Visible to the public Biblio

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2021-03-09
Tikhomirov, S., Moreno-Sanchez, P., Maffei, M..  2020.  A Quantitative Analysis of Security, Anonymity and Scalability for the Lightning Network. 2020 IEEE European Symposium on Security and Privacy Workshops (EuroS PW). :387—396.

Payment channel networks have been introduced to mitigate the scalability issues inherent to permissionless decentralized cryptocurrencies such as Bitcoin. Launched in 2018, the Lightning Network (LN) has been gaining popularity and consists today of more than 5000 nodes and 35000 payment channels that jointly hold 965 bitcoins (9.2M USD as of June 2020). This adoption has motivated research from both academia and industryPayment channels suffer from security vulnerabilities, such as the wormhole attack [39], anonymity issues [38], and scalability limitations related to the upper bound on the number of concurrent payments per channel [28], which have been pointed out by the scientific community but never quantitatively analyzedIn this work, we first analyze the proneness of the LN to the wormhole attack and attacks against anonymity. We observe that an adversary needs to control only 2% of nodes to learn sensitive payment information (e.g., sender, receiver, and amount) or to carry out the wormhole attack. Second, we study the management of concurrent payments in the LN and quantify its negative effect on scalability. We observe that for micropayments, the forwarding capability of up to 50% of channels is restricted to a value smaller than the channel capacity. This phenomenon hinders scalability and opens the door for denial-of-service attacks: we estimate that a network-wide DoS attack costs within 1.6M USD, while isolating the biggest community costs only 238k USDOur findings should prompt the LN community to consider the issues studied in this work when educating users about path selection algorithms, as well as to adopt multi-hop payment protocols that provide stronger security, privacy and scalability guarantees.

Lee, T., Chang, L., Syu, C..  2020.  Deep Learning Enabled Intrusion Detection and Prevention System over SDN Networks. 2020 IEEE International Conference on Communications Workshops (ICC Workshops). :1—6.

The Software Defined Network (SDN) provides higher programmable functionality for network configuration and management dynamically. Moreover, SDN introduces a centralized management approach by dividing the network into control and data planes. In this paper, we introduce a deep learning enabled intrusion detection and prevention system (DL-IDPS) to prevent secure shell (SSH) brute-force attacks and distributed denial-of-service (DDoS) attacks in SDN. The packet length in SDN switch has been collected as a sequence for deep learning models to identify anomalous and malicious packets. Four deep learning models, including Multilayer Perceptron (MLP), Convolutional Neural Network (CNN), Long Short-Term Memory (LSTM) and Stacked Auto-encoder (SAE), are implemented and compared for the proposed DL-IDPS. The experimental results show that the proposed MLP based DL-IDPS has the highest accuracy which can achieve nearly 99% and 100% accuracy to prevent SSH Brute-force and DDoS attacks, respectively.

