It’s (crypto)party time!

With our advanced free democracies resembling George Orwell’s “1984” more and more (your TV is spying on you, NSA global mass-surveillance, pre-crime repression of free speech  etc), there surely couldn’t be a better time to throw a CryptoParty!

Where?

New Academic Building
Goldsmiths, University of London
New Cross
London SE14 6NW
(OpenStreetMap)

When?

Saturday 30th November, 11am onwards

Cost/audience

The event is free & open to the public. Anyone who worries about the privacy and ultimately freedom of expression of their loved ones should attend.

Great lineup of speakers/presenters – check out the event schedule!

I will be doing a few workshops on mobile device privacy, encrypted Internet phone calls and using a computer without leaving any traces behind.

If you’re around on the 30th, join us for a day of practical tinkering with privacy tools!

…and here are the slide decks of the workshops I ran:

Qubes OS – a secure operating system: https://apapadop.files.wordpress.com/2013/12/qubes1.pdf

TAILS – This session never happened: https://apapadop.files.wordpress.com/2013/12/tails1.pdf

VoIP- Private voice calls: https://apapadop.files.wordpress.com/2013/12/voip1.pdf

Mobile privacy – how to keep your smartphone communications private: https://apapadop.files.wordpress.com/2013/12/mobile5.pdf

OTR – a gentle introduction to chatting Off The Record: https://apapadop.files.wordpress.com/2013/12/otr1.pdf

How to send and receive encrypted emails in Windows

Why use encrypted email?

It’s simple: the government is reading your emails. Edward Snowden’s revelations make this a plain truth. If you are not an American citizen it’s a little bit worse, because at least two governments are reading your emails: yours, and the American government.

There are many plugins/addons/guides out there that claim to “encrypt” your email, so that “nobody can read it”. Most of those are nonsense. There is currently only one well-known way of encrypting emails so that only the intended recipient will read them. That is the OpenPGP protocol. So if you’re not using the commercial PGP product, the free GnuPG product, or another well-known product that follows the OpenPGP protocol, your emails can still be read by the government.

But if you’ve been following the news you will wonder “Hang on – if OpenPGP is secure, why did a bunch of prominent Internet security experts like the Silent Circle board decide to shut down their Silent Mail service (which used OpenPGP)?” The answer is that OpenPGP is based on cryptographic keys. And Silent Mail tried to manage your keys for you, which made Silent Circle vulnerable to the law – as the law in most countries states that government agencies can force companies to disclose such secrets.

Therefore, the problem was key concentration. If Silent Circle holds all the keys, the FBI slaps them with a few subpoenas and grabs all of our secret keys. Heck, Silent Circle can not even tell us about it – by law!

So, OpenPGP is still considered trustworthy as a technology – what doesn’t work is concentrating key management, because by law the government can grab all secret keys, which will allow them to read all encrypted emails we’ve sent using those keys.

But what if we just manage our own keys? The government would not legally compel all of its citizens – directly, on a one-by-one basis – to give up their secrets. That would be much less politically palatable than a program like PRISM, where they just suck out the data from our service providers (Google, Yahoo!, Microsoft, Apple etc).

Using OpenPGP and managing our own keys, then, is the best we can do right now. Let me show you how.

Note: This tutorial will focus on making using encrypted emails as easy as possible. We will propose settings that are optimised for convenience, not security. If you are a journalist, an activist, a politician or anyone who needs a setup as secure as possible, let me know in the comments and I will propose more secure but inevitably slightly less convenient settings.

Setting up encrypted email

For this example, I will use a free Gmail account and setup access from my Windows 7 computer. Note that this method is not Gmail specific. It will work for any email account out there.

Get GnuPG

Installing GnuPG will allow your email program to encrypt your emails.

1. Download Gpg4win from http://gpg4win.org/download.html
2. Run the gpg4win-(version).exe installer to install the software, ensuring that GPA is selected for installation as well:
   

Get Thunderbird

Thunderbird is the email application we will use to send and receive emails. We can’t just use GMail’s webpage for encrypted emails – it will become cumbersome in the long run.

1. Download Thunderbird from https://www.mozilla.org/thunderbird
2. Run “Thunderbird Setup (version).exe” to install Thunderbird on your computer.

Connect Thunderbird with your email account

As soon as setup is finished and Thunderbird launches, you are asked whether you’d like a new email address. Let’s skip this for now and go with your existing email address.

