miTLS: Verifying Protocol Implementations against Real-World Attacks

International audienceThe TLS Internet Standard, previously known as SSL, is the default protocol for encrypting communications between clients and servers on the Web. Hence, TLS routinely protects our sensitive emails, health records, and payment information against network-based eavesdropping and tampering. For the past 20 years, TLS security has been analyzed in various cryptographic and programming models to establish strong formal guarantees for various protocol configurations. However, TLS deployments are still often vulnerable to attacks and rely on security experts to fix the protocol implementations. The miTLS project intends to solve this apparent contradiction between published proofs and real-world attacks, which reveals a gap between TLS theory and practice. To this end, the authors developed a verified reference implementation and a cryptographic security proof that account for the protocol's low-level details. The resulting formal development sheds light on recent attacks, yields security guarantees for typical TLS usages, and informs the design of the protocol's next version

Multi-ciphersuite security of the Secure Shell (SSH) protocol

The Secure Shell (SSH) protocol is widely used to provide secure remote access to servers, making it among the most important security protocols on the Internet. We show that the signed-Diffie--Hellman SSH ciphersuites of the SSH protocol are secure: each is a secure authenticated and confidential channel establishment (ACCE) protocol, the same security definition now used to describe the security of Transport Layer Security (TLS) ciphersuites. While the ACCE definition suffices to describe the security of individual ciphersuites, it does not cover the case where parties use the same long-term key with many different ciphersuites: it is common in practice for the server to use the same signing key with both finite field and elliptic curve Diffie--Hellman, for example. While TLS is vulnerable to attack in this case, we show that SSH is secure even when the same signing key is used across multiple ciphersuites. We introduce a new generic multi-ciphersuite composition framework to achieve this result in a black-box way

A Cryptographic Analysis of the WireGuard Protocol

WireGuard (Donenfeld, NDSS 2017) is a recently proposed secure network tunnel operating at layer 3. WireGuard aims to replace existing tunnelling solutions like IPsec and OpenVPN, while requiring less code, being more secure, more performant, and easier to use. The cryptographic design of WireGuard is based on the Noise framework. It makes use of a key exchange component which combines long-term and ephemeral Diffie-Hellman values (along with optional preshared keys). This is followed by the use of the established keys in an AEAD construction to encapsulate IP packets in UDP. To date, WireGuard has received no rigorous security analysis. In this paper, we, rectify this. We first observe that, in order to prevent Key Compromise Impersonation (KCI) attacks, any analysis of WireGuard\u27s key exchange component must take into account the first AEAD ciphertext from initiator to responder. This message effectively acts as a key confirmation and makes the key exchange component of WireGuard a 1.5 RTT protocol. However, the fact that this ciphertext is computed using the established session key rules out a proof of session key indistinguishability for WireGuard\u27s key exchange component, limiting the degree of modularity that is achievable when analysing the protocol\u27s security. To overcome this proof barrier, and as an alternative to performing a monolithic analysis of the entire WireGuard protocol, we add an extra message to the protocol. This is done in a minimally invasive way that does not increase the number of round trips needed by the overall WireGuard protocol. This change enables us to prove strong authentication and key indistinguishability properties for the key exchange component of WireGuard under standard cryptographic assumptions

CyberSPL: Framework for the verification of cybersecurity policy compliance of system configurations using software product lines

Cybersecurity attacks affect the compliance of cybersecurity policies of the organisations. Such disadvantages may be due to the absence of security configurations or the use of default configuration values of software products and systems. The complexity in the configuration of products and systems is a known challenge in the software industry since it includes a wide range of parameters to be taken into account. In other contexts, the configuration problems are solved using Software Product Lines. This is the reason why in this article the framework Cybersecurity Software Product Line (CyberSPL) is proposed. CyberSPL is based on a methodology to design product lines to verify cybersecurity policies according to the possible configurations. The patterns to configure the systems related to the cybersecurity aspects are grouped by defining various feature models. The automated analysis of these models allows us to diagnose possible problems in the security configurations, reducing or avoiding them. As support for this proposal, a multi-user and multi-platform solution has been implemented, enabling setting a catalogue of public or private feature models. Moreover, analysis and reasoning mechanisms have been integrated to obtain all the configurations of a model, to detect if a configuration is valid or not, including the root cause of problems for a given configuration. For validating the proposal, a real scenario is proposed where a catalogue of four different feature models is presented. In this scenario, the models have been analysed, different configurations have been validated, and several configurations with problems have been diagnosed.Ministerio de Ciencia y Tecnología RTI2018-094283-B-C3

Safely Exporting Keys from Secure Channels: On the Security of EAP-TLS and TLS Key Exporters

