Email Self-Defense - a guide to fighting surveillance with GnuPG encryption

Email Self-Defense - a guide to fighting surveillance with GnuPG
encryption
#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 or macOS). Learn more about free software at
fsf.org
Most GNU/Linux operating systems come with GnuPG installed on them, so if you're running one of these systems, you don't have to download it. If you're running macOS or Windows, steps to download GnuPG are below. Before configuring your encryption setup with this guide, though, you'll need a desktop email program installed on your computer. Many GNU/Linux distributions have one installed already, such as Icedove, which may be under the alternate name "Thunderbird." Programs like these are another way to access the same email accounts you can access in a browser (like Gmail), but provide extra features.
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. This usually starts from "Account Settings" → "Add Mail Account". You should get the email server settings from your systems administrator or the help section of your email account.
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.
I can't find the menu
In many new email programs, the main menu is represented by an image of
three stacked horizontal bars.
Don't see a solution to your problem?
Please let us know on the
feedback
page
Step 1.b
Install GnuPG
If you are using a GNU/Linux machine, you should already have GnuPG installed, and you can skip to
Section 2
If you are using a macOS or Windows machine, however, you need to first install the GnuPG program. Select your operating system below and follow the instructions. For the rest of this guide, the steps are the same for all operating systems.
macOS
Use a third-party package manager to install GnuPG
The default macOS package manager makes it difficult to install GnuPG and other pieces of free software (like Emacs, GIMP, or Inkscape). To make things easier, we recommend setting up the third-party package manager "Homebrew" to install GnuPG. For this, we will use a program called "Terminal," which is pre-installed on macOS.
# Copy the first command on the home page of
Homebrew
by clicking on the clipboard icon, and paste it in Terminal. Click "Enter" and wait for the installation to finalize.
# Then install GnuPG by entering the following code in Terminal:
brew install gnupg gnupg2
Windows
Get GnuPG by downloading GPG4Win
GPG4Win
is an email and file encryption software package that includes GnuPG. Download and install the latest version, choosing default options whenever asked. After it's installed, you can close any windows that it creates.
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. Most email programs provide an interface for GnuPG. There is also a newer version of GnuPG, called GnuPG2.
#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
Make your keypair
We will use the command line in a terminal to create a keypair using the
GnuPG program.
Whether on GNU/Linux, macOS or Windows, you can launch your
terminal ("Terminal" in macOS, "PowerShell" in Windows) from the Applications
menu (some GNU/Linux systems respond to the
Ctrl + Alt + T
shortcut).
# Enter
gpg --full-generate-key
to start the process.
# To answer what kind of key you would like to create, select the default option:
1 RSA and RSA
# Enter the following keysize:
4096
for a strong key.
# Choose the expiration date; we suggest
2y
(2 years).
Follow the prompts to continue setting up with your personal details.
Depending on your version of GPG, you may need to use
--gen-key
instead of
--full-generate-key
.
You can set further options by running
gpg --edit-key [your@email]
in a
terminal window.
Set your passphrase
On the screen titled "Passphrase," pick a strong passphrase! 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 passphrase 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 passphrase 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 passphrase 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.
Troubleshooting
GnuPG is not installed
You can check if this is the case with the command
gpg --version
.
If GnuPG is not installed, it will bring up the following result on most GNU/Linux operating systems, or something like it:
Command 'gpg' not found, but can be installed with:
sudo apt install gnupg
. Follow that command and install the program.
gpg --full-generate-key
command not working
Some distributions use a different version of GPG. When you receive an error code that is something along the lines of:
gpg: Invalid option "--full-generate-key"
, you can try the following commands:
sudo apt update
sudo apt install gnupg2
gpg2 --full-generate-key
If this resolved the issue, you need to continue to use the gpg2 identifier instead of gpg throughout the following steps of the guide.
Depending on your version of GPG, you may need to use
--gen-key
instead of
--full-generate-key
.
I took too long to create my passphrase
That's okay. It's important to think about your passphrase. When you're ready, just follow the steps from the beginning again to create your key.
How can I see my key?
Use the following command to see all keys:
gpg --list-keys
. Yours should be listed in there, and later, so will Edward's (
Section 3
).
If you want to see only your key, you can use
gpg --list-key [your@email]
.
You can also use
gpg --list-secret-key
to see your own private key.
More resources
For more information about this process, you can also refer to
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 4096 bits if you
want to be secure.
Don't see a solution to your problem?
Please let us know on the
feedback
page
Advanced
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 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
Some important steps following creation
Upload your key to a keyserver
We will upload your key to a keyserver, so if someone wants to send you an encrypted message, they 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 mostly all copies
of each other. Any server will work, but it's good to remember which one you uploaded your key to originally. Also keep in mind, sometimes takes a few hours for them to match each other when a new key is uploaded.