(For this example I will use the Gmail account jdoe18293@gmail.com)

Fill in your name, email address and Gmail password.

Thunderbird checks for the settings of your email provider

…and, in the case of a well-known service as Gmail, finds the right settings:

If everything works and the dialog disapears with no errors, great. If not, verify that whichever access method you choose (POP or IMAP), is supported and enabled for your account. For our example (Gmail), follow these instructions to enable IMAP.

If you see the following window, with your email account on the top left, you have configured Thunderbird correctly. Congratulations!

Get the encryption addon (EnigMail)

Click on the “menu” icon on the top right and then “Addons“.

Search for “enigmail” and install the addon.

Click on “Restart Now” – this will only restart Thunderbird, not your computer.

After Thunderbird has restarted, close the Add Ons tab – you’re done with this.

Create your encryption keys

Go to Options -> OpenPGP -> Setup Wizard

Go through the wizard, adjusting only the following settings:

In the “Signing” step of the wizard choose “No, I want to create per-recipient rules for emails that need to be signed“.

In the “No OpenPGP Key Found” step of the wizard choose “I want to create a new key pair for signing and encrypting my email”

In the “Create Key” step, choose the passphrase that will be required to read or send encrypted emails.

Note: Choose something that is easy to type and not too long. (remember, we’re optimising for usability here)

Good passphrase: “This is my favourite song!”

Bad passphrase: 9x$Z4;Fq (why?)

When the wizard completes, you will be prompted to generate a revocation certificate. This is a good idea – it’s like an insurance policy for when you lose your key:

Save this file on your Desktop for now – you can decide where to store it permanently (away from your computer! – e.g. on a CDROM or a USB stick you keep in a safe place) later.

Your passphrase is needed to generate the revocation certificate:

… at which point you are done!

Congratulations, you have created cryptographic keys and setup your email program to use them!

Sending email

You can only exchange encrypted emails with people who also use OpenPGP. Before you can send people encrypted email, you need to make your public key available to the world, otherwise your recipients will not be able to read your emails.

Publishing your public key

Open Thunderbird and click on its “options” button. Then OpenPGP -> Key Management.

Tick “Display All Keys by Default”:

Now click on your name (John Doe) to select your keys and go to Keyserver -> Upload Public Keys

In the next prompt just click OK:

Congratulations – you have published your public keys on the keyservers. Now anyone using OpenPGP can send you encrypted and signed email, and people can read the encrypted emails you send them!

Sending your first encrypted email

Let’s email our friend Bob. He also has a Gmail account and his Gmail address is anon7889@gmail.com

To start composing a new message in Thunderbird you click the “Write” button:

This brings up a new email window, where you can address and type your message.

Notice the pen and the key icons in the lower right corner? They are greyed-out, i.e. inactive, i.e. you are currently not signing (pen) or encrypting (key) your message.

Let’s click on the key icon to enable message encryption – the icon becomes colourful (gold), which means encryption has been activated:

Let’s attempt to send this message – click the “Send” button. You have just asked Thunderbird to encrypt this message for Bob (anon7889@gmail.com) – but Thunderbird hasn’t got Bob’s public key! And this is how public key encryption works – you need to have people’s public keys before you can encrypt stuff for them – and only them – to read. Therefore, Thunderbird complains that your recipient has not been found (in your OpenPGP keyring):

Click “Download missing keys” to look for Bob’s key on the keyservers – dedicated computers that host people’s keys.

Just hit OK to allow Thunderbird to look for Bob’s public key online.

And lo! Bob’s public key is there. Just tick it and click OK to import Bob’s key on your keyring. You only need to do this once.

If all went well, Thunderbird lets you know the import was successful:

Great, now you have Bob’s key. You have a new greyed-out line with Bob’s email address. Tick the box of that line and click on “Create per-recipient rule(s)“.

Here you will tell Thunderbird to always use this key to sign and encrypt your emails to Bob.

Click on “Select Key(s)…“:

…and make sure the line with Bob’s address is selected before clicking OK:

Now tell Thunderbird to always sign and encrypt your messages to Bob by changing these fields to “Always“:

Clicking “OK” closes this window and immediately prompts you for your passphrase, as you’re just about to cryptographically sign a message to somebody – that requires access to your secret key, which can only be accessed with the passphrase you setup earlier:

As soon as you hit “OK” with that passphrase – oh my! Look at all this gibberish – that’s encrypted text, otherwise called “ciphertext”. This is what the spooks will now see. This is what Google will store. This is what Bob will see as well, but because he has the right private key, he will be able to decrypt this ciphertext into your plaintext email message.

