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Secure your email with GnuPG/PGP/OpenPGP

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Category: Security

Secure email: Encrypt and sign your emails with PGP/GnuPG

Email is fundamentally insecure. There are such a plethora of issues with it, it is crazy to think about the kind of information sent with it. It is probably even crazier when you realize we’ve had a solution for sending secure email since 1991.

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Fundamental issues with email

There’s lots of fundamental issues with email. Here are some of them:

1. Email travels and is stored in plain text

This means that anyone managing a server or network device along the way can read (and modify) the email as they like. You may compare it to sending a postcard by regular mail. Any information in it should be regarded as publicly available. Ever heard of “leaked emails”? Yeah. It doesn’t take much of a hacker to do that.

2. There are no integrity checks

When you send an email, you don’t know whether it will end up at the recipient without modification. The recipient can’t trust the content, as they can’t be assured it haven’t been modified along the way. This happens much more than you think. Usually “just” some tracking code or ads are inserted.

3. There is no sender verification

Ever heard of phishing? Do you know how to impose as someone? Go into your email client and change the email address. Now you can send emails on behalf of that person. Usually, there is no way to detect if an email was really sent by someone or not.

Pretty Good Privacy (PGP)

Now, go more than two and a half decades back, to 1991. Phil Zimmermann is very much aware of these issues with email and invents a solution he calls Pretty Good Privacy, or PGP for short. PGP provides cryptographic privacy and authentication for just about any data.

PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications.

– Wikipedia on PGP

It works like this:

Cryptographic key pair

You create a cryptographic key pair. This pair consists of a private and a public key. The private key must be kept really, really secret and secure. The public key should be made as publicly available as possible: Uploaded to special key servers and posted on your blog and social media profiles.

Encrypted content

When someone wants to send you an email, they encrypt it with your public key. Only the secret key can be used to decrypt the contents. This means that only you can read the content.

Digital signature

Also, whether you choose to encrypt the content or not, you can digitally sign the email message you’re sending. Then you use your private key to generate and attach a signature based on the content of the email message. The recipient can then use your public key to verify that the signature was really made with your private key – thus really signed by you. This verifies both the sender and the content. If the signature doesn’t match with both the sender and the content, something phishy is going on.

Pretty good, but not full privacy

Encryption and signing solve all three issues I mentioned at the beginning. However, PGP doesn’t provide full privacy: Headers are still public. This includes info on who sent it, when they sent it, and possibly where did they send it from.

OpenPGP and GnuPG are free

Since 1997 there has been an open standard for PGP encryption called OpenPGP. This is the standard everybody is using today, and you don’t really have to worry about any incompatibilities at all.

GNU Privacy Guard (GnuPG or GPG) is a free software implementation of OpenPGP and is interoperable and compatible with other OpenPGP-compliant software.

In general, the terms GnuPG, GPG, GNU Privacy Guard, OpenPGP and PGP are used interchangeably. Technically, OpenPGP (Pretty Good Privacy) is the encryption standard, and GNU Privacy Guard (often shortened to GPG or GnuPG) is the program that implements the standard.

– Free Software Foundation

Why doesn’t everybody use secure email?

I don’t know. Maybe too difficult to get started with? Concept to advanced too understand? Not reached critical mass? Beats me. It’s not really difficult to get started, and when you are up and running, it is really easy to use.

With all kinds of email scandals, spear phishing attacks and corporate and governmental surveillance schemes, there seems to me that secure email has gotten more popular the last few years. More and more people and services are using it. Even Facebook will send you all emails encrypted and signed if you enter your public key in your profile settings. No more Facebook account phishing attacks for you!

Secure email settings in Facebook
To receive encrypted and signed emails from Facebook, go to Settings > Security and Login > Advanced > Encrypted notification emails

How to get started with secure email

The Free Software Foundation has published an excellent step-by-step tutorial that guides you through the steps, explaining everything nicely along the way. Just select if you use GNU/Linux, MacOS or Window at the top. You’ll find the guide “Email Self Defence” here.

