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The Tor network is currently by far the most popular system for providing anonymity on the Internet. Even though both latency and throughput have been significantly improved in recent years, Tor users still experience variable delays on connecting to servers. Such delays have been shown to be especially harmful for browsing the web and prevent altogether the use of protocols where a certain quality of service is indispensable.In this paper we propose and evaluate methods to measure and improve performance in the Tor network. To estimate the quality of circuits for future traffic, we use active Round-TripTime (RTT) measurements and a-priori information of the distribution of RTT values. In this way, slow circuits can be discarded before having negative impact on user experience. Using NavigaTor, our high performance measurement software which includes a custom Tor path generator, we are the first to conduct large-scale performance measurements on the live Tor network, building millions of circuits within days, without stressing the anonymity network. As part of our study, we conduct several experiments from PlanetLab on the live Tor network to analyze the trade-off between the quality of protection and the quality of service. We compare our Circuit-RTT method to the current state-of-the-art method Circuit Build Time (CBT) and the more recently proposed congestionaware scheme, finding that the congestion-aware scheme in its original design achieves only minor improvements on the current Tor network and that Circuit-RTT improves latency and throughput more effectively than CBT.

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Abstract-TLS is the most widely used cryptographic protocol on the Internet. While many recent studies focused on its use in HTTPS, none so far analyzed TLS usage in e-mail related protocols, which often carry highly sensitive information. Since end-to-end encryption mechanisms like PGP are seldomly used, today confidentiality in the e-mail ecosystem is mainly based on the encryption of the transport layer. A well-positioned attacker may be able to intercept plaintext passively and at global scale.In this paper we are the first to present a scalable methodology to assess the state of security mechanisms in the e-mail ecosystem using commodity hardware and open-source software. We draw a comprehensive picture of the current state of every e-mail related TLS configuration for the entire IPv4 range. We collected and scanned a massive data-set of 20 million IP/port combinations of all related protocols (SMTP, POP3, IMAP) and legacy ports. Over a time span of approx. three months we conducted more than 10 billion TLS handshakes. Additionally, we show that securing server-to-server communication using e.g. SMTP is inherently more difficult than securing client-toserver communication. Lastly, we analyze the volatility of TLS certificates and trust anchors in the e-mail ecosystem and argue that while the overall trend points in the right direction, there are still many steps needed towards secure e-mail.

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