specs: add validator set specs

state/validators.md

@@ -0,0 +1,40 @@
+# Sequencer Selection Scheme
+
+## Abstract
+
+The Sequencer Selection scheme describes the process of selecting a block proposer i.e. sequencer from the validator set.
+
+## Protocol/Component Description
+
+There is exactly one sequencer which is configured at genesis. `GenesisDoc` usually contains an array of validators as it is imported from `CometBFT`. If there is more than one validator defined
+in the genesis validator set, an error is thrown.
+
+The `State` struct defines a `Sequencer` field which contains the public key of the first and only validator of the genesis.
+
+The `Header` struct defines a field called `ProposerAddress` which is the pubkey of the original proposer of the block.
+
+The `SignedHeader` struct commits over the header and the proposer address and stores the result in `LastCommitHash`.
+
+A new untrusted header is verified by checking its `ProposerAddress` and matching it against the best-known header. In case of a mismatch, an error is thrown.
+
+When a new node is syncing, the block manager matches the `proposerKey` against the `Sequencer` field of the `lastState`. If a block is not signed by the expected proposer, it is ignored.
+
+## Message Structure/Communication Format
+
+The primary structures encompassing validator information include `SignedHeader`, `Header`, and `State`. Some fields are repurposed from CometBFT as seen in `GenesisDoc` `Validators`.
+
+## Assumptions and Considerations
+
+1. There must be exactly one validator defined in the genesis file, which determines the sequencer for all the blocks.
+
+## Implementation
+
+The implementation is split across multiple functions including `IsProposer`, `publishBlock`, `CreateBlock`, and `Verify` among others, which are defined in various files like `state.go`, `manager.go`, `block.go`, `header.go` etc., within the repository.
+
+See [block manager]
+
+## References
+
+[1] [Block Manager][block manager]
+
+[block manager]: https://github.com/rollkit/rollkit/blob/v0.11.x/block/block-manager.md