Send me a secure email message

If you want to send me an email, my fingerprint is:
5029 E0D0 F458 72E4 09D3 308D 1D51 378E E348 35B6

My full OpenPGP (GnuPG) public key is also available here.

Good luck, have fun and stay safe!

Published by Bjørn Johansen

Bjørn has been a full-time web developer since 2001, and have during those years touched many areas including consulting, training, project management, client support, and DevOps. He has worked with WordPress for more than 13 years, and he is a plugin author, core contributor, WordCamp speaker, WordCamp co-organizer and Translation Editor for Norwegian Bokmål.

4 thoughts on “Secure email: Encrypt and sign your emails with PGP/GnuPG”

  1. I’ve tried using PGP in the past, but always give up on it after a month or two. I use too many different devices and keeping the keys in sync is a chore I’d rather avoid. Every single time I’ve used it over the years, any email I receive that use PGP have to wait days longer than other email before I get around to a client that is configured to use it.

    I believe the main problem people have with PGP is that sooner or later they’ll loose their keychain, get frustrated that they can’t recover it, and never touch PGP again. The market move away from email clients to ad-funded webmail probably didn’t help either.

    I’d go so far as to say that I’m motivated to use PGP, yet even I find it too cumbersome to actually use it.

    For anyone interested in adopting PGP, then you should check out the Free Software Foundation’s Email Self Defense site.

    1. Maybe the issue then is that you use it too seldom? If you had the need to use it on a daily basis, and a large enough share of your important email was encrypted, you would perhaps have the motivation to setup your all your infrastructure/clients to use PGP?

      1. Possibly. However, when something is this difficult to use then no one will actually use it (including its inventor, who uses iOS.) I’m guessing that 90% of emails I’ve sent with PGP have gotten a reply saying the keys are lost or that the recipient otherwise can’t decrypt the message for some other reason. —attaching signatures to messages also creates a lot of confusion for non-PGP users who wastes their own and my time asking what the signature is all about.

        Mailpile was the webmail encryption crowdfunding star of 2013, but the project has yet to release a single stable version. They’re getting close, but their technology choices have already made it outdated before their first release.

        There are very few good email clients on the market now, and very fewer that support PGP. Even on Linux, there is only a handful of actively maintained email clients – and the most popular once either don’t support PGP at all or require the user to install weak dependencies or plugins.

        S/MIME on the other hand has better client support (including Outlook, iOS Mail, and the stock Mail app on Android) and a better user experience. The only problem? You have to pay a public certificate authority to issue your certificate on a yearly basis.


See original article here. 

The Tutorial below shows how to setup your Email Encryption with Mozilla Thunderbird. OpenPGP is now integrated on Thunderbird, so the Enigmail extension is not required anymore.

Or install the Mailvelope extension on your browser and use it on your webmail. Although Mailvelope being an extension for most of the current browsers has less features / options than Thunderbird. It encrypts your message and inserts it into your webmail on Gmail and possibly a few other email providers as well.
Also have noticed that Encrypted email sent with Thunderbird can't be decrypted with Mailvelope. Whereas Encrypted email sent with Mailvelope can be decrypted with Thunderbird. (this may not be the case anymore.) Also if you export your secret/private key to OpenKeyChain and setup your email on K9 Mail (and maybe R2Mail2) K9 Mail should be able to decrypt the emails sent with Thunderbird and Mailvelope, if you're wondering about being able to read your email on both mobile and stationary devices(computers).

If you have Microsoft Outlook and don't wish to switch to Thunderbird, please directly install GPG4WIN. Also use this guide to setup the email encryption on Outlook. It's a longer process on Outlook though, while still possible.

On your Android phone install K-9 Mail or R2Mail2 & OpenKeyChain. Create your key pairs on Thunderbird and then export your secret/private key to OpenKeychain. (Because exporting secret/private keys on OpenKeyChain creates PGP encrypted files with a long number which will have to be entered to decrypt on your computer. You'll need GPG4WIN, or an equivalent for Mac/IOS.) (R2Mail2 is not free)

On Mac you can install GPG Tools, and on IOS you could try PGP Everywhere.

