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matrix.go
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matrix.go
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package matrix
import (
"errors"
"fmt"
"io"
"github.com/ethereum-optimism/optimism/op-challenger/game/keccak/merkle"
"github.com/ethereum-optimism/optimism/op-challenger/game/keccak/types"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto"
)
// StateMatrix implements a stateful keccak sponge with the ability to create state commitments after each permutation
type StateMatrix struct {
s *state
//prestateMatrix is the state matrix snapshot after processing prestateLeaf but before processing poststateLeaf
prestateMatrix types.StateSnapshot
// prestateLeaf is the last prestate leaf.
// Used to retrieve the prestate to squeeze.
prestateLeaf types.Leaf
// poststateLeaf is the last poststate leaf.
// Used to retrieve the poststate to squeeze.
poststateLeaf types.Leaf
// merkleTree is the internal [merkle.BinaryMerkleTree] used to generate proofs
merkleTree *merkle.BinaryMerkleTree
}
var (
ErrInvalidMaxLen = errors.New("invalid max length to absorb")
ErrIncorrectCommitmentCount = errors.New("incorrect number of commitments for input length")
ErrValid = errors.New("state commitments are valid")
)
// Challenge creates a [types.Challenge] to invalidate the provided preimage data if possible.
// [ErrValid] is returned if the provided inputs are valid and no challenge can be created.
func Challenge(data io.Reader, commitments []common.Hash) (types.Challenge, error) {
s := NewStateMatrix()
lastValidState := s.StateSnapshot()
var lastValidLeaf types.Leaf
var firstInvalidLeaf types.Leaf
for i := 0; ; i++ {
if i >= len(commitments) {
// There should have been more commitments.
// The contracts should prevent this so it can't be challenged, return an error
return types.Challenge{}, ErrIncorrectCommitmentCount
}
claimedCommitment := commitments[i]
_, err := s.absorbNextLeafInput(data, func() common.Hash { return claimedCommitment })
isEOF := errors.Is(err, io.EOF)
if err != nil && !isEOF {
return types.Challenge{}, fmt.Errorf("failed to verify inputs: %w", err)
}
validCommitment := s.StateCommitment()
if firstInvalidLeaf == (types.Leaf{}) {
if validCommitment != claimedCommitment {
lastValidLeaf = s.prestateLeaf
firstInvalidLeaf = s.poststateLeaf
} else {
lastValidState = s.StateSnapshot()
}
}
if isEOF {
if i < len(commitments)-1 {
// We got too many commitments
// The contracts should prevent this so it can't be challenged, return an error
return types.Challenge{}, ErrIncorrectCommitmentCount
}
break
}
}
if firstInvalidLeaf != (types.Leaf{}) {
var prestateProof merkle.Proof
if lastValidLeaf != (types.Leaf{}) {
prestateProof = s.merkleTree.ProofAtIndex(lastValidLeaf.Index)
}
poststateProof := s.merkleTree.ProofAtIndex(firstInvalidLeaf.Index)
return types.Challenge{
StateMatrix: lastValidState,
Prestate: lastValidLeaf,
PrestateProof: prestateProof,
Poststate: firstInvalidLeaf,
PoststateProof: poststateProof,
}, nil
}
return types.Challenge{}, ErrValid
}
// NewStateMatrix creates a new state matrix initialized with the initial, zero keccak block.
func NewStateMatrix() *StateMatrix {
return &StateMatrix{
s: newLegacyKeccak256(),
merkleTree: merkle.NewBinaryMerkleTree(),
}
}
// StateCommitment returns the state commitment for the current state matrix.
// Additional data may be absorbed after calling this method.
func (d *StateMatrix) StateCommitment() common.Hash {
return crypto.Keccak256Hash(d.StateSnapshot().Pack())
}
func (d *StateMatrix) StateSnapshot() types.StateSnapshot {
var snap types.StateSnapshot
copy(snap[:], d.s.a[:])
return snap
}
// newLeafWithPadding creates a new [Leaf] from inputs, padding the input to the [BlockSize].
func (d *StateMatrix) newLeafWithPadding(input []byte, index uint64, commitment common.Hash, final bool) types.Leaf {
var paddedInput [types.BlockSize]byte
copy(paddedInput[:], input)
if final {
pad(input, &paddedInput, d.s.dsbyte)
}
return types.Leaf{
Input: paddedInput,
Index: index,
StateCommitment: commitment,
}
}
func pad(input []byte, paddedInput *[types.BlockSize]byte, dsbyte byte) {
// Pad with this instance's domain-separator bits. We know that there's
// at least one more byte of space in paddedInput because, if it were full,
// this wouldn't be the last block and the padding would be in the next block.
