Encryption is the method computer systems use to obscure information so that unintended third parties can't view it. At a high level, it works by scrambling a file's contents and requiring a password to put them back in the right order.
Encryption is utilized by many software products and over the course of a given day, you're probably using encryption frequently without even knowing it (such as when you send an iMessage via iOS or Mac OS X, or when you visit a website using the https protocol).
Not all computer activities are encrypted, however, and email stands out as one of the biggest examples of unencrypted systems that are in common use. When you send an email to someone, the message travels across the Internet, from server to server, in a manner that is very easy for an unauthorized third party to peek into.
While there are ways to encrypt email, most of them are somewhat involved and require both the sender and receiver to adjust their email programs to support encryption. This is not rocket science, but it's often more trouble than the average person wants to deal with.
So when you've got something that you want to share with another person via email, but don't want to put the time into constructing an end-to-end email encryption scheme, what can you do?
The simplest solution is to use a program that can encrypt a single file, and then email the encrypted file to your designated recipient and have them decrypt it on their end. While you'll both need to use encryption software, you won't need to deal with configuring your email programs to support encryption, and that makes the process much easier.
You can encrypt any type of file, so this method works great for documents, spreadsheets, media, and compressed files which can contain multiple files.
There are a variety of encryption standards and programs to choose from, but my favorite is a program called AES Crypt. AES Crypt uses the 256-bit AES encryption format, which is an industry standard and is very secure. And AES Crypt is free and open source, which means it's open to programmers from around the world to view its innards to ensure there aren't any backdoors or privacy-compromising techniques inserted inside on behalf of malicious third parties or governments, as can sometimes be the case with proprietary, closed-source solutions.
AES Crypt is available, for free, for Mac, iOS, Windows, Android, and Linux, and it's easy to install and use. Straightforward documentation is available and pretty much anyone can easily get it set up and running.
Once you have AES Crypt (or a similar program), you can encrypt an individual file and then email it to someone else, and as long as they have the password and AES Crypt (or something similar) on their end, they- and only they- will be able to decrypt and view the file.
Make sure you send the password in a secure manner as well- just typing it into a regular email message will allow a third party to grab it. Giving it out over the phone or via an encrypted messaging system like iMessage is an effective technique.
Before Edward Snowden's revelations and the accompanying avalanche of disclosures about the extent of government surveillance, encryption might have seemed unnecessary for most people. But now that we know that everything we send online that's not encrypted is likely viewed and stored by one or more third parties, it makes sense to have a solid tool in your arsenal to use when dealing with sensitive information.
Founding Partner, Techromatic