691 research outputs found
Computational Soundness for Dalvik Bytecode
Automatically analyzing information flow within Android applications that
rely on cryptographic operations with their computational security guarantees
imposes formidable challenges that existing approaches for understanding an
app's behavior struggle to meet. These approaches do not distinguish
cryptographic and non-cryptographic operations, and hence do not account for
cryptographic protections: f(m) is considered sensitive for a sensitive message
m irrespective of potential secrecy properties offered by a cryptographic
operation f. These approaches consequently provide a safe approximation of the
app's behavior, but they mistakenly classify a large fraction of apps as
potentially insecure and consequently yield overly pessimistic results.
In this paper, we show how cryptographic operations can be faithfully
included into existing approaches for automated app analysis. To this end, we
first show how cryptographic operations can be expressed as symbolic
abstractions within the comprehensive Dalvik bytecode language. These
abstractions are accessible to automated analysis, and they can be conveniently
added to existing app analysis tools using minor changes in their semantics.
Second, we show that our abstractions are faithful by providing the first
computational soundness result for Dalvik bytecode, i.e., the absence of
attacks against our symbolically abstracted program entails the absence of any
attacks against a suitable cryptographic program realization. We cast our
computational soundness result in the CoSP framework, which makes the result
modular and composable.Comment: Technical report for the ACM CCS 2016 conference pape
Formal Computational Unlinkability Proofs of RFID Protocols
We set up a framework for the formal proofs of RFID protocols in the
computational model. We rely on the so-called computationally complete symbolic
attacker model. Our contributions are: i) To design (and prove sound) axioms
reflecting the properties of hash functions (Collision-Resistance, PRF); ii) To
formalize computational unlinkability in the model; iii) To illustrate the
method, providing the first formal proofs of unlinkability of RFID protocols,
in the computational model
Cryptographically Secure Information Flow Control on Key-Value Stores
We present Clio, an information flow control (IFC) system that transparently
incorporates cryptography to enforce confidentiality and integrity policies on
untrusted storage. Clio insulates developers from explicitly manipulating keys
and cryptographic primitives by leveraging the policy language of the IFC
system to automatically use the appropriate keys and correct cryptographic
operations. We prove that Clio is secure with a novel proof technique that is
based on a proof style from cryptography together with standard programming
languages results. We present a prototype Clio implementation and a case study
that demonstrates Clio's practicality.Comment: Full version of conference paper appearing in CCS 201
Automated Cryptographic Analysis of the Pedersen Commitment Scheme
Aiming for strong security assurance, recently there has been an increasing
interest in formal verification of cryptographic constructions. This paper
presents a mechanised formal verification of the popular Pedersen commitment
protocol, proving its security properties of correctness, perfect hiding, and
computational binding. To formally verify the protocol, we extended the theory
of EasyCrypt, a framework which allows for reasoning in the computational
model, to support the discrete logarithm and an abstraction of commitment
protocols. Commitments are building blocks of many cryptographic constructions,
for example, verifiable secret sharing, zero-knowledge proofs, and e-voting.
Our work paves the way for the verification of those more complex
constructions.Comment: 12 pages, conference MMM-ACNS 201
A Survey of Symbolic Methods in Computational Analysis of Cryptographic Systems
Since the 1980s, two approaches have been developed for analyzing security protocols. One of the approaches relies on a computational model that considers issues of complexity and probability. This approach captures a strong notion of security, guaranteed against all probabilistic polynomial-time attacks. The other approach relies on a symbolic model of protocol executions in which cryptographic primitives are treated as black boxes. Since the seminal work of Dolev and Yao, it has been realized that this latter approach enables significantly simpler and often automated proofs. However, the guarantees that it offers have been quite unclear. For more than twenty years the two approaches have coexisted but evolved mostly independently. Recently, significant research efforts attempt to develop paradigms for cryptographic systems analysis that combines the best of both worlds. There are two broad directions that have been followed. {\em Computational soundness} aims to establish sufficient conditions under which results obtained using symbolic models imply security under computational models. The {\em direct approach} aims to apply the principles and the techniques developed in the context of symbolic models directly to computational ones. In this paper we survey existing results along both of these directions. Our goal is to provide a rather complete summary that could act as a quick reference for researchers who want to contribute to the field, want to make use of existing results, or just want to get a better picture of what results already exist
Equivalence-Checking on Infinite-State Systems: Techniques and Results
The paper presents a selection of recently developed and/or used techniques
for equivalence-checking on infinite-state systems, and an up-to-date overview
of existing results (as of September 2004)
The PER model of abstract non-interference
Abstract. In this paper, we study the relationship between two models of secure information flow: the PER model (which uses equivalence relations) and the abstract non-interference model (which uses upper closure operators). We embed the lattice of equivalence relations into the lattice of closures, re-interpreting abstract non-interference over the lattice of equivalence relations. For narrow abstract non-interference, we show non-interference it is strictly less general. The relational presentation of abstract non-interference leads to a simplified construction of the most concrete harmless attacker. Moreover, the PER model of abstract noninterference allows us to derive unconstrained attacker models, which do not necessarily either observe all public information or ignore all private information. Finally, we show how abstract domain completeness can be used for enforcing the PER model of abstract non-interference
How to prove security of communication protocols? A discussion on the soundness of formal models w.r.t. computational ones.
Security protocols are short programs that aim at securing communication over a public network. Their design is known to be error-prone with flaws found years later. That is why they deserve a careful security analysis, with rigorous proofs. Two main lines of research have been (independently) developed to analyse the security of protocols. On the one hand, formal methods provide with symbolic models and often automatic proofs. On the other hand, cryptographic models propose a tighter modeling but proofs are more difficult to write and to check. An approach developed during the last decade consists in bridging the two approaches, showing that symbolic models are sound w.r.t. symbolic ones, yielding strong security guarantees using automatic tools. These results have been developed for several cryptographic primitives (e.g. symmetric and asymmetric encryption, signatures, hash) and security properties.
While proving soundness of symbolic models is a very promising approach, several technical details are often not satisfactory. Focusing on symmetric encryption, we describe the difficulties and limitations of the available results
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