path: root/cmd/puppeth/genesis.go

// Copyright 2017 The go-ethereum Authors
// This file is part of go-ethereum.
//
// go-ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// go-ethereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.

package main

import (
    "encoding/binary"
    "errors"
    "math"
    "math/big"
    "strings"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/hexutil"
    math2 "github.com/ethereum/go-ethereum/common/math"
    "github.com/ethereum/go-ethereum/consensus/ethash"
    "github.com/ethereum/go-ethereum/core"
    "github.com/ethereum/go-ethereum/params"
)

// alethGenesisSpec represents the genesis specification format used by the
// C++ Ethereum implementation.
type alethGenesisSpec struct {
    SealEngine string `json:"sealEngine"`
    Params     struct {
        AccountStartNonce       math2.HexOrDecimal64   `json:"accountStartNonce"`
        MaximumExtraDataSize    hexutil.Uint64         `json:"maximumExtraDataSize"`
        HomesteadForkBlock      hexutil.Uint64         `json:"homesteadForkBlock"`
        DaoHardforkBlock        math2.HexOrDecimal64   `json:"daoHardforkBlock"`
        EIP150ForkBlock         hexutil.Uint64         `json:"EIP150ForkBlock"`
        EIP158ForkBlock         hexutil.Uint64         `json:"EIP158ForkBlock"`
        ByzantiumForkBlock      hexutil.Uint64         `json:"byzantiumForkBlock"`
        ConstantinopleForkBlock hexutil.Uint64         `json:"constantinopleForkBlock"`
        MinGasLimit             hexutil.Uint64         `json:"minGasLimit"`
        MaxGasLimit             hexutil.Uint64         `json:"maxGasLimit"`
        TieBreakingGas          bool                   `json:"tieBreakingGas"`
        GasLimitBoundDivisor    math2.HexOrDecimal64   `json:"gasLimitBoundDivisor"`
        MinimumDifficulty       *hexutil.Big           `json:"minimumDifficulty"`
        DifficultyBoundDivisor  *math2.HexOrDecimal256 `json:"difficultyBoundDivisor"`
        DurationLimit           *math2.HexOrDecimal256 `json:"durationLimit"`
        BlockReward             *hexutil.Big           `json:"blockReward"`
        NetworkID               hexutil.Uint64         `json:"networkID"`
        ChainID                 hexutil.Uint64         `json:"chainID"`
        AllowFutureBlocks       bool                   `json:"allowFutureBlocks"`
    } `json:"params"`

    Genesis struct {
        Nonce      hexutil.Bytes  `json:"nonce"`
        Difficulty *hexutil.Big   `json:"difficulty"`
        MixHash    common.Hash    `json:"mixHash"`
        Author     common.Address `json:"author"`
        Timestamp  hexutil.Uint64 `json:"timestamp"`
        ParentHash common.Hash    `json:"parentHash"`
        ExtraData  hexutil.Bytes  `json:"extraData"`
        GasLimit   hexutil.Uint64 `json:"gasLimit"`
    } `json:"genesis"`

    Accounts map[common.UnprefixedAddress]*alethGenesisSpecAccount `json:"accounts"`
}

// alethGenesisSpecAccount is the prefunded genesis account and/or precompiled
// contract definition.
type alethGenesisSpecAccount struct {
    Balance     *math2.HexOrDecimal256   `json:"balance"`
    Nonce       uint64                   `json:"nonce,omitempty"`
    Precompiled *alethGenesisSpecBuiltin `json:"precompiled,omitempty"`
}

// alethGenesisSpecBuiltin is the precompiled contract definition.
type alethGenesisSpecBuiltin struct {
    Name          string                         `json:"name,omitempty"`
    StartingBlock hexutil.Uint64                 `json:"startingBlock,omitempty"`
    Linear        *alethGenesisSpecLinearPricing `json:"linear,omitempty"`
}

type alethGenesisSpecLinearPricing struct {
    Base uint64 `json:"base"`
    Word uint64 `json:"word"`
}