2021-02-22
Li, Y., Liu, Y., Wang, Y., Guo, Z., Yin, H., Teng, H..  2020.  Synergetic Denial-of-Service Attacks and Defense in Underwater Named Data Networking. IEEE INFOCOM 2020 - IEEE Conference on Computer Communications. :1569–1578.
Due to the harsh environment and energy limitation, maintaining efficient communication is crucial to the lifetime of Underwater Sensor Networks (UWSN). Named Data Networking (NDN), one of future network architectures, begins to be applied to UWSN. Although Underwater Named Data Networking (UNDN) performs well in data transmission, it still faces some security threats, such as the Denial-of-Service (DoS) attacks caused by Interest Flooding Attacks (IFAs). In this paper, we present a new type of DoS attacks, named as Synergetic Denial-of-Service (SDoS). Attackers synergize with each other, taking turns to reply to malicious interests as late as possible. SDoS attacks will damage the Pending Interest Table, Content Store, and Forwarding Information Base in routers with high concealment. Simulation results demonstrate that the SDoS attacks quadruple the increased network traffic compared with normal IFAs and the existing IFA detection algorithm in UNDN is completely invalid to SDoS attacks. In addition, we analyze the infection problem in UNDN and propose a defense method Trident based on carefully designed adaptive threshold, burst traffic detection, and attacker identification. Experiment results illustrate that Trident can effectively detect and resist both SDoS attacks and normal IFAs. Meanwhile, Trident can robustly undertake burst traffic and congestion.
2021-01-25
Zhang, T.-Y., Ye, D..  2020.  Distributed Secure Control Against Denial-of-Service Attacks in Cyber-Physical Systems Based on K-Connected Communication Topology. IEEE Transactions on Cybernetics. 50:3094–3103.
In this article, the security problem in cyber-physical systems (CPSs) against denial-of-service (DoS) attacks is studied from the perspectives of the designs of communication topology and distributed controller. To resist the DoS attacks, a new construction algorithm of the k-connected communication topology is developed based on the proposed necessary and sufficient criteria of the k-connected graph. Furthermore, combined with the k-connected topology, a distributed event-triggered controller is designed to guarantee the consensus of CPSs under mode-switching DoS (MSDoS) attacks. Different from the existing distributed control schemes, a new technology, that is, the extended Laplacian matrix method, is combined to design the distributed controller independent on the knowledge and the dwell time of DoS attack modes. Finally, the simulation example illustrates the superiority and effectiveness of the proposed construction algorithm and a distributed control scheme.
2020-09-28
Killer, Christian, Rodrigues, Bruno, Stiller, Burkhard.  2019.  Security Management and Visualization in a Blockchain-based Collaborative Defense. 2019 IEEE International Conference on Blockchain and Cryptocurrency (ICBC). :108–111.
A cooperative network defense is one approach to fend off large-scale Distributed Denial-of-Service (DDoS) attacks. In this regard, the Blockchain Signaling System (BloSS) is a multi-domain, blockchain-based, cooperative DDoS defense system, where each Autonomous System (AS) is taking part in the defense alliance. Each AS can exchange attack information about ongoing attacks via the Ethereum blockchain. However, the currently operational implementation of BloSS is not interactive or visualized, but the DDoS mitigation is automated. In realworld defense systems, a human cybersecurity analyst decides whether a DDoS threat should be mitigated or not. Thus, this work presents the design of a security management dashboard for BloSS, designed for interactive use by cyber security analysts.
2020-08-17
Paudel, Ramesh, Muncy, Timothy, Eberle, William.  2019.  Detecting DoS Attack in Smart Home IoT Devices Using a Graph-Based Approach. 2019 IEEE International Conference on Big Data (Big Data). :5249–5258.
The use of the Internet of Things (IoT) devices has surged in recent years. However, due to the lack of substantial security, IoT devices are vulnerable to cyber-attacks like Denial-of-Service (DoS) attacks. Most of the current security solutions are either computationally expensive or unscalable as they require known attack signatures or full packet inspection. In this paper, we introduce a novel Graph-based Outlier Detection in Internet of Things (GODIT) approach that (i) represents smart home IoT traffic as a real-time graph stream, (ii) efficiently processes graph data, and (iii) detects DoS attack in real-time. The experimental results on real-world data collected from IoT-equipped smart home show that GODIT is more effective than the traditional machine learning approaches, and is able to outperform current graph-stream anomaly detection approaches.
2020-06-29
Kaljic, Enio, Maric, Almir, Njemcevic, Pamela.  2019.  DoS attack mitigation in SDN networks using a deeply programmable packet-switching node based on a hybrid FPGA/CPU data plane architecture. 2019 XXVII International Conference on Information, Communication and Automation Technologies (ICAT). :1–6.
The application of the concept of software-defined networks (SDN) has, on the one hand, led to the simplification and reduction of switches price, and on the other hand, has created a significant number of problems related to the security of the SDN network. In several studies was noted that these problems are related to the lack of flexibility and programmability of the data plane, which is likely first to suffer potential denial-of-service (DoS) attacks. One possible way to overcome this problem is to increase the flexibility of the data plane by increasing the depth of programmability of the packet-switching nodes below the level of flow table management. Therefore, this paper investigates the opportunity of using the architecture of deeply programmable packet-switching nodes (DPPSN) in the implementation of a firewall. Then, an architectural model of the firewall based on a hybrid FPGA/CPU data plane architecture has been proposed and implemented. Realized firewall supports three models of DoS attacks mitigation: DoS traffic filtering on the output interface, DoS traffic filtering on the input interface, and DoS attack redirection to the honeypot. Experimental evaluation of the implemented firewall has shown that DoS traffic filtering at the input interface is the best strategy for DoS attack mitigation, which justified the application of the concept of deep network programmability.
