The ebuild for net-wireless/osmocom-bb currently uses the git protocol for downloading the repo. The uri should be changed to "https://git.osmocom.org/osmocom-bb" to be able to fetch the sources securely.
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=b158e8480bedfaf5e5b9ab59948fad8711a7a88f