// newAlethGenesisSpec converts a go-ethereum genesis block into a Aleth-specific
// chain specification format.
func newAlethGenesisSpec(network string, genesis *core.Genesis) (*alethGenesisSpec, error) {
    // Only ethash is currently supported between go-ethereum and aleth
    if genesis.Config.Ethash == nil {
        return nil, errors.New("unsupported consensus engine")
    }
    // Reconstruct the chain spec in Aleth format
    spec := &alethGenesisSpec{
        SealEngine: "Ethash",
    }
    // Some defaults
    spec.Params.AccountStartNonce = 0
    spec.Params.TieBreakingGas = false
    spec.Params.AllowFutureBlocks = false
    spec.Params.DaoHardforkBlock = 0

    spec.Params.HomesteadForkBlock = (hexutil.Uint64)(genesis.Config.HomesteadBlock.Uint64())
    spec.Params.EIP150ForkBlock = (hexutil.Uint64)(genesis.Config.EIP150Block.Uint64())
    spec.Params.EIP158ForkBlock = (hexutil.Uint64)(genesis.Config.EIP158Block.Uint64())

    // Byzantium
    if num := genesis.Config.ByzantiumBlock; num != nil {
        spec.setByzantium(num)
    }
    // Constantinople
    if num := genesis.Config.ConstantinopleBlock; num != nil {
        spec.setConstantinople(num)
    }

    spec.Params.NetworkID = (hexutil.Uint64)(genesis.Config.ChainID.Uint64())
    spec.Params.ChainID = (hexutil.Uint64)(genesis.Config.ChainID.Uint64())
    spec.Params.MaximumExtraDataSize = (hexutil.Uint64)(params.MaximumExtraDataSize)
    spec.Params.MinGasLimit = (hexutil.Uint64)(params.MinGasLimit)
    spec.Params.MaxGasLimit = (hexutil.Uint64)(math.MaxInt64)
    spec.Params.MinimumDifficulty = (*hexutil.Big)(params.MinimumDifficulty)
    spec.Params.DifficultyBoundDivisor = (*math2.HexOrDecimal256)(params.DifficultyBoundDivisor)
    spec.Params.GasLimitBoundDivisor = (math2.HexOrDecimal64)(params.GasLimitBoundDivisor)
    spec.Params.DurationLimit = (*math2.HexOrDecimal256)(params.DurationLimit)
    spec.Params.BlockReward = (*hexutil.Big)(ethash.FrontierBlockReward)

    spec.Genesis.Nonce = (hexutil.Bytes)(make([]byte, 8))
    binary.LittleEndian.PutUint64(spec.Genesis.Nonce[:], genesis.Nonce)

    spec.Genesis.MixHash = genesis.Mixhash
    spec.Genesis.Difficulty = (*hexutil.Big)(genesis.Difficulty)
    spec.Genesis.Author = genesis.Coinbase
    spec.Genesis.Timestamp = (hexutil.Uint64)(genesis.Timestamp)
    spec.Genesis.ParentHash = genesis.ParentHash
    spec.Genesis.ExtraData = (hexutil.Bytes)(genesis.ExtraData)
    spec.Genesis.GasLimit = (hexutil.Uint64)(genesis.GasLimit)

    for address, account := range genesis.Alloc {
        spec.setAccount(address, account)
    }

    spec.setPrecompile(1, &alethGenesisSpecBuiltin{Name: "ecrecover",
        Linear: &alethGenesisSpecLinearPricing{Base: 3000}})
    spec.setPrecompile(2, &alethGenesisSpecBuiltin{Name: "sha256",
        Linear: &alethGenesisSpecLinearPricing{Base: 60, Word: 12}})
    spec.setPrecompile(3, &alethGenesisSpecBuiltin{Name: "ripemd160",
        Linear: &alethGenesisSpecLinearPricing{Base: 600, Word: 120}})
    spec.setPrecompile(4, &alethGenesisSpecBuiltin{Name: "identity",
        Linear: &alethGenesisSpecLinearPricing{Base: 15, Word: 3}})
    if genesis.Config.ByzantiumBlock != nil {
        spec.setPrecompile(5, &alethGenesisSpecBuiltin{Name: "modexp",
            StartingBlock: (hexutil.Uint64)(genesis.Config.ByzantiumBlock.Uint64())})
        spec.setPrecompile(6, &alethGenesisSpecBuiltin{Name: "alt_bn128_G1_add",
            StartingBlock: (hexutil.Uint64)(genesis.Config.ByzantiumBlock.Uint64()),
            Linear:        &alethGenesisSpecLinearPricing{Base: 500}})
        spec.setPrecompile(7, &alethGenesisSpecBuiltin{Name: "alt_bn128_G1_mul",
            StartingBlock: (hexutil.Uint64)(genesis.Config.ByzantiumBlock.Uint64()),
            Linear:        &alethGenesisSpecLinearPricing{Base: 40000}})
        spec.setPrecompile(8, &alethGenesisSpecBuiltin{Name: "alt_bn128_pairing_product",
            StartingBlock: (hexutil.Uint64)(genesis.Config.ByzantiumBlock.Uint64())})
    }
    return spec, nil
}

