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.

Tor provides anonymity to millions of users around the globe, which has made it a valuable target for malicious actors. As a low-latency anonymity system, it is vulnerable to traffic correlation attacks from strong passive adversaries, such as large autonomous systems. Estimations of the risk posed by such attackers as well as the evaluation of defense strategies are mostly based on simulations and data retrieved from BGP updates. However, this might only provide an incomplete view of the network and thereby influence the results of such analyses. It has already been acknowledged in previous studies that direct path measurements, e.g. with traceroute, could provide valuable information. But in the past, such measurements were thought to be impossible, because they require the placement of measurement nodes in the same ASes as the respective Tor network nodes. With the rise of new technologies and methodologies, this assumption needs to be re-evaluated. In this paper we present a novel methodology to utilize the RIPE Atlas framework, a network of more than 10,000 probes worldwide, to actively perform traceroute commands from and to Tor guard and exit relays to clients and destinations. Based on multiple global scans our results validate previous results and show the large influence on Tor posed by a limited set of ASes. These are in a strong position to carry out effective correlation attacks on Tor traffic. With this work, we provide an additional source of information that can be used together with BGP route information to increase the accuracy of future models and simulations of Tor and ultimately improve anonymity on the Internet.

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Transport Layer Security (TLS) is the fundament of today's web security, but the majority of deployments are misconfigured and left vulnerable to a phletora of attacks. This negatively affects the overall healthiness of the TLS ecosystem, and as such all the protocols that build on top of it. Scanning a larger number of hosts or protocols such as the numerous IPv4-wide scans published recently for a list of known attacks in TLS is non-trivial. This is due to the design of the TLS handshake, where the server chooses the specific cipher suite to be used. Current scanning approaches have to establish an unnecessary large number of connections and amount of traffic. In this paper we present and implemented different optimized strategies for TLS cipher suite scanning that, compared to the current best practice, perform up to 3.2 times faster and with 94% less connections used while being able to do exhaustive scanning for many vulnerabilities at once. We thoroughly evaluated the algorithms using practical scans and an additional simulation for evaluating current cipher suite practices at scale. With this work full TLS cipher suite scans are brought to a new level, making them a practical tool for further empiric research.

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