Cryptocat is available for Chrome, Firefox, Opera, Safari, OS X, and iOS.
Mailvelope is an email encryption tool that is designed to work with webmail services such as Gmail, Outlook.com, and Yahoo Mail. In my experience, Mailvelope works really well with Gmail, is a little shaky with Outlook.com, and I haven't tested it at all with Yahoo Mail.
PGP mail encryption is famously hard to use and perhaps fittingly, Mailvelope is the hardest to use of these three tools. That said, it's not difficult to understand and still rates as an easy-to-use tool.
Once you've installed it from the Chrome Web Store click on the Mailvelope button to the right of the address bar and select Options. This opens a new tab, which is the central hub of Mailvelope. Here you can generate a new key pair or import an existing one if you have it, as well as import the public keys of the people you're going to correspond with.
If you're not familiar with PGP-style key-based encryption check our previous tutorial on Enigmail for Mozilla Thunderbird.
Once that's done, it's time to start writing encrypted email.
Open a mail composition window in your webmail service of choice and you'll see a small pop-up icon of a pencil and paper. Click that and you'll get Mailvelope's composition window. This is where you want to create your encrypted email since most webmail clients auto-save your messages in unencrypted form as you write them. That's a nice feature, but it defeats the entire purpose of using encryption for better privacy.
Once you're done writing you can click the lock icon to choose a contact to encrypt the message to and/or choose the writing icon to sign the message with your key.
Once that's done, click transfer and your encrypted and/or signed message will be copied to the regular composition window for your service. Then just send the message as you would any other.
Mailvelope is available for both Chrome and Firefox.
The newest encryption tool for Chrome, miniLock—also from Cryptocat maker Kobeissi—helps you encrypt single files. You can do this to keep them secure for yourself or to make sure they can only be opened by the people they're intended for. I recently took an in-depth look at miniLock where you can find out exactly how to use this tool.
But generally, the app uses what's known as your miniLock ID to encrypt files for you. It's generated like many other encryption keys based on your email address and a password. Share this ID with others and they can use miniLock to encrypt files that only you can open. It's as simple as that.
Encryption is a great way to keep your data private and thanks to these tools for Chrome and other platforms, it's getting a lot easier to use.