Also recommend Password Safe, a simple Password Manager application for Windows designed by renowned security technologist Bruce Schneier with clones for Android & Mac/IOS, and RoboForm or Dashlane or LastPass. Password Safe is an OpenSource software that runs on your computer/phone and Dashlane & LastPass are online Password Manager accounts with browser extensions so they need a strong password for the Master Password, whereas Password Safe does not, unless you share use of a computer with others. (RoboForm is software that runs on a computer, and comes with extensions for most web browsers.)


#1 Get the pieces

This guide relies on software which is freely licensed; it's completely transparent and anyone can copy it or make their own version. This makes it safer from surveillance than proprietary software (like Windows). Learn more about free software at fsf.org.

Most GNU/Linux operating systems come with GnuPG installed on them, so you don't have to download it. Before configuring GnuPG though, you'll need the IceDove desktop email program installed on your computer. Most GNU/Linux distributions have IceDove installed already, though it may be under the alternate name "Thunderbird." Email programs are another way to access the same email accounts you can access in a browser (like Gmail), but provide extra features.

If you already have an email program, you can skip to Step 1.b.

Step 1.A: Install Wizard

Step 1.a Set up your email program with your email account

Open your email program and follow the wizard (step-by-step walkthrough) that sets it up with your email account.

Look for the letters SSL, TLS, or STARTTLS to the right of the servers when you're setting up your account. If you don't see them, you will still be able to use encryption, but this means that the people running your email system are running behind the industry standard in protecting your security and privacy. We recommend that you send them a friendly email asking them to enable SSL, TLS, or STARTTLS for your email server. They will know what you're talking about, so it's worth making the request even if you aren't an expert on these security systems.

Troubleshooting

The wizard doesn't launch
You can launch the wizard yourself, but the menu option for doing so is named differently in each email program. The button to launch it will be in the program's main menu, under "New" or something similar, titled something like "Add account" or "New/Existing email account."
The wizard can't find my account or isn't downloading my mail
Before searching the Web, we recommend you start by asking other people who use your email system, to figure out the correct settings.
  • Step 1.B: Tools -> Add-ons
  • Step 1.B: Search Add-ons
  • Step 1.B: Install Add-ons

Step 1.b Install the Enigmail plugin for your email program

In your email program's menu, select Add-ons (it may be in the Tools section). Make sure Extensions is selected on the left. Do you see Enigmail? Make sure it's the latest version. If so, skip this step.

If not, search "Enigmail" with the search bar in the upper right. You can take it from here. Restart your email program when you're done.

There are major security flaws in versions of GnuPG prior to 2.2.8, and Enigmail prior to 2.0.7. Make sure you have GnuPG 2.2.8 and Enigmail 2.0.7, or later versions.

Troubleshooting

I can't find the menu.
In many new email programs, the main menu is represented by an image of three stacked horizontal bars.
My email looks weird
Enigmail doesn't tend to play nice with HTML, which is used to format emails, so it may disable your HTML formatting automatically. To send an HTML-formatted email without encryption or a signature, hold down the Shift key when you select compose. You can then write an email as if Enigmail wasn't there.

#2 Make your keys

To use the GnuPG system, you'll need a public key and a private key (known together as a keypair). Each is a long string of randomly generated numbers and letters that are unique to you. Your public and private keys are linked together by a special mathematical function.

Your public key isn't like a physical key, because it's stored in the open in an online directory called a keyserver. People download it and use it, along with GnuPG, to encrypt emails they send to you. You can think of the keyserver as a phonebook; people who want to send you encrypted email can look up your public key.

Your private key is more like a physical key, because you keep it to yourself (on your computer). You use GnuPG and your private key together to descramble encrypted emails other people send to you. You should never share your private key with anyone, under any circumstances.

In addition to encryption and decryption, you can also use these keys to sign messages and check the authenticity of other people's signatures. We'll discuss this more in the next section.

