G-SINC: Global Synchronization Infrastructure for Network Clocks

Many critical computing applications rely on secure and dependable time which is reliably synchronized across large distributed systems. Today's time synchronization architectures are commonly based on global navigation satellite systems at the considerable risk of being exposed to outages, malfunction, or attacks against availability and accuracy. This paper describes a practical instantiation of a new global, Byzantine fault-tolerant clock synchronization approach that does not place trust in any single entity and is able to tolerate a fraction of faulty entities while still maintaining synchronization on a global scale among otherwise sovereign network topologies. Leveraging strong resilience and security properties provided by the path-aware SCION networking architecture, the presented design can be implemented as a backward compatible active standby solution for existing time synchronization deployments. Through extensive evaluation, we demonstrate that over 94% of time servers reliably minimize the offset of their local clocks to real-time in the presence of up to 20% malicious nodes, and all time servers remain synchronized with a skew of only 2 ms even after one year of reference clock outage

Security Implications of Insecure DNS Usage in the Internet

The Domain Name System (DNS) provides domain-to-address lookup-services used by almost all internet applications. Because of this ubiquitous use of the DNS, attacks against the DNS have become more and more critical. However, in the past, studies of DNS security have been mostly conducted against individual protocols and applications. In this thesis, we perform the first comprehensive evaluation of DNS-based attacks against a wide range of internet applications, ranging from time-synchronisation via NTP over internet resource management to security mechanisms. We show how to attack those applications by exploiting various weaknesses in the DNS. These attacks are based on both, already known weaknesses which are adapted to new attacks, as well as previously unknown attack vectors which have been found during the course of this thesis. We evaluate our attacks and provide the first taxonomy of DNS applications, to show how adversaries can systematically develop attacks exploiting the DNS. We analyze the attack surface created by our attacks in the internet and find that a significant number of applications and systems can be attacked. We work together with the developers of the vulnerable applications to develop patches and general countermeasures which can be applied by various parties to block our attacks. We also provide conceptual insights into the root causes allowing our attacks to help with the development of new applications and standards. The findings of this thesis are published in in 4 full-paper publications and 2 posters at international academic conferences. Additionally, we disclose our finding to developers which has lead to the registration of 8 Common Vulnerabilities and Exposures identifiers (CVE IDs) and patches in 10 software implementations. To raise awareness, we also presented our findings at several community meetings and via invited articles

Attacking and securing Network Time Protocol

Network Time Protocol (NTP) is used to synchronize time between computer systems communicating over unreliable, variable-latency, and untrusted network paths. Time is critical for many applications; in particular it is heavily utilized by cryptographic protocols. Despite its importance, the community still lacks visibility into the robustness of the NTP ecosystem itself, the integrity of the timing information transmitted by NTP, and the impact that any error in NTP might have upon the security of other protocols that rely on timing information. In this thesis, we seek to accomplish the following broad goals: 1. Demonstrate that the current design presents a security risk, by showing that network attackers can exploit NTP and then use it to attack other core Internet protocols that rely on time. 2. Improve NTP to make it more robust, and rigorously analyze the security of the improved protocol. 3. Establish formal and precise security requirements that should be satisfied by a network time-synchronization protocol, and prove that these are sufficient for the security of other protocols that rely on time. We take the following approach to achieve our goals incrementally. 1. We begin by (a) scrutinizing NTP's core protocol (RFC 5905) and (b) statically analyzing code of its reference implementation to identify vulnerabilities in protocol design, ambiguities in specifications, and flaws in reference implementations. We then leverage these observations to show several off- and on-path denial-of-service and time-shifting attacks on NTP clients. We then show cache-flushing and cache-sticking attacks on DNS(SEC) that leverage NTP. We quantify the attack surface using Internet measurements, and suggest simple countermeasures that can improve the security of NTP and DNS(SEC). 2. Next we move beyond identifying attacks and leverage ideas from Universal Composability (UC) security framework to develop a cryptographic model for attacks on NTP's datagram protocol. We use this model to prove the security of a new backwards-compatible protocol that correctly synchronizes time in the face of both off- and on-path network attackers. 3. Next, we propose general security notions for network time-synchronization protocols within the UC framework and formulate ideal functionalities that capture a number of prevalent forms of time measurement within existing systems. We show how they can be realized by real-world protocols (including but not limited to NTP), and how they can be used to assert security of time-reliant applications-specifically, cryptographic certificates with revocation and expiration times. Our security framework allows for a clear and modular treatment of the use of time in security-sensitive systems. Our work makes the core NTP protocol and its implementations more robust and secure, thus improving the security of applications and protocols that rely on time