The Cryptographic Security of the German Electronic Identity Card

In November 2010, the German government started to issue the new electronic identity card (eID) to its citizens. Besides its original utilization as a ’visual’ identification document, the eID card can be used by the cardholder to prove one’s identity at border control and to enhance security of authentication processes over the Internet, with the eID card serving as a token to reliably transmit personal data to service providers or terminals, respectively. To this end, the German Federal Office for Information Security (BSI) proposed several cryptographic protocols now deployed on the eID card. The Password Authenticated Connection Establishment (PACE) protocol secures the wireless communication between the eID card and the user’s local card reader, based on a cryptographically weak password like the PIN chosen by the card owner. Subsequently, the Extended Access Control (EAC) protocol is executed by the chip and the service provider to mutually authenticate and agree on a shared secret session key. This key is then used in the secure channel protocol, called Secure Messaging (SM). Finally, an optional protocol, called Restricted Identification (RI), provides a method to use pseudonyms such that they can be linked by individual service providers, but not across different service providers (even not by malicious ones). This thesis consists of two parts. First, we present the above protocols and provide a rigorous analysis on their security from a cryptographic point of view. We show that the Germen eID card provides reasonable security for authentication and exchange of sensitive information allaying concerns regarding its usage. In the second part of this thesis, we introduce two possible modifications to enhance the security of these protocols even further. Namely, we show how to (a) add to PACE an additional efficient chip authentication step, and (b) augment RI to allow also for signatures under pseudonyms

Privacy-Preserving Authenticated Key Exchange for Constrained Devices

In this paper we investigate the field of privacy-preserving authenticated key exchange protocols (PPAKE). First we make a cryptographic analysis of a previous PPAKE protocol. We show that most of its security properties, including privacy, are broken, despite the security proofs that are provided. Then we describe a strong security model which captures the security properties of a PPAKE: entity authentication, key indistinguishability, forward secrecy, and privacy. Finally, we present a PPAKE protocol in the symmetric-key setting which is suitable for constrained devices. We formally prove the security of this protocol in our model

Preuves mécanisées de protocoles cryptographiques et leur lien avec des implémentations vérifiées

