Add more GnuPG bits
Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
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Konstantin Ryabitsev
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1 changed files with 267 additions and 3 deletions
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@ -226,9 +226,9 @@ from other PGP users you come across.
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#### Installing GnuPG
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If you are using Linux, you should already have GnuPG installed. On a Mac,
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you should install [GPG-Suite](https://gpgtools.org). For all other platforms,
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you'll need to do your own research to find the correct places to download and
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install GnuPG.
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you should install [GPG-Suite](https://gpgtools.org) or you can use `brew
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install gnupg2`. For all other platforms, you'll need to do your own research
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to find the correct places to download and install GnuPG.
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##### GnuPG 1 vs. 2
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@ -248,3 +248,267 @@ command:
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If you see `gpg (GnuPG) 2.x.x`, then you are good to go. This guide will
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assume you have the version 2.2 of GnuPG (or later).
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##### Making sure you always use GnuPG2
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If you have both `gpg` and `gpg2` commands, you should make sure you are
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always using GnuPG v2, not the legacy version. You can make sure of it by
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setting the alias:
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alias gpg='/usr/bin/gpg2'
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You can put that in your `.bashrc` to make sure it's always loaded whenever
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you use the gpg commands.
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## Generating and protecting your master PGP key
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### Checklist
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- [ ] Generate the 4096-bit RSA master key _(ESSENTIAL)_
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- [ ] Back up the master key using paperkey _(ESSENTIAL)_
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- [ ] Add all relevant identities _(ESSENTIAL)_
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### Considerations
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#### Understanding the "Master" (Certify) key
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In this and next section we'll talk about the "master key" and "subkeys". It
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is important to understand the following:
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1. There are no technical differences between the "master key" and "subkeys."
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2. At creation time, we assign functional limitations to each key by
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giving it specific capabilities.
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3. A PGP key can have 4 capabilities.
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- **[S]** Key can be used for signing
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- **[E]** Key can be used for encryption
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- **[A]** Key can be used for authentication
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- **[C]** Key can be used for certifying other keys
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4. A single key may have multiple capabilities.
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The key carrying the **[C]** (certify) capability is considered the "master"
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key because it is the only key that can be used to indicate relationship with
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other keys. Only the **[C]** key can be used to:
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- add or revoke other keys (subkeys) with S/E/A capabilities
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- add, change or revoke identities (uids) associated with the key
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- add or change the expiration date on itself or any subkey
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- sign other people's keys for the web of trust purposes
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In the Free Software world, the **[C]** key is your digital identity. Once you
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create the key, you should take extra care to protect it and prevent it from
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falling into malicious hands.
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#### Before you create the master key
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Before you create your master key you need to pick your primary identity and
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your master passphrase.
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##### Primary identity
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An identity is basically in the same format as the From field in emails:
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Alice Engineer <alice.engineer@example.org>
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You can create new identities and revoke old ones, and you can also change
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which identity is your "primary" one at a later time. Since the primary
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identity is shown in all GnuPG operations, you should pick an
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address/description that is both professional and the most likely one to be
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used for PGP-enforced communication, such as your work address or the address
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you use for signing off on project commits.
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##### Passphrase
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The passphrase is used exclusively for encrypting the private key with a
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symmetric algorithm while it is stored on disk. If the contents of your
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`.gnupg` directory ever get leaked, a good passphrase is the last line of
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defense between the thief and them being able to impersonate you online, which
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is why it is important to set up a good passphrase.
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A good guideline for a strong passphrase is 3-4 words from a rich or mixed
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dictionary that are not quotes from popular sources (songs, books, slogans).
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You won't need to type the **[C]** key passphrase very frequently, so it does
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not need to be easy to type, just easy to remember.
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##### Algorithm and key strength
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Even though GnuPG has supported Elliptic Curve crypto for a while now, we'll be
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sticking to RSA keys, at least for a little while longer. While it is possible
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to start using ED25519 keys right now, it is possible that you will come
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across tools and hardware devices that will not be able to handle them
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correctly.
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For this reason, we will be generating RSA keys. For our master key, we'll use
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4096 bits, and for our subkeys we'll stick to 2048 bits -- it is easy enough
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to replace subkeys with stronger ones, but the master key must live on for a
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long time.
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#### Generate the master key
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To generate your key, issue the following command, putting in the right values
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instead of Alice Engineer:
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gpg --quick-generate-key 'Alice Engineer <alice@example.org>' rsa4096 cert
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A dialog will pop up asking to enter the passphrase. Then, you may need to
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move your mouse around or type on some keys to generate enough entropy until
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the command completes.
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Review the output of the command, it will be something like this:
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pub rsa4096 2017-12-06 [C] [expires: 2019-12-06]
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111122223333444455556666AAAABBBBCCCCDDDD
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uid Alice Engineer <alice@example.org>
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Note the long string on the 2nd line -- that is the full fingerprint of your
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newly generated key. Key ID can be represented in three different forms:
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- **fingerprint**, a full 40-character key identifier
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- **long**, last 16-characters of the fingerprint (`AAAABBBBCCCCDDDD`)
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- **short**, last 8 characters of the fingerprint (`CCCCDDDD`)
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You should avoid using 8-character "short key IDs" as they are not
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sufficiently unique.
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At this point, I suggest you open a text editor, copy the fingerprint of your
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new key and paste it there. You'll need to use it for the next few steps.
