The original idea for the Epadlock came when I needed to get some codes emailed to me, but the sender didn't use any form of encryption for email like PGP.
So I looked around for a simple system that he could use to encrypt the message, which means some form of public key/private key system - so I created the Epadlock to convey the codes securely.
Letters and Postcards
An email is like a postcard. Everything you write is in the public domain, it will be stored on a number of servers and can be read by anyone who gets into your email account. By giving the content a level of encryption you are effectively turning the postcard into a letter adding a layer of protection for your data. It is not impossible to read the true content, but it will take a concerted effort to do so - normally enough to deter most people.
The Epadlock Process
The padlock is in effect the public key. So the sender of the message uses it to encrypt the message and you use your private 'key' to decrypt the message. You create the padlock and key on your computer and keep the key safe and send the padlock to the sender of the information you want to receive. Only the key can unlock the padlock.
PGP Encryption: OpenPGP
Principles of Public/Private Key encryption (Wikipedia): DETAILS HERE