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We present an automated tool for elaborating security proofs of cryptographic systems from proof sketches—compact, formal representations of the essence of a proof as a sequence of games and hints. Proof sketches are checked automatically using off-the-shelf SMT solvers and automated theorem provers, and then compiled into verifiable proofs in the… (More)

Differential privacy is a notion of confidentiality that protects the privacy of individuals while allowing useful computations on their private data. Deriving differential privacy guarantees for real programs is a difficult and error-prone task that calls for principled approaches and tool support. Approaches based on linear types and static analysis have… (More)

As cryptographic proofs have become essentially unverifiable, cryptographers have argued in favor of developing techniques that help tame the complexity of their proofs. Game-based techniques provide a popular approach in which proofs are structured as sequences of games and in which proof steps establish the validity of transitions between successive… (More)

We investigate the security of Diffie-Hellman key exchange as used in popular Internet protocols and find it to be less secure than widely believed. First, we present Logjam, a novel flaw in TLS that lets a man-in-the-middle downgrade connections to "export-grade" Diffie-Hellman. To carry out this attack, we implement the number field sieve discrete log… (More)

The TLS Internet Standard features a mixed bag of cryptographic algorithms and constructions, letting clients and servers negotiate their use for each run of the handshake. Although many ciphersuites are now well-understood in isolation, their composition remains problematic, and yet it is critical to obtain practical security guarantees for TLS. We… (More)

OAEP is a widely used public-key encryption scheme based on trapdoor permutations. Its security proof has been scrutinized and amended repeatedly. Fifteen years after the introduction of OAEP, we present a machine-checked proof of its security against adaptive chosen-ciphertext attacks under the assumption that the underlying permutation is partial-domain… (More)

Computer-aided verification provides effective means of analyzing the security of cryptographic primitives. However, it has remained a challenge to achieve fully automated analyses yielding guarantees that hold against computational (rather than symbolic) attacks. This paper meets this challenge for public-key encryption schemes built from trapdoor… (More)

Provable security [6] is at the heart of modern cryptography. It advocates a mathematical approach in which the security of new cryptographic constructions is defined rigorously, and provably reduced to one or several assumptions, such as the hardness of a computational problem, or the existence of an ideal func-tionality. A typical provable security… (More)

Identity-based encryption (IBE) allows one party to send ciphered messages to another using an arbitrary identity string as an en-cryption key. Since IBE does not require prior generation and distribution of keys, it greatly simplifies key management in public-key cryptography. Although the concept of IBE was introduced by Shamir in 1981, constructing a… (More)

—EasyCrypt is a tool-assisted framework for reasoning about probabilistic computations in the presence of adver-sarial code, whose main application has been the verification of security properties of cryptographic constructions in the computational model. We report on a significantly enhanced version of EasyCrypt that accommodates a richer, user-extensible… (More)