pw protected invitation get destroyed after 3 failed retrieval attempts

server/invitation.go

@@ -2,6 +2,7 @@ package server
 
 import (
 	"crypto/rand"
+	"crypto/subtle"
 	"errors"
 	"fmt"
 	"math/big"
@@ -27,6 +28,24 @@ func (r *RedisRouter) StoreInvitation(invitation []byte, timeout int, password s
 }
 
 func (r *RedisRouter) GetInvitation(id string, password string) ([]byte, error) {
+	// Check failed attempts counter
+	failedAttemptsKey := "mwfa:" + id
+	failedAttempts := 0 // Default when key doesn't exist
+	val, err := r.Client.Get(failedAttemptsKey).Int()
+	if err == nil {
+		failedAttempts = val
+	} else if err != redis.Nil {
+		return nil, fmt.Errorf("failed to check attempts: %w", err)
+	}
+	// If err == redis.Nil, key doesn't exist, so failedAttempts stays 0
+
+	// If already hit the limit, delete invitation and fail
+	if failedAttempts >= 3 {
+		r.deleteInvitation(id)
+		return nil, errors.New("invitation locked due to too many failed attempts")
+	}
+
+	// Check if password is required
 	passRequired := false
 	expectedpass, err := r.Client.Get("mwpw:" + id).Result()
 	if err != nil {
@@ -34,16 +53,43 @@ func (r *RedisRouter) GetInvitation(id string, password string) ([]byte, error)
 	} else {
 		passRequired = true
 	}
-	if passRequired && password != expectedpass {
-		return nil, errors.New("auth failed")
+
+	// Validate password with constant-time comparison
+	if passRequired {
+		if subtle.ConstantTimeCompare([]byte(password), []byte(expectedpass)) != 1 {
+			// Increment failed attempts
+			newCount := failedAttempts + 1
+			r.Client.Set(failedAttemptsKey, newCount, 0)
+
+			// If this was the 3rd attempt, delete invitation
+			if newCount >= 3 {
+				r.deleteInvitation(id)
+				return nil, errors.New("auth failed - invitation destroyed after 3 attempts")
+			}
+			return nil, errors.New("auth failed")
+		}
 	}
+
+	// Success - get invitation data
 	mwiv, err := r.Client.Get("mwiv:" + id).Result()
 	if err != nil {
 		return nil, err
 	}
+
+	// Clear failed attempts counter on successful access
+	r.Client.Del(failedAttemptsKey)
+
 	return []byte(mwiv), nil
 }
 
+// deleteInvitation removes all invitation-related keys from Redis
+func (r *RedisRouter) deleteInvitation(id string) {
+	r.Client.Del("mwiv:" + id)  // invitation data
+	r.Client.Del("mwpw:" + id)  // password
+	r.Client.Del("mwfa:" + id)  // failed attempts
+	r.Client.Del("mwan:" + id)  // answer to invitation
+}
+
 func (r *RedisRouter) StoreAnswerToInvitation(id string, timeout int, invitation []byte, serverTimeout int) time.Time {
 	if timeout > serverTimeout {
 		timeout = serverTimeout