Wed, 25 Nov 2009
/Security/e-mail:
Basic E-mail Security
(For those who feel the need to send passwords, credit card numbers,
Social Security numbers, and various other sensitive information via
e-mail.)
I am going to talk about the network aspect of e-mail security, and
therefore will address points 1 to 5 in the diagram below. First, a
little very basic knowledge about what happens to your e-mail when it
passes through a network:
When you send an e-mail, to state the obvious, there is no direct
electrical connection between your computer and the computer of your
recipient. In fact, as it passes between your computers, the e-mail not
only passes through wires, but "hops" its way through many (conceivably
many, many) routers and switches. Every time the e-mail passes through a
router or switch, whomever controls that router or switch can VERY
EASILY capture the digital contents of the e-mail if it is not
encrypted. If you are sitting in a coffee shop using an open access
point, for instance, the person next to you may be recording your e-mail
during its very first hop from wireless card to wireless router. And the
owner of the shop could conceivably have software running in the
wireless router doing the same.
Summary of rules for secure e-mail communications:
- Sender and Receiver should use the same e-mail server.
- Only use https, pop3s, imaps (encrypted connections) to
your e-mail service.
- Use a small security-oriented e-mail service or a personal e-mail
server.
(1) (2) (3) (4) (5)
---------- -----------
| | | |
Sender =========| Sending |-----------| Receiving |========== Recipient
| Server | | Server |
| | | |
---------- -----------
(3) So, by the numbers: for various technical and historical reasons,
segment (3) above between the two servers is virtually always
unencrypted. It is not strictly true, but for simplicity at the moment
lets say that for the case of a simple unencrypted e-mail, YOU CAN NEVER
HAVE A SECURE COMMUNICATION IF SENDER AND RECEIVER ARE USING DIFFERENT
E-MAIL SERVERS. Ie. if I us Yahoo and you use Gmail, it does not matter
what else we do, when passing from the Yahoo servers to the Gmail
servers, the e-mail is exposed to snooping.
Thus Rule 'a' above. If (2) and (4) are the same server, we eliminate
all problems with segment (3). For Rule 'c', choose a small service with
an emphasis on privacy and security. The bigger the company, the more
employees who have potential access to your e-mail. (For the biggest of
the free public e-mail providers, this is probably at least hundreds of
people, and maybe thousands.) Best of all, use an e-mail server under
the personal control of either sender or receiver (ZERO employees who
have access to your e-mail).
(1)(5) To satisfy Rule 'b', only use an e-mail service that provides
encrypted connections to the server:
- use https, not http, if you use a webmail client.
- use pop3s and imaps, not pop3 and imap, if you use a desktop e-mail
client (free with both Gmail and gmx.com)
Finally, a brief mention of something that should see more use, at
least by technical people: make all of the above irrelevant by having
both sender and receiver use an e-mail client with GPG[1] encryption
configured and enabled. After sender and receiver exchange public
encryption keys for two specific e-mail addresses, all future e-mails
between those two e-mail addresses are encrypted from the moment they
leave the sender's e-mail client until the moment they are received by
the recipient's e-mail client. If encryption is not desired for any
particular (or even most) communications simply use a different e-mail
address then the one configured for encryption. A little effort is
involved on both ends for setup, but this is by far the best solution.
Most desktop e-mail clients have this capability built-in, it basically
just has to be turned on. Webmail users, particularly of gmail, may find
the Firefox FireGPG[2] plugin to be useful.
And if you should choose to ignore all of the above advice and send a
password, credit card number, or other personal information via insecure
e-mail, you would be advised to not include certain important key words
in your e-mail. You might think, for instance, that there is such a vast
amount of e-mail passing through an internet switch such that no one
will ever notice your insignificant little e-mail. But what if they are
filtering the traffic for key words, such as "password" or "credit
card"? Suddenly your "insignificant" e-mail containing the word
"password" becomes a part of a much shorter list of interesting (to a
hacker) e-mails.
Further reading: [3]
[1] http://gnupg.org/
[2] http://getfiregpg.org/
[3] http://www.sovereignman.com/personal-privacy/how-to-send-secure-email/
posted at: 05:23 | path: /Security/e-mail | permanent link to this entry
