Orbis is a hybrid secrets management engine designed as a decentralized custodial system. A hybrid decentralized custodial system is one where it acts as a single "custodial" service that is the owner and authority of a secret but is maintained by a decentralized group of actors. Any one actor in the system is unable to recover or access the owned secret. Instead, a threshold number of actors is required to coordinate to recover the managed secret.
However, instead of directly recovering the secret, which would reveal the plaintext to the system's actors, we apply encryption that prohibits the system from ever accessing the plaintext of your secret, called Proxy Re-Encryption (PRE). PRE Translates encrypted ciphertext from one public key to another without exposing the plaintext.
This project is still early in its architectural journey. Although the overall high-level design and goals are defined, the concrete implementation details are in flux.
Traditional centralized custodial secrets management engines like Vault or AWS KMS are designed for traditional cloud deployments with no byzantine or malicious faults. Moreover, as they are centrally owned and operated, a single authority is responsible for maintaining and disseminating managed secrets. This deployment works in the private application-specific deployment that cloud-native applications thrive in. However, for the purposes of a public permissionless use case, the centralization is a single point of failure, censorship, and control.
The solution to the centralized custodial system is a decentralized variant. Instead of relying on authority for security like in the centralized version, the decentralized version must be grounded in verifiable cryptographic and byzantine fault-tolerant primitives.
Secret Rings are the decentralized group of actors that collaboratively maintain a shared keypair for the purposes of secret management.
These shared keypairs are generated via a DKG algorithm and maintained by a PSS algorithm for long-term security. DKG and PSS provide a mechanism for nodes to collaboratively generate a shared keypair with the public key known to all but the private key known by none. Instead, the private key is split into "shares," where each node holds a share.
Users who want their secrets managed by a given secret will encrypt their secret s using the Secret Ring public key, along with a Proof of Encryption and an authorization policy to protect it.
Once stored by the SecretRing, no single node may access the underlying secret s. When a user wants to recover the secret, they submit a read request containing an ephemeral public key and a Proof of Authorization for the given policy.
When a SecretRing receives a read request, it verifies the Proof of Authorization and initiates a Proxy Re-Encryption of the secret s with their share of the private key sk_i (i denotes the ith node in the ring), and the provided ephemeral public key. This step produces a PRE share, which, when recovered, yields a ReKey_AB, which is the cryptographic key for migrating ciphertext between two public keys A and B- where A is the SecretRing public key, and B is the requesting ephemeral public key.
Once a threshold number of peers correctly generate and publish their PRE share, either the requesting reader on their local device or a delegated node can recover the ReKey_AB, apply the final re-encryption step, and recover the original secret s by decrypting it their local private key associated with the requesting ephemeral public key.
Each secret s will have an associated policy determining the conditions under which a requesting party can access the secret. This is a relatively abstract design of Orbis.
The goal is to delegate authorization to the CACP engine on the SourceHub, a Zanzibar-style system.
The core design of Orbis relies on various kinds of Multi-Party Computation (MPC) systems that enable cryptographically secure, verifiable, and byzantine fault tolerance.
Distributed Key Generation is a decentralized method of collecting nodes to collaboratively generate a cryptographic keypair, where all know the public, but no single node knows the private key. Instead, each node maintains its "share" of the private key, and a threshold number of nodes can compute the secret key.
Proactive Secret Sharing is an auxiliary algorithm to that of the DKG. Once a DKG has been initiated and the associated keypair generated, the committee can only tolerate up to a threshold of corrupted, malicious, or otherwise byzantine nodes. If the time scale for how long one or more adversaries need to exploit these nodes is unlimited, the likelihood of such an instance goes to 100%.
PSS allows us to solve the unbounded time property by introducing a bounded time, where any adversary who is timebound to T can effectively corrupt or exploit the necessary threshold numbers of nodes in T-1 time. By proactively recomputing each node's share of the private key without actually changing the underlying long-term keypair of the DKG, we can ensure any timebound adversary will never recover the private key.
This is achieved by dividing time into epochs of time T and initiating a proactivization ReShare protocol at the end of each epoch before starting the next. This ReShare protocol should still only require a threshold number of honest nodes and be able to change the committee and threshold size dynamically.
Proxy Re-Encryption is a very powerful cryptographic primitive that allows one to generate a special ReKey that transforms/migrates ciphertext that is encrypted under one public key, A, to another public key, B. Moreover, the responsibility of actually applying the re-encryption given the rekey rk_AB can be executed by a non-trusted server without ever recovering the original plaintext.
/orbis- Top-level entry that combines all the sub-packages into a single coherent system./pkg-/auth- Authorization interfaces. Implementations will include SourceHub ACP, ZK-KMS, and local Zanzibar./bulletin- Public (verifiable) broadcast "bulletin board" for posting to and reading from a peer-to-peer context./config- Top-level configuration objects/crypto- Cryptographic utilities/db- Database, key-value, and repo interfaces/pre- Proxy Re-Encryption interfaces. Implementations include ElGamal RPE in the semi-trusted server domain./pss- Proactive Secret Sharing. Implementations include AVPSS (eventually CHURP, ECPSS)/service- Top-level service interfaces, of which all the other components provide for./transport- Networking transport layer interfaces. Implementations include the basic LibP2P system./types- Types shared by several components and packages
/proto- Protobuf definitions. Primarily used for network message and database serialization/gen- Generated types based on the Protobuf definitions.
TODO