We investigate how to safely export additional cryptographic keys from secure channel protocols, modeled with the authenticated and confidential channel establishment (ACCE) security notion. For example, the EAP-TLS protocol uses the Transport Layer Security (TLS) handshake to output an additional shared secret which can be used for purposes outside of TLS, and the RFC 5705 standard specifies a general mechanism for exporting keying material from TLS. We show that, for a class of ACCE protocols we call “TLS-like” protocols, the EAP-TLS transformation can be used to export an additional key, and that the result is a secure AKE protocol in the Bellare–Rogaway model. Interestingly, we are able to carry out the proof without looking at the specifics of the TLS protocol itself (beyond the notion that it is “TLS-like”), but rather are able to use the ACCE property in a semi black-box way. To facilitate our modular proof, we develop a novel technique, notably an encryption-based key checking mechanism that is used by the security reduction. Our results imply that EAP-TLS using secure TLS 1.2 cipher-suites is a secure authenticated key exchange protocol

Handshake Privacy for TLS 1.3 - Technical report

TLS 1.3, the newest version of the Transport Layer Security (TLS) protocol, provides stronger authentication and confidentiality guarantees than prior TLS version. Despite additional encryption of handshake messages, some parts of the TLS 1.3 handshake, including the ClientHello, are still in the clear. For example, the protocol reveals the identity of the target server to network attackers, allowing the passive surveillance and active censorship of TLS connections. A recent privacy extension called Encrypted Client Hello (ECH, previously called ESNI) addresses this problem and offers more comprehensive handshake encryption and privacy for TLS 1.3. Surprisingly however, although the security of the TLS 1.3 handshake has been comprehensively analyzed in a variety of formal models, the privacy guarantees of handshake encryption have never been formally studied. This gap has resulted in several mis-steps: several of the initial designs for ECH were found to be vulnerable to passive and active network attacks. In this paper, we present the first mechanized formal analysis of privacy properties for the TLS 1.3 handshake. We study all standard modes of TLS 1.3, with and without ECH, using the symbolic protocol analyzer ProVerif. We discuss attacks on ECH, some found during the course of this study, and show how they are accounted for in the latest version. Our analysis has helped guide the standardization process for ECH and we provide concrete privacy recommendations for TLS implementors. We also contribute the most comprehensive model of TLS 1.3 to date, which can be used by designers experimenting with new extensions to the protocol. Ours is one of the largest privacy proofs attempted in ProVerif and our modeling strategies may be of general interest to protocol analysts

A Low-Energy Security Solution for IoT-Based Smart Farms

This work proposes a novel configuration of the Transport Layer Security protocol (TLS), suitable for low energy Internet of Things (IoT), applications. The motivation behind the redesign of TLS is energy consumption minimisation and sustainable farming, as exemplified by an application domain of aquaponic smart farms. The work therefore considers decentralisation of a formerly centralised security model, with a focus on reducing energy consumption for battery powered devices. The research presents a four-part investigation into the security solution, composed of a risk assessment, energy analysis of authentication and data exchange functions, and finally the design and verification of a novel consensus authorisation mechanism. The first investigation considered traditional risk-driven threat assessment, but to include energy reduction, working towards device longevity within a content-oriented framework. Since the aquaponics environments include limited but specific data exchanges, a content-oriented approach produced valuable insights into security and privacy requirements that would later be tested by implementing a variety of mechanisms available on the ESP32. The second and third investigations featured the energy analysis of authentication and data exchange functions respectively, where the results of the risk assessment were implemented to compare the re-configurations of TLS mechanisms and domain content. Results concluded that selective confidentiality and persistent secure sessions between paired devices enabled considerable improvements for energy consumptions, and were a good reflection of the possibilities suggested by the risk assessment. The fourth and final investigation proposed a granular authorisation design to increase the safety of access control that would otherwise be binary in TLS. The motivation was for damage mitigation from inside attacks or network faults. The approach involved an automated, hierarchy-based, decentralised network topology to reduce data duplication whilst still providing robustness beyond the vulnerability of central governance. Formal verification using model-checking indicated a safe design model, using four automated back-ends. The research concludes that lower energy IoT solutions for the smart farm application domain are possible

Design and Verification of Specialised Security Goals for Protocol Families

Communication Protocols form a fundamental backbone of our modern information networks. These protocols provide a framework to describe how agents - Computers, Smartphones, RFID Tags and more - should structure their communication. As a result, the security of these protocols is implicitly trusted to protect our personal data. In 1997, Lowe presented ‘A Hierarchy of Authentication Specifications’, formalising a set of security requirements that might be expected of communication protocols. The value of these requirements is that they can be formally tested and verified against a protocol specification. This allows a user to have confidence that their communications are protected in ways that are uniformly defined and universally agreed upon. Since that time, the range of objectives and applications of real-world protocols has grown. Novel requirements - such as checking the physical distance between participants, or evolving trust assumptions of intermediate nodes on the network - mean that new attack vectors are found on a frequent basis. The challenge, then, is to define security goals which will guarantee security, even when the nature of these attacks is not known. In this thesis, a methodology for the design of security goals is created. It is used to define a collection of specialised security goals for protocols in multiple different families, by considering tailor-made models for these specific scenarios. For complex requirements, theorems are proved that simplify analysis, allowing the verification of security goals to be efficiently modelled in automated prover tools