178 lines
6.3 KiB
Markdown
178 lines
6.3 KiB
Markdown
# GnuPG
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Key files are a secure method for certifying credentials digitally. Everything
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is stored in `~/.gnupg` and controlled through `gpg`. It's quite complicated...
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See `tldr gpg` for encryption, [devhints](https://devhints.io/gnupg) for a
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cheat sheet, the [Archwiki](https://wiki.archlinux.org/title/GnuPG) for a
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technical explanation and the [Debian wiki](https://wiki.debian.org/Subkeys) for
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a newbie-friendly one
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Terminology:
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* Public key - The one to share
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* Private key - The one to not share
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* Primary key - ??
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* Subkey - ??
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* Keygrip - The name of the key file
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* Key ID - The last few (8-16) characters of a fingerprint
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* Fingerprint - A unique identifier for a key
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* Keyring - Your entire collection of public or private keys
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* User ID - Email, part of name, Key ID, or Fingerprint of a key
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Consider this example output:
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```bash
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$ gpg --list-secret-keys --with-subkey-fingerprint --with-keygrip --keyid-format=long
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# ///--- Short for "secret key". It's "pub" for public keys
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# vvv vvvvvvvvvvvvvvvv Key ID
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> sec ed25519/ABCDEFG123456789 4040-04-04 [SC] [expires: 4040-04-04]
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> DDEEDF222222222222222222ABCDEFG123456789
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# ^^^^^^^^^^^^^^^^ Key ID also here
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# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Fingerprint
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> Keygrip = DDEBBA3482394AEE23432DEE32432BB2432432EE
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# Key is ~/.gnupg/private-keys-v1.d/DDEBBA3482394AEE23432DEE32432BB2432432EE.key
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> uid [ultimate] Emiliko Mirror <emiliko@mami2.moe>
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# ///--- Short for "secret subkey". It's "sub" for public subkeys
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# vvv vvvvvvvvvvvvvvvv Key ID
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> ssb cv25519/987654321ABCDEED 4040-04-04 [E] [expires: 4040-04-04]
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> 32423BDDAAAAAAAAAAAAAAAA987654321ABCDEED
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# ^^^^^^^^^^^^^^^^ Key ID also here
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# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Fingerprint from --with-subkey-fingerprint
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> Keygrip = 2493ADDEDDDFEFEFE23432432FDEEFDD24324232
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# Key is ~/.gnupg/private-keys-v1.d/2493ADDEDDDFEFEFE23432432FDEEFDD24324232.key
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```
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Providing the `--fingerprint` flag will alter the output slightly, tho it's the
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same fingerprint, for example:
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```bash
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> sec ed25519/ABCDEFG123456789 4040-04-04 [SC] [expires: 4040-04-04]
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> Key fingerprint = DDEE DF22 2222 2222 2222 2222 ABCD EFG1 2345 6789
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# Key ID is now here ^^^^^^^^^^^^^^^^^^^
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> Keygrip = DDEBBA3482394AEE23432DEE32432BB2432432EE
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> uid [ultimate] Emiliko Mirror <emiliko@mami2.moe>
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> ssb cv25519/987654321ABCDEED 4040-04-04 [E] [expires: 4040-04-04]
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> Key fingerprint = 3242 3BDD AAAA AAAA AAAA AAAA 9876 5432 1ABC DEED
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# Key ID is now here ^^^^^^^^^^^^^^^^^^^
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> Keygrip = 2493ADDEDDDFEFEFE23432432FDEEFDD24324232
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```
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## Creating a new key
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This closely follows the Archwiki, with an elliptic cipher
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```
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gpg --full-gen-key --expert
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> (9) ECC and ECC
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> (1) Curve 25519
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> 1y # Optional, 1 year is recommended
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> Your Name # This will be visible in the public key
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> emiliko@mami2.moe # This is also visible in the public key
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> No comment
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> Put a password on the primary key
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```
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## Signing and verification
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Git commits, binaries and really any file can be signed by a private key to
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prove authenticity of the file. For github, you'll need to paste your public key
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to your profile settings
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```bash
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gpg --list-secret-keys --keyid-format=long
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gpg --armor --export <user-id> | wl-copy
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```
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Git commits aren't signed by default. Either explicitly sign at commit time,
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with `git commit -S`, or add the following to your ~/.gitconfig. If the signing
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key you specify is a subkey, add an ! mark at the end
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```toml
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[user]
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name = Emiliko Mirror
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email = emiliko@mami2.moe
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signingkey = ABCDEF1234567890
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[commit]
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gpgsign = true
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```
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## Encryption
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Gpg can encrypt pretty much anything. Consider bundling into a tarball
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beforehand if it's more than one file
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The `-a/--armor` flag will make sure the encrypted file is made up entirely of
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ascii characters, which is easier to copy/paste than binary nonsense
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Encryption can be symmetric or asymmetric. Symmetric encryption uses 1 key and a
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password to encrypt. To decrypt, use the same key and re-enter the same
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password
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### Symmetric encryption
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Symmetric encryption uses 1 key and 1 password to encrypt. To decrypt, you'll
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need the same key and the same password
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### Asymmetric encryption
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Asymmetric encryption is meant for sending to a specific receiver. It uses 1
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public key to encrypt. To decrypt, you'll need the private key pair to that
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public key. `pass` uses this one
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```bash
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gpg -e -o encrypted_file -r emiliko@mami2.moe secret_file
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# Then emiliko can decrypt it with her private key
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gpg -d -o secret_file encrypted_file
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```
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## Moving keys
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You'll want to export your keys to other devices. Ideally, you'd only export
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subkeys and not the primary key. The primary key should be stored offline and
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used to generate revocation certificates for compromised subkeys
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```bash
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gpg -o pub_key.pgp -a --export emiliko@mami2.moe
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gpg -o sec_key.pgp -a --export-secret-key emiliko@mami2.moe
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scp pub_key.gpg emiliko@192.168.0.1:/tmp/safe_directory
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scp sec_key.gpg emiliko@192.168.0.1:/tmp/safe_directory
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gpg --import pub_key.gpg
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gpg --import sec_key.gpg
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```
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A safer method skips the creation of any intermediary files by sending it
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through ssh right away
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```bash
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gpg --export-secret-key <user-id> | ssh emiliko@192.168.0.1 'gpg --import'
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# Or if you're on the receiving system
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ssh emiliko@192.168.0.1 'gpg --export-secret-key emiliko@mami2.moe' | gpg --import
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```
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In either case, or actually whenever importing your keys, you'll need to edit
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the trust level after importing it
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```bash
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gpg --list-keys # Get the Key ID here
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gpg --edit-key <user-id>
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> trust
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> 5 # If it's your own key
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> y
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> quit
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```
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For use with `pass`, you can check if your encryption key is working by trying
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to add a new password, like `pass insert -e something` and see if it succeeds
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## Backing up keys
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Keys should be backed up on offline, physically inaccessible, media. Usb sticks
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you leave at home or a piece of paper are both good choices. For the paper
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version see `paperkey`
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```bash
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gpg -o /run/media/my_usb/keys.gpg --export-options backup --export-secret-keys emiliko@mami2.moe
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```
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Now later, or on another device, you can restore these keys
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```bash
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gpg --import-options restore --import keys.gpg
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```
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Then edit the trust level, as with the other transfer methods
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