The current one is only one key.
This is to fix the current debian build failure of the storage module [1]
That inlines [2] as our cassandra.asc file used within the build.
[1] https://jenkins.softwareheritage.org/view/Debian%20packages/job/debian/job/packages/job/DSTO/job/gbp-buildpackage/162/console
[2] https://downloads.apache.org/cassandra/KEYS