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2014-09-17
Durbeck, Lisa J. K., Athanas, Peter M., Macias, Nicholas J..  2014.  Secure-by-construction Composable Componentry for Network Processing. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :27:1–27:2.

Techniques commonly used for analyzing streaming video, audio, SIGINT, and network transmissions, at less-than-streaming rates, such as data decimation and ad-hoc sampling, can miss underlying structure, trends and specific events held in the data[3]. This work presents a secure-by-construction approach [7] for the upper-end data streams with rates from 10- to 100 Gigabits per second. The secure-by-construction approach strives to produce system security through the composition of individually secure hardware and software components. The proposed network processor can be used not only at data centers but also within networks and onboard embedded systems at the network periphery for a wide range of tasks, including preprocessing and data cleansing, signal encoding and compression, complex event processing, flow analysis, and other tasks related to collecting and analyzing streaming data. Our design employs a four-layer scalable hardware/software stack that can lead to inherently secure, easily constructed specialized high-speed stream processing. This work addresses the following contemporary problems: (1) There is a lack of hardware/software systems providing stream processing and data stream analysis operating at the target data rates; for high-rate streams the implementation options are limited: all-software solutions can't attain the target rates[1]. GPUs and GPGPUs are also infeasible: they were not designed for I/O at 10-100Gbps; they also have asymmetric resources for input and output and thus cannot be pipelined[4, 2], whereas custom chip-based solutions are costly and inflexible to changes, and FPGA-based solutions are historically hard to program[6]; (2) There is a distinct advantage to utilizing high-bandwidth or line-speed analytics to reduce time-to-discovery of information, particularly ones that can be pipelined together to conduct a series of processing tasks or data tests without impeding data rates; (3) There is potentially significant network infrastructure cost savings possible from compact and power-efficient analytic support deployed at the network periphery on the data source or one hop away; (4) There is a need for agile deployment in response to changing objectives; (5) There is an opportunity to constrain designs to use only secure components to achieve their specific objectives. We address these five problems in our stream processor design to provide secure, easily specified processing for low-latency, low-power 10-100Gbps in-line processing on top of a commodity high-end FPGA-based hardware accelerator network processor. With a standard interface a user can snap together various filter blocks, like Legos™, to form a custom processing chain. The overall design is a four-layer solution in which the structurally lowest layer provides the vast computational power to process line-speed streaming packets, and the uppermost layer provides the agility to easily shape the system to the properties of a given application. Current work has focused on design of the two lowest layers, highlighted in the design detail in Figure 1. The two layers shown in Figure 1 are the embeddable portion of the design; these layers, operating at up to 100Gbps, capture both the low- and high frequency components of a signal or stream, analyze them directly, and pass the lower frequency components, residues to the all-software upper layers, Layers 3 and 4; they also optionally supply the data-reduced output up to Layers 3 and 4 for additional processing. Layer 1 is analogous to a systolic array of processors on which simple low-level functions or actions are chained in series[5]. Examples of tasks accomplished at the lowest layer are: (a) check to see if Field 3 of the packet is greater than 5, or (b) count the number of X.75 packets, or (c) select individual fields from data packets. Layer 1 provides the lowest latency, highest throughput processing, analysis and data reduction, formulating raw facts from the stream; Layer 2, also accelerated in hardware and running at full network line rate, combines selected facts from Layer 1, forming a first level of information kernels. Layer 2 is comprised of a number of combiners intended to integrate facts extracted from Layer 1 for presentation to Layer 3. Still resident in FPGA hardware and hardware-accelerated, a Layer 2 combiner is comprised of state logic and soft-core microprocessors. Layer 3 runs in software on a host machine, and is essentially the bridge to the embeddable hardware; this layer exposes an API for the consumption of information kernels to create events and manage state. The generated events and state are also made available to an additional software Layer 4, supplying an interface to traditional software-based systems. As shown in the design detail, network data transitions systolically through Layer 1, through a series of light-weight processing filters that extract and/or modify packet contents. All filters have a similar interface: streams enter from the left, exit the right, and relevant facts are passed upward to Layer 2. The output of the end of the chain in Layer 1 shown in the Figure 1 can be (a) left unconnected (for purely monitoring activities), (b) redirected into the network (for bent pipe operations), or (c) passed to another identical processor, for extended processing on a given stream (scalability).