Step 2.A: Make a Keypair

Step 2.a Make a keypair

The Enigmail Setup wizard may start automatically. If it doesn't, select Enigmail → Setup Wizard from your email program's menu. You don't need to read the text in the window that pops up unless you'd like to, but it's good to read the text on the later screens of the wizard. Click Next with the default options selected, except in these instances, which are listed in the order they appear:

  • On the screen titled "Encryption," select "Encrypt all of my messages by default, because privacy is critical to me."
  • On the screen titled "Signing," select "Don't sign my messages by default."
  • On the screen titled "Key Selection," select "I want to create a new key pair for signing and encrypting my email."
  • On the screen titled "Create Key," pick a strong password! You can do it manually, or you can use the Diceware method. Doing it manually is faster but not as secure. Using Diceware takes longer and requires dice, but creates a password that is much harder for attackers to figure out. To use it, read the section "Make a secure passphrase with Diceware" in this article by Micah Lee.

If you'd like to pick a password manually, come up with something you can remember which is at least twelve characters long, and includes at least one lower case and upper case letter and at least one number or punctuation symbol. Never pick a password you've used elsewhere. Don't use any recognizable patterns, such as birthdays, telephone numbers, pets' names, song lyrics, quotes from books, and so on.

The program will take a little while to finish the next step, the "Key Creation" screen. While you wait, do something else with your computer, like watching a movie or browsing the Web. The more you use the computer at this point, the faster the key creation will go.

When the "Key Generation Completed" screen pops up, select Generate Certificate and choose to save it in a safe place on your computer (we recommend making a folder called "Revocation Certificate" in your home folder and keeping it there). This step is essential for your email self-defense, as you'll learn more about in Section 5.

Troubleshooting

I can't find the Enigmail menu.
In many new email programs, the main menu is represented by an image of three stacked horizontal bars. Enigmail may be inside a section called Tools.
The wizard says that it cannot find GnuPG.
Open whatever program you usually use for installing software, and search for GnuPG, then install it. Then restart the Enigmail setup wizard by going to Enigmail → Setup Wizard.
More resources
If you're having trouble with our instructions or just want to learn more, check out Enigmail's wiki instructions for key generation.

Advanced

Command line key generation
If you prefer using the command line for a higher degree of control, you can follow the documentation from The GNU Privacy Handbook. Make sure you stick with "RSA and RSA" (the default), because it's newer and more secure than the algorithms the documentation recommends. Also make sure your key is at least 2048 bits, or 4096 if you want to be extra secure.
Advanced key pairs
When GnuPG creates a new keypair, it compartmentalizes the encryption function from the signing function through subkeys. If you use subkeys carefully, you can keep your GnuPG identity much more secure and recover from a compromised key much more quickly. Alex Cabal and the Debian wiki provide good guides for setting up a secure subkey configuration.

Step 2.b Upload your public key to a keyserver

In your email program's menu, select Enigmail → Key Management.

Right click on your key and select Upload Public Keys to Keyserver. You don't have to use the default keyserver. If, after research, you would like to change to a different default keyserver, you can change that setting manually in the Enigmail preferences.

Now someone who wants to send you an encrypted message can download your public key from the Internet. There are multiple keyservers that you can select from the menu when you upload, but they are all copies of each other, so it doesn't matter which one you use. However, it sometimes takes a few hours for them to match each other when a new key is uploaded.

Troubleshooting

The progress bar never finishes
Close the upload popup, make sure you are connected to the Internet, and try again. If that doesn't work, try again, selecting a different keyserver.
My key doesn't appear in the list
Try checking "Display All Keys by Default."
More documentation
If you're having trouble with our instructions or just want to learn more, check out Enigmail's documentation.

Advanced

Uploading a key from the command line
You can also upload your keys to a keyserver through the command line. The sks Web site maintains a list of highly interconnected keyservers. You can also directly export your key as a file on your computer.

GnuPG, OpenPGP, what?

In general, the terms GnuPG, GPG, GNU Privacy Guard, OpenPGP and PGP are used interchangeably. Technically, OpenPGP (Pretty Good Privacy) is the encryption standard, and GNU Privacy Guard (often shortened to GPG or GnuPG) is the program that implements the standard. Enigmail is a plug-in program for your email program that provides an interface for GnuPG.

#3 Try it out!

Now you'll try a test correspondence with a computer program named Edward, who knows how to use encryption. Except where noted, these are the same steps you'd follow when corresponding with a real, live person.