2020-05-15
Chaves, Cesar G., Azad, Siavoosh Payandeh, Sepulveda, Johanna, Hollstein, Thomas.  2019.  Detecting and Mitigating Low-and-Slow DoS Attacks in NoC-based MPSoCs. 2019 14th International Symposium on Reconfigurable Communication-centric Systems-on-Chip (ReCoSoC). :82—89.
As Multi-Processor Systems-on-Chip (MPSoCs) permeate the Internet by powering IoT devices, they are exposed to new threats. One major threat is Denial-of-Service (DoS) attacks, which make communication services slow or even unavailable. While mainly studied on desktop and server systems, some DoS attacks on mobile devices and Network-on-Chip (NoC) platforms have also been considered. In the context of NoC-based MPSoC architectures, previous works have explored flooding DoS attacks and their countermeasures, however, these protection techniques are ineffective to mitigate new DoS attacks. Recently, a shift of the network attack paradigm from flooding DoS to Low-and-Slow DoS has been observed. To this end, we present two contributions. First, we demonstrate, for the first time, the impact of Low-and-Slow DoS attacks in NoC environments. Second, we propose a lightweight online monitor able to detect and mitigate these attacks. Results show that our countermeasure is feasible and that it effectively mitigates this new attack. Moreover, since the monitors are placed at the entry points of the network, both, single- and multi-source attacks can be neutralized.
Ravikumar, C.P., Swamy, S. Kendaganna, Uma, B.V..  2019.  A hierarchical approach to self-test, fault-tolerance and routing security in a Network-on-Chip. 2019 IEEE International Test Conference India (ITC India). :1—6.
Since the performance of bus interconnects does not scale with the number of processors connected to the bus, chip multiprocessors make use of on-chip networks that implement packet switching and virtual channel flow control to efficiently transport data. In this paper, we consider the test and fault-tolerance aspects of such a network-on-chip (NoC). Past work in this area has addressed the communication efficiency and deadlock-free properties in NoC, but when routing externally received data, aspects of security must be addressed. A malicious denial-of-service attack or a power virus can be launched by a malicious external agent. We propose a two-tier solution to this problem, where a local self-test manager in each processing element runs test algorithms to detect faults in local processing element and its associated physical and virtual channels. At the global level, the health of the NoC is tested using a sorting-based algorithm proposed in this paper. Similarly, we propose to handle fault-tolerance and security concerns in routing at two levels. At the local level, each node is capable of fault-tolerant routing by deflecting packets to an alternate path; when doing so, since a chance of deadlock may be created, the local router must be capable of guestimating a deadlock situation, switch to packet-switching instead of flit-switching and attempt to reroute the packet. At the global level, a routing agent plays the role of gathering fault data and provide the fault-information to nodes that seek this information periodically. Similarly, the agent is capable of detecting malformed packets coming from an external source and prevent injecting such packets into the network, thereby conserving the network bandwidth. The agent also attempts to guess attempts at denial-of-service attacks and power viruses and will reject packets. Use of a two-tier approach helps in keeping the IP modular and reduces their complexity, thereby making them easier to verify.
2020-05-11
Vashist, Abhishek, Keats, Andrew, Pudukotai Dinakarrao, Sai Manoj, Ganguly, Amlan.  2019.  Securing a Wireless Network-on-Chip Against Jamming Based Denial-of-Service Attacks. 2019 IEEE Computer Society Annual Symposium on VLSI (ISVLSI). :320–325.
Wireless Networks-on-Chips (NoCs) have emerged as a panacea to the non-scalable multi-hop data transmission paths in traditional wired NoC architectures. Using low-power transceivers in NoC switches, novel Wireless NoC (WiNoC) architectures have been shown to achieve higher energy efficiency with improved peak bandwidth and reduced on-chip data transfer latency. However, using wireless interconnects for data transfer within a chip makes the on-chip communications vulnerable to various security threats from either external attackers or internal hardware Trojans (HTs). In this work, we propose a mechanism to make the wireless communication in a WiNoC secure against persistent jamming based Denial-of-Service attacks from both external and internal attackers. Persistent jamming attacks on the on-chip wireless medium will cause interference in data transfer over the duration of the attack resulting in errors in contiguous bits, known as burst errors. Therefore, we use a burst error correction code to monitor the rate of burst errors received over the wireless medium and deploy a Machine Learning (ML) classifier to detect the persistent jamming attack and distinguish it from random burst errors. In the event of jamming attack, alternate routing strategies are proposed to avoid the DoS attack over the wireless medium, so that a secure data transfer can be sustained even in the presence of jamming. We evaluate the proposed technique on a secure WiNoC in the presence of DoS attacks. It has been observed that with the proposed defense mechanisms, WiNoC can outperform a wired NoC even in presence of attacks in terms of performance and security. On an average, 99.87% attack detection was achieved with the chosen ML Classifiers. A bandwidth degradation of \textbackslashtextless;3% is experienced in the event of internal attack, while the wireless interconnects are disabled in the presence of an external attacker.
2020-02-26
Gountia, Debasis, Roy, Sudip.  2019.  Checkpoints Assignment on Cyber-Physical Digital Microfluidic Biochips for Early Detection of Hardware Trojans. 2019 3rd International Conference on Trends in Electronics and Informatics (ICOEI). :16–21.