Yu, Xianqing, Ning, Peng, Vouk, Mladen A..  2014.  Securing Hadoop in Cloud. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :26:1–26:2.

Hadoop is a map-reduce implementation that rapidly processes data in parallel. Cloud provides reliability, flexibility, scalability, elasticity and cost saving to customers. Moving Hadoop into Cloud can be beneficial to Hadoop users. However, Hadoop has two vulnerabilities that can dramatically impact its security in a Cloud. The vulnerabilities are its overloaded authentication key, and the lack of fine-grained access control at the data access level. We propose and develop a security enhancement for Cloud-based Hadoop.

He, Xiaofan, Dai, Huaiyu, Shen, Wenbo, Ning, Peng.  2014.  Channel Correlation Modeling for Link Signature Security Assessment. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :25:1–25:2.

It is widely accepted that wireless channels decorrelate fast over space, and half a wavelength is the key distance metric used in link signature (LS) for security assurance. However, we believe that this channel correlation model is questionable, and will lead to false sense of security. In this project, we focus on establishing correct modeling of channel correlation so as to facilitate proper guard zone designs for LS security in various wireless environments of interest.

Forget, Alain, Komanduri, Saranga, Acquisti, Alessandro, Christin, Nicolas, Cranor, Lorrie Faith, Telang, Rahul.  2014.  Building the Security Behavior Observatory: An Infrastructure for Long-term Monitoring of Client Machines. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :24:1–24:2.

We present an architecture for the Security Behavior Observatory (SBO), a client-server infrastructure designed to collect a wide array of data on user and computer behavior from hundreds of participants over several years. The SBO infrastructure had to be carefully designed to fulfill several requirements. First, the SBO must scale with the desired length, breadth, and depth of data collection. Second, we must take extraordinary care to ensure the security of the collected data, which will inevitably include intimate participant behavioral data. Third, the SBO must serve our research interests, which will inevitably change as collected data is analyzed and interpreted. This short paper summarizes some of our design and implementation benefits and discusses a few hurdles and trade-offs to consider when designing such a data collection system.

Kästner, Christian, Pfeffer, Jürgen.  2014.  Limiting Recertification in Highly Configurable Systems: Analyzing Interactions and Isolation Among Configuration Options. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :23:1–23:2.

In highly configurable systems the configuration space is too big for (re-)certifying every configuration in isolation. In this project, we combine software analysis with network analysis to detect which configuration options interact and which have local effects. Instead of analyzing a system as Linux and SELinux for every combination of configuration settings one by one (>102000 even considering compile-time configurations only), we analyze the effect of each configuration option once for the entire configuration space. The analysis will guide us to designs separating interacting configuration options in a core system and isolating orthogonal and less trusted configuration options from this core.

Cao, Phuong, Li, Hongyang, Nahrstedt, Klara, Kalbarczyk, Zbigniew, Iyer, Ravishankar, Slagell, Adam J..  2014.  Personalized Password Guessing: A New Security Threat. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :22:1–22:2.

This paper presents a model for generating personalized passwords (i.e., passwords based on user and service profile). A user's password is generated from a list of personalized words, each word is drawn from a topic relating to a user and the service in use. The proposed model can be applied to: (i) assess the strength of a password (i.e., determine how many guesses are used to crack the password), and (ii) generate secure (i.e., contains digits, special characters, or capitalized characters) yet easy to memorize passwords.

Cao, Phuong, Chung, Key-whan, Kalbarczyk, Zbigniew, Iyer, Ravishankar, Slagell, Adam J..  2014.  Preemptive Intrusion Detection. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :21:1–21:2.

