509 standard defines a PKI as "The set of hardware, software, people and procedures needed to create, manage, store, distribute and revoke certificates based on public-key cryptography." PKI has three components in its basic form:

  • Public/Private keys
  • Digital Certificates, and
  • A Certificate Authority (CA)

In a typical PKI deployment, each user is assigned a pair of linked keys - a public key available to others through a CA, and a private key, which is kept secret on the user's client. A user sending a secure message uses the receiver's public key to encrypt the transmission so that only the intended recipient can read the message.