Try it out.

Step 3.a Send Edward your public key

This is a special step that you won't have to do when corresponding with real people. In your email program's menu, go to Enigmail → Key Management. You should see your key in the list that pops up. Right click on your key and select Send Public Keys by Email. This will create a new draft message, as if you had just hit the Write button.

Address the message to edward-en@fsf.org. Put at least one word (whatever you want) in the subject and body of the email. Don't send yet.

The lock icon in the top left should be yellow, meaning encryption is turned on. We want this first special message to be unencrypted, so click the icon once to turn it off. The lock should become grey, with a blue dot on it (to alert you that the setting has been changed from the default). Once encryption is off, hit Send.

It may take two or three minutes for Edward to respond. In the meantime, you might want to skip ahead and check out the Use it Well section of this guide. Once he's responded, head to the next step. From here on, you'll be doing just the same thing as when corresponding with a real person.

When you open Edward's reply, GnuPG may prompt you for your password before using your private key to decrypt it.

Step 3.b Send a test encrypted email

Write a new email in your email program, addressed to edward-en@fsf.org. Make the subject "Encryption test" or something similar and write something in the body.

The lock icon in the top left of the window should be yellow, meaning encryption is on. This will be your default from now on.

Next to the lock, you'll notice an icon of a pencil. We'll get to this in a moment.

Click Send. Enigmail will pop up a window that says "Recipients not valid, not trusted or not found."

To encrypt an email to Edward, you need his public key, so now you'll have Enigmail download it from a keyserver. Click Download Missing Keys and use the default in the pop-up that asks you to choose a keyserver. Once it finds keys, check the first one (Key ID starting with C), then select ok. Select ok in the next pop-up.

Now you are back at the "Recipients not valid, not trusted or not found" screen. Check the box in front of Edward's key and click Send.

Since you encrypted this email with Edward's public key, Edward's private key is required to decrypt it. Edward is the only one with his private key, so no one except him can decrypt it.

Troubleshooting

Enigmail can't find Edward's key
Close the pop-ups that have appeared since you clicked Send. Make sure you are connected to the Internet and try again. If that doesn't work, repeat the process, choosing a different keyserver when it asks you to pick one.
Unscrambled messages in the Sent folder
Even though you can't decrypt messages encrypted to someone else's key, your email program will automatically save a copy encrypted to your public key, which you'll be able to view from the Sent folder like a normal email. This is normal, and it doesn't mean that your email was not sent encrypted.
More resources
If you're still having trouble with our instructions or just want to learn more, check out Enigmail's wiki.

Advanced

Encrypt messages from the command line
You can also encrypt and decrypt messages and files from the command line, if that's your preference. The option --armor makes the encrypted output appear in the regular character set.

Important: Security tips

Even if you encrypt your email, the subject line is not encrypted, so don't put private information there. The sending and receiving addresses aren't encrypted either, so a surveillance system can still figure out who you're communicating with. Also, surveillance agents will know that you're using GnuPG, even if they can't figure out what you're saying. When you send attachments, Enigmail will give you the choice to encrypt them or not, independent of the actual email.

For greater security against potential attacks, you can turn off HTML. Instead, you can render the message body as plain text. In order to do this in Thunderbird, go to View > Message Body As > Plain Text.

Step 3.c Receive a response

When Edward receives your email, he will use his private key to decrypt it, then reply to you.

It may take two or three minutes for Edward to respond. In the meantime, you might want to skip ahead and check out the Use it Well section of this guide.

Step 3.d Send a test signed email

GnuPG includes a way for you to sign messages and files, verifying that they came from you and that they weren't tampered with along the way. These signatures are stronger than their pen-and-paper cousins -- they're impossible to forge, because they're impossible to create without your private key (another reason to keep your private key safe).

You can sign messages to anyone, so it's a great way to make people aware that you use GnuPG and that they can communicate with you securely. If they don't have GnuPG, they will be able to read your message and see your signature. If they do have GnuPG, they'll also be able to verify that your signature is authentic.

