git/Documentation/config/gpg.txt

gpg.program::
	Use this custom program instead of "`gpg`" found on `$PATH` when
	making or verifying a PGP signature. The program must support the
	same command-line interface as GPG, namely, to verify a detached
	signature, "`gpg --verify $signature - <$file`" is run, and the
	program is expected to signal a good signature by exiting with
	code 0, and to generate an ASCII-armored detached signature, the
	standard input of "`gpg -bsau $key`" is fed with the contents to be
	signed, and the program is expected to send the result to its
	standard output.

gpg.format::
	Specifies which key format to use when signing with `--gpg-sign`.
	Default is "openpgp" and another possible value is "x509".

gpg.<format>.program::
	Use this to customize the program used for the signing format you
	chose. (see `gpg.program` and `gpg.format`) `gpg.program` can still
	be used as a legacy synonym for `gpg.openpgp.program`. The default
	value for `gpg.x509.program` is "gpgsm".