func (spec *alethGenesisSpec) setPrecompile(address byte, data *alethGenesisSpecBuiltin) {
    if spec.Accounts == nil {
        spec.Accounts = make(map[common.UnprefixedAddress]*alethGenesisSpecAccount)
    }
    spec.Accounts[common.UnprefixedAddress(common.BytesToAddress([]byte{address}))].Precompiled = data
}

func (spec *alethGenesisSpec) setAccount(address common.Address, account core.GenesisAccount) {
    if spec.Accounts == nil {
        spec.Accounts = make(map[common.UnprefixedAddress]*alethGenesisSpecAccount)
    }

    a, exist := spec.Accounts[common.UnprefixedAddress(address)]
    if !exist {
        a = &alethGenesisSpecAccount{}
        spec.Accounts[common.UnprefixedAddress(address)] = a
    }
    a.Balance = (*math2.HexOrDecimal256)(account.Balance)
    a.Nonce = account.Nonce

}

func (spec *alethGenesisSpec) setByzantium(num *big.Int) {
    spec.Params.ByzantiumForkBlock = hexutil.Uint64(num.Uint64())
}

func (spec *alethGenesisSpec) setConstantinople(num *big.Int) {
    spec.Params.ConstantinopleForkBlock = hexutil.Uint64(num.Uint64())
}

// parityChainSpec is the chain specification format used by Parity.
type parityChainSpec struct {
    Name    string `json:"name"`
    Datadir string `json:"dataDir"`
    Engine  struct {
        Ethash struct {
            Params struct {
                MinimumDifficulty      *hexutil.Big      `json:"minimumDifficulty"`
                DifficultyBoundDivisor *hexutil.Big      `json:"difficultyBoundDivisor"`
                DurationLimit          *hexutil.Big      `json:"durationLimit"`
                BlockReward            map[string]string `json:"blockReward"`
                DifficultyBombDelays   map[string]string `json:"difficultyBombDelays"`
                HomesteadTransition    hexutil.Uint64    `json:"homesteadTransition"`
                EIP100bTransition      hexutil.Uint64    `json:"eip100bTransition"`
            } `json:"params"`
        } `json:"Ethash"`
    } `json:"engine"`

    Params struct {
        AccountStartNonce     hexutil.Uint64       `json:"accountStartNonce"`
        MaximumExtraDataSize  hexutil.Uint64       `json:"maximumExtraDataSize"`
        MinGasLimit           hexutil.Uint64       `json:"minGasLimit"`
        GasLimitBoundDivisor  math2.HexOrDecimal64 `json:"gasLimitBoundDivisor"`
        NetworkID             hexutil.Uint64       `json:"networkID"`
        ChainID               hexutil.Uint64       `json:"chainID"`
        MaxCodeSize           hexutil.Uint64       `json:"maxCodeSize"`
        MaxCodeSizeTransition hexutil.Uint64       `json:"maxCodeSizeTransition"`
        EIP98Transition       hexutil.Uint64       `json:"eip98Transition"`
        EIP150Transition      hexutil.Uint64       `json:"eip150Transition"`
        EIP160Transition      hexutil.Uint64       `json:"eip160Transition"`
        EIP161abcTransition   hexutil.Uint64       `json:"eip161abcTransition"`
        EIP161dTransition     hexutil.Uint64       `json:"eip161dTransition"`
        EIP155Transition      hexutil.Uint64       `json:"eip155Transition"`
        EIP140Transition      hexutil.Uint64       `json:"eip140Transition"`
        EIP211Transition      hexutil.Uint64       `json:"eip211Transition"`
        EIP214Transition      hexutil.Uint64       `json:"eip214Transition"`
        EIP658Transition      hexutil.Uint64       `json:"eip658Transition"`
        EIP145Transition      hexutil.Uint64       `json:"eip145Transition"`
        EIP1014Transition     hexutil.Uint64       `json:"eip1014Transition"`
        EIP1052Transition     hexutil.Uint64       `json:"eip1052Transition"`
        EIP1283Transition     hexutil.Uint64       `json:"eip1283Transition"`
    } `json:"params"`

