This thesis presents an automated method for verifying security properties of protocol implementations written in the C language. We assume that each successful run of a protocol follows the same path through the C code, justified by the fact that typical security protocols have linear structure. We then perform symbolic execution of that path to extract a model expressed in a process calculus similar to the one used by the CryptoVerif tool. The symbolic execution uses a novel algorithm that allows symbolic variables to represent bitstrings of potentially unknown length to model incoming protocol messages.
The extracted models do not use pointer-addressed memory, but they may still contain low-level details concerning message formats. In the next step we replace the message formatting expressions by abstract tupling and projection operators. The properties of these operators, such as the projection operation being the inverse of the tupling operation, are typically only satisfied with respect to inputs of correct types. Therefore we typecheck the model to ensure that all type-safety constraints are satisfied. The resulting model can then be verified with CryptoVerif to obtain a computational security result directly, or with ProVerif, to obtain a computational security result by invoking a computational soundness theorem.
Our method achieves high automation and does not require user input beyond what is necessary to specify the properties of the cryptographic primitives and the desired security goals. We evaluated the method on several protocol implementations, totalling over 3000 lines of code. The biggest case study was a 1000-line implementation that was independently written without verification in mind. We found several flaws that were acknowledged and fixed by the authors, and were able to verify the fixed code without any further modifications to it.
Consider the problem of verifying security properties of a cryptographic protocol coded in C. We propose an automatic solution that needs neither a pre-existing protocol description nor manual annotation of source code. First, symbolically execute the C program to obtain symbolic descriptions for the network messages sent by the protocol. Second, apply algebraic rewriting to obtain a process calculus description. Third, run an existing protocol analyser (ProVerif) to prove security properties or find attacks. We formalise our algorithm and appeal to existing results for ProVerif to establish c…
Cryptographic protocols with single blind copying were defined and modeled by Comon and Cortier using the new class $\mathcal C$ of first order clauses. They showed its satisfiability problem to be in 3-DEXPTIME. We improve this result by showing that satisfiability for this class is NEXPTIME-complete, using new resolution techniques. We show satisfiability to be DEXPTIME-complete if clauses are Horn, which is what is required for modeling cryptographic protocols. While translation to Horn clauses only gives a DEXPTIME upper bound for the secrecy problem for these protocols, we further show th…
A cryptographic protocol (CP) is a distributed algorithm designed to provide a secure communication in an insecure environment. CPs are used, for example, in electronic payments, electronic voting procedures, database access systems, etc. Errors in the CPs can lead to great financial and social damage, therefore it is necessary to use mathematical methods to justify the correctness and safety of the CPs. In this paper, a new mathematical model of a CP is introduced, which allows one to describe both the CPs and their properties. It is shown how, on the base of this model, it is possible to sol…
Internet of Things (IoT) is a system that consists of a large number of smart devices connected through a network. The number of these devices is increasing rapidly, which creates a massive and complex network with a vast amount of data communicated over that network. One way to protect this data in transit, i.e., to achieve data confidentiality, is to use lightweight encryption algorithms for IoT protocols. However, the design and implementation of such protocols is an error-prone task; flaws in the implementation can lead to devastating security vulnerabilities. These vulnerabilities can be …
Informal arguments that cryptographic protocols are secure can be made rigorous using inductive definitions. The approach is based on ordinary predicate calculus and copes with infinite-state systems. Proofs are generated using Isabelle/HOL. The human effort required to analyze a protocol can be as little as a week or two, yielding a proof script that takes a few minutes to run. Protocols are inductively defined as sets of traces. A trace is a list of communication events, perhaps comprising many interleaved protocol runs. Protocol descriptions incorporate attacks and accidental losses. The mo…
