Sequencer-Committee Interaction

When the SankoChain sequencer produces a data batch that it wants to post using the Committee, it sends the batch's data, along with an expiration time (normally three weeks in the future) via RPC to all Committee members in parallel. Each Committee member stores the data in its backing store, indexed by the data's hash. Then the member signs the (hash, expiration time) pair using its BLS key, and returns the signature with a success indicator to the sequencer.

Once the Sequencer has collected enough signatures, it can aggregate the signatures and create a valid DACert for the (hash, expiration time) pair. The Sequencer then posts that DACert to Arbitrum, making it available to the SankoChain software at L3.

If the Sequencer fails to collect enough signatures within a few minutes, it will abandon the attempt to use the Committee, and will "fall back to rollup" by posting the full data directly to Arbitrum. SankoChain can understand both data posting formats (via DACert or via full data) and will handle each one correctly.