Pretty Good Privacy (PGP) is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication.

from Wikipadia,

Gravity Forms PGP Encryption plugin allows you to receive encrypted emails from your visitors, without the need for them to use any specific software. To achieve this, the plugin only uses your PGP public key. You can test our online PGP key generator.

What is public key encryption?

Public key encryption (PKE) uses a system of two keys:

  • a private key, which only you use;
  • a public key, which other people use.

A message that is encrypted with one of these keys can be decrypted only with the other key in the pair.

For example, let’s say that Alice wants to send a message to Bob. She encrypts the message with Bob’s public key and sends it using her favorite email program. Once the message is encrypted with Bob’s public key, only Bob can decrypt the message using his private key. Even major governments using supercomputers would have to work for a very long time to decrypt this message without the private key.

Source: Sam Buchanan,

Gravity Forms PGP Encryption plugin helps you to simplify the process: any form submitted by a visitor on your website will be automatically encrypted with your public key, and will be sent to you. Your visitors have just to fill the form like usually, they don’t have any special action to do.

Ready-to-use PGP Software

You must have the necessary software on your computer to create a PGP key pair, if you do not already have, and to read encrypted e-mails received from your WordPress site. There are several software for using PGP, here are the main ones:

PGP Desktop software, works with Outlook, made in the USA
gpg4o for OutlookYesNoNowww.giepa.dePaid software, works with Outlook, made in Germany. Our Technical Team is in direct contact with gpg4o’s Developers to ensure optimal compatibility of the two products
Gpg4winYesNoNowww.gpg4win.orgFree software, works with Outlook and Thunderbird
GPGToolsNoYesNowww.gpgtools.orgFree software, works with Apple Mail
EnigmailYesYesYeswww.enigmail.netFree software, works with Thunderbird
MailvelopeYesYesYeswww.mailvelope.comFree browser extension, works with Google Chrome and Firefox
Mymail-Crypt for browser extension, works with Google Chrome
ProtonMailYesYesYesprotonmail.comSecure Email Based in Switzerland

The easiest way is to use a browser extension : Mailvelope or Mymail-Crypt for Gmail. But all these sotfwares will work without trouble.