Email is prone to disclosure of information. Most emails are currently transmitted in the clear (not encrypted). By means of some available tools, persons other than the designated recipients can read the email contents. Email encryption has been used by journalists and regular users to protect privacy.
Email encryption can rely on public-key cryptography, in which users can each publish a public key that others can use to encrypt messages to them, while keeping secret a private key they can use to decrypt such messages or to digitally encrypt and sign messages they send.
Protocols for email encryption include:
Mail sessions encryption
The STARTTLS SMTP extension is a TLS (SSL) layer on top of the SMTP connection. While it protects traffic from being sniffed during transmission, it is technically not encryption of emails because the content of messages is revealed to, and can be altered by, intermediate email relays. In other words, the encryption takes place between individual SMTP relays, not between the sender and the recipient. When both relays support STARTTLS, it may be used regardless of whether the email's contents are encrypted using another protocol. STARTTLS is also an extension of IMAP4 and POP3, as stated by RFC 2595.
Mandatory certificate verification is not viable for Internet mail delivery. As a result, most email that is delivered over TLS uses only opportunistic encryption. DANE is a proposed standard that makes an incremental transition to verified encryption for Internet mail delivery possible.
The Signed and Encrypted Email Over The Internet demonstration has shown that organizations can collaborate effectively using secure email. Previous barriers to adoption were overcome, including the use of a PKI bridge to provide a scalable public key infrastructure (PKI) and the use of network security guards checking encrypted content passing in and out of corporate network boundaries to avoid encryption being used to hide malware introduction and information leakage.
Setting up and using email encryption
Most full-featured email clients (like Apple Mail, Microsoft Outlook or Mozilla Thunderbird) provide native support for S/MIME secure email (digital signing and message encryption using certificates). Other encryption options include PGP and GNU Privacy Guard (GnuPG). Free and commercial software and add-ons are available as well, such as Gpg4win or PGP Desktop Email that support the OpenPGP type of encryption.
While PGP can protect messages, it can also be hard to use in the correct way. Researchers at Carnegie Mellon University published a paper in 1999 showing that most people couldn’t figure out how to sign and encrypt messages using the current version of PGP. Eight years later, another group of Carnegie Mellon researchers published a follow-up paper saying that, although a newer version of PGP made it easy to decrypt messages, most people still struggled with encrypting and signing messages, finding and verifying other people's public encryption keys, and sharing their own keys.
Because encryption can be difficult for users, security and compliance managers at companies and government agencies automate the process for employees and executives by using encryption appliances and services that automate encryption. Instead of relying on voluntary co-operation, automated encryption, based on defined policies, takes the decision and the process out of the users' hands. Emails are routed through a gateway appliance that has been configured to ensure compliance with regulatory and security policies. Emails that require it are automatically encrypted and sent.
If the recipient works at an organization that uses the same encryption gateway appliance, emails are automatically decrypted, making the process transparent to the user. Recipients who are not behind an encryption gateway then need to take an extra step, either procuring the public key, or logging into an online portal to retrieve the message.
- Email authentication
- Email privacy
- HTTP Secure - a widely used communications protocol for secure communication over a computer network
- Secure Messaging
- SMEmail – A New Protocol for the Secure E-mail in Mobile Environments, Proceedings of the Australian Telecommunications Networks and Applications Conference (ATNAC'08), pp. 39–44, Adelaide, Australia, Dec. 2008.
- Lee, Micah (July 2, 2013). "Encryption Works: How to Protect Your Privacy in the Age of NSA Surveillance". Freedom of the Press Foundation. Retrieved 1 May 2014.
- "Postfix TLS Support". Postfix.org. Retrieved 2014-04-16.
- Dukhovni; Hardaker (2015-10-14). SMTP Security via Opportunistic DANE TLS. IETF. RFC 7672. https://tools.ietf.org/html/rfc7672.
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