Obscuro: rollup primitives beyond privacy
Community-contributed Russian translation here
If you’re already familiar with Obscuro (now known as Ten), you know its core proposition is to enable private smart contracts on an Ethereum Layer 2 solution. If you’re not, here’s an introduction. Obscuro is the only rollup solution providing fully private smart contracts, and as such it solves the privacy trilemma.
This is already crazy, but wait, I‘m going to share a little secret with you. What if Obscuro was also improving on other primitives like decentralization and bridge UX?
POBI: a private, scalable & secure consensus mechanism
Let’s have a look at the consensus protocol of Obscuro to understand what’s going on. It’s called POBI (Proof of Block Inclusion).
Note: this is a high-level view of POBI, if you want to explore further, check out this section of the white-paper.
This is how it works:
POBI and sequencer decentralization
Whereas rollup solutions like Arbitrum, Optimism, Zksync and StarkNet are using a centralized sequencer, the POBI protocol leverage TEEs in a way that make the aggregator set decentralized from day one — aggregators are responsible for the sequencing of transactions in Obscuro.
As a reminder, a TEE is secure enclave inside a processor that preserves data confidentiality. It’s like a black box. To be accepted as an aggregator, the code running inside the TEE of a server must be attested by a specific contract deployed on Ethereum L1.
Users’ transactions are then processed in the TEEs of aggregators to create rollups according to the POBI protocol described in the diagram above. As their code is attested, TEEs cannot execute malicious code, and node operators can’t even see the transactions they are processing.
This trustless set of aggregators makes Obscuro unstoppable and un-censorable.
Obscuro also leverages aggregators to provide a fully decentralized bridge between Ethereum and Obscuro.
Fast withdrawals from the Obscuro bridge
Long withdrawal periods are a known hindrance to user experience in fraud proof rollups like Arbitrum and Optimism where users must wait for a 7 days challenge period. To bypass this delay, users will sometimes choose to pay an un-trusted third party (Synapse, Across, Hop) to pay them back directly on L1 for a fee. This obviously adds third party risks and we’ve seen repeatedly how bridges are a target of choice for attackers.
But Obscuro users will enjoy a trustless native bridge with a short withdrawal period. How?
As shown in the diagram above, the POBI protocol is synchronizing the publishing of roll-ups to the cadence of L1 blocks to give Obscuro a quick finality. And as we know, each aggregator is executing attested code inside their TEE. There is therefore no need to wait for a 7 days window to challenge their output.
A small time window (a few Ethereum blocks) is still required in case of exceptional events like a TEE hack, where a mechanism based on fraud proofs kicks in. Note that in such a case the integrity of the ledger would not be compromised and Obscuro would fall back to a regular rollup behavior.
Wait, so Obscuro enables scalability and privacy for smart contract, all the while offering a better bridge UX and full sequencer decentralization? Comfy.
