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/common/math"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/crypto/bn256"
    "github.com/ethereum/go-ethereum/params"
    "golang.org/x/crypto/ripemd160"
)

// PrecompiledContract 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
}

// PrecompiledContractsHomestead contains the default set of pre-compiled Ethereum
// contracts used in the Frontier and Homestead releases.
var PrecompiledContractsHomestead = map[common.Address]PrecompiledContract{
    common.BytesToAddress([]byte{1}): &ecrecover{},
    common.BytesToAddress([]byte{2}): &sha256hash{},
    common.BytesToAddress([]byte{3}): &ripemd160hash{},
    common.BytesToAddress([]byte{4}): &dataCopy{},
}

// PrecompiledContractsByzantium contains the default set of pre-compiled Ethereum
// contracts used in the Byzantium release.
var PrecompiledContractsByzantium = map[common.Address]PrecompiledContract{
    common.BytesToAddress([]byte{1}): &ecrecover{},
    common.BytesToAddress([]byte{2}): &sha256hash{},
    common.BytesToAddress([]byte{3}): &ripemd160hash{},
    common.BytesToAddress([]byte{4}): &dataCopy{},
    common.BytesToAddress([]byte{5}): &bigModExp{},
    common.BytesToAddress([]byte{6}): &bn256Add{},
    common.BytesToAddress([]byte{7}): &bn256ScalarMul{},
    common.BytesToAddress([]byte{8}): &bn256Pairing{},
}

// RunPrecompiledContract runs and evaluates the output of a precompiled contract.
func RunPrecompiledContract(p PrecompiledContract, input []byte, contract *Contract) (ret []byte, err error) {
    gas := p.RequiredGas(input)
    if contract.UseGas(gas) {
        return p.Run(input)
    }
    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(input []byte) ([]byte, error) {
    const ecRecoverInputLength = 128

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

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

    // tighter sig s values input homestead only apply to tx sigs
    if !allZero(input[32:63]) || !crypto.ValidateSignatureValues(v, r, s, false) {
        return nil, nil
    }
    // v needs to be at the end for libsecp256k1
    pubKey, err := crypto.Ecrecover(input[:32], append(input[64:128], v))
    // make sure the public key is a valid one
    if err != nil {
        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.Sha256PerWordGas + params.Sha256BaseGas
}
func (c *sha256hash) Run(input []byte) ([]byte, error) {
    h := sha256.Sum256(input)
    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.Ripemd160PerWordGas + params.Ripemd160BaseGas
}
func (c *ripemd160hash) Run(input []byte) ([]byte, error) {
    ripemd := ripemd160.New()
    ripemd.Write(input)
    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.IdentityPerWordGas + params.IdentityBaseGas
}
func (c *dataCopy) Run(in []byte) ([]byte, error) {
    return in, nil
}

// bigModExp implements a native big integer exponential modular operation.
type bigModExp struct{}

var (
    big1      = big.NewInt(1)
    big4      = big.NewInt(4)
    big8      = big.NewInt(8)
    big16     = big.NewInt(16)
    big32     = big.NewInt(32)
    big64     = big.NewInt(64)
    big96     = big.NewInt(96)
    big480    = big.NewInt(480)
    big1024   = big.NewInt(1024)
    big3072   = big.NewInt(3072)
    big199680 = big.NewInt(199680)
)

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bigModExp) RequiredGas(input []byte) uint64 {
    var (
        baseLen = new(big.Int).SetBytes(getData(input, 0, 32))
        expLen  = new(big.Int).SetBytes(getData(input, 32, 32))
        modLen  = new(big.Int).SetBytes(getData(input, 64, 32))
    )
    if len(input) > 96 {
        input = input[96:]
    } else {
        input = input[:0]
    }
    // Retrieve the head 32 bytes of exp for the adjusted exponent length
    var expHead *big.Int
    if big.NewInt(int64(len(input))).Cmp(baseLen) <= 0 {
        expHead = new(big.Int)
    } else {
        if expLen.Cmp(big32) > 0 {
            expHead = new(big.Int).SetBytes(getData(input, baseLen.Uint64(), 32))
        } else {
            expHead = new(big.Int).SetBytes(getData(input, baseLen.Uint64(), expLen.Uint64()))
        }
    }
    // Calculate the adjusted exponent length
    var msb int
    if bitlen := expHead.BitLen(); bitlen > 0 {
        msb = bitlen - 1
    }
    adjExpLen := new(big.Int)
    if expLen.Cmp(big32) > 0 {
        adjExpLen.Sub(expLen, big32)
        adjExpLen.Mul(big8, adjExpLen)
    }
    adjExpLen.Add(adjExpLen, big.NewInt(int64(msb)))