See, it doesn’t matter that Google and the spooks can still read your email, because now it looks like gibberish, and it can only be decrypted and read by your intended recipients (in this case, Bob). You can use this method to communicate in private with anyone in the world, as long as they use OpenPGP too.

Congratulations! You have just sent you first cryptographically signed and encrypted message, using the most robust encryption technology known to mankind: OpenPGP.

Sending your second, third… 1000’th email

Things are much simpler now that you’ve done all the hard work in advance. All you need to do is compose an email to Bob. Thunderbird will automatically sign and encrypt your message with the right key, so that only Bob can read it. Pretty slick.

Notice the blue “+” next to the pen and the key? That means your message to Bob will be automatically

• signed – so that Bob knows the message came from you and it has not been altered in any way) and
• encrypted – so that no one else but Bob can read its contents.

Enjoy your private chats with Bob!

Receiving email

Receiving OpenPGP encrypted email is not a problem – you just need to provide your passphrase and you will be able to read the message.

Using GnuPG with QubesOS

So Alice and Bob want to exchange private emails and files.

They realise that secure endpoint operating systems are an absolute requirement for any real privacy. What’s the point of protecting data in transit with PGP, when the spooks can remotely take over your machine and grab your stuff from the source? So they’ve taken the time to learn how to use Qubes OS – a security-by-separation operating system based on Xen and Fedora GNU/Linux.

Alice and Bob will use the non-networked “vault” AppVM to create and store their master cryptographic keys. They will then create a “daily use” keypair which will be available to their “personal” AppVM to send emails to each other.

Note: OpenPGP key management is complicated. To protect you from mistakes, this tutorial sets the expiry date of keys to one week after their creation. Once you are comfortable with this process you can always extend the life of your keys.

Create a new keypair

[user@vault ~]$ gpg --gen-key
gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

gpg: directory `/home/alice/.gnupg' created
gpg: new configuration file `/home/alice/.gnupg/gpg.conf' created
gpg: WARNING: options in `/home/alice/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/home/alice/.gnupg/secring.gpg' created
gpg: keyring `/home/alice/.gnupg/pubring.gpg' created
Please select what kind of key you want:
(1) RSA and RSA (default)
(2) DSA and Elgamal
(3) DSA (sign only)
(4) RSA (sign only)
Your selection? 1
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
0 = key does not expire
<n>  = key expires in n days
<n>w = key expires in n weeks
<n>m = key expires in n months
<n>y = key expires in n years
Key is valid for? (0) 1w
Key expires at Thu Aug 22 18:38:49 2013 BST
Is this correct? (y/N) y

You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
"Heinrich Heine (Der Dichter) <heinrichh@duesseldorf.de>"

Real name: Alice
Email address: alice@domain.com
Comment:
You selected this USER-ID:
"Alice <alice@domain.com>"

Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O
You need a Passphrase to protect your secret key.

Enter passphrase: <Alice's long passphrase>
Repeat passphrase: <Alice's long passphrase>
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

Not enough random bytes available.  Please do some other work to give
the OS a chance to collect more entropy! (Need 246 more bytes)
..............+++++
gpg: /home/alice/.gnupg/trustdb.gpg: trustdb created
gpg: key 32D49659 marked as ultimately trusted
public and secret key created and signed.

gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
gpg: next trustdb check due at 2013-08-22
pub   4096R/32D49659 2013-08-15 [expires: 2013-08-22]
Key fingerprint = 0346 5C7A 6412 A70B ED13  0196 9652 5380 32D4 9659
uid                  Alice <alice@domain.com>
sub   4096R/E19F81C0 2013-08-15 [expires: 2013-08-22]

[user@vault ~]$

Set strong cipher preferences

[user@vault ~]$ gpg --edit-key alice
gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC
trust: ultimate      validity: ultimate
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E
[ultimate] (1). Alice <alice@domain.com>

gpg> setpref SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES CAST5 ZLIB BZIP2 ZIP
Set preference list to:
Cipher: AES256, AES192, AES, CAST5, 3DES
Digest: SHA512, SHA384, SHA256, SHA224, SHA1
Compression: ZLIB, BZIP2, ZIP, Uncompressed
Features: MDC, Keyserver no-modify
Really update the preferences? (y/N) y

