Understanding Graphene: Shared Secret Key

[testz]

Does the Graphene protocol make use of a shared secret key by the set of block producing witnesses in each round?  If yes, please describe the protocol for generating the shared secret key and what current and potential function(s) is served by its use.  References within the code are also appreciated.

Secret key was removed, please listen here: https://youtu.be/uaF3yWlC6s8?t=8m10s
Or read here from: https://beyondbitcoin.org/bitshares-dev-hangout-bytemaster-transaction-propagation-voting-peer-to-peer-protocols/

[00:08:56] bytemaster: We identified the primary culprit is the Witness scheduler and the random numbers … that we’ve been using. So we’ve put a lot of work into optimizing that. And concluded, amazingly, that we can eliminate the need for Witnesses to post commitments and reveal secrets while retaining all the benefits of Witness shuffling. And it has the impact of saving the blockchain over 1GB of storage per year … of just better random ___.

[Fox]

Does the Graphene protocol make use of a shared secret key by the set of block producing witnesses in each round?  If yes, please describe the protocol for generating the shared secret key and what current and potential function(s) is served by its use.  References within the code are also appreciated.