    Genesis struct {
        Seal struct {
            Ethereum struct {
                Nonce   hexutil.Bytes `json:"nonce"`
                MixHash hexutil.Bytes `json:"mixHash"`
            } `json:"ethereum"`
        } `json:"seal"`

        Difficulty *hexutil.Big   `json:"difficulty"`
        Author     common.Address `json:"author"`
        Timestamp  hexutil.Uint64 `json:"timestamp"`
        ParentHash common.Hash    `json:"parentHash"`
        ExtraData  hexutil.Bytes  `json:"extraData"`
        GasLimit   hexutil.Uint64 `json:"gasLimit"`
    } `json:"genesis"`

    Nodes    []string                                             `json:"nodes"`
    Accounts map[common.UnprefixedAddress]*parityChainSpecAccount `json:"accounts"`
}

// parityChainSpecAccount is the prefunded genesis account and/or precompiled
// contract definition.
type parityChainSpecAccount struct {
    Balance math2.HexOrDecimal256   `json:"balance"`
    Nonce   math2.HexOrDecimal64    `json:"nonce,omitempty"`
    Builtin *parityChainSpecBuiltin `json:"builtin,omitempty"`
}

// parityChainSpecBuiltin is the precompiled contract definition.
type parityChainSpecBuiltin struct {
    Name       string                  `json:"name,omitempty"`
    ActivateAt math2.HexOrDecimal64    `json:"activate_at,omitempty"`
    Pricing    *parityChainSpecPricing `json:"pricing,omitempty"`
}

// parityChainSpecPricing represents the different pricing models that builtin
// contracts might advertise using.
type parityChainSpecPricing struct {
    Linear       *parityChainSpecLinearPricing       `json:"linear,omitempty"`
    ModExp       *parityChainSpecModExpPricing       `json:"modexp,omitempty"`
    AltBnPairing *parityChainSpecAltBnPairingPricing `json:"alt_bn128_pairing,omitempty"`
}

type parityChainSpecLinearPricing struct {
    Base uint64 `json:"base"`
    Word uint64 `json:"word"`
}

type parityChainSpecModExpPricing struct {
    Divisor uint64 `json:"divisor"`
}

type parityChainSpecAltBnPairingPricing struct {
    Base uint64 `json:"base"`
    Pair uint64 `json:"pair"`
}

// newParityChainSpec converts a go-ethereum genesis block into a Parity specific
// chain specification format.
func newParityChainSpec(network string, genesis *core.Genesis, bootnodes []string) (*parityChainSpec, error) {
    // Only ethash is currently supported between go-ethereum and Parity
    if genesis.Config.Ethash == nil {
        return nil, errors.New("unsupported consensus engine")
    }
    // Reconstruct the chain spec in Parity's format
    spec := &parityChainSpec{
        Name:    network,
        Nodes:   bootnodes,
        Datadir: strings.ToLower(network),
    }
    spec.Engine.Ethash.Params.BlockReward = make(map[string]string)
    spec.Engine.Ethash.Params.DifficultyBombDelays = make(map[string]string)
    // Frontier
    spec.Engine.Ethash.Params.MinimumDifficulty = (*hexutil.Big)(params.MinimumDifficulty)
    spec.Engine.Ethash.Params.DifficultyBoundDivisor = (*hexutil.Big)(params.DifficultyBoundDivisor)
    spec.Engine.Ethash.Params.DurationLimit = (*hexutil.Big)(params.DurationLimit)
    spec.Engine.Ethash.Params.BlockReward["0x0"] = hexutil.EncodeBig(ethash.FrontierBlockReward)

    // Homestead
    spec.Engine.Ethash.Params.HomesteadTransition = hexutil.Uint64(genesis.Config.HomesteadBlock.Uint64())