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#### Back up your master key
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For disaster recovery purposes -- and especially if you intend to use the Web
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of Trust and collect key signatures from other project developers -- you
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should create a hardcopy backup of your private key. This is supposed to be a
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"last resort" measure in case all other backup mechanisms have failed.
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The best way to create a printable hardcopy of your private key is using
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`paperkey` software written for this very purpose. Paperkey is available on
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all Linux distros, as well installable via `brew install paperkey` on Macs.
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Run the following command, replacing `[fpr]` with the full fingerprint of your
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key:
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gpg --export-secret-key [fpr] | paperkey > /tmp/key-backup.txt
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The output will be in a format that is easy to OCR or input by hand, should
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you ever need to recover it. Print out that file, then take a pen and write
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the key passphrase on the margin of the paper. This is a required step because
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the key printout is still encrypted with the passphrase, and if you ever
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change the passphrase on your key, you will not remember what it used to be
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when you had first created it -- guaranteed.
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Put the resulting printout and the hand-written passphrase into an envelope
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and store in a secure and well-protected place that is away from your home,
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such as your bank vault.
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**NOTE ON PRINTERS**: Long gone are days when printers were dumb devices
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connected to the computer's parallel port. These days they have full operating
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systems, hard drives, and cloud integration. Since the key content we send to
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the printer will be encrypted with the passphrase, this is a fairly safe
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operation, but use your best paranoid judgement.
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#### Add relevant identities
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If you have multiple relevant email addresses (personal, work, open-source
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project, etc), you should add them to your master key. You don't need to do
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this for any addresses that you don't expect to use with PGP (e.g. probably
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not your school alumni address).
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The command is (put the full key fingerprint instead of `[fpr]`):
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gpg --quick-add-uid [fpr] 'Alice Engineer <allie@example.net>'
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You can review the IDs you've already added using:
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gpg --list-key [fpr] | grep ^uid
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##### Pick the primary UID
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GnuPG will make the latest UID you add as your primary UID, so if that is
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different from what you want, you should fix it back:
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gpg --quick-set-primary-uid [fpr] 'Alice Engineer <alice@example.org>'
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## Generating PGP subkeys
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### Checklist
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- [ ] Generate a 2048-bit Encryption key _(ESSENTIAL)_
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- [ ] Generate a 2048-bit Signing key _(ESSENTIAL)_
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- [ ] Generate a 2048-bit Authentication key _(NICE)_
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### Considerations
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Now that we've created the master key, let's create the keys you'll actually
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be using for day-to-day work. We create 2048-bit keys because a lot of
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specialized hardware (we'll discuss this further) does not handle larger keys,
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but also for pragmatic reasons. If we ever find ourselves in a world where
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2048-bit RSA keys are not considered good enough, it will be because of
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fundamental problems with the RSA protocol and longer 4096-bit keys will not
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make much difference.
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#### Create the Sign and Encrypt subkeys
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To create the subkeys, run:
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gpg --quick-add-key [fpr] rsa2048 encr
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gpg --quick-add-key [fpr] rsa2048 sign
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You can also create the Authentication key, which will allow you to use your
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PGP key for ssh purposes (covered in other guides):
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gpg --quick-add-key [fpr] rsa2048 auth
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You can review your key information using `gpg --list-key [fpr]`:
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pub rsa4096 2017-12-06 [C] [expires: 2019-12-06]
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111122223333444455556666AAAABBBBCCCCDDDD
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uid [ultimate] Alice Engineer <alice@example.org>
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uid [ultimate] Alice Engineer <allie@example.net>
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sub rsa2048 2017-12-06 [E]
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sub rsa2048 2017-12-06 [S]
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## Moving your master key to offline storage
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### Checklist
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- [ ] Prepare encrypted detachable storage _(ESSENTIAL)_
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- [ ] Back up your GnuPG directory _(ESSENTIAL)_
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- [ ] Remove the master key from your home directory _(NICE)_
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#### Back up your GnuPG directory
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It is important to have a readily available backup of your PGP keys should you
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need to recover them (this is different from the disaster-level preparedness
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we did with `paperkey`).
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**This step is especially important if you are going to remove your master key
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or use smartcard hardware. Do not skip this step!**
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#### Prepare detachable encrypted storage
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Start by getting a detachable USB drive (preferably two) that you will use for
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backup purposes. They do not need to be large. You will first need to encrypt
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them:
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- [Apple instructions](https://support.apple.com/kb/PH25745)
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- [Linux instructions](https://help.ubuntu.com/community/EncryptedFilesystemsOnRemovableStorage)
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For the encryption passphrase, you can use the same one as on your master key.
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#### Back up your GnuPG directory
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Once the encryption process is over, re-insert the USB drive and make sure it
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gets properly mounted. Find out the full mount point of the device, for
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example by running the `mount` command (under Linux, external media usually
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gets mounted under `/media/disk`, under Mac it's `/Volumes`).
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Once you know the full mount path, copy your entire GnuPG directory there:
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cp -rp $HOME/.gnupg [/media/disk/some/path]/gnupg-backup
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You should now test to make sure it still works:
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gpg --homedir=[/media/disk/some/path]/gnupg-backup --list-key [fpr]
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If you don't get any errors, then you should be good to go. Unmount the USB
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drive, label it accordingly so you don't blow it away next time you need to
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use a quick USB drive, and put in a safe place.
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