Project Everest began at Microsoft Research in 2016, aiming to spur research in program verification to produce industrial-grade software. In collaboration with INRIA and Carnegie Mellon University, Project Everest’s goal was to produce drop-in verified replacements of secure communications software used in the HTTPS ecosystem, including TLS, the underlying cryptography, and related subprotocols. Now, almost a decade later, we reflect on the project, sharing both its successes and failures, and look ahead to the next decade of program verification research.

Memory coloring is a software-based technique to ensure microarchitectural isolation between trust domains sharing a CPU. Prior coloring schemes target individual microarchitectural components and thus provide only partial solutions. In this paper, we provide theoretical foundations and practical algorithms to infer comprehensive coloring schemes for modern cloud CPUs.

We present Marghera, a system design that prevents cross-VM microarchitectural side-channel attacks in the cloud. Marghera is based on isolation contracts which, for a given CPU, describe partitions of physical threads and memory that prevent information leakage through shared microarchitectural resources.

Abstract Syntax Notation One (ASN.1) is a language for structured data exchange between computers, standardized by both ITU-T and ISO/IEC since 1984. The Distinguished Encoding Rules (DER) specify its non-malleable binary format: for a given ASN.1 data type, every value has a distinct, unique binary representation. ASN.1 DER is used in many security-critical interfaces for telecommunications and networking, such as the X.509 public key infrastructure, where non-malleability is essential. However, due to the expressiveness and flexibility of the general-purpose ASN.1 language, correctly parsing ASN.1 DER data formats is still considered a serious security challenge in practice. We present ASN1*, the first formalization of ASN.1 DER with a mechanized proof of non-malleability. Our development provides a shallow embedding of ASN.1 in the F* proof assistant and formalizes its DER semantics within the EverParse parser generator framework. It guarantees that any ASN.1 data encoded using our DER semantics is non-malleable. It yields verified code that parses valid binary representations into values of the corresponding ASN.1 data type while rejecting invalid ones. We empirically confirm that our semantics models ASN.1 DER usage in practice by evaluating ASN1* parsers extracted to OCaml on both positive and negative test cases involving X.509 certificates and Certificate Revocation Lists (CRLs).

Confidentiality, integrity protection, and high availability, abbreviated to CIA, are essential properties for trustworthy data systems. The rise of cloud computing and the growing demand for multiparty applications however means that building modern CIA systems is more challenging than ever. In response, we present the Confidential Consortium Framework (CCF), a general-purpose foundation for developing secure stateful CIA applications. CCF combines centralized compute with decentralized trust, supporting deployment on untrusted cloud infrastructure and transparent governance by mutually untrusted parties. CCF leverages hardware-based trusted execution environments for remotely verifiable confidentiality and code integrity. This is coupled with state machine replication backed by an auditable immutable ledger for data integrity and high availability. CCF enables each service to bring its own application logic, custom multiparty governance model, and deployment scenario, decoupling the operators of nodes from the consortium that governs them. CCF is open-source and available now at https://github.com/microsoft/CCF.

Advances in graphics and machine learning have led to the general availability of easy-to-use tools for modifying and synthesizing media. The proliferation of these tools threatens to cast doubt on the veracity of all media. One approach to thwarting the flow of fake media is to detect modified or synthesized media through machine learning methods. While detection may help in the short term, we believe that it is destined to fail as the quality of fake media generation continues to improve. Soon, neither humans nor algorithms will be able to reliably distinguish fake versus real content. Thus, pipelines for assuring the source and integrity of media will be required---and increasingly relied upon. We present AMP, a system that ensures the authentication of media via certifying provenance. AMP creates one or more publisher-signed manifests for a media instance uploaded by a content provider. These manifests are stored in a database allowing fast lookup from applications such as browsers. For reference, the manifests are also registered and signed by a permissioned ledger, implemented using the Confidential Consortium Framework (CCF). CCF employs both software and hardware techniques to ensure the integrity and transparency of all registered manifests. AMP, through its use of CCF, enables a consortium of media providers to govern the service while making all its operations auditable. The authenticity of the media can be communicated to the user via visual elements in the browser, indicating that an AMP manifest has been successfully located and verified.