This paper presents a system named SPOT to achieve high accuracy and preemptive detection of attacks. We use security logs of real-incidents that occurred over a six-year period at National Center for Supercomputing Applications (NCSA) to evaluate SPOT. Our data consists of attacks that led directly to the target system being compromised, i.e., not detected in advance, either by the security analysts or by intrusion detection systems. Our approach can detect 75 percent of attacks as early as minutes to tens of hours before attack payloads are executed.

Ibrahim, Naseem.  2014.  Trustworthy Context-dependent Services. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :20:1–20:2.

With the wide popularity of Cloud Computing, Service-oriented Computing is becoming the de-facto approach for the development of distributed systems. This has introduced the issue of trustworthiness with respect to the services being provided. Service Requesters are provided with a wide range of services that they can select from. Usually the service requester compare between these services according to their cost and quality. One essential part of the quality of a service is the trustworthiness properties of such services. Traditional service models focuses on service functionalities and cost when defining services. This paper introduces a new service model that extends traditional service models to support trustworthiness properties.

Kurilova, Darya, Omar, Cyrus, Nistor, Ligia, Chung, Benjamin, Potanin, Alex, Aldrich, Jonathan.  2014.  Type-specific Languages to Fight Injection Attacks. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :18:1–18:2.

Injection vulnerabilities have topped rankings of the most critical web application vulnerabilities for several years [1, 2]. They can occur anywhere where user input may be erroneously executed as code. The injected input is typically aimed at gaining unauthorized access to the system or to private information within it, corrupting the system's data, or disturbing system availability. Injection vulnerabilities are tedious and difficult to prevent.

Huang, Jingwei, Nicol, David M..  2014.  Evidence-based Trust Reasoning. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :17:1–17:2.

Trust is a necessary component in cybersecurity. It is a common task for a system to make a decision about whether or not to trust the credential of an entity from another domain, issued by a third party. Generally, in the cyberspace, connected and interacting systems largely rely on each other with respect to security, privacy, and performance. In their interactions, one entity or system needs to trust others, and this "trust" frequently becomes a vulnerability of that system. Aiming at mitigating the vulnerability, we are developing a computational theory of trust, as a part of our efforts towards Science of Security. Previously, we developed a formal-semantics-based calculus of trust [3, 2], in which trust can be calculated based on a trustor's direct observation on the performance of the trustee, or based on a trust network. In this paper, we construct a framework for making trust reasoning based on the observed evidence. We take privacy in cloud computing as a driving application case [5].

Ray, Arnab, Cleaveland, Rance.  2014.  An Analysis Method for Medical Device Security. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :16:1–16:2.

This paper is a proposal for a poster. In it we describe a medical device security approach that researchers at Fraunhofer used to analyze different kinds of medical devices for security vulnerabilities. These medical devices were provided to Fraunhofer by a medical device manufacturer whose name we cannot disclose due to non-disclosure agreements.

Layman, Lucas, Zazworka, Nico.  2014.  InViz: Instant Visualization of Security Attacks. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :15:1–15:2.

The InViz tool is a functional prototype that provides graphical visualizations of log file events to support real-time attack investigation. Through visualization, both experts and novices in cybersecurity can analyze patterns of application behavior and investigate potential cybersecurity attacks. The goal of this research is to identify and evaluate the cybersecurity information to visualize that reduces the amount of time required to perform cyber forensics.

Xu, Shouhuai.  2014.  Cybersecurity Dynamics. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :14:1–14:2.

We explore the emerging field of Cybersecurity Dynamics, a candidate foundation for the Science of Cybersecurity.

Xu, Shouhuai.  2014.  Emergent Behavior in Cybersecurity. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :13:1–13:2.

We argue that emergent behavior is inherent to cybersecurity.

Mitra, Sayan.  2014.  Proving Abstractions of Dynamical Systems Through Numerical Simulations. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :12:1–12:9.

