Configure Git Commit Signing with GPG after Changing Email

TLDR

Check out the awesome guide How to Sign Git Commits if you have not configure git signature before.

Generate a key from $ gpg --full-generate-key
Update [user] credentials in git config
(Optional) Export the key to GitHub

Steps

1. Create a New Key

Follow GitHub's "Generating a GPG key" if the key is to be used on GitHub.

$ gpg --full-generate-key

The output should look something like the following:

# Keep the key ID (where the BDKEY5KEY78KEY48 is) for step 3
gpg: key BDKEY5KEY78KEY48 marked as ultimately trusted
gpg: revocation certificate stored as ...
public and secret key created and signed.
 
# Keep the public key (where the 4044FKEYFKEY... is) for step 2
pub   rsa4096 2021-05-17 [SC]
      4044FKEYKEYMOREKEYSKEYKEYKEYKEYMOREKEYS8
uid                      Danny Cheng-Hsuan Han <chenghsuan.han@gmail.com>
sub   rsa4096 2021-05-17 [E]

2. Update [user] credentials in git config

Don't forget to do a test commit when done updating credentials!

Refer to GitHub's "Telling Git about your GPG key" if you have multiple keys.

# Add --global to set it globally
$ git config --edit

The template should be like the following:

# .gitconfig

# ...omitted

[user]
  name = (user your desired name, i.e., Danny Cheng-Hsuan Han)
  email = (use your email in key generation, i.e., chenghsuan.han@gmail.com)
  signingKey = (use the public key from key generation, i.e., 4044FKEYKEYMOREKEYSKEYKEYKEYKEYMOREKEYS8)

# ...omitted

3. Export the key to GitHub

Refer to GitHub's "Adding a GPG key" for more details.

3-1

$ gpg --list-secret-keys --keyid-format LONG

3-2

# Use the key ID from step 1 here
# In case you lose the key ID, use pub key from `$ gpg --list-keys` is ok too
$ gpg --armor --export BDKEY5KEY78KEY48

3-3

Quoting from GitHub, Copy your GPG key, beginning with -----BEGIN PGP PUBLIC KEY BLOCK----- and ending with -----END PGP PUBLIC KEY BLOCK----- then paste it to your GitHub account. Done!

References

How to Sign Git Commits