Cryptographic protocols are one of the foundations for the trust people put in computer systems nowadays, be it online banking, any web or cloud services, or secure messaging. One of the best theoretical assurances for cryptographic protocol security is reached through proofs in the computational model. Writing such proofs is prone to subtle errors that can lead to invalidation of the security guarantees and, thus, to undesired security breaches. Proof assistants strive to improve this situation, have got traction, and have increasingly been used to analyse important real-world protocols and to inform their development. Writing proofs using such assistants requires a substantial amount of work. It is an ongoing endeavour to extend their scope through, for example, more automation and detailed modelling of cryptographic building blocks. This thesis shows on the example of the CryptoVerif proof assistant and two case studies, that mechanized cryptographic proofs are practicable and useful in analysing and designing complex real-world protocols.The first case study is on the free and open source Virtual Private Network (VPN) protocol WireGuard that has recently found its way into the Linux kernel. We contribute proofs for several properties that are typical for secure channel protocols. Furthermore, we extend CryptoVerif with a model of unprecedented detail of the popular Diffie-Hellman group Curve25519 used in WireGuard.The second case study is on the new Internet standard Hybrid Public Key Encryption (HPKE), that has already been picked up for use in a privacy-enhancing extension of the TLS protocol (ECH), and in the Messaging Layer Security secure group messaging protocol. We accompanied the development of this standard from its early stages with comprehensive formal cryptographic analysis. We provided constructive feedback that led to significant improvements in its cryptographic design. Eventually, we became an official co-author. We conduct a detailed cryptographic analysis of one of HPKE's modes, published at Eurocrypt 2021, an encouraging step forward to make mechanized cryptographic proofs more accessible to the broader cryptographic community.The third contribution of this thesis is of methodological nature. For practical purposes, security of implementations of cryptographic protocols is crucial. However, there is frequently a gap between a cryptographic security analysis and an implementation that have both been based on a protocol specification: no formal guarantee exists that the two interpretations of the specification match, and thus, it is unclear if the executable implementation has the guarantees proved by the cryptographic analysis. In this thesis, we close this gap for proofs written in CryptoVerif and implementations written in F*. We develop cv2fstar, a compiler from CryptoVerif models to executable F* specifications using the HACL* verified cryptographic library as backend. cv2fstar translates non-cryptographic assumptions about, e.g., message formats, from the CryptoVerif model to F* lemmas. This allows to prove these assumptions for the specific implementation, further deepening the formal link between the two analysis frameworks. We showcase cv2fstar on the example of the Needham-Schroeder-Lowe protocol. cv2fstar connects CryptoVerif to the large F* ecosystem, eventually allowing to formally guarantee cryptographic properties on verified, efficient low-level code.Les protocoles cryptographiques sont l'un des fondements de la confiance que la société accorde aujourd'hui aux systèmes informatiques, qu'il s'agisse de la banque en ligne, d'un service web, ou de la messagerie sécurisée. Une façon d'obtenir des garanties théoriques fortes sur la sécurité des protocoles cryptographiques est de les prouver dans le modèle calculatoire. L'écriture de ces preuves est délicate : des erreurs subtiles peuvent entraîner l'invalidation des garanties de sécurité et, par conséquent, des failles de sécurité. Les assistants de preuve visent à améliorer cette situation. Ils ont gagné en popularité et ont été de plus en plus utilisés pour analyser des protocoles importants du monde réel, et pour contribuer à leur développement. L'écriture de preuves à l'aide de tels assistants nécessite une quantité substantielle de travail. Un effort continu est nécessaire pour étendre leur champ d'application, par exemple, par une automatisation plus poussée et une modélisation plus détaillée des primitives cryptographiques. Cette thèse montre sur l'exemple de l'assistant de preuve CryptoVerif et deux études de cas, que les preuves cryptographiques mécanisées sont praticables et utiles pour analyser et concevoir des protocoles complexes du monde réel. La première étude de cas porte sur le protocole de réseau virtuel privé (VPN) libre et open source WireGuard qui a récemment été intégré au noyau Linux. Nous contribuons des preuves pour plusieurs propriétés typiques des protocoles de canaux sécurisés. En outre, nous étendons CryptoVerif avec un modèle d'un niveau de détail sans précédent du groupe Diffie-Hellman populaire Curve25519 utilisé dans WireGuard. La deuxième étude de cas porte sur la nouvelle norme Internet Hybrid Public Key Encryption (HPKE), qui est déjà utilisée dans une extension du protocole TLS destinée à améliorer la protection de la vie privée (ECH), et dans Messaging Layer Security, un protocole de messagerie de groupe sécurisée. Nous avons accompagné le développement de cette norme dès les premiers stades avec une analyse cryptographique formelle. Nous avons fourni des commentaires constructifs ce qui a conduit à des améliorations significatives dans sa conception cryptographique. Finalement, nous sommes devenus un co-auteur officiel. Nous effectuons une analyse cryptographique détaillée de l'un des modes de HPKE, publiée à Eurocrypt 2021, un pas encourageant pour rendre les preuves cryptographiques mécanisées plus accessibles à la communauté des cryptographes. La troisième contribution de cette thèse est de nature méthodologique. Pour des utilisations pratiques, la sécurité des implémentations de protocoles cryptographiques est cruciale. Cependant, il y a souvent un écart entre l'analyse de la sécurité cryptographique et l'implémentation, tous les deux basées sur la même spécification d'un protocole : il n'existe pas de garantie formelle que les deux interprétations de la spécification correspondent, et donc, il n'est pas clair si l'implémentation exécutable a les garanties prouvées par l'analyse cryptographique. Dans cette thèse, nous comblons cet écart pour les preuves écrites en CryptoVerif et les implémentations écrites en F*. Nous développons cv2fstar, un compilateur de modèles CryptoVerif vers des spécifications exécutables F* en utilisant la bibliothèque cryptographique vérifiée HACL* comme fournisseur de primitives cryptographiques. cv2fstar traduit les hypothèses non cryptographiques concernant, par exemple, les formats de messages, du modèle CryptoVerif vers des lemmes F*. Cela permet de prouver ces hypothèses pour l'implémentation spécifique, ce qui approfondit le lien formel entre les deux cadres d'analyse. Nous présentons cv2fstar sur l'exemple du protocole Needham-Schroeder-Lowe. cv2fstar connecte CryptoVerif au grand écosystème F*, permettant finalement de garantir formellement des propriétés cryptographiques sur du code de bas niveau efficace vérifié

Using Large-Scale Empirical Methods to Understand Fragile Cryptographic Ecosystems

Cryptography is a key component of the security of the Internet. Unfortunately, the process of using cryptography to secure the Internet is fraught with failure. Cryptography is often fragile, as a single mistake can have devastating consequences on security, and this fragility is further complicated by the diverse and distributed nature of the Internet. This dissertation shows how to use empirical methods in the form of Internet-wide scanning to study how cryptography is deployed on the Internet, and shows this methodology can discover vulnerabilities and gain insights into fragile cryptographic ecosystems that are not possible without an empirical approach. I introduce improvements to ZMap, the fast Internet-wide scanner, that allow it to fully utilize a 10 GigE connection, and then use Internet-wide scanning to measure cryptography on the Internet. First, I study how Diffie-Hellman is deployed, and show that implementations are fragile and not resilient to small subgroup attacks. Next, I measure the prevalence of ``export-grade'' cryptography. Although regulations limiting the strength of cryptography that could be exported from the United States were lifted in 1999, Internet-wide scanning shows that support for various forms of export cryptography remains widespread. I show how purposefully weakening TLS to comply with these export regulations led to the FREAK, Logjam, and DROWN vulnerabilities, each of which exploits obsolete export-grade cryptography to attack modern clients. I conclude by discussing how empirical cryptography improved protocol design, and I present further opportunities for empirical research in cryptography.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149809/1/davadria_1.pd