Sep 7, 2017

Google’s source code is stored in a central repository where both current and past versions of the service are auditable.

The infrastructure can additionally be configured to require that a service's binaries be built from specific reviewed, checked in, and tested source code. Such code reviews require inspection and approval from at least one engineer other than the author, and the system enforces that code modifications to any system must be approved by the owners of that system. These requirements limit the ability of an insider or adversary to make malicious modifications to source code and also provide a forensic trail from a service back to its source.