You need a passphrase to unlock the secret key for
user: "Alice <alice@domain.com>"
4096-bit RSA key, ID 32D49659, created 2013-08-15

Enter passphrase: <Alice's long passphrase>
pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC
trust: ultimate      validity: ultimate
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E
[ultimate] (1). Alice <alice@domain.com>

gpg> save
[user@vault ~]$

Add a signing subkey

[user@vault ~]$ gpg --edit-key alice
gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC
trust: ultimate      validity: ultimate
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E
[ultimate] (1). Alice <alice@domain.com>

gpg> addkey
Key is protected.

You need a passphrase to unlock the secret key for
user: "Alice <alice@domain.com>"
4096-bit RSA key, ID 32D49659, created 2013-08-15

Enter passphrase: <Alice's long passphrase>
Please select what kind of key you want:
(3) DSA (sign only)
(4) RSA (sign only)
(5) Elgamal (encrypt only)
(6) RSA (encrypt only)
Your selection? 4
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 4096
Requested keysize is 4096 bits
Please specify how long the key should be valid.
0 = key does not expire
<n>  = key expires in n days
<n>w = key expires in n weeks
<n>m = key expires in n months
<n>y = key expires in n years
Key is valid for? (0) 1w
Key expires at Thu Aug 22 18:53:32 2013 BST
Is this correct? (y/N) y
Really create? (y/N) y
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.

Not enough random bytes available.  Please do some other work to give
the OS a chance to collect more entropy! (Need 269 more bytes)
.+++++
...........................+++++

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC
trust: ultimate      validity: ultimate
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E
sub  4096R/29E78F35  created: 2013-08-15  expires: 2013-08-22  usage: S
[ultimate] (1). Alice <alice@domain.com>

gpg> save
[user@vault ~]$

Generate a revocation certificate

A general-purpose revocation certificate that specifies no reason why you are revoking your keys:

[user@vault ~]$ gpg --output revocation.cert --gen-revoke alice

sec  4096R/32D49659 2013-08-15 Alice <alice@domain.com>

Create a revocation certificate for this key? (y/N) y
Please select the reason for the revocation:
0 = No reason specified
1 = Key has been compromised
2 = Key is superseded
3 = Key is no longer used
Q = Cancel
(Probably you want to select 1 here)
Your decision? 0
Enter an optional description; end it with an empty line:
>
Reason for revocation: No reason specified
(No description given)
Is this okay? (y/N) y

You need a passphrase to unlock the secret key for
user: "Alice <alice@domain.com>"
4096-bit RSA key, ID 32D49659, created 2013-08-15

Enter passphrase: <Alice's long passphrase>
ASCII armored output forced.
Revocation certificate created.

Please move it to a medium which you can hide away; if Mallory gets
access to this certificate he can use it to make your key unusable.
It is smart to print this certificate and store it away, just in case
your media become unreadable.  But have some caution:  The print system of
your machine might store the data and make it available to others!
[user@vault ~]$

Backup your precious master keys and revocation certificate

Create a backup of Alice’s private key:

[user@vault ~]$ gpg --export-secret-keys --armor alice > alice_gpg_private.key

Create a backup of Alice’s public key:

[user@vault ~]$ gpg --export --armor alice > alice_gpg_public.key

Keep these files safe!

[user@vault ~]$ tar -cf gpg_master_keys.tar alice_gpg*.key revocation.cert

The file gpg_master_keys.tar contains everything one needs to fully impersonate Alice or invalidate her keys, except for her passphrase.

Shred the files we backed up – now everything is in the tar file:

[user@vault ~]$ shred -u alice_gpg*.key revocation.cert

Create a daily-use keyring

This keyring will *not* include your master signing key. It will be a restricted, lesser keyring, which you can expose to untrusted environments (like your smartphone, or your networked AppVMs).

Export all subkeys to a temporary file:

[user@vault ~]$ gpg --export-secret-subkeys alice@domain.com > subkeys

Delete your master signing key from your keyring:

[user@vault ~]$ gpg --delete-secret-key alice@domain.com
 gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
 This is free software: you are free to change and redistribute it.
 There is NO WARRANTY, to the extent permitted by law.
sec 4096R/32D49659 2013-08-15 Alice <alice@domain.com>
Delete this key from the keyring? (y/N) y
 This is a secret key! - really delete? (y/N) y
 [user@vault ~]$

Re-import the subkeys we exported earlier.

