can't ban for this yet, but may want to eventually

mixing/mixpool/errors.go

@@ -91,10 +91,6 @@ var (
 	// position of a peer's own PR is outside of the possible bounds of
 	// the previously seen messages.
 	ErrPeerPositionOutOfBounds = newBannableError("peer position cannot be a valid seen PRs index", 0)
-
-	// ErrEarlyKE is returned by AcceptMessage if a key exchange message
-	// with a stated epoch is sent too early for that epoch time.
-	ErrEarlyKE = newBannableError("KE received too early for stated epoch", 0)
 )
 
 // IsBannable returns whether the error condition is such that the peer with

mixing/mixpool/mixpool.go

@@ -1396,8 +1396,9 @@ func (p *Pool) checkAcceptKE(ke *wire.MsgMixKeyExchange) error {
 	}
 
 	keEpoch := time.Unix(int64(ke.Epoch), 0)
-	if keEpoch.Add(earlyKEDuration).Before(time.Now()) {
-		return ruleError(ErrEarlyKE)
+	if time.Now().Add(-earlyKEDuration).Before(keEpoch) {
+		err := fmt.Errorf("KE received too early for stated epoch")
+		return ruleError(err)
 	}
 
 	return nil