Drawing on earlier protocol-verification work, we investigate the security of the QUIC record layer, as standardized by the IETF in draft version 30. This version features major differences compared to Google’s original protocol and early IETF drafts. It serves as a useful test case for our verification methodology and toolchain, while also, hopefully, drawing attention to a little studied yet crucially important emerging standard.We model QUIC packet and header encryption, which uses a custom construction for privacy. To capture its goals, we propose a security definition for authenticated encryption with semi-implicit nonces. We show that QUIC uses an instance of a generic construction parameterized by a standard AEAD-secure scheme and a PRF-secure cipher. We formalize and verify the security of this construction in F. The proof uncovers interesting limitations of nonce confidentiality, due to the malleability of short headers and the ability to choose the number of least significant bits included in the packet counter. We propose improvements that simplify the proof and increase robustness against strong attacker models. In addition to the verified security model, we also give a concrete functional specification for the record layer, and prove that it satisfies important functionality properties (such as the correct successful decryption of encrypted packets) after fixing more errors in the draft. We then provide a high-performance implementation of the record layer that we prove to be memory safe, correct with respect to our concrete specification (inheriting its functional correctness properties), and secure with respect to our verified model. To evaluate this component, we develop a provably-safe implementation of the rest of the QUIC protocol. Our record layer achieves nearly 2 GB/s throughput, and our QUIC implementation’s performance is within 21% of an unverified baseline.

We present EverCrypt: a comprehensive collection of verified, high-performance cryptographic functionalities available via a carefully designed API. The API provably supports agility (choosing between multiple algorithms for the same functionality) and multiplexing (choosing between multiple implementations of the same algorithm). Through abstraction and zero-cost generic programming, we show how agility can simplify verification without sacrificing performance, and we demonstrate how C and assembly can be composed and verified against shared specifications. We substantiate the effectiveness of these techniques with new verified implementations (including hashes, Curve25519, and AES-GCM) whose performance matches or exceeds the best unverified implementations. We validate the API design with two high-performance verified case studies built atop EverCrypt, resulting in line-rate performance for a secure network protocol and a Merkle-tree library, used in a production blockchain, that supports 2.7 million insertions/sec. Altogether, EverCrypt consists of over 124K verified lines of specs, code, and proofs, and it produces over 29K lines of C and 14K lines of assembly code.

Relational properties describe multiple runs of one or more programs. They characterize many useful notions of security, program refinement, and equivalence for programs with diverse computational effects, and they have received much attention in the recent literature. Rather than developing separate tools for special classes of effects and relational properties, we advocate using a general purpose proof assistant as a unifying framework for the relational verification of effectful programs. The essence of our approach is to model effectful computations using monads and to prove relational properties on their monadic representations, making the most of existing support for reasoning about pure programs. We apply this method in F* and evaluate it by encoding a variety of relational program analyses, including information flow control, program equivalence and refinement at higher order, correctness of program optimizations and game-based cryptographic security. By relying on SMT-based automation, unary weakest preconditions, user-defined effects, and monadic reification, we show that, compared to unary properties, verifying relational properties requires little additional effort from the F* programmer.

We study the interaction of the programming construct “new,” which generates statically scoped names, with communication via messages on channels. This interaction is crucial in security protocols, which are the main motivating examples for our work; it also appears in other programming-language contexts. We define the applied pi calculus, a simple, general extension of the pi calculus in which values can be formed from names via the application of built-in functions, subject to equations, and be sent as messages. (In contrast, the pure pi calculus lacks built-in functions; its only messages are atomic names.) We develop semantics and proof techniques for this extended language and apply them in reasoning about security protocols. This article essentially subsumes the conference paper that introduced the applied pi calculus in 2001. It fills gaps, incorporates improvements, and further explains and studies the applied pi calculus. Since 2001, the applied pi calculus has been the basis for much further work, described in many research publications and sometimes embodied in useful software, such as the tool ProVerif, which relies on the applied pi calculus to support the specification and automatic analysis of security protocols. Although this article does not aim to be a complete review of the subject, it benefits from that further work and provides better foundations for some of it. In particular, the applied pi calculus has evolved through its implementation in ProVerif, and the present definition reflects that evolution.

We provide a way to ease the verification of programs whose state evolves monotonically. The main idea is that a property witnessed in a prior state can be soundly recalled in the current state, provided (1) state evolves according to a given preorder, and (2) the property is preserved by this preorder. In many scenarios, such monotonic reasoning yields concise modular proofs, saving the need for explicit program invariants. We distill our approach into the monotonic-state monad , a general yet compact interface for Hoare-style reasoning about monotonic state in a dependently typed language. We prove the soundness of the monotonic-state monad and use it as a unified foundation for reasoning about monotonic state in the F ⋆ verification system. Based on this foundation, we build libraries for various mutable data structures like monotonic references and apply these libraries at scale to the verification of several distributed applications.

