feat: Optimism Derivation Proof Composition

[hashcashier]

OP Composition

This PR introduces the proof composition program for optimism block derivation. The goal of this composition is to stitch together sequential optimism block derivation proofs into a single composed proofs about the contiguous chain of optimism blocks.

Input

pub struct ComposeInput {
    pub derive_image_id: [u32; 8],
    pub compose_image_id: [u32; 8],
    pub operation: ComposeInputOperation,
    pub eth_chain_root: [u8; 32],
}

The input given to the composition predicate consists of:

1. The image id used for op block derivation
2. The image id of the composition guest itself
3. The “operation” which this invocation of the guest should perform (prep/lift/join/finish)
4. The Merkle-tree root of the Ethereum blockchain using which all derivation should be performed.

Operations

pub enum ComposeInputOperation {
    PREP {
        eth_blocks: Vec<Header>,
        prior_prep: Option<(ComposeOutput, MerkleMountainRange)>,
    },
    LIFT {
        derivation: DeriveOutput,
        eth_tail_proof: MerkleProof,
    },
    JOIN {
        left: ComposeOutput,
        right: ComposeOutput,
    },
    FINISH {
        prep: ComposeOutput,
        aggregate: ComposeOutput,
    },
}

The composer can be asked to perform any one of four possible operations, described below.

Join

The join operation is where the stitching logic happens. Joining can only succeed if:

1. The optimism “tail” of the left proof is equal to the optimism “head” of the right proof (i.e. the optimism blocks in the right proof’s chain start off where the left proof chain ends).
2. The ethereum blocks used for derivation in both proofs are on the same chain. (security)

The first condition is checked during the join operation, while the second condition is already validated during the pre-requisite “lift” operation using the eth_chain_root.

Lift

Lifting converts a block derivation proof into an equivalent proof, only after verifying that the last ethereum block read during derivation belongs to the continuous chain committed to under eth_chain_root. This is done using a merkle inclusion proof.

Preparation

This operation takes as input a chain of ethereum blocks and inserts them into a Merkle-tree, resulting in a composition statement about an eth_chain_root value. This operation can also be performed incrementally when given a Merkle mountain range (and corresponding proof) as input if the ethereum chain is too large for one session.

Finish

Finalization takes as input a composition “preparation” proof about the merkle root eth_chain_root, asserting its commitment to a continuous chain of ethereum blocks, and a composition “aggregation” proof about the derivation of a series of op-blocks from the ethereum blocks under eth_chain_root.

[Wollac]

Will look at it one last time when all the sub-PRs are merged.

[Wollac]

Let's create the issues we discussed, but other than that, let's finally merge this beast!