    // Tangerine Whistle : 150
    // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-608.md
    spec.Params.EIP150Transition = hexutil.Uint64(genesis.Config.EIP150Block.Uint64())

    // Spurious Dragon: 155, 160, 161, 170
    // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-607.md
    spec.Params.EIP155Transition = hexutil.Uint64(genesis.Config.EIP155Block.Uint64())
    spec.Params.EIP160Transition = hexutil.Uint64(genesis.Config.EIP155Block.Uint64())
    spec.Params.EIP161abcTransition = hexutil.Uint64(genesis.Config.EIP158Block.Uint64())
    spec.Params.EIP161dTransition = hexutil.Uint64(genesis.Config.EIP158Block.Uint64())

    // Byzantium
    if num := genesis.Config.ByzantiumBlock; num != nil {
        spec.setByzantium(num)
    }
    // Constantinople
    if num := genesis.Config.ConstantinopleBlock; num != nil {
        spec.setConstantinople(num)
    }
    spec.Params.MaximumExtraDataSize = (hexutil.Uint64)(params.MaximumExtraDataSize)
    spec.Params.MinGasLimit = (hexutil.Uint64)(params.MinGasLimit)
    spec.Params.GasLimitBoundDivisor = (math2.HexOrDecimal64)(params.GasLimitBoundDivisor)
    spec.Params.NetworkID = (hexutil.Uint64)(genesis.Config.ChainID.Uint64())
    spec.Params.ChainID = (hexutil.Uint64)(genesis.Config.ChainID.Uint64())
    spec.Params.MaxCodeSize = params.MaxCodeSize
    // geth has it set from zero
    spec.Params.MaxCodeSizeTransition = 0

    // Disable this one
    spec.Params.EIP98Transition = math.MaxInt64

    spec.Genesis.Seal.Ethereum.Nonce = (hexutil.Bytes)(make([]byte, 8))
    binary.LittleEndian.PutUint64(spec.Genesis.Seal.Ethereum.Nonce[:], genesis.Nonce)

    spec.Genesis.Seal.Ethereum.MixHash = (hexutil.Bytes)(genesis.Mixhash[:])
    spec.Genesis.Difficulty = (*hexutil.Big)(genesis.Difficulty)
    spec.Genesis.Author = genesis.Coinbase
    spec.Genesis.Timestamp = (hexutil.Uint64)(genesis.Timestamp)
    spec.Genesis.ParentHash = genesis.ParentHash
    spec.Genesis.ExtraData = (hexutil.Bytes)(genesis.ExtraData)
    spec.Genesis.GasLimit = (hexutil.Uint64)(genesis.GasLimit)

    spec.Accounts = make(map[common.UnprefixedAddress]*parityChainSpecAccount)
    for address, account := range genesis.Alloc {
        bal := math2.HexOrDecimal256(*account.Balance)

        spec.Accounts[common.UnprefixedAddress(address)] = &parityChainSpecAccount{
            Balance: bal,
            Nonce:   math2.HexOrDecimal64(account.Nonce),
        }
    }
    spec.setPrecompile(1, &parityChainSpecBuiltin{Name: "ecrecover",
        Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 3000}}})

    spec.setPrecompile(2, &parityChainSpecBuiltin{
        Name: "sha256", Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 60, Word: 12}},
    })
    spec.setPrecompile(3, &parityChainSpecBuiltin{
        Name: "ripemd160", Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 600, Word: 120}},
    })
    spec.setPrecompile(4, &parityChainSpecBuiltin{
        Name: "identity", Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 15, Word: 3}},
    })
    if genesis.Config.ByzantiumBlock != nil {
        blnum := math2.HexOrDecimal64(genesis.Config.ByzantiumBlock.Uint64())
        spec.setPrecompile(5, &parityChainSpecBuiltin{
            Name: "modexp", ActivateAt: blnum, Pricing: &parityChainSpecPricing{ModExp: &parityChainSpecModExpPricing{Divisor: 20}},
        })
        spec.setPrecompile(6, &parityChainSpecBuiltin{
            Name: "alt_bn128_add", ActivateAt: blnum, Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 500}},
        })
        spec.setPrecompile(7, &parityChainSpecBuiltin{
            Name: "alt_bn128_mul", ActivateAt: blnum, Pricing: &parityChainSpecPricing{Linear: &parityChainSpecLinearPricing{Base: 40000}},
        })
        spec.setPrecompile(8, &parityChainSpecBuiltin{
            Name: "alt_bn128_pairing", ActivateAt: blnum, Pricing: &parityChainSpecPricing{AltBnPairing: &parityChainSpecAltBnPairingPricing{Base: 100000, Pair: 80000}},
        })
    }
    return spec, nil
}

