tendermint/types/evidence.go

package types

import (
	"bytes"
	"fmt"

	"github.com/tendermint/go-crypto"
	"github.com/tendermint/tmlibs/merkle"
)

// ErrEvidenceInvalid wraps a piece of evidence and the error denoting how or why it is invalid.
type ErrEvidenceInvalid struct {
	Evidence   Evidence
	ErrorValue error
}

func NewEvidenceInvalidErr(ev Evidence, err error) *ErrEvidenceInvalid {
	return &ErrEvidenceInvalid{ev, err}
}

// Error returns a string representation of the error.
func (err *ErrEvidenceInvalid) Error() string {
	return fmt.Sprintf("Invalid evidence: %v. Evidence: %v", err.ErrorValue, err.Evidence)
}

//-------------------------------------------

// Evidence represents any provable malicious activity by a validator
type Evidence interface {
	Height() int                 // height of the equivocation
	Address() []byte             // address of the equivocating validator
	Index() int                  // index of the validator in the validator set
	Hash() []byte                // hash of the evidence
	Verify(chainID string) error // verify the evidence
	Equal(Evidence) bool         // check equality of evidence

	String() string
}

//-------------------------------------------

// EvidenceList is a list of Evidence. Evidences is not a word.
type EvidenceList []Evidence

// Hash returns the simple merkle root hash of the EvidenceList.
func (evl EvidenceList) Hash() []byte {
	// Recursive impl.
	// Copied from tmlibs/merkle to avoid allocations
	switch len(evl) {
	case 0:
		return nil
	case 1:
		return evl[0].Hash()
	default:
		left := EvidenceList(evl[:(len(evl)+1)/2]).Hash()
		right := EvidenceList(evl[(len(evl)+1)/2:]).Hash()
		return merkle.SimpleHashFromTwoHashes(left, right)
	}
}

func (evl EvidenceList) String() string {
	s := ""
	for _, e := range evl {
		s += fmt.Sprintf("%s\t\t", e)
	}
	return s
}

// Has returns true if the evidence is in the EvidenceList.
func (evl EvidenceList) Has(evidence Evidence) bool {
	for _, ev := range evl {
		if ev.Equal(evidence) {
			return true
		}
	}
	return false
}

//-------------------------------------------

// DuplicateVoteEvidence contains evidence a validator signed two conflicting votes.
type DuplicateVoteEvidence struct {
	PubKey crypto.PubKey
	VoteA  *Vote
	VoteB  *Vote
}

// String returns a string representation of the evidence.
func (dve *DuplicateVoteEvidence) String() string {
	return fmt.Sprintf("VoteA: %v; VoteB: %v", dve.VoteA, dve.VoteB)

}

// Height returns the height this evidence refers to.
func (dve *DuplicateVoteEvidence) Height() int {
	return dve.VoteA.Height
}

// Address returns the address of the validator.
func (dve *DuplicateVoteEvidence) Address() []byte {
	return dve.PubKey.Address()
}

// Index returns the index of the validator.
func (dve *DuplicateVoteEvidence) Index() int {
	return dve.VoteA.ValidatorIndex
}

// Hash returns the hash of the evidence.
func (dve *DuplicateVoteEvidence) Hash() []byte {
	return merkle.SimpleHashFromBinary(dve)
}

// Verify returns an error if the two votes aren't conflicting.
// To be conflicting, they must be from the same validator, for the same H/R/S, but for different blocks.
func (dve *DuplicateVoteEvidence) Verify(chainID string) error {

	// TODO: verify (cs.Height - dve.Height) < MaxHeightDiff

	// H/R/S must be the same
	if dve.VoteA.Height != dve.VoteB.Height ||
		dve.VoteA.Round != dve.VoteB.Round ||
		dve.VoteA.Type != dve.VoteB.Type {
		return fmt.Errorf("DuplicateVoteEvidence Error: H/R/S does not match. Got %v and %v", dve.VoteA, dve.VoteB)
	}

	// Address must be the same
	if !bytes.Equal(dve.VoteA.ValidatorAddress, dve.VoteB.ValidatorAddress) {
		return fmt.Errorf("DuplicateVoteEvidence Error: Validator addresses do not match. Got %X and %X", dve.VoteA.ValidatorAddress, dve.VoteB.ValidatorAddress)
	}
	// XXX: Should we enforce index is the same ?
	if dve.VoteA.ValidatorIndex != dve.VoteB.ValidatorIndex {
		return fmt.Errorf("DuplicateVoteEvidence Error: Validator indices do not match. Got %d and %d", dve.VoteA.ValidatorIndex, dve.VoteB.ValidatorIndex)
	}

	// BlockIDs must be different
	if dve.VoteA.BlockID.Equals(dve.VoteB.BlockID) {
		return fmt.Errorf("DuplicateVoteEvidence Error: BlockIDs are the same (%v) - not a real duplicate vote!", dve.VoteA.BlockID)
	}

	// Signatures must be valid
	if !dve.PubKey.VerifyBytes(SignBytes(chainID, dve.VoteA), dve.VoteA.Signature) {
		return ErrVoteInvalidSignature
	}
	if !dve.PubKey.VerifyBytes(SignBytes(chainID, dve.VoteB), dve.VoteB.Signature) {
		return ErrVoteInvalidSignature
	}

	return nil
}

// Equal checks if two pieces of evidence are equal.
func (dve *DuplicateVoteEvidence) Equal(ev Evidence) bool {
	if _, ok := ev.(*DuplicateVoteEvidence); !ok {
		return false
	}

	// just check their hashes
	return bytes.Equal(merkle.SimpleHashFromBinary(dve), merkle.SimpleHashFromBinary(ev))
}