A key question that arises in rigorous analysis of cyberphysical systems under attack involves establishing whether or not the attacked system deviates significantly from the ideal allowed behavior. This is the problem of deciding whether or not the ideal system is an abstraction of the attacked system. A quantitative variation of this question can capture how much the attacked system deviates from the ideal. Thus, algorithms for deciding abstraction relations can help measure the effect of attacks on cyberphysical systems and to develop attack detection strategies. In this paper, we present a decision procedure for proving that one nonlinear dynamical system is a quantitative abstraction of another. Directly computing the reach sets of these nonlinear systems are undecidable in general and reach set over-approximations do not give a direct way for proving abstraction. Our procedure uses (possibly inaccurate) numerical simulations and a model annotation to compute tight approximations of the observable behaviors of the system and then uses these approximations to decide on abstraction. We show that the procedure is sound and that it is guaranteed to terminate under reasonable robustness assumptions.

Das, Anupam, Borisov, Nikita, Caesar, Matthew.  2014.  Analyzing an Adaptive Reputation Metric for Anonymity Systems. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :11:1–11:11.

Low-latency anonymity systems such as Tor rely on intermediate relays to forward user traffic; these relays, however, are often unreliable, resulting in a degraded user experience. Worse yet, malicious relays may introduce deliberate failures in a strategic manner in order to increase their chance of compromising anonymity. In this paper we propose using a reputation metric that can profile the reliability of relays in an anonymity system based on users' past experience. The two main challenges in building a reputation-based system for an anonymity system are: first, malicious participants can strategically oscillate between good and malicious nature to evade detection, and second, an observed failure in an anonymous communication cannot be uniquely attributed to a single relay. Our proposed framework addresses the former challenge by using a proportional-integral-derivative (PID) controller-based reputation metric that ensures malicious relays adopting time-varying strategic behavior obtain low reputation scores over time, and the latter by introducing a filtering scheme based on the evaluated reputation score to effectively discard relays mounting attacks. We collect data from the live Tor network and perform simulations to validate the proposed reputation-based filtering scheme. We show that an attacker does not gain any significant benefit by performing deliberate failures in the presence of the proposed reputation framework.

Han, Yujuan, Lu, Wenlian, Xu, Shouhuai.  2014.  Characterizing the Power of Moving Target Defense via Cyber Epidemic Dynamics. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :10:1–10:12.

Moving Target Defense (MTD) can enhance the resilience of cyber systems against attacks. Although there have been many MTD techniques, there is no systematic understanding and quantitative characterization of the power of MTD. In this paper, we propose to use a cyber epidemic dynamics approach to characterize the power of MTD. We define and investigate two complementary measures that are applicable when the defender aims to deploy MTD to achieve a certain security goal. One measure emphasizes the maximum portion of time during which the system can afford to stay in an undesired configuration (or posture), without considering the cost of deploying MTD. The other measure emphasizes the minimum cost of deploying MTD, while accommodating that the system has to stay in an undesired configuration (or posture) for a given portion of time. Our analytic studies lead to algorithms for optimally deploying MTD.

Layman, Lucas, Diffo, Sylvain David, Zazworka, Nico.  2014.  Human Factors in Webserver Log File Analysis: A Controlled Experiment on Investigating Malicious Activity. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :9:1–9:11.

While automated methods are the first line of defense for detecting attacks on webservers, a human agent is required to understand the attacker's intent and the attack process. The goal of this research is to understand the value of various log fields and the cognitive processes by which log information is grouped, searched, and correlated. Such knowledge will enable the development of human-focused log file investigation technologies. We performed controlled experiments with 65 subjects (IT professionals and novices) who investigated excerpts from six webserver log files. Quantitative and qualitative data were gathered to: 1) analyze subject accuracy in identifying malicious activity; 2) identify the most useful pieces of log file information; and 3) understand the techniques and strategies used by subjects to process the information. Statistically significant effects were observed in the accuracy of identifying attacks and time taken depending on the type of attack. Systematic differences were also observed in the log fields used by high-performing and low-performing groups. The findings include: 1) new insights into how specific log data fields are used to effectively assess potentially malicious activity; 2) obfuscating factors in log data from a human cognitive perspective; and 3) practical implications for tools to support log file investigations.