// dsbyte also contains the first one bit for the padding. See the comment in the state struct.
paddedInput[len(input)] = dsbyte
// The remaining bytes are already zeros since paddedInput is a new array.
// This adds the final one bit for the padding. Because of the way that
// bits are numbered from the LSB upwards, the final bit is the MSB of
// the last byte.
paddedInput[types.BlockSize-1] ^= 0x80
}
func (d *StateMatrix) AbsorbUpTo(in io.Reader, maxLen int) (types.InputData, error) {
if maxLen < types.BlockSize || maxLen%types.BlockSize != 0 {
return types.InputData{}, ErrInvalidMaxLen
}
input := make([]byte, 0, maxLen)
commitments := make([]common.Hash, 0, maxLen/types.BlockSize)
for len(input)+types.BlockSize <= maxLen {
readData, err := d.absorbNextLeafInput(in, d.StateCommitment)
if errors.Is(err, io.EOF) {
input = append(input, readData...)
commitments = append(commitments, d.StateCommitment())
return types.InputData{
Input: input,
Commitments: commitments,
Finalize: true,
}, io.EOF
} else if err != nil {
return types.InputData{}, err
}
input = append(input, readData...)
commitments = append(commitments, d.StateCommitment())
}
return types.InputData{
Input: input,
Commitments: commitments,
Finalize: false,
}, nil
}
func (d *StateMatrix) PrestateMatrix() types.StateSnapshot {
return d.prestateMatrix
}
// PrestateWithProof returns the prestate leaf with its merkle proof.
func (d *StateMatrix) PrestateWithProof() (types.Leaf, merkle.Proof) {
proof := d.merkleTree.ProofAtIndex(d.prestateLeaf.Index)
return d.prestateLeaf, proof
}
// PoststateWithProof returns the poststate leaf with its merkle proof.
func (d *StateMatrix) PoststateWithProof() (types.Leaf, merkle.Proof) {
proof := d.merkleTree.ProofAtIndex(d.poststateLeaf.Index)
return d.poststateLeaf, proof
}
// absorbNextLeafInput reads up to [BlockSize] bytes from in and absorbs them into the state matrix.
// If EOF is reached while reading, the state matrix is finalized and [io.EOF] is returned.
func (d *StateMatrix) absorbNextLeafInput(in io.Reader, stateCommitment func() common.Hash) ([]byte, error) {
data := make([]byte, types.BlockSize)
read := 0
final := false
for read < types.BlockSize {
n, err := in.Read(data[read:])
if errors.Is(err, io.EOF) {
read += n
final = true
break
} else if err != nil {
return nil, err
}
read += n
}
input := data[:read]
// Don't add the padding if we read a full block of input data, even if we reached EOF.
// Just absorb the full block and return so the caller can capture the state commitment after the block
// The next call will read no data from the Reader (already at EOF) and so add the final padding as an
// additional block. We can then return EOF to indicate there are no further blocks.
final = final && len(input) < types.BlockSize
d.prestateMatrix = d.StateSnapshot()
d.absorbLeafInput(input, final)
commitment := stateCommitment()
if d.poststateLeaf == (types.Leaf{}) {
d.prestateLeaf = types.Leaf{}
d.poststateLeaf = d.newLeafWithPadding(input, 0, commitment, final)
} else {
d.prestateLeaf = d.poststateLeaf
d.poststateLeaf = d.newLeafWithPadding(input, d.prestateLeaf.Index+1, commitment, final)
}
d.merkleTree.AddLeaf(d.poststateLeaf.Hash())
if final {
return input, io.EOF
}
return input, nil
}
// absorbLeafInput absorbs the specified data into the keccak sponge.
// If final is true, the data is padded to the required length, otherwise it must be exactly [types.BlockSize] bytes.
func (d *StateMatrix) absorbLeafInput(data []byte, final bool) {
if !final && len(data) != types.BlockSize {
panic("sha3: Incorrect leaf data length")
}
_, _ = d.s.Write(data[:])
if final {
d.s.padAndPermute(d.s.dsbyte)
}
}
// Hash finalizes the keccak permutation and returns the final hash.
// No further leaves can be absorbed after this is called
func (d *StateMatrix) Hash() (h common.Hash) {
_, _ = d.s.Read(h[:])
return h
}