Most of our objects use int64 timestamps derived from `UnixNano()` instead of
`time.Time` objects. Switch the keyring metadata to use `UnixNano()` for
consistency across the API.
When the `Full` flag is passed for key rotation, we kick off a core
job to decrypt and re-encrypt all the secure variables so that they
use the new key.
The blocking query for `Keyring.List` appended the keys for each pass
through the blocking query to the response. This results in mulitple
copies of keys in the response. Overwrite the `reply.Keys` field on
each pass through the blocking query to ensure we only get the
expected page of responses.
After internal design review, we decided to remove exposing algorithm
choice to the end-user for the initial release. We'll solve nonce
rotation by forcing rotations automatically on key GC (in a core job,
not included in this changeset). Default to AES-256 GCM for the
following criteria:
* faster implementation when hardware acceleration is available
* FIPS compliant
* implementation in pure go
* post-quantum resistance
Also fixed a bug in the decoding from keystore and switched to a
harder-to-misuse encoding method.
When a server becomes leader, it will check if there are any keys in
the state store, and create one if there is not. The key metadata will
be replicated via raft to all followers, who will then get the key
material via key replication (not implemented in this changeset).
This changeset implements the keystore serialization/deserialization:
* Adds a JSON serialization extension for the `RootKey` struct, along with a metadata stub. When we serialize RootKey to the on-disk keystore, we want to base64 encode the key material but also exclude any frequently-changing fields which are stored in raft.
* Implements methods for loading/saving keys to the keystore.
* Implements methods for restoring the whole keystore from disk.
* Wires it all up with the `Keyring` RPC handlers and fixes up any fallout on tests.
