GPG Key Configuration for Signing Commits with Git and GitHub

A step-by-step guide to generating a GPG key, configuring Git to use it for signing commits, adding the key to GitHub, verifying commit signatures, and setting up GPG agent for passphrase caching.

Generate a GPG Key

Open a terminal and run:
```
gpg --full-generate-key
```
Follow the prompts to select the key type, key size (recommend 4096 bits for RSA), and expiration. Enter your name and email address.

Configure Git to Sign Commits with GPG Key

List GPG keys to find your key ID:
```
gpg --list-secret-keys --keyid-format LONG
```
Look for the sec line followed by the key type and size, and then the key ID in this format: rsa4096/ABCDEFGH12345678 2021-01-01 [SC]. The key ID in this example is ABCDEFGH12345678.
Configure Git to use your GPG key:
```
git config --global user.signingkey YOUR_GPG_KEY_ID
```
You can now sign your commits using git commit -S.
To sign all commits by default in all repositories, use:
```
git config --global commit.gpgSign true
```

Add Your GPG Key to GitHub

Via GitHub Web Interface

Export your public GPG key:
```
gpg --armor --export YOUR_GPG_KEY_ID
```
Copy the exported key (including the -----BEGIN PGP PUBLIC KEY BLOCK----- and -----END PGP PUBLIC KEY BLOCK-----).
Go to GitHub > Settings > SSH and GPG keys > New GPG key, paste your key, and save.

Via `gh` CLI

Run to add your GPG key to GitHub:

gh api user/gpg_keys -F armored_public_key="$(gpg --armor --export YOUR_GPG_KEY_ID)"

Verify Commit Signature

To verify the signature of the latest commit, run:

git log --show-signature -1

Configure GPG Agent for Passphrase Caching

Edit ~/.gnupg/gpg-agent.conf (create if it doesn’t exist):
```
vim ~/.gnupg/gpg-agent.conf
```
Add or modify the following lines:
```
default-cache-ttl 3600
max-cache-ttl 86400
```
Adjust the values according to your security and convenience needs.

Restart the GPG agent:

gpgconf --kill gpg-agent
gpg-agent --daemon

Stay in Your Terminal when Prompted for Passphrase

To avoid the passphrase prompt from opening a new window, add the following line to your shell configuration file (e.g., ~/.bashrc, ~/.zshrc):

export GPG_TTY=$(tty)