Present security study involving analysis of manipulation of individual droplets of samples and reagents by digital microfluidic biochip has remarked that the biochip design flow is vulnerable to piracy attacks, hardware Trojans attacks, overproduction, Denial-of-Service attacks, and counterfeiting. Attackers can introduce bioprotocol manipulation attacks against biochips used for medical diagnosis, biochemical analysis, and frequent diseases detection in healthcare industry. Among these attacks, hardware Trojans have created a major threatening issue in its security concern with multiple ways to crack the sensitive data or alter original functionality by doing malicious operations in biochips. In this paper, we present a systematic algorithm for the assignment of checkpoints required for error-recovery of available bioprotocols in case of hardware Trojans attacks in performing operations by biochip. Moreover, it can guide the placement and timing of checkpoints so that the result of an attack is reduced, and hence enhance the security concerns of digital microfluidic biochips. Comparative study with traditional checkpoint schemes demonstrate the superiority of the proposed algorithm without overhead of the bioprotocol completion time with higher error detection accuracy.

2019-12-18
Kuka, Mário, Vojanec, Kamil, Kučera, Jan, Benáček, Pavel.  2019.  Accelerated DDoS Attacks Mitigation using Programmable Data Plane. 2019 ACM/IEEE Symposium on Architectures for Networking and Communications Systems (ANCS). :1–3.

DDoS attacks are a significant threat to internet service or infrastructure providers. This poster presents an FPGA-accelerated device and DDoS mitigation technique to overcome such attacks. Our work addresses amplification attacks whose goal is to generate enough traffic to saturate the victims links. The main idea of the device is to efficiently filter malicious traffic at high-speeds directly in the backbone infrastructure before it even reaches the victim's network. We implemented our solution for two FPGA platforms using the high-level description in P4, and we report on its performance in terms of throughput and hardware resources.

2018-10-26
Ulz, T., Pieber, T., Steger, C., Matischek, R., Bock, H..  2017.  Towards trustworthy data in networked control systems: A hardware-based approach. 2017 22nd IEEE International Conference on Emerging Technologies and Factory Automation (ETFA). :1–8.

The importance of Networked Control Systems (NCS) is steadily increasing due to recent trends such as smart factories. Correct functionality of such NCS needs to be protected as malfunctioning systems could have severe consequences for the controlled process or even threaten human lives. However, with the increase in NCS, also attacks targeting these systems are becoming more frequent. To mitigate attacks that utilize captured sensor data in an NCS, transferred data needs to be protected. While using well-known methods such as Transport Layer Security (TLS) might be suitable to protect the data, resource constraint devices such as sensors often are not powerful enough to perform the necessary cryptographic operations. Also, as we will show in this paper, applying simple encryption in an NCS may enable easy Denial-of-Service (DoS) attacks by attacking single bits of the encrypted data. Therefore, in this paper, we present a hardware-based approach that enables sensors to perform the necessary encryption while being robust against (injected) bit failures.