Numerous exploits of client-server protocols and applications involve modifying clients to behave in ways that untampered clients would not, such as crafting malicious packets. In this paper, we demonstrate practical verification of a cryptographic protocol client's messaging behavior as being consistent with the client program it is believed to be running. Moreover, we accomplish this without modifying the client in any way, and without knowing all of the client-side inputs driving its behavior. Our toolchain for verifying a client's messages explores multiple candidate execution paths in the…
Achieving secure communication between an Implantable Medical Device (IMD) inside the body and a gateway outside the body has showed its criticality with recent reports of hackings. The use of asymmetric cryptography is not a practical solution for IMDs due to the scarce computational and power resources, symmetric key cryptography is preferred. One of the factors in security of a symmetric cryptographic system is to use a strong key for encryption. A solution without using extensive resources in an IMD, is to extract it from the body physiological signals. To have a strong enough key, the phy…
Security of cryptographic protocols can be analysed by creating a model in a formal language and verifying the model in a tool. All such tools focus on the last part of the analysis, verification, and the interpretation of the specification is only explained in papers. Rather, we focus on the interpretation and modelling part by presenting a tool to aid the cryptographer throughout the process and automatically generating code in a target language. We adopt a data-centric approach where the protocol design is stored in a structured way rather than as textual specifications. Previous work shows…
The internet of things (IoT) is able to provide a prediction of linked, universal, and smart nodes that have autonomous interaction when they present services. Because of wide openness, relatively high processing power, and wide distribution of IoT things, they are ideal for attacks of the gray hole. In the gray hole attack, the attacker fakes itself as the shortest path to the destination that is a thing here. This causes the routing packets not to reach the destination. The proposed method is based on the AODV routing protocol and is presented under the MTISS-IoT name which means for the red…
An AI Approach to Verified Production Cryptographic Libraries
Stanford University（斯坦福大学）；University of North Carolina at Chapel Hill（北卡罗来纳大学教堂山分校）；VMware Research by Broadcom（博通旗下VMware研究院）；Amherst College（阿默斯特学院）
This work presents a new tool to verify the correctness of cryptographic implementations with respect to cache attacks. Our methodology discovers vulnerabilities that are hard to find with other techniques, observed as exploitable leakage. The methodology works by identifying secret dependent memory and introducing forced evictions inside potentially vulnerable code to obtain cache traces that are analyzed using Mutual Information. If dependence is observed, the cryptographic implementation is classified as to leak information. We demonstrate the viability of our technique in the design of the…
Knowledge extraction, typically studied in the classical setting, is at the heart of several cryptographic protocols. We introduce the notion of secure quantum extraction protocols. A secure quantum extraction protocol for an NP relation $\mathcal{R}$ is a classical interactive protocol between a sender and a receiver, where the sender gets the instance $z$ and a witness $w$, while the receiver only gets the instance $z$. For any efficient quantum adversarial sender (who follows the protocol but can choose its own randomness), there exists a quantum extractor that can extract a witness $w'$ su…
This paper is the first thorough investigation into the coarsest notion of bisimilarity for the applied pi-calculus that is a congruence relation: open barbed bisimilarity. An open variant of labelled bisimilarity (quasi-open bisimilarity), better suited to constructing bisimulations, is proven to coincide with open barbed bisimilarity. These bisimilary congruences are shown to be characterised by an intuitionistic modal logic that can be used, for example, to describe an attack on privacy whenever a privacy property is violated. Open barbed bisimilarity provides a compositional approach to ve…
Implementation attacks like side-channel and fault attacks pose a considerable threat to cryptographic devices that are physically accessible by an attacker. As a consequence, devices like smart cards implement corresponding countermeasures like redundant computation and masking. Recently, statistically ineffective fault attacks (SIFA) were shown to be able to circumvent these classical countermeasure techniques. We present a new approach for verifying the SIFA protection of arbitrary masked implementations in both hardware and software. The proposed method uses Boolean dependency analysis, fa…
