GnuPG 1.4.x, 2.0.x, and 2.1.x treats a key flags subpacket with all bits
cleared (no usage permitted) as if it has all bits set (all usage permitted),
which might allow remote attackers to bypass intended cryptographic protection
mechanisms by leveraging the subkey.
Signed-off-by: Ming Liu <ming.liu@windriver.com> Signed-off-by: Jackie Huang <jackie.huang@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>