Glossary

Auth Token
Used to identify the user after starting a session. Contains the user application ID and the expiration date.

Change Stream
A Spanner feature that emits a record for every change to a watched table or column. Sync watches the payload_link column so an offloaded payload’s GCS object can be cleaned up when the row stops pointing at it. See Payload Offload.

Cluster
Group of webheads and storage devices that make up a set of Service Nodes.

Finalize
Marking an offloaded GCS object as permanent, by setting its committed metadata to true and pinning its customTime to the maximum value so the bucket’s lifecycle policy can never delete it. Done by the reconciler, not by syncserver.

Generation Number
An integer that may be included in an identity certificate.
The issuing server increases this value whenever the user changes their password. By rejecting assertions with a generation number lower than the previously seen maximum for that user, the Login Server can reject assertions generated using an old password.

Hawk Auth
An HTTP authentication method using a message authentication code (MAC) algorithm to provide cryptographic verification of portions of HTTP requests.

See https://github.com/hueniverse/hawk/

HKDF
HMAC-based Key Derivation Function, a method for deriving multiple secret keys from a single master secret.

See https://tools.ietf.org/html/rfc5869

Login Server
Used to authenticate user, returns tokens that can be used to authenticate to our services.

Master Secret
A secret shared between Login Server and Service Node.
Never used directly, only for deriving other secrets.

Node
A URL that identifies a service, like http://phx345.

Node Assignment Server
A service that can attribute to a user a node.

Orphan
An offloaded GCS object that no BSO row points at any more, because the row’s payload_link was replaced or the row was deleted. The reconciler deletes orphans.

Payload Link
The gs:// URL stored in a BSO’s payload_link column when its payload lives in GCS rather than inline in Spanner.

Payload Offload
Storing a BSO payload in a GCS object instead of inline in the database, which lifts the per-record size limit. Off by default, opt-in per collection, Spanner only. See Payload Offload.

Service
A service Mozilla provides, like Sync.

Service Node
A server that contains the service, and can be mapped to several Nodes (URLs).

Signing Secret
Derived from the master secret, used to sign the auth token.

Token Secret
Derived from the master secret and auth token, used as secret.
This is the only secret shared with the client and is different for each auth token.

User DB
A database that keeps the user/node relation.

Weave
The original code name for the Firefox Sync service and project.