<!-- TITLE: Ethereum Chain Spec Format --> This is a format to describe any Ethereum-like chain. It is derived from the `genesis.json` format but includes parameters to change and configure the consensus algorithm, to specify infrastructure information, to specify boot nodes and to specify any built-in contracts together with their cost. ### Format It is JSON, with the top level being an object with six keys: - `name`: A string value specifying the chain name. e.g. "Frontier/Homestead", "Morden", "Olympic". - `forkName`: An optional string value specifying a sub-identifier, in case two different chains have equivalent genesis blocks. - `engine`: A enum value specifying the consensus engine. e.g. "Ethash", "Null". - `params`: An object specifying various attributes of the consensus engine, allowing configuration. - `genesis`: An object specifying the header of the genesis block. - `nodes`: An array of strings, each one a node address in enode format. - `accounts`: An object specifying accounts of the genesis block. This includes builtin contracts and premines. #### Subformat: engine There are two valid engines, `Ethash` and `Null`. - `Null`: Nonoperative engine. - `Ethash`: Sealing engine used by ethereum. - `params`: Engine specific params. - `minimumDifficulty`: Integer specifying the minimum difficulty a block may have. - `gasLimitBoundDivisor`: Integer specifying the according value in the Yellow Paper. - `difficultyBoundDivisor`: Integer specifying the according value in the Yellow Paper. - `durationLimit`: Integer specifying the boundary point at which difficulty is increased. - `blockReward`: Integer specifying the reward given for authoring a block. - `registrar`: `0x`-prefixed, 40-nibble datum of the address of the registrar contract on this chain. #### Subformat: params Different consensus engines may allow different keys in the `params` object, however there exist a few common to all: - `accountStartNonce`: Integer specifying what nonce all newly created accounts should have. - `frontierCompatibilityModeLimit`: Integer specifying the number of the block that Frontier-compatibility mode finishes and Homestead mode begins. - `maximumExtraDataSize`: Integer specifying the maximum size in bytes of the extra_data field of the header. - `minGasLimit`: Integer specifying the minimum amount of gas a block may be limited at. - `networkID`: Integer specifying the index of this chain on the network. Note: all integers are `0x`-prefixed, hex-encoded strings. #### Subformat: genesis The keys in genesis specify the according fields in the chain's genesis block. All are hex-encoded, `0x` prefixed. The fields required are: - `seal` - `difficulty` - `author` - `timestamp` - `parentHash` - `extraData` - `gasLimit` #### Subformat: accounts The `accounts` object maps from addresses (40-nibble strings without the `0x` prefix) to objects, each with a number of allowed keys: - `balance`: Integer to specify the balance of the account at genesis in wei. - `nonce`: Integer to specify the nonce of the account at genesis. - `code`: `0x`-prefixed hex specifying the code of the account at genesis. - `storage`: Object mapping hex-encoded integers for the account's storage at genesis. - `builtin`: Alternative to `code`, used to specify that the account's code is natively implemented. Value is an object with further fields: - "name": The name of the builtin code to execute as a string. e.g. `"identity"`, `"ecrecover"`. - "pricing": Enum to specify the cost of calling this contract. - "linear": Specify a linear cost to calling this contract. Value is an object with two fields: `base` which is the basic cost in Wei and is always paid; and `word` which is the cost per word of input, rounded up. ### Example This is the Morden ECS JSON file ```json { "name": "Morden", "engine": { "Ethash": { "params": { "tieBreakingGas": false, "gasLimitBoundDivisor": "0x0400", "minimumDifficulty": "0x020000", "difficultyBoundDivisor": "0x0800", "durationLimit": "0x0d", "blockReward": "0x4563918244F40000", "registrar" : "0xc6d9d2cd449a754c494264e1809c50e34d64562b" } } }, "params": { "accountStartNonce": "0x0100000", "frontierCompatibilityModeLimit": "0x789b0", "maximumExtraDataSize": "0x20", "tieBreakingGas": false, "minGasLimit": "0x1388", "networkID" : "0x2" }, "genesis": { "seal": { "ethereum": { "nonce": "0x0000000000000042", "mixHash": "0x0000000000000000000000000000000000000000000000000000000000000000" } }, "difficulty": "0x20000", "author": "0x0000000000000000000000000000000000000000", "timestamp": "0x00", "parentHash": "0x0000000000000000000000000000000000000000000000000000000000000000", "extraData": "0x", "gasLimit": "0x2fefd8" }, "nodes": [ "enode://b1217cbaa440e35ed471157123fe468e19e8b5ad5bedb4b1fdbcbdab6fb2f5ed3e95dd9c24a22a79fdb2352204cea207df27d92bfd21bfd41545e8b16f637499@104.44.138.37:30303" ], "accounts": { "0000000000000000000000000000000000000001": { "balance": "1", "nonce": "1048576", "builtin": { "name": "ecrecover", "pricing": { "linear": { "base": 3000, "word": 0 } } } }, "0000000000000000000000000000000000000002": { "balance": "1", "nonce": "1048576", "builtin": { "name": "sha256", "pricing": { "linear": { "base": 60, "word": 12 } } } }, "0000000000000000000000000000000000000003": { "balance": "1", "nonce": "1048576", "builtin": { "name": "ripemd160", "pricing": { "linear": { "base": 600, "word": 120 } } } }, "0000000000000000000000000000000000000004": { "balance": "1", "nonce": "1048576", "builtin": { "name": "identity", "pricing": { "linear": { "base": 15, "word": 3 } } } }, "102e61f5d8f9bc71d0ad4a084df4e65e05ce0e1c": { "balance": "1606938044258990275541962092341162602522202993782792835301376", "nonce": "1048576" } } } ``` Note: the builtin accounts enable usage of Solidity language. Running without them included in the chain definition file may result in unexpected behavior.