Main Chain Internals

The ELA main chain is a UTXO-based blockchain secured by Bitcoin merged mining (AuxPoW) with BPoS finality. This page covers its internal architecture — from block structure to consensus to the full transaction type catalog.

Consensus Evolution

Elastos consensus evolved through four phases:

Phase	Height Range	Mechanism
1. Pure AuxPoW	Genesis to 343,400	Merged mining with Bitcoin only
2. CRC-Only DPoS	343,400 to 402,680	12 hardcoded Council arbiters provide finality
3. Public DPoS	402,680 to 1,405,000	Full public validator election
4. BPoS	1,405,000+	Time-locked staking with logarithmic weight

AuxPoW (Merged Mining)

Every ELA block header contains an AuxPow structure proving that a Bitcoin miner committed to the ELA block hash:

• The ELA block hash is embedded in the Bitcoin coinbase's scriptSig after magic bytes 0xfabe6d6d
• Chain ID 1224 produces a deterministic expected index in the aux Merkle tree
• The block hash is computed from the header without the AuxPow field (SerializeNoAux())

Block validation checks AuxPoW proof, PoW difficulty, timestamp bounds, Merkle root, and coinbase structure.

BPoS Confirmation

After BPoS activation, every block carries a Confirm — a collection of validator signatures proving BFT consensus:

1. On-duty validator proposes a block via DPOSProposal
2. Other validators validate and broadcast DPOSProposalVote (accept/reject)
3. When 2/3+1 accept votes are collected, a Confirm is formed
4. The confirmed block is final — no reorganization is possible

BFT Threshold: 2/3 supermajority of the active validator set.

PoW Fallback

If BPoS consensus stalls for 12 hours, the chain automatically reverts to pure PoW mode via a RevertToPOW transaction (type 0x41). Cross-chain transfers are blocked during PoW mode as a safety measure. Normal operation resumes via RevertToDPOS (type 0x42).

Block Structure

Component	Description
Header	Version, previous hash, Merkle root, timestamp, difficulty bits, nonce, height, AuxPow proof
Block	Header + ordered list of transactions
DposBlock	Block + optional Confirm (validator signature collection)

The header's Height field is explicit (unlike Bitcoin, which derives height from the chain).

Transaction Lifecycle

Every transaction passes through two validation stages:

Sanity Check (stateless):

• Valid size, serialization, type code, payload format, signature format

Context Check (stateful):

• All referenced UTXOs exist and are unspent
• Input values >= output values + fee
• Fee meets minimum threshold
• Per-type business logic rules
• No double-spend against mempool

Complete Transaction Type Reference

Base Transactions (0x00–0x08)

Code	Name	Purpose
0x00	CoinBase	Block reward distribution
0x01	RegisterAsset	Register new asset type
0x02	TransferAsset	Standard ELA transfer
0x03	Record	Data recording on-chain
0x04	Deploy	Reserved (unused)
0x05	SideChainPow	Sidechain PoW proof submission
0x06	RechargeToSideChain	Deposit ELA to sidechain
0x07	WithdrawFromSideChain	Withdraw ELA from sidechain
0x08	TransferCrossChainAsset	Cross-chain transfer

BPoS Validator Transactions (0x09–0x15)

Code	Name	Purpose
0x09	RegisterProducer	Register as BPoS validator
0x0a	CancelProducer	Cancel producer registration
0x0b	UpdateProducer	Update producer info
0x0c	ReturnDepositCoin	Retrieve staked deposit
0x0d	ActivateProducer	Re-activate after inactivity
0x0e	IllegalProposalEvidence	Report illegal DPoS proposal
0x0f	IllegalVoteEvidence	Report illegal DPoS vote
0x10	IllegalBlockEvidence	Report illegal block production
0x11	IllegalSidechainEvidence	Report sidechain misbehavior
0x12	InactiveArbitrators	Mark arbiters as inactive
0x13	UpdateVersion	Protocol version update
0x14	NextTurnDPOSInfo	Announce next arbiter set
0x15	ProposalResult	Record proposal outcome

