14,784 research outputs found
Logical Relations for Encryption (Extended Abstract)
The theory of relational parametricity and its logical relations proof technique are powerful tools for reasoning about information hiding in the polymorphic λ-calculus. We investigate the application of these tools in the security domain by defining a cryptographic λ-calculus -- an extension of the standard simply typed λ-calculus with primitives for encryption, decryption, and key generation -- and introducing logical relations for this calculus that can be used to prove behavioral equivalences between programs that rely on encryption.
We illustrate the framework by encoding some simple security protocols, including the Needham-Schroeder public-key protocol. We give a natural account of the well-known attack on the original protocol and a straightforward proof that the improved variant of the protocol is secure
The Budget-Constrained Functional Dependency
Armstrong's axioms of functional dependency form a well-known logical system
that captures properties of functional dependencies between sets of database
attributes. This article assumes that there are costs associated with
attributes and proposes an extension of Armstrong's system for reasoning about
budget-constrained functional dependencies in such a setting.
The main technical result of this article is the completeness theorem for the
proposed logical system. Although the proposed axioms are obtained by just
adding cost subscript to the original Armstrong's axioms, the proof of the
completeness for the proposed system is significantly more complicated than
that for the Armstrong's system
Relating two standard notions of secrecy
Two styles of definitions are usually considered to express that a security
protocol preserves the confidentiality of a data s. Reachability-based secrecy
means that s should never be disclosed while equivalence-based secrecy states
that two executions of a protocol with distinct instances for s should be
indistinguishable to an attacker. Although the second formulation ensures a
higher level of security and is closer to cryptographic notions of secrecy,
decidability results and automatic tools have mainly focused on the first
definition so far.
This paper initiates a systematic investigation of the situations where
syntactic secrecy entails strong secrecy. We show that in the passive case,
reachability-based secrecy actually implies equivalence-based secrecy for
digital signatures, symmetric and asymmetric encryption provided that the
primitives are probabilistic. For active adversaries, we provide sufficient
(and rather tight) conditions on the protocol for this implication to hold.Comment: 29 pages, published in LMC
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