2018-09-05
King, Z., Yu, Shucheng.  2017.  Investigating and securing communications in the Controller Area Network (CAN). 2017 International Conference on Computing, Networking and Communications (ICNC). :814–818.
The Controller Area Network (CAN) is a broadcast communications network invented by Robert Bosch GmbH in 1986. CAN is the standard communication network found in automobiles, industry equipment, and many space applications. To be used in these environments, CAN is designed for efficiency and reliability, rather than security. This research paper closely examines the security risks within the CAN protocol and proposes a feasible solution. In this research, we investigate the problems with implementing certain security features in the CAN protocol, such as message authentication and protections against replay and denial-of-service (DoS) attacks. We identify the restrictions of the CAN bus, and we demonstrate how our proposed implementation meets these restrictions. Many previously proposed solutions lack security, feasibility, and/or efficiency; however, a solution must not drastically hinder the real-time operation speed of the network. The solution proposed in this research is tested with a simulative CAN environment. This paper proposes an alteration to the standard CAN bus nodes and the CAN protocol to better protect automobiles and other CAN-related systems from attacks.
2018-05-09
Atli, A. V., Uluderya, M. S., Tatlicioglu, S., Gorkemli, B., Balci, A. M..  2017.  Protecting SDN controller with per-flow buffering inside OpenFlow switches. 2017 IEEE International Black Sea Conference on Communications and Networking (BlackSeaCom). :1–5.

Software Defined Networking (SDN) is a paradigm shift that changes the working principles of IP networks by separating the control logic from routers and switches, and logically centralizing it within a controller. In this architecture the control plane (controller) communicates with the data plane (switches) through a control channel using a standards-compliant protocol, that is, OpenFlow. While having a centralized controller creates an opportunity to monitor and program the entire network, as a side effect, it causes the control plane to become a single point of failure. Denial of service (DoS) attacks or even heavy control traffic conditions can easily become real threats to the proper functioning of the controller, which indirectly detriments the entire network. In this paper, we propose a solution to reduce the control traffic generated primarily during table-miss events. We utilize the buffer\_id feature of the OpenFlow protocol, which has been designed to identify individually buffered packets within a switch, reusing it to identify flows buffered as a series of packets during table-miss, which happens when there is no related rule in the switch flow tables that matches the received packet. Thus, we allow the OpenFlow switch to send only the first packet of a flow to the controller for a table-miss while buffering the rest of the packets in the switch memory until the controller responds or time out occurs. The test results show that OpenFlow traffic is significantly reduced when the proposed method is used.

2018-04-11
Cui, T., Yu, H., Hao, F..  2017.  Security Control for Linear Systems Subject to Denial-of-Service Attacks. 2017 36th Chinese Control Conference (CCC). :7673–7678.

This paper studies the stability of event-triggered control systems subject to Denial-of-Service attacks. An improved method is provided to increase frequency and duration of the DoS attacks where closed-loop stability is not destroyed. A two-mode switching control method is adopted to maintain stability of event-triggered control systems in the presence of attacks. Moreover, this paper reveals the relationship between robustness of systems against DoS attacks and lower bound of the inter-event times, namely, enlarging the inter-execution time contributes to enhancing the robustness of the systems against DoS attacks. Finally, some simulations are presented to illustrate the efficiency and feasibility of the obtained results.

2018-02-28
Hong, H., Choi, H., Kim, D., Kim, H., Hong, B., Noh, J., Kim, Y..  2017.  When Cellular Networks Met IPv6: Security Problems of Middleboxes in IPv6 Cellular Networks. 2017 IEEE European Symposium on Security and Privacy (EuroS P). :595–609.

Recently, cellular operators have started migrating to IPv6 in response to the increasing demand for IP addresses. With the introduction of IPv6, cellular middleboxes, such as firewalls for preventing malicious traffic from the Internet and stateful NAT64 boxes for providing backward compatibility with legacy IPv4 services, have become crucial to maintain stability of cellular networks. This paper presents security problems of the currently deployed IPv6 middleboxes of five major operators. To this end, we first investigate several key features of the current IPv6 deployment that can harm the safety of a cellular network as well as its customers. These features combined with the currently deployed IPv6 middlebox allow an adversary to launch six different attacks. First, firewalls in IPv6 cellular networks fail to block incoming packets properly. Thus, an adversary could fingerprint cellular devices with scanning, and further, she could launch denial-of-service or over-billing attacks. Second, vulnerabilities in the stateful NAT64 box, a middlebox that maps an IPv6 address to an IPv4 address (and vice versa), allow an adversary to launch three different attacks: 1) NAT overflow attack that allows an adversary to overflow the NAT resources, 2) NAT wiping attack that removes active NAT mappings by exploiting the lack of TCP sequence number verification of firewalls, and 3) NAT bricking attack that targets services adopting IP-based blacklisting by preventing the shared external IPv4 address from accessing the service. We confirmed the feasibility of these attacks with an empirical analysis. We also propose effective countermeasures for each attack.

