Mathematical Algorithms & Anomaly Detection Peer-Reviewed Journal

Pages: 19 (5790 words)  ·  Style: IEEE  ·  Bibliography Sources: 25  ·  File: .docx  ·  Level: Doctorate  ·  Topic: Mathematics  ·  Written: May 31, 2019

The traces of system calls are utilized to identify repeated patterns and enable the detection of anomalies [12].

Lastly, with regards to IDS location, it should be noted that the use of side channel intrusion detection systems utilizing physical characteristics including timings, vibrations, electromagnetic radiation, and power consumption is gaining popularity in cybersecurity intrusion detection systems research [13] and particularly focuses on utilizing physical host level data [14, 15]. In the case of side-channel detection systems, the main advantage is the isolation of such systems from the hosts which hinders attackers from tampering with the IDSs.

1.3. Detection Techniques

Signature matching detection identifies attacks through matching data packets with predefined attack signature samples. The matching process usually takes a lot of time providing attackers with ample time to do their damage [16]. Moreover, only known and predefined attack signatures can be matched/ detected utilizing this detection technique, which is a big problem considering the growing number of self-modifying malware and pattern detection evasion methods utilized by attackers.

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Anomaly based detection is an upgrade of signature matching detection in the sense that it reduces need for detection and updating predefined attack signature databases in the IDSs. This is because it utilizes statistical methods to identify normal behavior and any variations, which allows for the detection of previously undefined or unknown attack signatures. However, while they are good conceptually, they have not been adopted widely since they usually report relatively high numbers of false alarms which makes them difficult to use [17, 16]. Reducing the number of false positives is, thus, key to making anomaly based detection IDSs practical and convenient to use.

Peer-Reviewed Journal on Mathematical Algorithms & Anomaly Detection Assignment

According to Rehak [18] anomaly based detection false positives can be divided into unstructured and structured false positives. The former are random noise resulting from network traffic stochasticity, while the latter are the result of regular but abnormal behavior particularly found in smaller network hosts such as DNS and mail servers. This work proposes the use of mathematical algorithms to reduce false positives (unstructured ones) and to, therefore, assist with anomaly detection.

1.4. Classi?cation of False Positives

For the purpose of this work, the assumption that the network anomaly IDS monitors several network events (for example, HTTP connections, NetFlow [19], etc) generated by different hosts in a network is held. The IDS system maintains internal scoring systems that assign either a one or zero to each event, with zero showing that an event is normal while one shows that an event is a possible attack. The assumption that malicious activities have different statistical characteristics from ordinary ones is held [16]. As indicated before, anomaly detection IDSs produce a huge number of false positives because most rare events are usually not the result of attacks. According to Rehak [18] false positives are categorized into structured and unstructured false positives.

· Unstructured false positives are often short term and are usually distributed across network hosts based on traffic volume share. They usually triggered by behaviors that are uniformly distributed (e.g. browsing the web) and are in this work modeled as white noise (finite variance and zero mean) added to the output of an anomaly detector. Thus, if an event xihas an anomaly score of yito calculate the score one would need to use the formula below


Where the value g(xi) represents the real anomaly score for the event and ?ii represents the white noise that hides the true anomaly value.

· Structured false positives are often long term, regular but abnormal behavior particularly found in smaller network hosts. They are flagged as anomalies because they are not normal. Examples of structured false positives include uncommon network APIs making regular calls, and software updates by uncommon applications [16]. Because structured false positives often come from only a few network hosts and their behavior is regular, they can usually be identified and eliminated utilizing white lists. However, the white lists usually have to be very specific for the structured false positives. This makes them hard to create prior to deployment. The mixed distributions formula below defines these false positives


Where the value ?jis the false positive. Its weight is ?j. Each structured false positive value has variance when compared to unstructured false positive values but the means of each component are generally different from one another.

2. Proposed Method

The proposed LAMS (Local adaptive multivariate smoothing) method aims to substitute the anomaly detector’s output by the mean anomaly score of comparable previous events, whereby the comparability/ similarity/ context between 2 events is captured as . This successfully smooths anomaly detector output and, thus, significantly reduces the rate of unstructured false alarms. Mathematically, the smoothing can be shown as follows


In which case {xi}ni=1 is the value which represents network events, is the value which shows the anticipated event x anomaly, and this value {yi}ni=1 represents the corresponding set of anomaly detector outputs. The space Xwhere the smoothing is defined could be arbitrary. However, Euclidean’s space Gaussian kernel, defined as , is the most often used combination. In the definition, the h parameterizes the kernel’s width.

The estimator (3) is commonly referred to as the Nadaraya-Watson estimator and it is a non-parametric one of a random variable’s conditional expectation [9, 10, 16].

The statements below explain how smoothing reduce unstructured and structured false alarms:

· Unstructured false alarms are significantly cut by the estimator defined above through averaging similar events. Because unstructured false alarms are in the following form yi=g(xi) + ?i, under multiple assumptions, it has been proven that they converge to g(xi). This is as per Devroye et al. [20]. Below is its mathematical expression



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