Private I: Encrypting email with public keys

In recent weeks, Ive written about protecting data stored locally on a hard drive, against both people with physical access and potential remote attacks. But your data is much more vulnerable in transit, as it passes between end points or via servers.

This problem is effectively solved for instant messages with iMessage, which uses strong end-to-end encryption designed in such a way thatApple saysnot even they can decrypt your messages. This is accomplished by creating local encryption keys through a process that cant be reverse-engineered on their side. Even though iMessages pass through intermediate points on the Internet, theres no opportunity for others to grab the plain text, images, and audio within. (The same is true with FaceTime audio and video.)

But its still a mess for email, whether Mail in iOS or OS X, or third-party email software. The problem arises from email protocols working too well. Yes, I know how that sounds, as Apples Mail app frustrates on both its platforms. But the diversity of what you can choose among native and Web apps has to do with no company or organization controlling how email works. iMessage is entirely Apples ecosystem, which is the case for most messaging systems, including Facebooks WhatsApp and the messaging component of Microsofts Skype. In contrast, there are thousands of native email programs across all platforms and all time, and hundreds remain in wide use.

The email protocols comprise POP3 (ancient and still in use) and IMAP for email retrieval and synchronization, while SMTP handles sending. Because they emerged from the dawn of Internet, they have evolved in fits and starts with weird vestigial pieces. Email continues to function because of compromises and a tacit agreement that nobody can break or refuse to support major componentspartly because no one controls a big enough piece to force change.

One of the biggest problems past and present in Apples Mail.app is, in fact, because Google has an odd setup for its IMAP service, and Apple dances around fully embracing it. Google cant break IMAP entirely, because then millions of users who pull in Gmail messages through Outlook or other software would be out in the cold, and potentially switch away. (Android has three separate email apps, in fact: two that work with Gmail in different ways, and third for regular email accounts.) Likewise, Apple cant invent a new, superior way to send email because every mail server in the world would need to be updated to receive it.

In the last few years, enough standardization and upgrading have taken place that one aspect is well secured: the connection between an email client and an email server. Email flows from a client to a server run by your ISP or company or email host, and from there typically directly to the recipients corresponding email server. By default, Apples mail clients and those of other companies try to set up a new account to use SSL/TLS, the same session-based encryption technology used for secure Web interactions.

But SSL/TLS protects just the link between an email client and an email server. The data is encrypted in transit for that session, and then decrypted at the server, before being packaged and sent on to the next server. Now, in practice, even thats becoming more secure. Most email serversall of those run by major companiesare in data centers. And after the Edward Snowden disclosure, Google and other companies have stepped up the security of links among their own data centers.

The weak points still remain when email is decrypted, whether its for microseconds on a server before being wrapped up to send to another server over an encrypted link, or for much longer, when a server communicates insecurelywhich is typicalwith another email server. At those weak points, a criminal or government agent could gain access.

iMessage suffers from none of these weaknesses because of its strong end-to-end encryption. So how can we achieve the same in email? Through the use of public-key (PK) cryptography, something thats been available for encrypting documents and email messages since 1991 in one form or another. A decade ago, I reviewed an updated and well-designed commercial version of PGP (originally standing for Pretty Good Privacy) in Macworld, and hoped it would usher in a new age of encrypted email. I guess Im a pretty optimistic fellow.

Still, hope springs eternal, and I think were ripe for another pass at PK becoming something that could be used readily and safely, rather than by those with command-line facility. Let me first explain public-key cryptography briefly. In the next column, Ill explain how to use it practicallyon a Mac at least.

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Private I: Encrypting email with public keys