The record layer is the main bridge between TLS applications and internal sub-protocols. Its core functionality is an elaborate form of authenticated encryption: streams of messages for each sub-protocol (handshake, alert, and application data) are fragmented, multiplexed, and encrypted with optional padding to hide their lengths. Conversely, the sub-protocols may provide fresh keys or signal stream termination to the record layer. Compared to prior versions, TLS 1.3 discards obsolete schemes in favor of a common construction for Authenticated Encryption with Associated Data (AEAD), instantiated with algorithms such as AES-GCM and ChaCha20-Poly1305. It differs from TLS 1.2 in its use of padding, associated data and nonces. It also encrypts the content-type used to multiplex between sub-protocols. New protocol features such as early application data (0-RTT and 0.5-RTT) and late handshake messages require additional keys and a more general model of stateful encryption. We build and verify a reference implementation of the TLS record layer and its cryptographic algorithms in F*, a dependently typed language where security and functional guarantees can be specified as pre-and post-conditions. We reduce the high-level security of the record layer to cryptographic assumptions on its ciphers. Each step in the reduction is verified by typing an F* module, for each step that involves a cryptographic assumption, this module precisely captures the corresponding game. We first verify the functional correctness and injectivity properties of our implementations of one-time MAC algorithms (Poly1305 and GHASH) and provide a generic proof of their security given these two properties. We show the security of a generic AEAD construction built from any secure one-time MAC and PRF. We extend AEAD, first to stream encryption, then to length-hiding, multiplexed encryption. Finally, we build a security model of the record layer against an adversary that controls the TLS sub-protocols. We compute concrete security bounds for the AES_128_GCM, AES_256_GCM, and CHACHA20_POLY1305 ciphersuites, and derive recommended limits on sent data before re-keying. We plug our implementation of the record layer into the miTLS library, confirm that they interoperate with Chrome and Firefox, and report initial performance results. Combining our functional correctness, security, and experimental results, we conclude that the new TLS record layer (as described in RFCs and cryptographic standards) is provably secure, and we provide its first verified implementation.

We present Low*, a language for low-level programming and verification, and its application to high-assurance optimized cryptographic libraries. Low* is a shallow embedding of a small, sequential, well-behaved subset of C in F*, a dependently- typed variant of ML aimed at program verification. Departing from ML, Low* does not involve any garbage collection or implicit heap allocation; instead, it has a structured memory model à la CompCert, and it provides the control required for writing efficient low-level security-critical code. By virtue of typing, any Low* program is memory safe. In addition, the programmer can make full use of the verification power of F* to write high-level specifications and verify the functional correctness of Low* code using a combination of SMT automation and sophisticated manual proofs. At extraction time, specifications and proofs are erased, and the remaining code enjoys a predictable translation to C. We prove that this translation preserves semantics and side-channel resistance. We provide a new compiler back-end from Low* to C and, to evaluate our approach, we implement and verify various cryptographic algorithms, constructions, and tools for a total of about 28,000 lines of code. We show that our Low* code delivers performance competitive with existing (unverified) C cryptographic libraries, suggesting our approach may be applicable to larger-scale low-level software.

Proof systems for verifiable computation (VC) have the potential to make cloud outsourcing more trustworthy. Recent schemes enable a verifier with limited resources to delegate large computations and verify their outcome based on succinct arguments: verification complexity is linear in the size of the inputs and outputs (not the size of the computation). However, cloud computing also often involves large amounts of data, which may exceed the local storage and I/O capabilities of the verifier, and thus limit the use of VC. In this paper, we investigate multi-relation hash & prove schemes for verifiable computations that operate on succinct data hashes. Hence, the verifier delegates both storage and computation to an untrusted worker. She uploads data and keeps hashes; exchanges hashes with other parties; verifies arguments that consume and produce hashes; and selectively downloads the actual data she needs to access.