    // Calculate the gas cost of the operation
    gas := new(big.Int).Set(math.BigMax(modLen, baseLen))
    switch {
    case gas.Cmp(big64) <= 0:
        gas.Mul(gas, gas)
    case gas.Cmp(big1024) <= 0:
        gas = new(big.Int).Add(
            new(big.Int).Div(new(big.Int).Mul(gas, gas), big4),
            new(big.Int).Sub(new(big.Int).Mul(big96, gas), big3072),
        )
    default:
        gas = new(big.Int).Add(
            new(big.Int).Div(new(big.Int).Mul(gas, gas), big16),
            new(big.Int).Sub(new(big.Int).Mul(big480, gas), big199680),
        )
    }
    gas.Mul(gas, math.BigMax(adjExpLen, big1))
    gas.Div(gas, new(big.Int).SetUint64(params.ModExpQuadCoeffDiv))

    if gas.BitLen() > 64 {
        return math.MaxUint64
    }
    return gas.Uint64()
}

func (c *bigModExp) Run(input []byte) ([]byte, error) {
    var (
        baseLen = new(big.Int).SetBytes(getData(input, 0, 32)).Uint64()
        expLen  = new(big.Int).SetBytes(getData(input, 32, 32)).Uint64()
        modLen  = new(big.Int).SetBytes(getData(input, 64, 32)).Uint64()
    )
    if len(input) > 96 {
        input = input[96:]
    } else {
        input = input[:0]
    }
    // Handle a special case when both the base and mod length is zero
    if baseLen == 0 && modLen == 0 {
        return []byte{}, nil
    }
    // Retrieve the operands and execute the exponentiation
    var (
        base = new(big.Int).SetBytes(getData(input, 0, baseLen))
        exp  = new(big.Int).SetBytes(getData(input, baseLen, expLen))
        mod  = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
    )
    if mod.BitLen() == 0 {
        // Modulo 0 is undefined, return zero
        return common.LeftPadBytes([]byte{}, int(modLen)), nil
    }
    return common.LeftPadBytes(base.Exp(base, exp, mod).Bytes(), int(modLen)), nil
}

// newCurvePoint unmarshals a binary blob into a bn256 elliptic curve point,
// returning it, or an error if the point is invalid.
func newCurvePoint(blob []byte) (*bn256.G1, error) {
    p := new(bn256.G1)
    if _, err := p.Unmarshal(blob); err != nil {
        return nil, err
    }
    return p, nil
}

// newTwistPoint unmarshals a binary blob into a bn256 elliptic curve point,
// returning it, or an error if the point is invalid.
func newTwistPoint(blob []byte) (*bn256.G2, error) {
    p := new(bn256.G2)
    if _, err := p.Unmarshal(blob); err != nil {
        return nil, err
    }
    return p, nil
}

// bn256Add implements a native elliptic curve point addition.
type bn256Add struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256Add) RequiredGas(input []byte) uint64 {
    return params.Bn256AddGas
}

func (c *bn256Add) Run(input []byte) ([]byte, error) {
    x, err := newCurvePoint(getData(input, 0, 64))
    if err != nil {
        return nil, err
    }
    y, err := newCurvePoint(getData(input, 64, 64))
    if err != nil {
        return nil, err
    }
    res := new(bn256.G1)
    res.Add(x, y)
    return res.Marshal(), nil
}

// bn256ScalarMul implements a native elliptic curve scalar multiplication.
type bn256ScalarMul struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256ScalarMul) RequiredGas(input []byte) uint64 {
    return params.Bn256ScalarMulGas
}

func (c *bn256ScalarMul) Run(input []byte) ([]byte, error) {
    p, err := newCurvePoint(getData(input, 0, 64))
    if err != nil {
        return nil, err
    }
    res := new(bn256.G1)
    res.ScalarMult(p, new(big.Int).SetBytes(getData(input, 64, 32)))
    return res.Marshal(), nil
}

var (
    // true32Byte is returned if the bn256 pairing check succeeds.
    true32Byte = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}

    // false32Byte is returned if the bn256 pairing check fails.
    false32Byte = make([]byte, 32)

    // errBadPairingInput is returned if the bn256 pairing input is invalid.
    errBadPairingInput = errors.New("bad elliptic curve pairing size")
)

// bn256Pairing implements a pairing pre-compile for the bn256 curve
type bn256Pairing struct{}

// RequiredGas returns the gas required to execute the pre-compiled contract.
func (c *bn256Pairing) RequiredGas(input []byte) uint64 {
    return params.Bn256PairingBaseGas + uint64(len(input)/192)*params.Bn256PairingPerPointGas
}

func (c *bn256Pairing) Run(input []byte) ([]byte, error) {
    // Handle some corner cases cheaply
    if len(input)%192 > 0 {
        return nil, errBadPairingInput
    }
    // Convert the input into a set of coordinates
    var (
        cs []*bn256.G1
        ts []*bn256.G2
    )
    for i := 0; i < len(input); i += 192 {
        c, err := newCurvePoint(input[i : i+64])
        if err != nil {
            return nil, err
        }
        t, err := newTwistPoint(input[i+64 : i+192])
        if err != nil {
            return nil, err
        }
        cs = append(cs, c)
        ts = append(ts, t)
    }
    // Execute the pairing checks and return the results
    if bn256.PairingCheck(cs, ts) {
        return true32Byte, nil
    }
    return false32Byte, nil
}