[user@vault ~]$ gpg --import subkeys
 gpg: key 32D49659: secret key imported
 gpg: key 32D49659: "Alice <alice@domain.com>" 1 new signature
 gpg: Total number processed: 1
 gpg: new signatures: 1
 gpg: secret keys read: 1
 gpg: secret keys imported: 1
 [user@vault ~]$

Get rid of the temporary file:

[user@vault ~]$ shred -u subkeys

Verify that the master signing key is missing:

[user@vault ~]$ gpg -K
 /home/alice/.gnupg/secring.gpg
 -----------------------------
 sec# 4096R/32D49659 2013-08-15 [expires: 2013-08-22]
 uid Alice <alice@domain.com>
 ssb 4096R/E19F81C0 2013-08-15
 ssb 4096R/29E78F35 2013-08-15
[user@vault ~]$

See that “#”? That means that the master signing key is not there. Congratulations – this is your daily-use, lower-risk keyring! It only contains Alice’s encryption and signing subkeys, but no master (certification) signing key.

Move the daily-use keyring to Alice’s “personal” AppVM

Alice runs her email client and exchanges email with Bob using her “personal” AppVM. She therefore needs to have her daily-use keyring there.

Export Alice’s “lesser” private key:

[user@vault ~]$ gpg --export-secret-keys --armor alice > alice_gpg_private_lesser.key

Export Alice’s “lesser” public key:

[user@vault ~]$ gpg --export --armor alice > alice_gpg_public_lesser.key

Copy these out of the vault and into Alice’s networked “personal” AppVM:

[user@vault ~]$ qvm-copy-to-vm personal alice_gpg_p*_lesser.key
sent 14/15 KB
[user@vault ~]$

You will be prompted by Qubes if you want to allow this transfer. Click “Yes” to allow your “vault” AppVM to write to your “personal” AppVM.

Install Alice’s daily-use keyring in the “personal” AppVM

First, Alice needs to import the keys into her keyring:

[user@personal ~]$ cd QubesIncoming/vault/
[user@personal vault]$ gpg --import alice_gpg_p*_lesser.key
gpg: directory `/home/user/.gnupg' created
gpg: new configuration file `/home/user/.gnupg/gpg.conf' created
gpg: WARNING: options in `/home/user/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/home/user/.gnupg/secring.gpg' created
gpg: keyring `/home/user/.gnupg/pubring.gpg' created
gpg: key 46205B22: secret key imported
gpg: /home/user/.gnupg/trustdb.gpg: trustdb created
gpg: key 46205B22: public key "Alice <alice@domain.com>" imported
gpg: key 46205B22: "Alice <alice@domain.com>" 1 new signature
gpg: Total number processed: 2
gpg:               imported: 1  (RSA: 1)
gpg:         new signatures: 1
gpg:       secret keys read: 1
gpg:   secret keys imported: 1
[user@personal vault]$

Verify that the keys are there, but not the master certification key:

[user@personal vault]$ gpg -K
/home/user/.gnupg/secring.gpg
-----------------------------
sec#  4096R/46205B22 2013-10-04 [expires: 2013-10-11]
uid                  Alice <alice@domain.com>
ssb   4096R/DB739DBC 2013-10-04
ssb   4096R/E58DA355 2013-10-04
[user@personal vault]$

Good. That “#” means the certification key is not there.

Alice can now get rid of the exported key files:

[user@personal vault]$ shred -u alice_gpg_p*_lesser.key

At this point, Alice’s setup is done.

Here is what Alice has achieved:

1. Alice has generated new OpenPGP keys in a secure environment (the vault)
2. Alice created a “lesser” version of her keyring that excludes the all-important certification key. This “lesser” version will be used for daily use to communicate with Bob and anyone else using OpenPGP. If this “lesser” version of her keys is stolen (e.g. because the attacker compromises Alice’s “personal” AppVM), the attacker will not be able to create more keys in Alice’s name, or assign Alice’s trust to other keys. Alice only has to revoke her key and the attacker is left with nothing.
3. Alice created a backup of her full certification keyring in a secure environment, the vault.

