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gpg

Generate private and public key
Generate key 
gpg --default-new-key-algo rsa4096 --gen-key
Set encryption flag on key 
gpg --edit-key me@email.com change-usage
List
List public keys 
gpg --list-public-keys --keyid-format long
List private keys 
gpg --list-secret-keys --keyid-format long --with-keygrip --with-subkey-fingerprints
Extract image from key 
gpg --list-options show-photos --photo-viewer "cat > <path>/0x%k.%t" --list-keys [key_identifier]
Sign and verify
clear-sign (original file content plus signature) 
gpg --clear-sign --local-user me@email.com --output test.txt.asc test.txt
Verify clear-sign 
gpg --verify test.txt.asc
Detached signature (signature only) 
gpg --detach-sign --local-user me@email.com --armor --output test.txt.asc2 test.txt
Verify detached signature 
gpg --verify test.txt.asc2 test.txt
Encrypt and decrypt
Encrypt file 
gpg --encrypt --recipient username@email.com --output test.txt.gpg test.txt
Sign and encrypt file (and optionally specify signing algorithm) 
gpg --sign --encrypt --digest-algo SHA256 [...]
Specify algorithm 
gpg --encrypt --cipher-algo AES256 [...]
Disable compression 
gpg --encrypt --compress-algo none [...]
List recipients hints of encrypted file via Sequoia (note: this can be spoofed) 
sq inspect test.txt.gpg
Decrypt file (and automatically check signature, if available) 
gpg --decrypt test.txt.gpg --output test.decrypted.txt
Inspect .gpg file 
gpg --list-packets -vv --show-session-key test.txt.gpg
Export
Export public key 
gpg --output public.asc --armor --export username@email.com
Export private key 
gpg --output private.asc --armor --export-secret-key username@email.com
Renew
Renew key and all non-expired subkeys 
gpg --quick-set-expire 1111111190ABCDEF1234567890ABCDEF11111111 7w '*'
CLI Language
Set language to english 
LANG=en gpg --version
Password generation
Without special characters 
cat /dev/urandom | tr -dc 'a-zA-Z0-9' | head -c 12 | sed -r 's/(.{4})/\1-/g' | sed -r 's/(.*)-$/\1\n/g'
Use GPG key for SSH connections
Print SSH Public key 
gpg --export-ssh-key 1111111190ABCDEF1234567890ABCDEF11111111

sign vs. clear-sign vs. detach-sign

  • sign: The user needs to have gpg installed to read the resulting .gpg file. The .gpg file contains both, the original file content plus the signature. The content is compressed.
  • clear-sign: The output file contains both, the original file content plus the signature. The content is retained in plain-text, so no additional program like gpg is needed to read it on the other side. The content is not compressed though, so the resulting file size might be bigger.
  • detach-sign: The output file contains the signature only. To have a signature in ASCII format, use the --armor flag. Otherwise, it will be a binary signature.

In general, I also like to specify the --local-user flag explicitly to the signing commands. If you do not specify it, the default private key is used. The default key is the first key found in the secret keyring.

To set a default signing key, edit the file ~/.gnupg/gpg.conf and add the line:

default-key <key-id>

Where key-id is either the long keyid or the fingerprint of your key.

list-packets

list-packets shows detailed information about a .gpg file.

This information includes:

  • who the recipient is The keyid hints who can decrypt the file. This info can be spoofed though.
  • which algorithm has been used for the symmetric part See here for a list of algorithms.

gpg: session key: ‘8:32050C047C47C519E76901EFC47FDFED0CD87CDB85809AFE’

You can see the algorithm in the session key, the number before the colon. In this case, the algorithm is 8 (= AES192).

In my case it showed 9.2, which is AES256 in OCB mode.

TPM: Card error

I have seen this error when trying to encrypt and sign a file without specifying the digest-algo.

So if the algorithm is not compatible with the TPM, you might just see Card error instead of a proper error message.

Fix: Explicitly set the algorithm to SHA256, which must be supported by the TPM.

gpg --sign --encrypt --digest-algo SHA256 [...]

Nitrokey

Move private key to external smart card (e.g. Nitrokey)

gpg --edit-key --expert username@email.com

It will show you some info, then type the keytocard command to transfer the key to the NitroKey. I had to enter the admin PIN twice (default: 12345678). After this, type quit and confirm.

Import reference to private key on another computer

Import public key from file or server

gpg --import public.asc

Reference private key on smartcard

gpg --card-edit

then enter fetch and quit to import the reference to the secret key on the NitroKey.