In cryptology, verifiable computing aims at verifying the remote execution of a program on an untrusted machine, based on its I/O and constant-sized evidence collected during its execution. Recent cryptographic schemes and compilers enable practical verifiable computations for some programs written in C, but their soundness with regards to C semantics remains informal and poorly understood. We present the first certified, semantics-preserving compiler for verifiable computing. Based on CompCert and developed in Coq, our compiler targets an architecture whose instructions consist solely of quadratic equations over a large finite field, amenable to succinct verification using the Pinocchio cryptographic scheme. We explain how to encode the integer operations of a C program first to quadratic equations, then to a single cryptographically-checkable polynomial test. We formally prove that, when compilation succeeds, there is a correct execution of the source program for any I/O that pass this test. We link our compiler to the Pinocchio cryptographic runtime, and report experimental results as we compile, run, and verify the execution of sample C programs.

We present a new, completely redesigned, version of F*, a language that works both as a proof assistant as well as a general-purpose, verification-oriented, effectful programming language. In support of these complementary roles, F* is a dependently typed, higher-order, call-by-value language with _primitive_ effects including state, exceptions, divergence and IO. Although primitive, programmers choose the granularity at which to specify effects by equipping each effect with a monadic, predicate transformer semantics. F* uses this to efficiently compute weakest preconditions and discharges the resulting proof obligations using a combination of SMT solving and manual proofs. Isolated from the effects, the core of F* is a language of pure functions used to write specifications and proof terms---its consistency is maintained by a semantic termination check based on a well-founded order. We evaluate our design on more than 55,000 lines of F* we have authored in the last year, focusing on three main case studies. Showcasing its use as a general-purpose programming language, F* is programmed (but not verified) in F*, and bootstraps in both OCaml and F#. Our experience confirms F*'s pay-as-you-go cost model: writing idiomatic ML-like code with no finer specifications imposes no user burden. As a verification-oriented language, our most significant evaluation of F* is in verifying several key modules in an implementation of the TLS-1.2 protocol standard. For the modules we considered, we are able to prove more properties, with fewer annotations using F* than in a prior verified implementation of TLS-1.2. Finally, as a proof assistant, we discuss our use of F* in mechanizing the metatheory of a range of lambda calculi, starting from the simply typed lambda calculus to System F-omega and even micro-F*, a sizeable fragment of F* itself---these proofs make essential use of F*'s flexible combination of SMT automation and constructive proofs, enabling a tactic-free style of programming and proving at a relatively large scale.

Key-exchange protocols such as TLS, SSH, IPsec, and ZRTP are highly configurable, with typical deployments supporting multiple protocol versions, cryptographic algorithms and parameters. In the first messages of the protocol, the peers negotiate one specific combination: the protocol mode, based on their local configurations. With few notable exceptions, most cryptographic analyses of configurable protocols consider a single mode at a time. In contrast, downgrade attacks, where a network adversary forces peers to use a mode weaker than the one they would normally negotiate, are a recurrent problem in practice. How to support configurability while at the same time guaranteeing the preferred mode is negotiated? We set to answer this question by designing a formal framework to study downgrade resilience and its relation to other security properties of key-exchange protocols. First, we study the causes of downgrade attacks by dissecting and classifying known and novel attacks against widely used protocols. Second, we survey what is known about the downgrade resilience of existing standards. Third, we combine these findings to define downgrade security, and analyze the conditions under which several protocols achieve it. Finally, we discuss patterns that guarantee downgrade security by design, and explain how to use them to strengthen the security of existing protocols, including a newly proposed draft of TLS 1.3.

Despite advances in security engineering, authentication in applications such as email and the Web still primarily relies on the X.509 public key infrastructure introduced in 1988. This PKI has many issues but is nearly impossible to replace. Leveraging recent progress in verifiable computation, we propose a novel use of existing X.509 certificates and infrastructure. Instead of receiving and validating chains of certificates, our applications receive and verify proofs of their knowledge, their validity, and their compliance with application policies. This yields smaller messages (by omitting certificates), stronger privacy (by hiding certificate contents), and stronger integrity (by embedding additional checks, e.g. for revocation). X.509 certificate validation is famously complex and error-prone, as it involves parsing ASN.1 data structures and interpreting them against diverse application policies. To manage this diversity, we propose a new format for writing application policies by composing X.509 templates, and we provide a template compiler that generates C code for validating certificates within a given policy. We then use the Geppetto cryptographic compiler to produce a zero-knowledge verifiable computation scheme for that policy. To optimize the resulting scheme, we develop new C libraries for RSA-PKCS#1 signatures and ASN.1 parsing, carefully tailored for cryptographic verifiability. We evaluate our approach by providing two real-world applications of verifiable computation: a drop-in replacement for certificates within TLS, and access control for the Helios voting protocol. For TLS, we support fine-grained validation policies, with revocation checking and selective disclosure of certificate contents, effectively turning X.509 certificates into anonymous credentials. For Helios, we obtain additional privacy and verifiability guarantees for voters equipped with X.509 certificates, such as those readily available from some national ID cards.

