MESS — Modified Exponential Subjective Scoring

MESS (ECBP-1100) is an artificial finality mechanism for Ethereum Classic. It penalizes deep reorganizations by applying an exponential scoring penalty to alternative chains that diverge far from the canonical head.

Network activation

MESS shipped as a temporary safety measure, not a permanent consensus rule, so it is not part of the fork ID — core-geth classifies ECBP-1100 as a cross-compatible transition rather than a hard fork, so it never enters the forkid block list. In go-ethereum-classic it is configured only for Classic mainnet (params/config_etc.go):

Network	MESS activated	MESS deactivated
Classic (mainnet)	11,380,000 (09 Oct 2020)	19,250,000 (31 Jan 2024, with the Spiral hard fork)
Mordor (testnet)	not configured	not configured

ECIP-1110 ties MESS deactivation to the Spiral activation block (19,250,000), which Ethereum Classic announced for 31 Jan 2024.

Mordor divergence (intentional): getc's MordorChainConfig leaves ECBP1100Transition / ECBP1100DeactivateTransition unset, so IsECBP1100 is always false on Mordor — a deliberate divergence from core-geth. This does not affect syncing or block validity: MESS is a fork-choice / reorg policy (it only vetoes deep reorgs against a competing chain via reorgFilter), never a block-validity rule, and it is only active once a node is already synced — not during catch-up. Mordor replays to the same canonical chain with or without it. The only thing getc forgoes is MESS's deep-reorg protection during the elapsed 2,380,000 → 10,400,000 window.

Note: MESS activated at 11,380,000 — distinct from Etchash (ECIP-1099) at 11,700,000. Etchash is a consensus fork (it changes the PoW DAG) and counts toward the fork ID, which is why it appears in the fork list and MESS does not.

Metric	Value
Dedicated files	3
Extension points	6
Upstream files touched	5

Architecture

Fork-choice flow

block arrives → blockchain.go writeKnownBlock / writeBlockAndSetHead
  → forker.ReorgNeeded(current, extern)       [core/forkchoice_pow.go]
    → TD comparison
    → reorgFilter(current, extern)
      → IsMESSEnabled() && IsECBP1100(num)
      → findCommonAncestor()
          → if unresolved (no ancestor / missing header) → REJECT + log (fail-closed)
      → ecbp1100(): antigravity polynomial check
          → REJECT (errReorgFinality) + log, or ALLOW

Note the fail-closed stance: if the common ancestor cannot be resolved, MESS rejects the reorg rather than allowing it — a reorg it cannot verify is exactly the case MESS exists to guard. (core-geth propagates the same error in its equivalent ForkChoice.ReorgNeeded.)

Activation lifecycle

chainSyncer loop  [eth/sync_pow.go]            — on sync done / when already synced
  → checkMESSActivation()                      [eth/sync_mess.go]
      enable:  !enabled && shouldEnableMESS() && peers ≥ 5  → EnableMESS(true,  "synced")
      disable: enabled && peers < 5                         → EnableMESS(false, "low peers")
      shouldEnableMESS() = !messForceDisable && (messForceEnable || IsECBP1100(head))

messSafetyLoop  [eth/sync_mess.go]             — separate ticker, 30 × blocktime ≈ 6.5 min (ECIP-1100)
  → if enabled && head stale → EnableMESS(false, "stale head")

Dedicated Files

These files are entirely new and exist only for MESS. Files that MESS merely hooks into — like the revived core/forkchoice_pow.go — are shown under Fork Choice below, not here.

File	Description	Changed
core/blockchain_mess.go · diff	MESS algorithm — ecbp1100 polynomial, findCommonAncestor, NewForkChoiceWithMESS	+270 -0
core/blockchain_mess_test.go · diff	MESS unit tests	+700 -0
eth/sync_mess.go · diff	MESS activation control — messSafetyLoop, checkMESSActivation, shouldEnableMESS	+107 -0

Fork Choice — revived, with the MESS hook

core/forkchoice_pow.go is not a MESS-only file: it transplants back the pre-purge total-difficulty fork choice that upstream removed with TD. MESS only adds a hook here — the reorgFilter / reorgAllowed callback that lets the MESS algorithm veto a reorg. The symbols below are that revived fork choice (full picture in the Total Difficulty subsystem); the MESS algorithm itself lives in core/blockchain_mess.go.

Symbol	Original	Current	Status	Diff
ChainReader	forkchoice	forkchoice_pow	✅	view
ForkChoice 📋	forkchoice	forkchoice_pow	+10 -0	view
NewForkChoice	forkchoice	forkchoice_pow	✅	view
ForkChoice.ReorgNeeded 📋	forkchoice	forkchoice_pow	+13 -10	view
ForkChoice.reorgAllowed	—	forkchoice_pow	🆕	view

Extension Points

Modifications to upstream files that wire in MESS behavior.

Struct Fields

#	File	Name	Lines	Description	Wires To
1	params/config.go	ChainConfig ETC fields	497-507	ECIP fork blocks (1017/1041/1099/Spiral), era rounds, DieHard bomb pause, MESS (ECBP-1100) activation/deactivation	params/config_etc.go
2	eth/handler.go	handler.messForceEnable/Disable	126-127	MESS emergency override flags propagated from ethconfig	eth/sync_mess.go
3	eth/ethconfig/config.go	Config.MESSForceEnable/Disable	214-215	Emergency MESS overrides — force enable or force disable regardless of chain config	eth/ethconfig/config.go

Conditional Blocks

#	File	Name	Lines	Description	Wires To
4	eth/handler.go	isPow in Start (PoW syncer)	467-477	Starts chainSyncer, block fetcher, and MESS safety loop for PoW chains	eth/handler_pow.go, eth/sync_pow.go
5	core/blockchain.go	IsPow in NewBlockChain	428-429	Initializes ForkChoice with MESS for PoW chains	core/forkchoice_pow.go

Config Plumbing

#	File	Name	Lines	Description	Wires To
6	eth/backend.go	MESS flags passthrough	343-344	Passes MESSForceEnable/Disable from ethconfig to handler config	eth/handler.go