What is Email Encryption? - Definition & Methods

Instructor: Martin Gibbs

Martin has 16 years experience in Human Resources Information Systems and has a PhD in Information Technology Management. He is an adjunct professor of computer science and computer programming.

In this lesson, we will define email encryption, and we will also look at examples of current encryption methods. Even though there are robust tools for securing email, it is an ever-evolving science.

Email Encryption

By default, email messages are not secure. They are sent across the Internet in plain text: An unscrupulous individual can snatch the messages from cyberspace and gain access to your personal communication.

A little overview of encryption

Encryption takes a set of data (the email message), and applies a coding scheme to it. Think of decoder rings sold in cereal boxes: You needed to use the decoder to read out secret messages. For example, the letter A may have been represented by a 1, B = 2, or maybe something more complicated. Once you had the key to the code, you could decipher the secret message: Drink your Ovaltine.

Computer encryption takes this simple concept and expands it the way only the power of computer processing can read. The coded messages are incredibly complex and need the right keys to open them.

Encryption for Email

Email encryption applies the principles mentioned earlier to email. Users publish a public key that is accessible by others in order to encrypt messages. The sender also has a secret private key that is used to decrypt (decode) the messages and encrypt (code) their own messages.

The email messages are scrambled into an unreadable format in order to hide them from the bad guys. The public key is used to encrypt and is shared with everyone. The private key is used to decrypt and is private.

Think of the decoder ring example: Companies send out thousands of coded (encrypted) messages to consumers. But the decoder rings (the decryption) are only owned by private individuals.

A simple diagram of how encryption works
encryption example

Encryption Methods

While the basic concept of encryption is detailed in the prior section, there are specific methods which expand upon the foundation. The overall goal is always security: Protecting the information sent in the message from unwanted eyes. Keep in mind, however, that no security option is infallible: There are hackers out there, and they want your information.

There are numerous methods for email encryption; this lesson will discuss three major players in encryption:

  • PGP
  • S/MIME
  • TLS

PGP: Pretty Good Privacy

PGP (Pretty Good Privacy) is a hybrid approach: When user data is encrypted with PGP, PGP compresses the text; this not only saves disk space but increases security. A lot of hacking attempts try to read the plain text but may stumble on the compressed information.

Next, PGP creates a session key, which is a one-time use secret key. The text is encrypted, including the session key with it; the public encrypted session key is sent along with the coded/encrypted text.

On the receiver's side, the decryption works in reverse order: The recipient uses a private key to retrieve the session key, and PGP then decrypts the encrypted code.

PGP encryption/decryption process
pgp encryption decryption


S/MIME stands for Secure Multi-Purpose Internet Mail Extension. S/MIME uses a digital signature as well as encryption to secure the email transmissions.

The following occurs when the message is created:

  1. Message is entered/composed
  2. Unique information regarding the sender is retrieved
  3. A digital signature is added to the message using the sender's unique information
  4. This signature is added to the message
  5. Message is sent

When the message is received at the other end, the following occurs:

  1. Message received
  2. The digital signature is read
  3. The message body is read
  4. Identifying information from sender is read
  5. A signing operation is run on the message
  6. The digital signature on the message is compared against the signature read on receipt
  7. If the signatures match, the message is verified

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