Background and Purpose There are many different types of secrets inside an oxide rack. At the base of the system we have the Device Id and Alias keys stored on the Ro T and used for platform identity and measurement signing for attestation respectively [RFD 36]. These keys along with a 3rd Ro T hosted keypair used for authenticating ephemeral Diffie-Hellman agreement provide the ability for sleds to form secure sprockets sessions for application layer messages [RFD 238].

These sprockets sessions provide each sled the ability to confidentially share information in a point-to-point fashion, where the integrity of messages is protected, the authenticity of the endpoint and the attestation of its running software is guaranteed. In order to provide the rack-level security guarantees such that an attacker cannot walk off with a subset of sleds or drives and recover any useful information, we have designed a Trust Quorum [RFD 238]. The primary protection mechanism behind the trust quorum is shamir secret sharing.

A shared rack-level secret which is used as a key-derivation source for other keys used to protect storage at rest. The rack secret is split into N unique key shares by a dealer process and distributed over sprockets sessions to each bootstrap agent along with the unique platform identities of the N trust quorum members. These platform identities are baked into the public key certificates on the Ro T to allow verification that an entity is who they say they are.

After distribution of this information, bootstrap agents can establish sprockets connections to other bootstrap agents, verify membership in the group (via the exchanged certs), and retrieve K-1 shares from other agents such that they can reconstruct the rack secret from K shares. Importantly, without obtaining K shares, no information about the rack secret can be learned. As described in [RFD 238], individual shares are stored unencrypted on each sled’s M.2 drives.

An attacker would have to steal at least K of these drives to reconstruct the rack secret, which is infeasible without significant time and disruption during physical access. In the future we plan to "seal" these secrets with the help of our root of trust (Ro T) such that they are only decrypted on sled boot. Sealing would mean that an attacker would have to steal K whole sleds and be able to boot them to recover the rack secret.

The weight of K sleds makes this prohibitive for a casual attacker.