Tembe, Rucha, Zielinska, Olga, Liu, Yuqi, Hong, Kyung Wha, Murphy-Hill, Emerson, Mayhorn, Chris, Ge, Xi.  2014.  Phishing in International Waters: Exploring Cross-national Differences in Phishing Conceptualizations Between Chinese, Indian and American Samples. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :8:1–8:7.

One hundred-sixty four participants from the United States, India and China completed a survey designed to assess past phishing experiences and whether they engaged in certain online safety practices (e.g., reading a privacy policy). The study investigated participants' reported agreement regarding the characteristics of phishing attacks, types of media where phishing occurs and the consequences of phishing. A multivariate analysis of covariance indicated that there were significant differences in agreement regarding phishing characteristics, phishing consequences and types of media where phishing occurs for these three nationalities. Chronological age and education did not influence the agreement ratings; therefore, the samples were demographically equivalent with regards to these variables. A logistic regression analysis was conducted to analyze the categorical variables and nationality data. Results based on self-report data indicated that (1) Indians were more likely to be phished than Americans, (2) Americans took protective actions more frequently than Indians by destroying old documents, and (3) Americans were more likely to notice the "padlock" security icon than either Indian or Chinese respondents. The potential implications of these results are discussed in terms of designing culturally sensitive anti-phishing solutions.

Rao, Ashwini, Hibshi, Hanan, Breaux, Travis, Lehker, Jean-Michel, Niu, Jianwei.  2014.  Less is More?: Investigating the Role of Examples in Security Studies Using Analogical Transfer Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :7:1–7:12.

Information system developers and administrators often overlook critical security requirements and best practices. This may be due to lack of tools and techniques that allow practitioners to tailor security knowledge to their particular context. In order to explore the impact of new security methods, we must improve our ability to study the impact of security tools and methods on software and system development. In this paper, we present early findings of an experiment to assess the extent to which the number and type of examples used in security training stimuli can impact security problem solving. To motivate this research, we formulate hypotheses from analogical transfer theory in psychology. The independent variables include number of problem surfaces and schemas, and the dependent variable is the answer accuracy. Our study results do not show a statistically significant difference in performance when the number and types of examples are varied. We discuss the limitations, threats to validity and opportunities for future studies in this area.

Da, Gaofeng, Xu, Maochao, Xu, Shouhuai.  2014.  A New Approach to Modeling and Analyzing Security of Networked Systems. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :6:1–6:12.

Modeling and analyzing security of networked systems is an important problem in the emerging Science of Security and has been under active investigation. In this paper, we propose a new approach towards tackling the problem. Our approach is inspired by the shock model and random environment techniques in the Theory of Reliability, while accommodating security ingredients. To the best of our knowledge, our model is the first that can accommodate a certain degree of adaptiveness of attacks, which substantially weakens the often-made independence and exponential attack inter-arrival time assumptions. The approach leads to a stochastic process model with two security metrics, and we attain some analytic results in terms of the security metrics.

King, Jason, Williams, Laurie.  2014.  Log Your CRUD: Design Principles for Software Logging Mechanisms. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :5:1–5:10.

According to a 2011 survey in healthcare, the most commonly reported breaches of protected health information involved employees snooping into medical records of friends and relatives. Logging mechanisms can provide a means for forensic analysis of user activity in software systems by proving that a user performed certain actions in the system. However, logging mechanisms often inconsistently capture user interactions with sensitive data, creating gaps in traces of user activity. Explicit design principles and systematic testing of logging mechanisms within the software development lifecycle may help strengthen the overall security of software. The objective of this research is to observe the current state of logging mechanisms by performing an exploratory case study in which we systematically evaluate logging mechanisms by supplementing the expected results of existing functional black-box test cases to include log output. We perform an exploratory case study of four open-source electronic health record (EHR) logging mechanisms: OpenEMR, OSCAR, Tolven eCHR, and WorldVistA. We supplement the expected results of 30 United States government-sanctioned test cases to include log output to track access of sensitive data. We then execute the test cases on each EHR system. Six of the 30 (20%) test cases failed on all four EHR systems because user interactions with sensitive data are not logged. We find that viewing protected data is often not logged by default, allowing unauthorized views of data to go undetected. Based on our results, we propose a set of principles that developers should consider when developing logging mechanisms to ensure the ability to capture adequate traces of user activity.