To sign an email to Edward, compose any message to him and click the pencil icon next to the lock icon so that it turns gold. If you sign a message, GnuPG may ask you for your password before it sends the message, because it needs to unlock your private key for signing.

With the lock and pencil icons, you can choose whether each message will be encrypted, signed, both, or neither.

Step 3.e Receive a response

When Edward receives your email, he will use your public key (which you sent him in Step 3.A) to verify the message you sent has not been tampered with and to encrypt his reply to you.

It may take two or three minutes for Edward to respond. In the meantime, you might want to skip ahead and check out the Use it Well section of this guide.

Edward's reply will arrive encrypted, because he prefers to use encryption whenever possible. If everything goes according to plan, it should say "Your signature was verified." If your test signed email was also encrypted, he will mention that first.

When you receive Edward's email and open it, Enigmail will automatically detect that it is encrypted with your public key, and then it will use your private key to decrypt it.

Notice the bar that Enigmail shows you above the message, with information about the status of Edward's key.

#4 Learn the Web of Trust

Email encryption is a powerful technology, but it has a weakness; it requires a way to verify that a person's public key is actually theirs. Otherwise, there would be no way to stop an attacker from making an email address with your friend's name, creating keys to go with it and impersonating your friend. That's why the free software programmers that developed email encryption created keysigning and the Web of Trust.

When you sign someone's key, you are publicly saying that you've verified that it belongs to them and not someone else.

Signing keys and signing messages use the same type of mathematical operation, but they carry very different implications. It's a good practice to generally sign your email, but if you casually sign people's keys, you may accidently end up vouching for the identity of an imposter.

People who use your public key can see who has signed it. Once you've used GnuPG for a long time, your key may have hundreds of signatures. You can consider a key to be more trustworthy if it has many signatures from people that you trust. The Web of Trust is a constellation of GnuPG users, connected to each other by chains of trust expressed through signatures.

Section 4: Web of Trust

Step 4.a Sign a key

In your email program's menu, go to Enigmail → Key Management.

Right click on Edward's public key and select Sign Key from the context menu.

In the window that pops up, select "I will not answer" and click ok.

Now you should be back at the Key Management menu. Select Keyserver → Upload Public Keys and hit ok.

You've just effectively said "I trust that Edward's public key actually belongs to Edward." This doesn't mean much because Edward isn't a real person, but it's good practice.

Identifying keys: Fingerprints and IDs

People's public keys are usually identified by their key fingerprint, which is a string of digits like F357AA1A5B1FA42CFD9FE52A9FF2194CC09A61E8 (for Edward's key). You can see the fingerprint for your public key, and other public keys saved on your computer, by going to Enigmail → Key Management in your email program's menu, then right clicking on the key and choosing Key Properties. It's good practice to share your fingerprint wherever you share your email address, so that people can double-check that they have the correct public key when they download yours from a keyserver.

You may also see public keys referred to by a shorter key ID. This key ID is visible directly from the Key Management window. These eight character key IDs were previously used for identification, which used to be safe, but is no longer reliable. You need to check the full fingerprint as part of verifying you have the correct key for the person you are trying to contact. Spoofing, in which someone intentionally generates a key with a fingerprint whose final eight characters are the same as another, is unfortunately common.

Important: What to consider when signing keys

Before signing a person's key, you need to be confident that it actually belongs to them, and that they are who they say they are. Ideally, this confidence comes from having interactions and conversations with them over time, and witnessing interactions between them and others. Whenever signing a key, ask to see the full public key fingerprint, and not just the shorter key ID. If you feel it's important to sign the key of someone you've just met, also ask them to show you their government identification, and make sure the name on the ID matches the name on the public key. In Enigmail, answer honestly in the window that pops up and asks "How carefully have you verified that the key you are about to sign actually belongs to the person(s) named above?"

Advanced

Master the Web of Trust
Unfortunately, trust does not spread between users the way many people think. One of best ways to strengthen the GnuPG community is to deeply understand the Web of Trust and to carefully sign as many people's keys as circumstances permit.
Set ownertrust
If you trust someone enough to validate other people's keys, you can assign them an ownertrust level through Enigmails's key management window. Right click on the other person's key, go to the "Select Owner Trust" menu option, select the trustlevel and click OK. Only do this once you feel you have a deep understanding of the Web of Trust.