# Copy your keyID:
gpg --list-key [your@email]
will list your public ("pub") key information, including your keyID, which is a unique list of numbers and letters. Copy this keyID, so you can use it in the following command.
# Upload your key to a server:
gpg --send-key [keyID]
Export your key to a file
Use the following command to export your secret key so you can import it into your email client at the next
step
. To avoid getting your key compromised, store this in a safe place, and make sure that if it is transferred, it is done so in a trusted way. Exporting your keys can be done with the following commands:
$ gpg --export-secret-keys -a [keyID] > my_secret_key.asc
$ gpg --export -a [keyID] > my_public_key.asc
Generate a revocation certificate
Just in case you lose your key, or it gets compromised, you want to generate a certificate and choose to save it in a safe place on your computer for now (please refer to
Step 6.C
for how to best store your revocation cerficate safely). This step is essential for your email self-defense, as you'll learn more about in
Section 5
# Copy your keyID:
gpg --list-key [your@email]
will list your public ("pub") key information, including your keyID, which is a unique list of numbers and letters. Copy this keyID, so you can use it in the following command.
# Generate a revocation certificate:
gpg --gen-revoke --output revoke.asc [keyID]
# It will prompt you to give a reason for revocation, we recommend to use
1 = key has been compromised
# You don't have to fill in a reason, but you can; then press "Enter" for an empty line, and confirm your selection.
Troubleshooting
Sending my key to the keyserver is not working
Instead of using the general command to upload your key to the keyserver, you can use a more specific command and add the keyserver to your command
gpg --keyserver keys.openpgp.org --send-key [keyID]
.
My key doesn't seem to be working or I get a "permission denied."
Like every other file or folder, gpg keys are subject to permissions. If these are not set correctly, your system may not be accepting your keys. You can follow the next steps to check, and update to the right permissions.
# Check your permissions:
ls -l ~/.gnupg/*
# Set permissions to read, write, execute for only yourself, no others. These are the recommended permissions for your folder.
You can use the command:
chmod 700 ~/.gnupg
# Set permissions to read and write for yourself only, no others. These are the recommended permissions for the keys inside your folder.
You can use the code:
chmod 600 ~/.gnupg/*
If you have (for any reason) created your own folders inside ~/.gnupg, you must also additionally apply execute permissions to that folder. Folders require execution privileges to be opened. For more information on permissions, you can check out
this detailed information guide
Don't see a solution to your problem?
Please let us know on the
feedback
page
Advanced
More about keyservers
You can find some more keyserver information
in this manual
. You can also
directly export
your key
as a file on your computer.
Transferring your keys
Use the following commands to transfer your keys. To avoid getting your key compromised, store it in a safe place, and make sure that if it is transferred, it is done so in a trusted way. Importing and exporting a key can be done with the following commands:
$ gpg --export-secret-keys -a [keyID] > my_private_key.asc
$ gpg --export -a [keyID] > my_public_key.asc
$ gpg --import my_private_key.asc
$ gpg --import my_public_key.asc
Ensure that the keyID printed is the correct one, and if so, then go ahead and add ultimate trust for it:
$ gpg --edit-key [your@email]
Because this is your key, you should choose
ultimate
. You shouldn't trust anyone else's key ultimately.
Refer to
Troubleshooting in Step 2.B
for more information on permissions. When transferring keys, your permissions may get mixed, and errors may be prompted. These are easily avoided when your folders and files have the right permissions
#3
Set up email encryption
The Icedove (or Thunderbird) email program has PGP functionality integrated, which makes it pretty easy to work with. We'll take you through the steps of integrating and using your key in these email clients.
Step 3.a
Set up your email with encryption
Once you have set up your email with encryption, you can start contributing to encrypted traffic on the Internet. First we'll get your email client to import your secret key, and we will also learn how to get other people's public keys from servers so you can send and receive encrypted email.
# Open your email client and use "Tools" →
OpenPGP Key Manager
# Under "File" →
Import Secret Key(s) From File
# Select the file you saved under the name [my_secret_key.asc] in
Step 2.B
when you exported your key
# Unlock with your passphrase
# You will receive a "OpenPGP keys successfully imported" window to confirm success
# Go to "Account settings" → "End-To-End Encryption," and make sure your key is imported and select
Treat this key as a Personal Key
Troubleshooting
I'm not sure the import worked correctly
Look for "Account settings" → "End-To-End Encryption." Here you can see if your personal key associated with this email is found. If it is not, you can try again via the
Add key
option. Make sure you have the correct, active, secret key file.