The use of public cloud infrastructure for storing and processing large datasets raises new security concerns. Current solutions propose encrypting all data, and accessing it in plaintext only within secure hardware. Nonetheless, the distributed processing of large amounts of data still involves intensive encrypted communications between different processing and network storage units, and those communications patterns may leak sensitive information. We consider secure implementation of MapReduce jobs, and analyze their intermediate traffic between mappers and reducers. Using datasets that include personal and geographical data, we show how an adversary that observes the runs of typical jobs can infer precise information about their input. We give a new definition of data privacy for MapReduce, and describe two provably-secure, practical solutions. We implement our solutions on top of VC3, a secure implementation of Hadoop, and evaluate their performance.

Current proposals for adding gradual typing to JavaScript, such as Closure, TypeScript and Dart, forgo soundness to deal with issues of scale, code reuse, and popular programming patterns. We show how to address these issues in practice while retaining soundness. We design and implement a new gradual type system, prototyped for expediency as a 'Safe' compilation mode for TypeScript. Our compiler achieves soundness by enforcing stricter static checks and embedding residual runtime checks in compiled code. It emits plain JavaScript that runs on stock virtual machines. Our main theorem is a simulation that ensures that the checks introduced by Safe TypeScript (1) catch any dynamic type error, and (2) do not alter the semantics of type-safe TypeScript code.

Implementations of the Transport Layer Security (TLS) protocol must handle a variety of protocol versions and extensions, authentication modes, and key exchange methods. Confusingly, each combination may prescribe a different message sequence between the client and the server. We address the problem of designing a robust composite state machine that correctly multiplexes between these different protocol modes. We systematically test popular open-source TLS implementations for state machine bugs and discover several critical security vulnerabilities that have lain hidden in these libraries for years, and have now finally been patched due to our disclosures. Several of these vulnerabilities, including the recently publicized FREAK flaw, enable a network attacker to break into TLS connections between authenticated clients and servers. We argue that state machine bugs stem from incorrect compositions of individually correct state machines. We present the first verified implementation of a composite TLS state machine in C that can be embedded into OpenSSL and accounts for all its supported cipher suites. Our attacks expose the need for the formal verification of core components in cryptographic protocol libraries, our implementation demonstrates that such mechanized proofs are within reach, even for mainstream TLS implementations.

Cloud computing sparked interest in Verifiable Computation protocols, which allow a weak client to securely outsource computations to remote parties. Recent work has dramatically reduced the client's cost to verify the correctness of their results, but the overhead to produce proofs remains largely impractical. Geppetto introduces complementary techniques for reducing prover overhead and increasing prover flexibility. With Multi QAPs, Geppetto reduces the cost of sharing state between computations (e.g, For MapReduce) or within a single computation by up to two orders of magnitude. Via a careful choice of cryptographic primitives, Geppetto's instantiation of bounded proof bootstrapping improves on prior bootstrapped systems by up to five orders of magnitude, albeit at some cost in universality. Geppetto also efficiently verifies the correct execution of proprietary (i.e, Secret) algorithms. Finally, Geppetto's use of energy-saving circuits brings the prover's costs more in line with the program's actual (rather than worst-case) execution time. Geppetto is implemented in a full-fledged, scalable compiler and runtime that consume LLVM code generated from a variety of source C programs and cryptographic libraries.

We present VC3, the first system that allows users to run distributed MapReduce computations in the cloud while keeping their code and data secret, and ensuring the correctness and completeness of their results. VC3 runs on unmodified Hadoop, but crucially keeps Hadoop, the operating system and the hyper visor out of the TCB, thus, confidentiality and integrity are preserved even if these large components are compromised. VC3 relies on SGX processors to isolate memory regions on individual computers, and to deploy new protocols that secure distributed MapReduce computations. VC3 optionally enforces region self-integrity invariants for all MapReduce code running within isolated regions, to prevent attacks due to unsafe memory reads and writes. Experimental results on common benchmarks show that VC3 performs well compared with unprotected Hadoop: VC3's average runtime overhead is negligible for its base security guarantees, 4.5% with write integrity and 8% with read/write integrity.

