Starting up with GnuPG
- Set algorithm preferences
- Creating the primary key
- Creating the subkeys
Before jumping into the key creation, you should really decide why it is that you want a key, what your intended uses for it are and how secure you wish to be. Security and convenience are on opposite ends of the scale, and you need to determine how much effort you’re willing to put in for a given level of security and vice versa.
It’s best to do the research and make the decisions up front, because once you’ve started, and especially once you’ve published your keys, it could be troublesome to change tack.
- OpenPGP for beginners
- OpenPGP: Getting started
- and of course the The GNU Privacy Guard Manual
The rest of the post is primarily a record of the decisions that I’ve taken, mostly for my own benefit, but it could possibly help you get going too.
Please be advised that I make absolutely no guarantee that this is best practise, or even good practise for that matter. I’m not an expert. Look elsewhere if you want something more authoritative (perhaps start with the links above). I take no responsibility whatsoever for anything that happens as a result of you having read this post.
Set algorithm preferences
It’s probably wise to make sure that your environment is set up optimally before You
begin creating keys, as some of this stuff is harder to change later. You’ll want to
specify your preferred algorithms and hashes, in decending priority, for both key
signing and encryption. You can set the default preferences in
taken the complete file from Jacob Applebaum’s duraconf collection.
More information can be found at dkg’s Debian weblog, at the KDE UserBase wiki, the fantastic RiseUp OpenPGP Best practices article, and a StackExchange answer.
If you’ve already created a key and would like to set the preferences on that key, the
more common preference setting seems to be this one:
setpref SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES CAST5 ZLIB BZIP2 ZIP Uncompressed
Creating the primary key
It’s recommened (just about everywhere, I’m not going to bother to reference this) that you generate and use your primary key as securely as possible. Think along the lines of a non-networked computer, with the hard-drives removed, booting from a Tails Live CD. It’s up to you to decide far to go, but this is where you want to be as secure as you can possibly be.
My opinion: a Raspberry Pi with a keyboard, mouse and monitor (no network, ever!) makes a wonderfully useful, cheap and secure environment for working with your primary key. You can transfer keys to and from your Pi with a USB stick (or a Pi camera and QR codes if you’re really serious about it), and once done, store your Raspberry Pi somewhere safe until you need it to work on your primary key again.
With that in mind, and hopefully in a secure environment, fire up gpg with expert mode on.
gpg --expert --gen-key
Strongly prefer RSA1 as your algorithm of choice. Select option 8 so that we can remove some fo the capabilities from the primary key.
gpg (GnuPG) 2.0.30; Copyright (C) 2015 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. 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) (7) DSA (set your own capabilities) (8) RSA (set your own capabilities) Your selection? 8
The primary key should Certify only2. Remove the options to Sign and Encrypt. We’ll create seperate subkeys for signing, encryption and authentication later.
Possible actions for a RSA key: Sign Certify Encrypt Authenticate Current allowed actions: Sign Certify Encrypt (S) Toggle the sign capability (E) Toggle the encrypt capability (A) Toggle the authenticate capability (Q) Finished
The primary key should have the largest1 key-length3 possible, currently
We can probably afford to make some of the subkey key-lengths shorter, depending on how they are to be used.
RSA keys may be between 1024 and 4096 bits long. What keysize do you want? (2048) 4096 Requested keysize is 4096 bits
Set expiry4 date5 to 1 year. Some articles say it should be longer, some say it should be the same period as the subkeys, as you’ll need your primary key to extend their expiry dates anyway. I’m still deciding what my policy will be. Fortunately its fairly easy to chance expiry dates after the fact. It’s also a good idea to create a calendar entry to remind yourself when to extend them.
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) 1y
Enter your name and e-mail7. You’ll get the option to add more addresses later if you wish to. Leave the comment6 field empty. In fact, that last link is important6. It has a lot to say about how you identify yourself to others. It’s worth reading.
GnuPG needs to construct a user ID to identify your key. Real name: Rick Roller Email address: email@example.com Comment: You selected this USER-ID: "Rick Roller <firstname.lastname@example.org>" Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit?
Choose a suitably secure password8. I’ve used a randomly-generated 24 character password consisting of a mix of letters (upper and lower case), numbers and special characters. No, I’m not going to remember it. I’ll have it written down and securly stored offline, along with my primary key once I’m done. It’s seldomly used, so this is OK.
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. gpg: key 3714877A marked as ultimately trusted public and secret key created and signed.
Now you’ll need to generate some entropy for the key generation. This take a second or two, or very much longer, depending on algorithm selected, key length, and the OS and hardware that you’re running on.
If everything went OK, you should get something similar to this
gpg: checking the trustdb gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model gpg: depth: 0 valid: 3 signed: 0 trust: 0-, 0q, 0n, 0m, 0f, 3u gpg: next trustdb check due at 2017-04-13 pub 4096R/3714877A 2016-04-13 [expires: 2017-04-13] Key fingerprint = D067 6D8E 5AB5 B780 E748 E7D8 C9FA FEAA 3714 877A uid [ultimate] Rick Roller <email@example.com>
Create one subkey each for sign, encrypt and authenticate
Creating the subkeys
From here onwards, you’ll be editing the primary key you just created. You’ll get into edit mode
gpg --expert --edit-key firstname.lastname@example.org, obviously substituting in the email address
that you selected. I’ll use this fake address consistently from here on.
gpg (GnuPG) 2.0.30; Copyright (C) 2015 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/3714877A created: 2016-04-13 expires: 2017-04-13 usage: C trust: ultimate validity: ultimate [ultimate] (1). Rick Roller <email@example.com>
Add a photo
There is some disagreement about whether this is a good idea or not. Personally, I like it, especially if the photo matches up with one used on one or more social media accounts. Of course it shouldn’t be the only form of identity, but I guess it can compliment official goverment-issued, photo-bearing identity documents.
Pick an image to use for your photo ID. The image must be a JPEG file. Remember that the image is stored within your public key. If you use a very large picture, your key will become very large as well! Keeping the image close to 240x288 is a good size to use. Enter JPEG filename for photo ID: photo.jpg Is this photo correct (y/N/q)? y You need a passphrase to unlock the secret key for user: "Rick Roller <firstname.lastname@example.org>" 4096-bit RSA key, ID 3714877A, created 2016-04-13 pub 4096R/3714877A created: 2016-04-13 expires: 2017-04-13 usage: C trust: ultimate validity: ultimate [ultimate] (1). Rick Roller <email@example.com> [ unknown] (2) [jpeg image of size 5986]
None of this work is my own. I’ve merely collated resources from others who hopefully know better and compiled it in such a way that is useful for me, and made a few tweaks here and there to suit my use cases. Most of my information has been extracted from these articles.
- OpenPGP Best Practices
- Generating More Secure GPG Keys: A Step-by-Step Guide
- Creating the perfect GPG keypair
This is a summary of the specific resources that I’ve referenced in my post to justify some of the decisions I’ve made.