In an electronic networked world, these are no longer possible. The goal of a PKI, or Private Key Infrastructure, is to replace those traditional forms of trust. With authentication you can be sure of the originator of the message. Integrity guarantees that the message was not changed in transit.
Confidentiality prevents third parties from intercepting the message.
And with non-repudiation, you can be sure that the sending party can not deny sending the message. Non-repudiation can also be used to prevent the receiving party from denying the receipt of a message. The operation of a PKI is based on asymmetric encryption. In addition the sender of the message can sign the message. To take advantage of asymmetric encryption, you need to have the public keys of all the people with whom you wish to communicate.