Relational program logics have been used for mechanizing formal proofs of various cryptographic constructions. With an eye towards scaling these successes towards end-to-end security proofs for implementations of distributed systems, we present RF*, a relational extension of F*, a general-purpose higher-order stateful programming language with a verification system based on refinement types. The distinguishing feature of F* is a relational Hoare logic for a higher-order, stateful, probabilistic language. Through careful language design, we adapt the F* typechecker to generate both classic and relational verification conditions, and to automatically discharge their proofs using an SMT solver. Thus, we are able to benefit from the existing features of F*, including its abstraction facilities for modular reasoning about program fragments. We evaluate RF* experimentally by programming a series of cryptographic constructions and protocols, and by verifying their security properties, ranging from information flow to unlinkability, integrity, and privacy. Moreover, we validate the design of RF* by formalizing in Coq a core probabilistic λ calculus and a relational refinement type system and proving the soundness of the latter against a denotational semantics of the probabilistic lambda λ calculus.

JavaScript's flexible semantics makes writing correct code hard and writing secure code extremely difficult. To address the former problem, various forms of gradual typing have been proposed, such as Closure and TypeScript. However, supporting all common programming idioms is not easy; for example, TypeScript deliberately gives up type soundness for programming convenience. In this paper, we propose a gradual type system and implementation techniques that provide important safety and security guarantees.

TLS was designed as a transparent channel abstraction to allow developers with no cryptographic expertise to protect their application against attackers that may control some clients, some servers, and may have the capability to tamper with network connections. However, the security guarantees of TLS fall short of those of a secure channel, leading to a variety of attacks. We show how some widespread false beliefs about these guarantees can be exploited to attack popular applications and defeat several standard authentication methods that rely too naively on TLS. We present new client impersonation attacks against TLS renegotiations, wireless networks, challenge-response protocols, and channel-bound cookies. Our attacks exploit combinations of RSA and Diffie-Hellman key exchange, session resumption, and renegotiation to bypass many recent countermeasures. We also demonstrate new ways to exploit known weaknesses of HTTP over TLS. We investigate the root causes for these attacks and propose new countermeasures. At the protocol level, we design and implement two new TLS extensions that strengthen the authentication guarantees of the handshake. At the application level, we develop an exemplary HTTPS client library that implements several mitigations, on top of a previously verified TLS implementation, and verify that their composition provides strong, simple application security.

Many tools allow programmers to develop applications in high-level languages and deploy them in web browsers via compilation to JavaScript. While practical and widely used, these compilers are ad hoc: no guarantee is provided on their correctness for whole programs, nor their security for programs executed within arbitrary JavaScript contexts. This paper presents a compiler with such guarantees. We compile an ML-like language with higher-order functions and references to JavaScript, while preserving all source program properties. Relying on type-based invariants and applicative bisimilarity, we show full abstraction: two programs are equivalent in all source contexts if and only if their wrapped translations are equivalent in all JavaScript contexts. We evaluate our compiler on sample programs, including a series of secure libraries.

TLS is possibly the most used protocol for secure communications, with a 18-year history of flaws and fixes, ranging from its protocol logic to its cryptographic design, and from the Internet standard to its diverse implementations. We develop a verified reference implementation of TLS 1.2. Our code fully supports its wire formats, ciphersuites, sessions and connections, re-handshakes and resumptions, alerts and errors, and data fragmentation, as prescribed in the RFCs; it interoperates with mainstream web browsers and servers. At the same time, our code is carefully structured to enable its modular, automated verification, from its main API down to computational assumptions on its cryptographic algorithms. Our implementation is written in F# and specified in F7. We present security specifications for its main components, such as authenticated stream encryption for the record layer and key establishment for the handshake. We describe their verification using the F7 typechecker. To this end, we equip each cryptographic primitive and construction of TLS with a new typed interface that captures its security properties, and we gradually replace concrete implementations with ideal functionalities. We finally typecheck the protocol state machine, and obtain precise security theorems for TLS, as it is implemented and deployed. We also revisit classic attacks and report a few new ones.

