Generate GPG key pair for git commits

Use command:

$ gpg --gen-key

Select default options (or specify other).

• Select what kind of key you want: (1) RSA and RSA (default).
• RSA keys may be between 1024 and 4096 bits long.
• Please specify how long the key should be valid: 0 = key does not expire.

Then enter your real name, email address and comment.
Then we need to generate a lot of random bytes for entropy. Load computer with disk operations to provide random number generator a better chance to gain enough entropy.
Wait while public and secret keys will be created.

List keys:

$ gpg --list-keys
/home/username/.gnupg/pubring.gpg
-----------------------------------
pub   2048R/9DA4A3D1 

...

Configure the key before using it for single repository, or globally if you are going to use the same key for every repository:

$ git config user.signingkey 9DA4A3D1 

$ git config --global user.signingkey 9DA4A3D1

Done.