Recent GnuTLS packages on Ubuntu 16.04 have them disabled.
From /usr/share/doc/libgnutls30/changelog.Debian.gz:
gnutls28 (3.4.10-4ubuntu1.5) xenial-security; urgency=medium
* SECURITY UPDATE: Lucky-13 issues
[...]
- debian/patches/CVE-2018-1084x-4.patch: hmac-sha384 and sha256
ciphersuites were removed from defaults in lib/gnutls_priority.c,
tests/priorities.c.
Since we do want to test the ciphersuites, explicitly re-enable them in the
server's priority string. (This is a no-op with versions of GnuTLS where those
are already enabled by default.)
Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
244d06637f