#5 Use it well

Everyone uses GnuPG a little differently, but it's important to follow some basic practices to keep your email secure. Not following them, you risk the privacy of the people you communicate with, as well as your own, and damage the Web of Trust.

Section 5: Use it Well (1)

When should I encrypt? When should I sign?

The more you can encrypt your messages, the better. If you only encrypt emails occasionally, each encrypted message could raise a red flag for surveillance systems. If all or most of your email is encrypted, people doing surveillance won't know where to start. That's not to say that only encrypting some of your email isn't helpful -- it's a great start and it makes bulk surveillance more difficult.

Unless you don't want to reveal your own identity (which requires other protective measures), there's no reason not to sign every message, whether or not you are encrypting. In addition to allowing those with GnuPG to verify that the message came from you, signing is a non-intrusive way to remind everyone that you use GnuPG and show support for secure communication. If you often send signed messages to people that aren't familiar with GnuPG, it's nice to also include a link to this guide in your standard email signature (the text kind, not the cryptographic kind).

Section 5: Use it Well (2)

Be wary of invalid keys

GnuPG makes email safer, but it's still important to watch out for invalid keys, which might have fallen into the wrong hands. Email encrypted with invalid keys might be readable by surveillance programs.

In your email program, go back to the first encrypted email that Edward sent you. Because Edward encrypted it with your public key, it will have a message from Enigmail at the top, which most likely says "Enigmail: Part of this message encrypted."

When using GnuPG, make a habit of glancing at that bar. The program will warn you there if you get an email signed with a key that can't be trusted.

Copy your revocation certificate to somewhere safe

Remember when you created your keys and saved the revocation certificate that GnuPG made? It's time to copy that certificate onto the safest digital storage that you have -- the ideal thing is a flash drive, disk, or hard drive stored in a safe place in your home, not on a device you carry with you regularly.

If your private key ever gets lost or stolen, you'll need this certificate file to let people know that you are no longer using that keypair.

Important: act swiftly if someone gets your private key

If you lose your private key or someone else gets ahold of it (say, by stealing or cracking your computer), it's important to revoke it immediately before someone else uses it to read your encrypted email or forge your signature. This guide doesn't cover how to revoke a key, but you can follow these instructions. After you're done revoking, make a new key and send an email to everyone with whom you usually use your key to make sure they know, including a copy of your new key.

Transferring you key

You can use Enigmail's key management window to import and export keys. If you want to be able to read your encrypted email on a different computer, you will need to export your secret key from here. Be warned, if you transfer the key without encrypting the drive it's on the transfer will be dramatically less secure.

Webmail and GnuPG

When you use a web browser to access your email, you're using webmail, an email program stored on a distant website. Unlike webmail, your desktop email program runs on your own computer. Although webmail can't decrypt encrypted email, it will still display it in its encrypted form. If you primarily use webmail, you'll know to open your email client when you receive a scrambled email.

Make your public key part of your online identity

First add your public key fingerprint to your email signature, then compose an email to at least five of your friends, telling them you just set up GnuPG and mentioning your public key fingerprint. Link to this guide and ask them to join you. Don't forget that there's also an awesome infographic to share.

Start writing your public key fingerprint anywhere someone would see your email address: your social media profiles, blog, Website, or business card. (At the Free Software Foundation, we put ours on our staff page.) We need to get our culture to the point that we feel like something is missing when we see an email address without a public key fingerprint.

Great job! Check out the next steps.

FAQ

My key expired
Answer coming soon.
Who can read encrypted messages? Who can read signed ones?
Answer coming soon.
My email program is opening at times I don't want it to open/is now my default program and I don't want it to be.
Answer coming soon.
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Find the above article at emailselfdefense.fsf.org 

The fingerprint for my email is:


3643 E3E1 18AA 14E1 8944 A6FC DDA1 063C 25D5 B297

 

My GnuPG/PGP public key is also available here.

 

The above articles were combined here by WholisticApproches.net

 

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