In resource-constrained IoT networks, the use of conventional message authentication codes (MACs) to provide message authentication and integrity is not possible due to the large size of the MAC output. A straightforward yet naive solution to this problem is to employ a truncated MAC which undesirably sacrifices cryptographic strength in exchange for reduced communication overhead. In this paper, we address this problem by proposing a novel approach for message authentication called \textit{Cumulative Message Authentication Code} (CuMAC), which consists of two distinctive procedures: \textit{a…
Physical Unclonable Functions (PUFs) exploit variations in the manufacturing process to derive bit sequences from integrated circuits, which can be used as secure cryptographic keys. Instead of storing the keys in an insecure, non-volatile memory, they can be reproduced when needed. Since the reproduced sequences are not stable due to physical reasons, error correction must be applied. Recently, convolutional codes were shown to be suitable for key reproduction in PUFs based on SRAM. This work shows how to further decrease the reconstruction failure probability and PUF implementation size usin…
We present a new technique for verifying correspondences in security protocols. In particular, correspondences can be used to formalize authentication. Our technique is fully automatic, it can handle an unbounded number of sessions of the protocol, and it is efficient in practice. It significantly extends a previous technique for the verification of secrecy. The protocol is represented in an extension of the pi calculus with fairly arbitrary cryptographic primitives. This protocol representation includes the specification of the correspondence to be verified, but no other annotation. This repr…
The increasing development speed via Agile may introduce overlooked security steps in the process, with an example being the Iowa Caucus application. Verifying the protection of confidential information such as social security numbers requires security at all levels, providing protection through any connected applications. CryptoGuard is a static code analyzer for Java. This program verifies that developers do not leave vulnerabilities in their applications. The program aids the developer by identifying cryptographic misuses such as hard-coded keys, weak program hashes, and using insecure prot…
We give new proofs for the hardness amplification of efficiently samplable predicates and of weakly verifiable puzzles which generalize to new settings. More concretely, in the first part of the paper, we give a new proof of Yao's XOR-Lemma that additionally applies to related theorems in the cryptographic setting. Our proof seems simpler than previous ones, yet immediately generalizes to statements similar in spirit such as the extraction lemma used to obtain pseudo-random generators from one-way functions [Hastad, Impagliazzo, Levin, Luby, SIAM J. on Comp. 1999]. In the second part of the pa…
Based on our previous work on truly concurrent process algebras APTC, we use it to verify the security protocols. This work (called Secure APTC, abbreviated SAPTC) have the following advantages in verifying security protocols: (1) It has a firmly theoretic foundations, including equational logics, structured operational semantics, and axiomatizations between them; (2) It has rich expressive powers to describe security protocols. Cryptographic operations are modeled as atomic actions and can be extended, explicit parallelism and communication mechanism to modeling communication operations and p…
In this paper, we consider the problem of verifying anonymity and unlinkability in the symbolic model, where protocols are represented as processes in a variant of the applied pi calculus, notably used in the ProVerif tool. Existing tools and techniques do not allow to verify directly these properties, expressed as behavioral equivalences. We propose a different approach: we design two conditions on protocols which are sufficient to ensure anonymity and unlinkability, and which can then be effectively checked automatically using ProVerif. Our two conditions correspond to two broad classes of a…
Companies and network operators perform risk assessment to inform policy-making, guide infrastructure investments or to comply with security standards such as ISO 27001. Due to the size and complexity of these networks, risk assessment techniques such as attack graphs or trees describe the attacker with a finite set of rules. This characterization of the attacker can easily miss attack vectors or overstate them, potentially leading to incorrect risk estimation. In this work, we propose the first methodology to justify a rule-based attacker model. Conceptually, we add another layer of abstracti…
Exact Bias of Linear TRNG Correctors -- Spectral Approach
University of Luxembourg（卢森堡大学）；Czech Technical University in Prague（布拉格捷克理工大学）；Rey Juan Carlos University（雷伊胡安卡洛斯大学）；Lehrstuhl für Nachrichtentechnik, Technische Universität Dortmund（多特蒙德工业大学通信工程系）；Information Theory and Security Laboratory (ITSL), Linköping University（林雪平大学信息理论与安全实验室）
