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291 lines
9.5 KiB
291 lines
9.5 KiB
package light
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import (
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"bytes"
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"errors"
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"fmt"
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"time"
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tmmath "github.com/tendermint/tendermint/libs/math"
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"github.com/tendermint/tendermint/types"
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)
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var (
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// DefaultTrustLevel - new header can be trusted if at least one correct
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// validator signed it.
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DefaultTrustLevel = tmmath.Fraction{Numerator: 1, Denominator: 3}
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)
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// VerifyNonAdjacent verifies non-adjacent untrustedHeader against
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// trustedHeader. It ensures that:
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//
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// a) trustedHeader can still be trusted (if not, ErrOldHeaderExpired is returned)
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// b) untrustedHeader is valid (if not, ErrInvalidHeader is returned)
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// c) trustLevel ([1/3, 1]) of trustedHeaderVals (or trustedHeaderNextVals)
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// signed correctly (if not, ErrNewValSetCantBeTrusted is returned)
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// d) more than 2/3 of untrustedVals have signed h2
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// (otherwise, ErrInvalidHeader is returned)
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// e) headers are non-adjacent.
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//
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// maxClockDrift defines how much untrustedHeader.Time can drift into the
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// future.
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// trustedHeader must have a ChainID, Height and Time
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func VerifyNonAdjacent(
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trustedHeader *types.SignedHeader, // height=X
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trustedVals *types.ValidatorSet, // height=X or height=X+1
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untrustedHeader *types.SignedHeader, // height=Y
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untrustedVals *types.ValidatorSet, // height=Y
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trustingPeriod time.Duration,
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now time.Time,
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maxClockDrift time.Duration,
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trustLevel tmmath.Fraction,
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) error {
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if err := checkRequiredHeaderFields(trustedHeader); err != nil {
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return err
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}
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if untrustedHeader.Height == trustedHeader.Height+1 {
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return errors.New("headers must be non adjacent in height")
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}
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if err := ValidateTrustLevel(trustLevel); err != nil {
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return err
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}
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// check if the untrusted header is within the trust period
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if HeaderExpired(untrustedHeader, trustingPeriod, now) {
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return ErrOldHeaderExpired{untrustedHeader.Time.Add(trustingPeriod), now}
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}
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if err := verifyNewHeaderAndVals(
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untrustedHeader, untrustedVals,
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trustedHeader,
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now, maxClockDrift); err != nil {
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return ErrInvalidHeader{err}
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}
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// Ensure that +`trustLevel` (default 1/3) or more in voting power of the last trusted validator
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// set signed correctly.
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err := trustedVals.VerifyCommitLightTrusting(trustedHeader.ChainID, untrustedHeader.Commit, trustLevel)
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if err != nil {
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switch e := err.(type) {
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case types.ErrNotEnoughVotingPowerSigned:
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return ErrNewValSetCantBeTrusted{e}
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default:
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return ErrInvalidHeader{e}
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}
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}
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// Ensure that +2/3 of new validators signed correctly.
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//
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// NOTE: this should always be the last check because untrustedVals can be
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// intentionally made very large to DOS the light client. not the case for
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// VerifyAdjacent, where validator set is known in advance.
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if err := untrustedVals.VerifyCommitLight(trustedHeader.ChainID, untrustedHeader.Commit.BlockID,
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untrustedHeader.Height, untrustedHeader.Commit); err != nil {
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return ErrInvalidHeader{err}
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}
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return nil
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}
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// VerifyAdjacent verifies directly adjacent untrustedHeader against
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// trustedHeader. It ensures that:
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//
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// a) trustedHeader can still be trusted (if not, ErrOldHeaderExpired is returned)
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// b) untrustedHeader is valid (if not, ErrInvalidHeader is returned)
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// c) untrustedHeader.ValidatorsHash equals trustedHeader.NextValidatorsHash
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// d) more than 2/3 of new validators (untrustedVals) have signed h2
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// (otherwise, ErrInvalidHeader is returned)
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// e) headers are adjacent.
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//
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// maxClockDrift defines how much untrustedHeader.Time can drift into the
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// future.
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// trustedHeader must have a ChainID, Height, Time and NextValidatorsHash
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func VerifyAdjacent(
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trustedHeader *types.SignedHeader, // height=X
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untrustedHeader *types.SignedHeader, // height=X+1
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untrustedVals *types.ValidatorSet, // height=X+1
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trustingPeriod time.Duration,
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now time.Time,
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maxClockDrift time.Duration,
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) error {
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if err := checkRequiredHeaderFields(trustedHeader); err != nil {
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return err
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}
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if len(trustedHeader.NextValidatorsHash) == 0 {
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return errors.New("next validators hash in trusted header is empty")
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}
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if untrustedHeader.Height != trustedHeader.Height+1 {
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return errors.New("headers must be adjacent in height")
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}
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// check if the untrusted header is within the trust period
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if HeaderExpired(untrustedHeader, trustingPeriod, now) {
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return ErrOldHeaderExpired{untrustedHeader.Time.Add(trustingPeriod), now}
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}
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if err := verifyNewHeaderAndVals(
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untrustedHeader, untrustedVals,
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trustedHeader,
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now, maxClockDrift); err != nil {
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return ErrInvalidHeader{err}
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}
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// Check the validator hashes are the same
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if !bytes.Equal(untrustedHeader.ValidatorsHash, trustedHeader.NextValidatorsHash) {
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err := fmt.Errorf("expected old header's next validators (%X) to match those from new header (%X)",
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trustedHeader.NextValidatorsHash,
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untrustedHeader.ValidatorsHash,
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)
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return ErrInvalidHeader{err}
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}
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// Ensure that +2/3 of new validators signed correctly.