DAO Transactions (0x21–0x31)

Code	Name	Purpose
0x21	RegisterCR	Register as Council candidate
0x22	UnregisterCR	Unregister candidacy
0x23	UpdateCR	Update candidate info
0x24	ReturnCRDepositCoin	Return Council deposit
0x25	CRCProposal	Submit Council proposal
0x26	CRCProposalReview	Council member reviews proposal
0x27	CRCProposalTracking	Track proposal progress
0x28	CRCAppropriation	Appropriate funds from treasury
0x29	CRCProposalWithdraw	Withdraw proposal funds
0x2a	CRCProposalRealWithdraw	Execute actual withdrawal
0x2b	CRAssetsRectify	Rectify CR asset UTXOs
0x2c	ReturnCrossChainDepositCoin	Return failed cross-chain deposits
0x31	CRCouncilMemberClaimNode	Council member claims DPoS node

System Transitions (0x41–0x51)

Code	Name	Purpose
0x41	RevertToPOW	Switch to pure PoW
0x42	RevertToDPOS	Restore DPoS consensus
0x51	ReturnSideChainDepositCoin	Return failed sidechain deposits

BPoS Staking (0x60–0x66)

Code	Name	Purpose
0x60	DposV2ClaimReward	Claim BPoS voter rewards
0x61	DposV2ClaimRewardRealWithdraw	Execute reward withdrawal
0x62	ExchangeVotes	Convert ELA to stake votes
0x63	Voting	Cast BPoS votes with lock time
0x64	ReturnVotes	Return staked votes
0x65	VotesRealWithdraw	Execute vote return
0x66	RecordSponsor	Record block confirm sponsor

NFT Transactions (0x71–0x72)

Code	Name	Purpose
0x71	CreateNFT	Create NFT from staking position
0x72	NFTDestroyFromSideChain	Destroy NFT returning from sidechain

UTXO Model

ELA uses a UTXO model like Bitcoin. Each transaction consumes previous outputs (inputs) and creates new ones.

Output types:

Code	Name	Purpose
0	OTNone	Standard transfer
1	OTVote	DPoS v1 voting
2	OTMapping	Mapping payload
3	OTCrossChain	Cross-chain transfer metadata
4	OTWithdrawFromSideChain	Sidechain withdrawal metadata
5	OTReturnSideChainDepositCoin	Failed deposit return
6	OTDposV2Vote	BPoS voting with lock time
7	OTStake	Staking/exchange votes

The node maintains an in-memory LRU UTXO cache (100,000 entries). Cache misses fall through to the database.

Validator Election

Composition: ~70 community-elected validators + 12 Council validators (always active). See nodes.elastos.net for current counts.

BPoS weight formula:

weight = log10((LockTime - BlockHeight) / 7200 * 10)
effectiveVotes = stakedELA * weight

Producer states: Pending -> Active -> Inactive/Canceled/Illegal -> Returned

• Inactivity: 1,440 missed rounds (~2 days) triggers Inactive state
• Illegal behavior: 200 ELA deducted from deposit; can re-register with a new deposit

Coinbase Distribution

Halving: Every 1,051,200 blocks (~4 years). Current reward: 0.761 ELA. See ELA Halving.

Fee Model

Fee	Amount	ELA
Min transaction fee	100 sela	0.000001
Min cross-chain fee	10,000 sela	0.0001
Deposit return fee	100 sela	0.000001
Proposal withdrawal fee	10,000 sela	0.0001

1 ELA = 100,000,000 sela. Transactions are prioritized by fee-per-KB for block inclusion.

Source Code

The main chain node is implemented in Go: Elastos.ELA

Key packages: blockchain/ (chain, store, validation), dpos/ (consensus), pow/ (mining), cr/state/ (DAO governance), core/types/ (block/tx structures), servers/ (RPC interfaces).