What is Public-Key Cryptography?
There are several approaches to protecting the privacy and integrity of messages in transit. Public-Key Cryptography (PKC) is the most common and secure technology in use today. It is based on asymmetric algorithms that generate two separate but mathematically related keys. The public key (which, as the name suggests, is publicly available) is used to encrypt data. The corresponding private key signs and decrypts data messages and is known only to and used only by the key owner.
What is a Digital Signature?
Digitally signed emails prove to the recipient of the email, that the sender sent exactly this content. Emails are signed with the sender’s private key, and the signature is then verified by the recipient using the publicly available public key of the sender. Signing is mostly used to assure that noone can unrightfully claim to be the sender of a certain message. Especially when it comes to sensitive data this can be essential. Signing can also be used as a means against phishing and similar fraud. See an illustration of how digital signatures work.