path: root/core/vm/contracts.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "crypto/sha256"
    "errors"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/params"
    "golang.org/x/crypto/ripemd160"
)

var errBadPrecompileInput = errors.New("bad pre compile input")

// Precompiled contract is the basic interface for native Go contracts. The implementation
// requires a deterministic gas count based on the input size of the Run method of the
// contract.
type PrecompiledContract interface {
    RequiredGas(input []byte) uint64  // RequiredPrice calculates the contract gas use
    Run(input []byte) ([]byte, error) // Run runs the precompiled contract
}

// PrecompiledContracts contains the default set of ethereum contracts
var PrecompiledContracts = map[common.Address]PrecompiledContract{
    common.BytesToAddress([]byte{1}): &ecrecover{},
    common.BytesToAddress([]byte{2}): &sha256hash{},
    common.BytesToAddress([]byte{3}): &ripemd160hash{},
    common.BytesToAddress([]byte{4}): &dataCopy{},
}

// RunPrecompile runs and evaluate the output of a precompiled contract defined in contracts.go
func RunPrecompiledContract(p PrecompiledContract, input []byte, contract *Contract) (ret []byte, err error) {
    gas := p.RequiredGas(input)
    if contract.UseGas(gas) {
        return p.Run(input)
    } else {
        return nil, ErrOutOfGas
    }
}

// ECRECOVER implemented as a native contract
type ecrecover struct{}

func (c *ecrecover) RequiredGas(input []byte) uint64 {
    return params.EcrecoverGas
}

func (c *ecrecover) Run(in []byte) ([]byte, error) {
    const ecRecoverInputLength = 128

    in = common.RightPadBytes(in, ecRecoverInputLength)
    // "in" is (hash, v, r, s), each 32 bytes
    // but for ecrecover we want (r, s, v)

    r := new(big.Int).SetBytes(in[64:96])
    s := new(big.Int).SetBytes(in[96:128])
    v := in[63] - 27

    // tighter sig s values in homestead only apply to tx sigs
    if !allZero(in[32:63]) || !crypto.ValidateSignatureValues(v, r, s, false) {
        log.Trace("ECRECOVER error: v, r or s value invalid")
        return nil, nil
    }
    // v needs to be at the end for libsecp256k1
    pubKey, err := crypto.Ecrecover(in[:32], append(in[64:128], v))
    // make sure the public key is a valid one
    if err != nil {
        log.Trace("ECRECOVER failed", "err", err)
        return nil, nil
    }

    // the first byte of pubkey is bitcoin heritage
    return common.LeftPadBytes(crypto.Keccak256(pubKey[1:])[12:], 32), nil
}

// SHA256 implemented as a native contract
type sha256hash struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *sha256hash) RequiredGas(input []byte) uint64 {
    return uint64(len(input)+31)/32*params.Sha256WordGas + params.Sha256Gas
}
func (c *sha256hash) Run(in []byte) ([]byte, error) {
    h := sha256.Sum256(in)
    return h[:], nil
}

// RIPMED160 implemented as a native contract
type ripemd160hash struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *ripemd160hash) RequiredGas(input []byte) uint64 {
    return uint64(len(input)+31)/32*params.Ripemd160WordGas + params.Ripemd160Gas
}
func (c *ripemd160hash) Run(in []byte) ([]byte, error) {
    ripemd := ripemd160.New()
    ripemd.Write(in)
    return common.LeftPadBytes(ripemd.Sum(nil), 32), nil
}

// data copy implemented as a native contract
type dataCopy struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
//
// This method does not require any overflow checking as the input size gas costs
// required for anything significant is so high it's impossible to pay for.
func (c *dataCopy) RequiredGas(input []byte) uint64 {
    return uint64(len(input)+31)/32*params.IdentityWordGas + params.IdentityGas
}
func (c *dataCopy) Run(in []byte) ([]byte, error) {
    return in, nil
}