2017-03-07
Senejohnny, D., Tesi, P., Persis, C. De.  2015.  Self-triggered coordination over a shared network under Denial-of-Service. 2015 54th IEEE Conference on Decision and Control (CDC). :3469–3474.

The issue of security has become ever more prevalent in the analysis and design of cyber-physical systems. In this paper, we analyze a consensus network in the presence of Denial-of-Service (DoS) attacks, namely attacks that prevent communication among the network agents. By introducing a notion of Persistency-of-Communication (PoC), we provide a characterization of DoS frequency and duration such that consensus is not destroyed. An example is given to substantiate the analysis.

2017-02-14
J. Brynielsson, R. Sharma.  2015.  "Detectability of low-rate HTTP server DoS attacks using spectral analysis". 2015 IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM). :954-961.

Denial-of-Service (DoS) attacks pose a threat to any service provider on the internet. While traditional DoS flooding attacks require the attacker to control at least as much resources as the service provider in order to be effective, so-called low-rate DoS attacks can exploit weaknesses in careless design to effectively deny a service using minimal amounts of network traffic. This paper investigates one such weakness found within version 2.2 of the popular Apache HTTP Server software. The weakness concerns how the server handles the persistent connection feature in HTTP 1.1. An attack simulator exploiting this weakness has been developed and shown to be effective. The attack was then studied with spectral analysis for the purpose of examining how well the attack could be detected. Similar to other papers on spectral analysis of low-rate DoS attacks, the results show that disproportionate amounts of energy in the lower frequencies can be detected when the attack is present. However, by randomizing the attack pattern, an attacker can efficiently reduce this disproportion to a degree where it might be impossible to correctly identify an attack in a real world scenario.

2015-05-06
Junho Hong, Chen-Ching Liu, Govindarasu, M..  2014.  Detection of cyber intrusions using network-based multicast messages for substation automation. Innovative Smart Grid Technologies Conference (ISGT), 2014 IEEE PES. :1-5.

This paper proposes a new network-based cyber intrusion detection system (NIDS) using multicast messages in substation automation systems (SASs). The proposed network-based intrusion detection system monitors anomalies and malicious activities of multicast messages based on IEC 61850, e.g., Generic Object Oriented Substation Event (GOOSE) and Sampled Value (SV). NIDS detects anomalies and intrusions that violate predefined security rules using a specification-based algorithm. The performance test has been conducted for different cyber intrusion scenarios (e.g., packet modification, replay and denial-of-service attacks) using a cyber security testbed. The IEEE 39-bus system model has been used for testing of the proposed intrusion detection method for simultaneous cyber attacks. The false negative ratio (FNR) is the number of misclassified abnormal packets divided by the total number of abnormal packets. The results demonstrate that the proposed NIDS achieves a low fault negative rate.
 

2015-05-01
Soderi, S., Dainelli, G., Iinatti, J., Hamalainen, M..  2014.  Signal fingerprinting in cognitive wireless networks. Cognitive Radio Oriented Wireless Networks and Communications (CROWNCOM), 2014 9th International Conference on. :266-270.

Future wireless communications are made up of different wireless technologies. In such a scenario, cognitive and cooperative principles create a promising framework for the interaction of these systems. The opportunistic behavior of cognitive radio (CR) provides an efficient use of radio spectrum and makes wireless network setup easier. However more and more frequently, CR features are exploited by malicious attacks, e.g., denial-of-service (DoS). This paper introduces active radio frequency fingerprinting (RFF) with double application scenario. CRs could encapsulate common-control-channel (CCC) information in an existing channel using active RFF and avoiding any additional or dedicated link. On the other hand, a node inside a network could use the same technique to exchange a public key during the setup of secure communication. Results indicate how the active RFF aims to a valuable technique for cognitive radio manager (CRM) framework facilitating data exchange between CRs without any dedicated channel or additional radio resource.