Summary With the widespread use of encrypted data transport, network traffic encryption is becoming a standard nowadays. This presents a challenge for traffic measurement, especially for analysis and anomaly detection methods, which are dependent on the type of network traffic. In this paper, we survey existing approaches for classification and analysis of encrypted traffic. First, we describe the most widespread encryption protocols used throughout the Internet. We show that the initiation of an encrypted connection and the protocol structure give away much information for encrypted traffic classification and analysis. Then, we survey payload and feature‐based classification methods for encrypted traffic and categorize them using an established taxonomy. The advantage of some of described classification methods is the ability to recognize the encrypted application protocol in addition to the encryption protocol. Finally, we make a comprehensive comparison of the surveyed feature‐based classification methods and present their weaknesses and strengths. Copyright © 2015 John Wiley & Sons, Ltd.

The encryption of network traffic complicates legitimate network monitoring, traffic analysis, and network forensics. In this paper, we present real-time lightweight identification of HTTPS clients based on network monitoring and SSL/TLS fingerprinting. Our experiment shows that it is possible to estimate the User-Agent of a client in HTTPS communication via the analysis of the SSL/TLS handshake. The fingerprints of SSL/TLS handshakes, including a list of supported cipher suites, differ among clients and correlate to User-Agent values from a HTTP header. We built up a dictionary of SSL/TLS cipher suite lists and HTTP User-Agents and assigned the User-Agents to the observed SSL/TLS connections to identify communicating clients. The dictionary was used to classify live HTTPS network traffic. We were able to retrieve client types from 95.4 % of HTTPS network traffic. Further, we discussed host-based and network-based methods of dictionary retrieval and estimated the quality of the data.

Adversary thinking is an essential skill for cybersecurity experts, enabling them to understand cyber attacks and set up effective defenses. While this skill is commonly exercised by Capture the Flag games and hands-on activities, we complement these approaches with a key innovation: undergraduate students learn methods of network attack and defense by creating educational games in a cyber range. In this paper, we present the design of two courses, instruction and assessment techniques, as well as our observations over the last three semesters. The students report they had a unique opportunity to deeply understand the topic and practice their soft skills, as they presented their results at a faculty open day event. Their peers, who played the created games, rated the quality and educational value of the games overwhelmingly positively. Moreover, the open day raised awareness about cybersecurity and research and development in this field at our faculty. We believe that sharing our teaching experience will be valuable for instructors planning to introduce active learning of cybersecurity and adversary thinking.

The exchange of security alerts is a current trend in network security and incident response. Alerts from network intrusion detection systems are shared among organizations so that it is possible to see the "big picture" of current security situation. However, the quality and redundancy of the input data seem to be underrated. We present four use cases of aggregation of the alerts from network intrusion detection systems. Alerts from a sharing platform deployed in the Czech national research and education network were examined in a case study. Volumes of raw and aggregated data are presented and a rule of thumb is proposed: up to 85 % of alerts can be aggregated. Finally, we discuss the practical implications of alert aggregation for the network intrusion detection system, such as (in)completeness of the alerts and optimal time windows for aggregation.

Abstract-The growing share of encrypted network traffic complicates network traffic analysis and network forensics. In this paper, we present real-time lightweight identification of HTTPS clients based on network monitoring and SSL/TLS fingerprinting. Our experiment shows that it is possible to estimate the UserAgent of a client in HTTPS communication via the analysis of the SSL/TLS handshake. The fingerprints of SSL/TLS handshakes, including a list of supported cipher suites, differ among clients and correlate to User-Agent values from a HTTP header. We built up a dictionary of SSL/TLS cipher suite lists and HTTP UserAgents and assigned the User-Agents to the observed SSL/TLS connections to identify communicating clients. We discuss hostbased and network-based methods of dictionary retrieval and estimate the quality of the data. The usability of the proposed method is demonstrated on two case studies of network forensics.

Analyzing IP flows is an essential part of traffic measurement for cyber security. Based on information from IP flows, it is possible to discover the majority of concurrent cyber threats in high-speed, large-scale networks. Some major prevailing challenges for IP flow analysis include, but are not limited to, analysis over a large volume of IP flows, scalability issues, and detecting cyber threats in real time. In this article, we discuss the transformation of present IP flow analysis into a stream-based approach to face the above-mentioned challenges. We examine the possible positive and negative impacts of the transformation and present examples of real-world applications, along with our recommendations. Our ongoing results show that stream-based IP flow analysis successfully meets the abovementioned challenges and is suitable for achieving real-time network security analysis and situational awareness.

Abstract-Modern distributed stream processing systems can potentially be applied to real time network flow processing. However, differences in performance make some systems more suitable than others for being applied to this domain. We propose a novel performance benchmark, which is based on common security analysis algorithms of NetFlow data to determine the suitability of distributed stream processing systems. Three of the most used distributed stream processing systems are benchmarked and the results are compared with NetFlow data processing challenges and requirements. The benchmark results show that each system reached a sufficient data processing speed using a basic deployment scenario with little to no configuration tuning. Our benchmark, unlike any other, enables the performance of small structured messages to be processed on any stream processing system.

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