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if err := untrustedVals.VerifyCommitLight(trustedHeader.ChainID, untrustedHeader.Commit.BlockID,
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untrustedHeader.Height, untrustedHeader.Commit); err != nil {
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return ErrInvalidHeader{err}
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}
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return nil
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}
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// Verify combines both VerifyAdjacent and VerifyNonAdjacent functions.
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func Verify(
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trustedHeader *types.SignedHeader, // height=X
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trustedVals *types.ValidatorSet, // height=X or height=X+1
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untrustedHeader *types.SignedHeader, // height=Y
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untrustedVals *types.ValidatorSet, // height=Y
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trustingPeriod time.Duration,
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now time.Time,
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maxClockDrift time.Duration,
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trustLevel tmmath.Fraction) error {
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if untrustedHeader.Height != trustedHeader.Height+1 {
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return VerifyNonAdjacent(trustedHeader, trustedVals, untrustedHeader, untrustedVals,
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trustingPeriod, now, maxClockDrift, trustLevel)
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}
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return VerifyAdjacent(trustedHeader, untrustedHeader, untrustedVals, trustingPeriod, now, maxClockDrift)
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}
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// ValidateTrustLevel checks that trustLevel is within the allowed range [1/3,
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// 1]. If not, it returns an error. 1/3 is the minimum amount of trust needed
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// which does not break the security model. Must be strictly less than 1.
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func ValidateTrustLevel(lvl tmmath.Fraction) error {
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if lvl.Numerator*3 < lvl.Denominator || // < 1/3
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lvl.Numerator >= lvl.Denominator || // >= 1
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lvl.Denominator == 0 {
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return fmt.Errorf("trustLevel must be within [1/3, 1], given %v", lvl)
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}
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return nil
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}
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// HeaderExpired return true if the given header expired.
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func HeaderExpired(h *types.SignedHeader, trustingPeriod time.Duration, now time.Time) bool {
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expirationTime := h.Time.Add(trustingPeriod)
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return !expirationTime.After(now)
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}
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// VerifyBackwards verifies an untrusted header with a height one less than
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// that of an adjacent trusted header. It ensures that:
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//
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// a) untrusted header is valid
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// b) untrusted header has a time before the trusted header
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// c) that the LastBlockID hash of the trusted header is the same as the hash
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// of the trusted header
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//
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// For any of these cases ErrInvalidHeader is returned.
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// NOTE: This does not check whether the trusted or untrusted header has expired
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// or not. These checks are not necessary because the detector never runs during
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// backwards verification and thus evidence that needs to be within a certain
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// time bound is never sent.
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func VerifyBackwards(untrustedHeader, trustedHeader *types.Header) error {
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if err := untrustedHeader.ValidateBasic(); err != nil {
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return ErrInvalidHeader{err}
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}
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if untrustedHeader.ChainID != trustedHeader.ChainID {
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return ErrInvalidHeader{fmt.Errorf("new header belongs to a different chain (%s != %s)",
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untrustedHeader.ChainID, trustedHeader.ChainID)}
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}
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if !untrustedHeader.Time.Before(trustedHeader.Time) {
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return ErrInvalidHeader{
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fmt.Errorf("expected older header time %v to be before new header time %v",
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untrustedHeader.Time,
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trustedHeader.Time)}
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}
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if !bytes.Equal(untrustedHeader.Hash(), trustedHeader.LastBlockID.Hash) {
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return ErrInvalidHeader{
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fmt.Errorf("older header hash %X does not match trusted header's last block %X",
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untrustedHeader.Hash(),
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trustedHeader.LastBlockID.Hash)}
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}
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return nil
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}
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// NOTE: This function assumes that untrustedHeader is after trustedHeader.
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// Do not use for backwards verification.
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func verifyNewHeaderAndVals(
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untrustedHeader *types.SignedHeader,
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untrustedVals *types.ValidatorSet,
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trustedHeader *types.SignedHeader,
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now time.Time,
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maxClockDrift time.Duration) error {
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if err := untrustedHeader.ValidateBasic(trustedHeader.ChainID); err != nil {
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return fmt.Errorf("untrustedHeader.ValidateBasic failed: %w", err)
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}
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if untrustedHeader.Height <= trustedHeader.Height {
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return fmt.Errorf("expected new header height %d to be greater than one of old header %d",
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untrustedHeader.Height,
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trustedHeader.Height)
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}
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if !untrustedHeader.Time.After(trustedHeader.Time) {
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return fmt.Errorf("expected new header time %v to be after old header time %v",
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untrustedHeader.Time,
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trustedHeader.Time)
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}
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if !untrustedHeader.Time.Before(now.Add(maxClockDrift)) {
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return fmt.Errorf("new header has a time from the future %v (now: %v; max clock drift: %v)",
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untrustedHeader.Time,
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now,
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maxClockDrift)
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}
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if !bytes.Equal(untrustedHeader.ValidatorsHash, untrustedVals.Hash()) {
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return fmt.Errorf("expected new header validators (%X) to match those that were supplied (%X) at height %d",
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untrustedHeader.ValidatorsHash,
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untrustedVals.Hash(),
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untrustedHeader.Height,
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)
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}
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return nil
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}
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func checkRequiredHeaderFields(h *types.SignedHeader) error {
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if h.Height == 0 {
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return errors.New("height in trusted header must be set (non zero")
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}
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zeroTime := time.Time{}
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if h.Time == zeroTime {
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return errors.New("time in trusted header must be set")
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}
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if h.ChainID == "" {
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return errors.New("chain ID in trusted header must be set")
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}
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return nil
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}
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