mixing: Allow more than mixing.MaxPeers in KE messages

mixing/limits.go

@@ -22,7 +22,7 @@ const (
 	// MaxPeers is the maximum number of peers allowed together in a
 	// single mix session.  This restricts the maximum dimensions of the
 	// slot reservation and XOR DC-net matrices and the maximum number of
-	// previous messages that may be referenced by mix messages.
+	// previous messages that may be referenced by non-KE mix messages.
 	MaxPeers = 64
 
 	// MaxMcount is the maximum number of mixed messages that any single

mixing/mixclient/client.go

@@ -943,6 +943,23 @@ func (c *Client) epochTicker(ctx context.Context) error {
 			c.logf("Have %d compatible/%d local PRs waiting for pairing %x",
 				len(prs), len(localPeers), p.pairing)
 
+			// Limit initial PR set to the higher wire max peer
+			// limit.
+			if len(prs) > wire.MaxMixPeers {
+				// Place local peers first, then others, and
+				// trim length.
+				keptPRs := make([]*wire.MsgMixPairReq, 0, len(prs))
+				for _, p := range localPeers {
+					keptPRs = append(keptPRs, p.pr)
+				}
+				for _, pr := range prs {
+					if _, ok := localPeers[pr.Identity]; !ok {
+						keptPRs = append(keptPRs, pr)
+					}
+				}
+				prs = keptPRs[:wire.MaxMixPeers]
+			}
+
 			// pairSession calls pairingWG.Done once the session
 			// is formed and the selected peers have been removed
 			// from then pending pairing.

mixing/mixpool/limits.go

@@ -24,15 +24,6 @@ func checkPRLimits(pr *wire.MsgMixPairReq) error {
 	return nil
 }
 
-func checkKELimits(ke *wire.MsgMixKeyExchange) error {
-	if len(ke.SeenPRs) > mixing.MaxPeers {
-		return ruleError(fmt.Errorf("%d referenced PRs exceeds max peers %d",
-			len(ke.SeenPRs), mixing.MaxPeers))
-	}
-
-	return nil
-}
-
 func checkCTLimits(ct *wire.MsgMixCiphertexts) error {
 	if len(ct.Ciphertexts) > mixing.MaxPeers {
 		return ruleError(fmt.Errorf("%d ciphertexts exceeds max peers %d",

mixing/mixpool/mixpool.go

@@ -1667,10 +1667,6 @@ func validateOwnerProofP2PKHv0(extractFunc func([]byte) []byte, pkscript, pubkey
 }
 
 func (p *Pool) checkAcceptKE(ke *wire.MsgMixKeyExchange) error {
-	if err := checkKELimits(ke); err != nil {
-		return err
-	}
-
 	// Validate PR order and session ID.
 	if err := mixing.ValidateSession(ke); err != nil {
 		return ruleError(err)