Don't see a solution to your problem?
Please let us know on the
feedback
page
#4
Try it out!
Now you'll try a test correspondence with an FSF 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.
Step 4.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 "Tools" → "OpenPGP Key
Manager." 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, but in the attachment you will find your public keyfile.
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.
We want Edward to be able to open the email with your keyfile, so we want this first special message to be unencrypted. Make sure encryption is turned off by using the dropdown menu "Security" and select
Do Not Encrypt
. 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 you have received a response,
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 passphrase
before using your private key to decrypt it.
Step 4.b
Send a test encrypted email
Get Edward's key
To encrypt an email to Edward, you need its public key, so now you'll have
to download it from a keyserver. You can do this in two different ways:
Option 1.
In the email answer you received from Edward as a response to your first email, Edward's public key was included. On the right of the email, just above the writing area, you will find an "OpenPGP" button that has a lock and a little wheel next to it. Click that, and select
Discover
next to the text: "This message was signed with a key that you don't yet have." A popup with Edward's key details will follow.
Option 2.
Open your OpenPGP Key manager, and under "Keyserver" choose
Discover Keys Online
. Here, fill in Edward's email address, and import Edward's key.
The option
Accepted (unverified)
will add this key to your key manager, and now it can be used to send encrypted emails and to verify digital signatures from Edward.
In the popup window confirming if you want to import Edward's key, you'll see many different emails that are all associated with its key. This is correct; you can safely import the key.
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
its private key, so no one except Edward can decrypt it.
Send Edward an 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.
This time, make sure encryption is turned on by using the dropdown menu "Security" and select
Require Encryption
. Once encryption is on, hit Send.
Troubleshooting
"Recipients not valid, not trusted or not found"
You could get the above error message, or something along these lines: "Unable to send this message with end-to-end encryption, because there are problems with the keys of the following recipients: ..." In these cases, you may be trying to send an encrypted email to someone when you do not have their public key yet. Make sure you follow the steps above to import the key to your key manager. Open the OpenPGP Key Manager to make sure the recipient is listed there.
Unable to send message
You could get the following message when trying to send your encrypted email: "Unable to send this message with end-to-end encryption, because there are problems with the keys of the following recipients: edward-en@fsf.org." This usually means you imported the key with the "Not accepted (undecided)" option. Go to the "key properties" of this key by right clicking on the key in the OpenPGP Key Manager, and select the option
Yes, but I have not verified that this is the correct key
in the "Acceptance" option at the bottom of this window. Resend the email.
I 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, you can download the key manually from
the keyserver
, and import it by using the
Import Public Key(s) from File
option in the OpenPGP Key Manager.
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.
Don't see a solution to your problem?
Please let us know on the
feedback
page
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, you can choose 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 Icedove or Thunderbird, go to "View" → "Message Body As" →
Plain
Text
Step 4.c
Receive a response
When Edward receives your email, it will use its 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.
Edward will send you an encrypted email back saying your email was received and decrypted. Your email client will automatically decrypt Edward's message.
The OpenPGP button in the email will show a little green checkmark over the lock symbol to show the message is encrypted, and a little orange warning sign which means that you have accepted the key, but not verified it. When you have not yet accepted the key, you will see a little question mark there. Clicking the prompts in this button will lead you to key properties as well.
Step 4.d
Send a signed test 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 the email address 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 passphrase before it sends the message,
because it needs to unlock your private key for signing.
In "Account Settings" → "End-To-End-Encryption" you can opt to
add digital signature by default
Step 4.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 a 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, your email client will
automatically detect that it is encrypted with your public key, and
then it will use your private key to decrypt it.
#5
Learn about 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 accidentally 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.
Step 5.a
Sign a key
In your email program's menu, go to OpenPGP Key Manager and select
Key properties
by right clicking on Edward's key.
Under "Your Acceptance," you can select
Yes, I've verified in person this key has the correct fingerprint
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, and for real people it is important. You can read more about signing a person's key in the
check IDs before signing
section.
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 OpenPGP 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
keyID. This keyID is visible directly from the Key Management
window. These eight character keyIDs 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
keyID. 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.
Advanced
Master the Web of Trust
Unfortunately, trust does not spread between users the way
many people
think
. One of the 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.
#6
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.
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).
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
green checkmark on the "OpenPGP" button.
When using GnuPG, make a habit of glancing at that button. 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 storage that you have -- a flash drive, disk, or hard drive stored in a safe place in your home could work, not on a device you carry with you regularly. The safest way we know is actually to print the revocation certificate and store it in a safe place.
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 a hold
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.
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.