Publishing your public key on a keyserver for others to find

She should publish her key on the keyservers so that her friend Bob can easily find it: (note that the key to be sent must be selected with its key ID:

[user@personal ~]$ gpg --list-keys
/home/user/.gnupg/pubring.gpg
-----------------------------
pub   4096R/32D49659 2013-08-15 [expires: 2013-08-22]
uid                  Alice <alice@domain.com>
sub   4096R/E19F81C0 2013-08-15 [expires: 2013-08-22]
sub   4096R/29E78F35 2013-08-15 [expires: 2013-08-22]

[user@personal ~]$

So, let’s send key ID 32D49659 to the keyservers:

[user@personal ~]$ gpg --keyserver sks.keyservers.net --send-keys 32D49659
 gpg: sending key 32D49659 to hkp server sks.keyservers.net
 [user@personal ~]$

By knowing her public key’s fingerprint…

[user@personal ~]$ gpg --fingerprint alice@domain.com
 pub 4096R/32D49659 2013-08-15 [expires: 2013-08-22]
 Key fingerprint = 0346 5C7A 6412 A70B ED13 0196 9652 5380 32D4 9659
 uid Alice <alice@domain.com>
 sub 4096R/E19F81C0 2013-08-15 [expires: 2013-08-22]
 sub 4096R/29E78F35 2013-08-15 [expires: 2013-08-22]
[user@personal ~]$

…Alice can verify her key has been successfully published. All she needs to do is visit http://sks.keyservers.net/ and search for her email or name, then verify that the fingerprint shown matches the one of her local key.

In the meantime, Bob has been busy doing these exact same steps on his computer, for his name and email address. His key, tied to his email address bob@domain.com has also been published to the keyservers. He has also taken a proactive security precaution and only exposed a “lesser” version of his keyring to his networked AppVMs, with his certification key safely stored in the vault.

Communicating

Alice and Bob want to send private emails to each others. Emails about apple pie and silly gossip and deep meaningful conversations. It doesn’t matter. They just want to keep their conversations private. If they’ve both followed the steps above, this is what they need to do to email each other in private.

Importing Bob’s key

Alice needs to import Bob’s (public) key from the keyservers. She asks the keyserver to find Bob’s key:

[user@personal ~]$ gpg --keyserver sks.keyservers.net --search-keys bob@domain.com
gpg: searching for "bob@domain.com" from hkp server sks.keyservers.net
(1)	Robert <bob@domain.com>
	  4096 bit RSA key F19F159D, created: 2013-08-15, expires: 2013-08-22
(2)	Waldemar Retzlaff (Schlüssel zur domain.) <bob@eu-wedding.com>
	  1024 bit DSA key 96268EF6, created: 2003-12-16
Keys 1-2 of 2 for "bob@domain.com".  Enter number(s), N)ext, or Q)uit > 1
gpg: requesting key F19F159D from hkp server sks.keyservers.net
gpg: key F19F159D: public key "Robert <bob@domain.com>" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
[user@personal ~]$

Whoops – found multiple keys – but once she selected Bob’s key, it was automatically imported into Alice’s keyring.

Verifying Bob’s key

Alice can already use this key to send Bob private email messages or files, but she wants to be really really certain that is Bob’s key, and not some impostor’s! Alice either meets or calls Bob on the phone and asks him to read out to her his key’s fingerprint. She verifies it matches the fingerprint of the key she imported from the keyservers:

[user@personal ~]$ gpg --fingerprint bob@domain.com
pub   4096R/F19F159D 2013-08-15 [expires: 2013-08-22]
      Key fingerprint = FF24 73AF 8658 5280 85A4  C2BD 4440 516C F19F 159D
uid                  Robert <bob@domain.com>
sub   4096R/E12896F5 2013-08-15 [expires: 2013-08-22]
sub   4096R/734A2C3B 2013-08-15 [expires: 2013-08-22]

[user@personal ~]$

While they’re on the phone, Bob quickly imports Alice’s key from the keyserver and asks her to confirm her key’s fingerprint as well. Alice reads out her key’s fingerprint:

[user@personal ~]$ gpg --fingerprint alice@domain.com
pub   4096R/32D49659 2013-08-15 [expires: 2013-08-22]
      Key fingerprint = 0346 5C7A 6412 A70B ED13  0196 9652 5380 32D4 9659
uid                  Alice <alice@domain.com>
sub   4096R/E19F81C0 2013-08-15 [expires: 2013-08-22]
sub   4096R/29E78F35 2013-08-15 [expires: 2013-08-22]

[user@personal ~]$

Fingerprints of public keys are public information. So Alice and Bob don’t need to worry about other people listening in. Their fingerprints are not secret.

