Email encryption is a way of protecting electronic communications. It is like sending a message in code. Only someone who knows the code can read what is written in the email. This allows private information to be sent via email without fear that an unintended person will read it.
Email has become a common way of communicating. People use it for everything from keeping in touch with friends to making business deals. Email encryption allows those conversations to be kept private.
Sending an unencrypted email is like posting a message to someone on the office bulletin board. The intended recipient can see it, but so can everyone else in the office who looks at the board. When email encryption is used to protect a message, it is as though the message was put it in an envelope and placed in someone’s mailbox. An unintended person still might read it, but it would be more difficult for that person to access.
One of the most common forms of email encryption is public key cryptography. This system uses two keys, a public key and a private key. The sender is the only one who has the private key. The sender can give the public key to anyone he or she might email. A public key can even be openly released so that anyone, even complete strangers, can use it to email the person whose key it is.
When someone wants to send that person an email message, he or she can encrypt it using the public key. That way, it can be decrypted using the private key. Anyone who didn't have the key would see the email as a meaningless string of numbers. The public key encryption system gives full security coverage only when both parties in the conversation are using it.
A common version of this kind of email encryption is called Pretty Good Privacy (PGP). It is used by many email service providers. The system was created by Phil Zimmerman in 1991.
When you send an email using PGP, the email is first compressed. The system then creates a one-time-use secret key called a session key. This key is used to encrypt the email. The session key is then encrypted using the recipient’s public key. When the recipient gets the email, his or her copy of PGP decrypts the session key then uses it to decrypt the email.