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package lite
import (
"bytes"
"time"
"github.com/pkg/errors"
tmmath "github.com/tendermint/tendermint/libs/math"
"github.com/tendermint/tendermint/types"
)
var (
// DefaultTrustLevel - new header can be trusted if at least one correct old
// validator signed it.
DefaultTrustLevel = tmmath.Fraction{Numerator: 1, Denominator: 3}
)
func Verify(
chainID string,
h1 *types.SignedHeader,
h1NextVals *types.ValidatorSet,
h2 *types.SignedHeader,
h2Vals *types.ValidatorSet,
trustingPeriod time.Duration,
now time.Time,
trustLevel tmmath.Fraction) error {
if err := ValidateTrustLevel(trustLevel); err != nil {
return err
}
// Ensure last header can still be trusted.
expirationTime := h1.Time.Add(trustingPeriod)
if !expirationTime.After(now) {
return ErrOldHeaderExpired{expirationTime, now}
}
if err := verifyNewHeaderAndVals(chainID, h2, h2Vals, h1, now); err != nil {
return err
}
if h2.Height == h1.Height+1 {
if !bytes.Equal(h2.ValidatorsHash, h1NextVals.Hash()) {
return errors.Errorf("expected old header validators (%X) to match those from new header (%X)",
h1NextVals.Hash(),
h2.ValidatorsHash,
)
}
} else {
// Ensure that +`trustLevel` (default 1/3) or more of last trusted validators signed correctly.
err := h1NextVals.VerifyCommitTrusting(chainID, h2.Commit.BlockID, h2.Height, h2.Commit, trustLevel)
if err != nil {
return err
}
}
// Ensure that +2/3 of new validators signed correctly.
err := h2Vals.VerifyCommit(chainID, h2.Commit.BlockID, h2.Height, h2.Commit)
if err != nil {
return err
}
return nil
}
func verifyNewHeaderAndVals(
chainID string,
h2 *types.SignedHeader,
h2Vals *types.ValidatorSet,
h1 *types.SignedHeader,
now time.Time) error {
if err := h2.ValidateBasic(chainID); err != nil {
return errors.Wrap(err, "h2.ValidateBasic failed")
}
if h2.Height <= h1.Height {
return errors.Errorf("expected new header height %d to be greater than one of old header %d",
h2.Height,
h1.Height)
}
if !h2.Time.After(h1.Time) {
return errors.Errorf("expected new header time %v to be after old header time %v",
h2.Time,
h1.Time)
}
if !h2.Time.Before(now) {
return errors.Errorf("new header has a time from the future %v (now: %v)",
h2.Time,
now)
}
if !bytes.Equal(h2.ValidatorsHash, h2Vals.Hash()) {
return errors.Errorf("expected new header validators (%X) to match those that were supplied (%X)",
h2Vals.Hash(),
h2.NextValidatorsHash,
)
}
return nil
}
// ValidateTrustLevel checks that trustLevel is within the allowed range [1/3,
// 1]. If not, it returns an error. 1/3 is the minimum amount of trust needed
// which does not break the security model.
func ValidateTrustLevel(lvl tmmath.Fraction) error {
if lvl.Numerator*3 < lvl.Denominator || // < 1/3
lvl.Numerator > lvl.Denominator || // > 1
lvl.Denominator == 0 {
return errors.Errorf("trustLevel must be within [1/3, 1], given %v", lvl)
}
return nil
}