Feigenbaum, Joan, Jaggard, Aaron D., Wright, Rebecca N..  2014.  Open vs. Closed Systems for Accountability. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :4:1–4:11.

The relationship between accountability and identity in online life presents many interesting questions. Here, we first systematically survey the various (directed) relationships among principals, system identities (nyms) used by principals, and actions carried out by principals using those nyms. We also map these relationships to corresponding accountability-related properties from the literature. Because punishment is fundamental to accountability, we then focus on the relationship between punishment and the strength of the connection between principals and nyms. To study this particular relationship, we formulate a utility-theoretic framework that distinguishes between principals and the identities they may use to commit violations. In doing so, we argue that the analogue applicable to our setting of the well known concept of quasilinear utility is insufficiently rich to capture important properties such as reputation. We propose more general utilities with linear transfer that do seem suitable for this model. In our use of this framework, we define notions of "open" and "closed" systems. This distinction captures the degree to which system participants are required to be bound to their system identities as a condition of participating in the system. This allows us to study the relationship between the strength of identity binding and the accountability properties of a system.

Escobar, Santiago, Meadows, Catherine, Meseguer, José, Santiago, Sonia.  2014.  A Rewriting-based Forwards Semantics for Maude-NPA. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :3:1–3:12.

The Maude-NRL Protocol Analyzer (Maude-NPA) is a tool for reasoning about the security of cryptographic protocols in which the cryptosystems satisfy different equational properties. It tries to find secrecy or authentication attacks by searching backwards from an insecure attack state pattern that may contain logical variables, in such a way that logical variables become properly instantiated in order to find an initial state. The execution mechanism for this logical reachability is narrowing modulo an equational theory. Although Maude-NPA also possesses a forwards semantics naturally derivable from the backwards semantics, it is not suitable for state space exploration or protocol simulation. In this paper we define an executable forwards semantics for Maude-NPA, instead of its usual backwards one, and restrict it to the case of concrete states, that is, to terms without logical variables. This case corresponds to standard rewriting modulo an equational theory. We prove soundness and completeness of the backwards narrowing-based semantics with respect to the rewriting-based forwards semantics. We show its effectiveness as an analysis method that complements the backwards analysis with new prototyping, simulation, and explicit-state model checking features by providing some experimental results.

Schmerl, Bradley, Cámara, Javier, Gennari, Jeffrey, Garlan, David, Casanova, Paulo, Moreno, Gabriel A., Glazier, Thomas J., Barnes, Jeffrey M..  2014.  Architecture-based Self-protection: Composing and Reasoning About Denial-of-service Mitigations. Proceedings of the 2014 Symposium and Bootcamp on the Science of Security. :2:1–2:12.

Security features are often hardwired into software applications, making it difficult to adapt security responses to reflect changes in runtime context and new attacks. In prior work, we proposed the idea of architecture-based self-protection as a way of separating adaptation logic from application logic and providing a global perspective for reasoning about security adaptations in the context of other business goals. In this paper, we present an approach, based on this idea, for combating denial-of-service (DoS) attacks. Our approach allows DoS-related tactics to be composed into more sophisticated mitigation strategies that encapsulate possible responses to a security problem. Then, utility-based reasoning can be used to consider different business contexts and qualities. We describe how this approach forms the underpinnings of a scientific approach to self-protection, allowing us to reason about how to make the best choice of mitigation at runtime. Moreover, we also show how formal analysis can be used to determine whether the mitigations cover the range of conditions the system is likely to encounter, and the effect of mitigations on other quality attributes of the system. We evaluate the approach using the Rainbow self-adaptive framework and show how Rainbow chooses DoS mitigation tactics that are sensitive to different business contexts.