A Jcat file can be used to store GPG, PKCS-7 and SHA-256 checksums for multiple
files. This allows us to sign a firmware or metadata multiple times (perhaps
by the OEM and also then the LVFS) which further decentralizes the trust model
of the LVFS.
The Jcat format was chosen as the Microsoft catalog format is nonfree and not
documented. We also don't want to modify an existing .cat file created from WU
as this may make it unsuitable to use on Windows.
More information can be found here: https://github.com/hughsie/libjcat
d5aab65f30