Great! So far Alice and Bob have generated and successfully exchanged keys. Now all they need to do is use an application like Thunderbird with the Enigmail plugin (on Windows/Mac/Linux) or K9 with the APG app (on Android) to exchange encrypted and signed emails and files, being pretty certain that nobody can read or alter the contents of their messages.

When disaster strikes

Oh no! Alice’s smartphone has been stolen! Or one of her AppVMs might have opened an infected PDF, or ran some suspicious Java applet that might have installed a trojan on her personal AppVM. Nothing in that AppVM can be trusted any longer. This includes the GnuPG keys she was using on a daily basis.

Luckily Alice is prepared.

Revoking compromised keys

Alice needs to use her safe environment (the vault) to revoke the compromised subkeys (she only exposed subkeys to her networked AppVMs and devices, remember?) and optionally issue new ones.

The beauty of this is that she does not have to throw away the whole key. Alice can carry on using the same master key, which may, over the years, have accumulated a lot of trust from other Web Of Trust members. She just needs to revoke the compromised subkeys and issue new ones.

Working with our master key

Alice fires up her vault and imports the master keyring she had backed up when she created her keys:

[user@vault ~]$ tar xvf gpg_master_keys.tar
alice_gpg_private.key
alice_gpg_public.key
revocation.cert
[user@vault ~]$ 

Here are the files Alice backed up. Let’s import them to start using them – but first temporarily move .gnupg out of the way to ensure we’re not upsetting any preexisting configuration in the vault:

[user@vault ~]$ mv .gnupg .gnupg-ORIG
[user@vault ~]$ gpg --import alice_gpg_p*.key
gpg: directory `/home/user/.gnupg' created
gpg: new configuration file `/home/user/.gnupg/gpg.conf' created
gpg: WARNING: options in `/home/user/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/home/user/.gnupg/secring.gpg' created
gpg: keyring `/home/user/.gnupg/pubring.gpg' created
gpg: key 32D49659: secret key imported
gpg: /home/user/.gnupg/trustdb.gpg: trustdb created
gpg: key 32D49659: public key "Alice <alice@domain.com>" imported
gpg: key 32D49659: "Alice <alice@domain.com>" 1 new signature
gpg: Total number processed: 2
gpg:               imported: 1  (RSA: 1)
gpg:         new signatures: 1
gpg:       secret keys read: 1
gpg:   secret keys imported: 1
[user@vault ~]$

Verify what we imported:

[user@vault ~]$ gpg --edit-key alice
gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: unknown       validity: unknown
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E   
sub  4096R/29E78F35  created: 2013-08-15  expires: 2013-08-22  usage: S   
[ unknown] (1). Alice <alice@domain.com>

gpg>

Yup, there they are.

• The all-important master key with usage: SC (for “sign & certify”, which means to sign other keys)
• One subkey with usage: E – for “encrypt”
• One subkey with usage: S – for “sign”

Revoking compromised subkeys

gpg> list

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: unknown       validity: unknown
sub  4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E   
sub  4096R/29E78F35  created: 2013-08-15  expires: 2013-08-22  usage: S   
[ unknown] (1). Alice <alice@domain.com>

gpg> key 1

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: unknown       validity: unknown
sub* 4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E   
sub  4096R/29E78F35  created: 2013-08-15  expires: 2013-08-22  usage: S   
[ unknown] (1). Alice <alice@domain.com>

gpg> key 2

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: unknown       validity: unknown
sub* 4096R/E19F81C0  created: 2013-08-15  expires: 2013-08-22  usage: E   
sub* 4096R/29E78F35  created: 2013-08-15  expires: 2013-08-22  usage: S   
[ unknown] (1). Alice <alice@domain.com>

gpg> revkey
Do you really want to revoke the selected subkeys? (y/N) y
Please select the reason for the revocation:
  0 = No reason specified
  1 = Key has been compromised
  2 = Key is superseded
  3 = Key is no longer used
  Q = Cancel
Your decision? 1
Enter an optional description; end it with an empty line:
> 
Reason for revocation: Key has been compromised
(No description given)
Is this okay? (y/N) y

