Signing Commit

~/.gitconfig

[user]
  name = Foo
  email = bar@baz.com
  signingKey = ~/.ssh/prikey
[gpg]
  format = ssh
[commit]
  gpgSign = true

~/.ssh/config

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/prikey
  IdentitiesOnly yes