func (spec *parityChainSpec) setPrecompile(address byte, data *parityChainSpecBuiltin) {
    if spec.Accounts == nil {
        spec.Accounts = make(map[common.UnprefixedAddress]*parityChainSpecAccount)
    }
    a := common.UnprefixedAddress(common.BytesToAddress([]byte{address}))
    if _, exist := spec.Accounts[a]; !exist {
        spec.Accounts[a] = &parityChainSpecAccount{}
    }
    spec.Accounts[a].Builtin = data
}

func (spec *parityChainSpec) setByzantium(num *big.Int) {
    spec.Engine.Ethash.Params.BlockReward[hexutil.EncodeBig(num)] = hexutil.EncodeBig(ethash.ByzantiumBlockReward)
    spec.Engine.Ethash.Params.DifficultyBombDelays[hexutil.EncodeBig(num)] = hexutil.EncodeUint64(3000000)
    n := hexutil.Uint64(num.Uint64())
    spec.Engine.Ethash.Params.EIP100bTransition = n
    spec.Params.EIP140Transition = n
    spec.Params.EIP211Transition = n
    spec.Params.EIP214Transition = n
    spec.Params.EIP658Transition = n
}

func (spec *parityChainSpec) setConstantinople(num *big.Int) {
    spec.Engine.Ethash.Params.BlockReward[hexutil.EncodeBig(num)] = hexutil.EncodeBig(ethash.ConstantinopleBlockReward)
    spec.Engine.Ethash.Params.DifficultyBombDelays[hexutil.EncodeBig(num)] = hexutil.EncodeUint64(2000000)
    n := hexutil.Uint64(num.Uint64())
    spec.Params.EIP145Transition = n
    spec.Params.EIP1014Transition = n
    spec.Params.EIP1052Transition = n
    spec.Params.EIP1283Transition = n
}

// pyEthereumGenesisSpec represents the genesis specification format used by the
// Python Ethereum implementation.
type pyEthereumGenesisSpec struct {
    Nonce      hexutil.Bytes     `json:"nonce"`
    Timestamp  hexutil.Uint64    `json:"timestamp"`
    ExtraData  hexutil.Bytes     `json:"extraData"`
    GasLimit   hexutil.Uint64    `json:"gasLimit"`
    Difficulty *hexutil.Big      `json:"difficulty"`
    Mixhash    common.Hash       `json:"mixhash"`
    Coinbase   common.Address    `json:"coinbase"`
    Alloc      core.GenesisAlloc `json:"alloc"`
    ParentHash common.Hash       `json:"parentHash"`
}

// newPyEthereumGenesisSpec converts a go-ethereum genesis block into a Parity specific
// chain specification format.
func newPyEthereumGenesisSpec(network string, genesis *core.Genesis) (*pyEthereumGenesisSpec, error) {
    // Only ethash is currently supported between go-ethereum and pyethereum
    if genesis.Config.Ethash == nil {
        return nil, errors.New("unsupported consensus engine")
    }
    spec := &pyEthereumGenesisSpec{
        Timestamp:  (hexutil.Uint64)(genesis.Timestamp),
        ExtraData:  genesis.ExtraData,
        GasLimit:   (hexutil.Uint64)(genesis.GasLimit),
        Difficulty: (*hexutil.Big)(genesis.Difficulty),
        Mixhash:    genesis.Mixhash,
        Coinbase:   genesis.Coinbase,
        Alloc:      genesis.Alloc,
        ParentHash: genesis.ParentHash,
    }
    spec.Nonce = (hexutil.Bytes)(make([]byte, 8))
    binary.LittleEndian.PutUint64(spec.Nonce[:], genesis.Nonce)

    return spec, nil
}