You need a passphrase to unlock the secret key for
user: "Alice <alice@domain.com>"
4096-bit RSA key, ID 32D49659, created 2013-08-15

You need a passphrase to unlock the secret key for
user: "Alice <alice@domain.com>"
4096-bit RSA key, ID 32D49659, created 2013-08-15

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: unknown       validity: unknown
This key was revoked on 2013-08-16 by RSA key 32D49659 Alice <alice@domain.com>
sub  4096R/E19F81C0  created: 2013-08-15  revoked: 2013-08-16  usage: E   
This key was revoked on 2013-08-16 by RSA key 32D49659 Alice <alice@domain.com>
sub  4096R/29E78F35  created: 2013-08-15  revoked: 2013-08-16  usage: S   
[ unknown] (1). Alice <alice@domain.com>

gpg> save
[user@vault ~]$

As you can see the all-important certification key has the power to revoke subkeys. Good thing Alice kept it safe in her offline vault all this time!

Export the revoked keys in a ASCII file

[user@vault ~]$ gpg --export -a > revoked_keys.asc

Move the revoked keys in your networked AppVM

[user@vault ~]$ qvm-copy-to-vm personal revoked_keys.asc 
sent 7/8 KB
[user@vault ~]$

From your networked AppVM now, tell the world you have revoked the subkeys

[user@personal ~]$ gpg --import QubesIncoming/vault/revoked_keys.asc 
gpg: key 32D49659: "Alice <alice@domain.com>" 2 new signatures
gpg: Total number processed: 1
gpg:         new signatures: 2

[user@personal ~]$ gpg --edit-key alice
gpg (GnuPG) 1.4.14; Copyright (C) 2013 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Secret key is available.

pub  4096R/32D49659  created: 2013-08-15  expires: 2013-08-22  usage: SC  
                     trust: ultimate      validity: ultimate
This key was revoked on 2013-08-16 by RSA key 32D49659 Alice <alice@domain.com>
sub  4096R/E19F81C0  created: 2013-08-15  revoked: 2013-08-16  usage: E   
This key was revoked on 2013-08-16 by RSA key 32D49659 Alice <alice@domain.com>
sub  4096R/29E78F35  created: 2013-08-15  revoked: 2013-08-16  usage: S   
[ultimate] (1). Alice <alice@domain.com>

gpg> quit

[user@personal ~]$ gpg --keyserver sks.keyservers.net --send-keys E19F81C0
gpg: sending key 32D49659 to hkp server sks.keyservers.net
[user@personal ~]$ gpg --keyserver sks.keyservers.net --send-keys 29E78F35
gpg: sending key 32D49659 to hkp server sks.keyservers.net
[user@personal ~]$ rm QubesIncoming/vault/revoked_keys.asc
[user@personal ~]

That’s it!

You have now revoked the two compromised subkeys and may create new subkeys with your untainted master key that was kept safe in your vault all along. Whoever managed to compromise your keys may be able to read everything encrypted with those keys (if they kept copies of the ciphertext).

Notes

Restricted keys (missing the master signing key, as we created above) can not currently be used by APG on Android. Use Mike Cardwell’s version of APG that works with such keys: download the apk from here.

Government requests for your personal data

The latest Google Transparency report makes a sobering read. It documents how governments are ordering Google to hand over user data (i.e. everything that Google knows about you, which is a lot*)

For per-country statistics for User Data Requests click here. Sample to pique your interest:

US authorities asked for the personal data of 16,281 users/accounts in the first six months of 2012. Google will not say exactly how many they handed over, but 90% is implied to be a reasonable estimate.

Citizens of other countries, please refer to the report before celebrating too much.

* Some things Google knows about you, and will continue knowing for the foreseeable future (remember, computers don’t forget what you clicked on 6 years ago):

• Every email you have ever sent.
• Every email you have ever received.
• Every link you have ever clicked in an email
• Everything you have typed in the Google “chat” box, and everything your chatting partner said.
• Everything you have searched for on the web, while being logged in to your Google account.
• Google maps
• Picasa & Google albums
• …and much more, even about your connections’ connections, to a surprising degree – check out your Google profile (note: you have to be logged in to Google for this to work) for more.