Program Architecture

Header Range

The header range program computes the data root and state root commitments for a range of headers. The program does the following:

1. The first header in the range is the trusted header (matching the latestHeader on the SP1Vector.sol contract when the proof is verified).
2. There exists a valid justification by an authority set in the SP1Vector.sol contract for the target block with an authority set id >= the authority set id of the trusted header.
3. The intermediate headers are linked in order by number and parent hash. Note: There is no way to produce a valid linked header range that does not match the real range as long as the justification on the target block is valid and the trusted header is also valid.
4. The authority set hash of the justification matches the authority set hash of the target block.

graph TD;
    subgraph SP1Vector.sol
        LatestBlock[Latest Block]
        AuthoritySetIdToHash[Authority Set Id to Hash]
        DataRootCommitments[Data Root Commitments]
        StateRootCommitments[State Root Commitments]
    end

    subgraph Program
        LatestBlock -->|latest block| TrustedHeaderHash[Trusted Header Hash]
        TrustedHeaderHash[Trusted Header Hash] -->|matches first header in| HeaderData
        AuthoritySetIdToHash -->|includes| AuthoritySetHash[Authority Set Hash]
        AuthoritySetHash -->|preimage| AuthoritySetPubkeys[Authority Set Pubkeys]
        AuthoritySetPubkeys -->|signs| TargetJustification[Target Justification]
        TargetJustification -->|includes| TargetBlockHash[Target Block Hash]
        TargetBlockHash -->|matches last header in| HeaderData[Header Data]
        HeaderData -->|verify header hashes and numbers are linked| ValidatedHeaderData[Validated Header Data]
        ValidatedHeaderData -->|hash data and state roots of headers| MerkleCommitments[Data Root and State Root Merkle Commitments]
        MerkleCommitments -->|data root commitment| DataRootCommitments[Data Root Commitments]
        MerkleCommitments -->|state root commitment| StateRootCommitments[State Root Commitments]
    end

Rotate

The rotate program computes the next authority set hash from the last header in an epoch signed by the current authority set. The program does the following:

1. The current authority set signed the justification for the target block.
2. The preimage of the target block hash which will be used for extracting the next validator set matches the target block hash signed in the justification.
3. Extract the next validator set from the epoch end header. In this process, validate that this epoch end header is valid.
4. Compute the next authority set hash from the next validator set.

graph TD;
    subgraph SP1Vector.sol
        CurrentAuthoritySet[Current Authority Set Hash]
        NextAuthoritySet[Next Authority Set Hash]
    end

    subgraph Program
        CurrentAuthoritySet -->|preimage| CurrentAuthoritySetPubkeys[Current Authority Set Pubkeys]
        CurrentAuthoritySetPubkeys[Current Authority Set Pubkeys] -->|signs| Justification[Circuit Justification]
        Justification -->|includes| TargetBlockHash[Target Block Hash]
        TargetBlockHash -->|preimage| EncodedHeaderData[Encoded Header Data]
        EncodedHeaderData -->|contains| NewPubkeys[Next Pubkeys]
        NewPubkeys -->|hash| NextAuthoritySetHash[Next Authority Set Hash]
        NextAuthoritySetHash --> NextAuthoritySet[Next Authority Set Hash]
    end