Abstract Distributed applications are difficult to program reliably and securely. Dependently typed functional languages promise to prevent broad classes of errors and vulnerabilities, and to enable program verification to proceed side-by-side with development. However, as recursion, effects, and rich libraries are added, using types to reason about programs, specifications, and proofs becomes challenging. We present F*, a full-fledged design and implementation of a new dependently typed language for secure distributed programming. Our language provides arbitrary recursion while maintaining a logically consistent core; it enables modular reasoning about state and other effects using affine types; and it supports proofs of refinement properties using a mixture of cryptographic evidence and logical proof terms. The key mechanism is a new kind system that tracks several sub-languages within F* and controls their interaction. F* subsumes two previous languages, F7 and Fine. We prove type soundness (with proofs mechanized in Coq) and logical consistency for F*. We have implemented a compiler that translates F* to .NET bytecode, based on a prototype for Fine. F* provides access to libraries for concurrency, networking, cryptography, and interoperability with C#, F#, and the other .NET languages. The compiler produces verifiable binaries with 60% code size overhead for proofs and types, as much as a 45x improvement over the Fine compiler, while still enabling efficient bytecode verification. We have programmed and verified nearly 50,000 lines of F* including new schemes for multi-party sessions; a zero-knowledge privacy-preserving payment protocol; a provenance-aware curated database; a suite of web-browser extensions verified for authorization properties; a cloud-hosted multi-tier web application with a verified reference monitor; the core F* typechecker itself; and programs translated to F* from other languages such as F7 and JavaScript.

Well-established dependently-typed languages like Agda and Coq provide reliable ways to build and check formal proofs. Several other dependently-typed languages such as Aura, ATS, Cayenne, Epigram, F*, F7, Fine, Guru, PCML5, and Ur also explore reliable ways to develop and verify programs. All these languages shine in their own regard, but their implementations do not themselves enjoy the degree of safety provided by machine-checked verification. We propose a general technique called self-certification that allows a typechecker for a suitably expressive language to be certified for correctness. We have implemented this technique for F*, a dependently typed language on the .NET platform. Self-certification involves implementing a typechecker for F* in F*, while using all the conveniences F* provides for the compiler-writer (e.g., partiality, effects, implicit conversions, proof automation, libraries). This typechecker is given a specification (in~F*) strong enough to ensure that it computes valid typing derivations. We obtain a typing derivation for the core typechecker by running it on itself, and we export it to Coq as a type-derivation certificate. By typechecking this derivation (in Coq) and applying the F* metatheory (also mechanized in Coq), we conclude that our type checker is correct. Once certified in this manner, the F* typechecker is emancipated from Coq.

We narrow the gap between concrete implementations of cryptographic protocols and their verified models. We develop and verify a small functional implementation of the Transport Layer Security protocol (TLS 1.0). We make use of the same executable code for interoperability testing against mainstream implementations for automated symbolic cryptographic verification and automated computational cryptographic verification. We rely on a combination of recent tools and also develop a new tool for extracting computational models from executable code. We obtain strong security guarantees for TLS as used in typical deployments.

Type systems are effective tools for verifying the security of cryptographic programs. They provide automation, modularity and scalability, and have been applied to large security protocols. However, they traditionally rely on abstract assumptions on the underlying cryptographic primitives, expressed in symbolic models. Cryptographers usually reason on security assumptions using lower level, computational models that precisely account for the complexity and success probability of attacks. These models are more realistic, but they are harder to formalize and automate. We present the first modular automated program verification method based on standard cryptographic assumptions. We show how to verify ideal functionalities and protocols written in ML by typing them against new cryptographic interfaces using F7, a refinement type checker coupled with an SMT-solver. We develop a probabilistic core calculus for F7 and formalize its type safety in Coq.

We develop a flexible information-flow type system for a range of encryption primitives, precisely reflecting their diverse functional and security features. Our rules enable encryption, blinding, homomorphic computation, and decryption, with selective key re-use for different types of payloads. We show that, under standard cryptographic assumptions, any well-typed probabilistic program using encryptions is secure that is, computationally non-interferent) against active adversaries, both for confidentiality and integrity. We illustrate our approach using %on classic schemes such as ElGamal and Paillier encryption. We present two applications of cryptographic verification by typing: (1) private search on data streams; and (2) the bootstrapping part of Gentry's fully homomorphic encryption. We provide a prototype typechecker for our system.

Distributed applications are difficult to program reliably and securely. Dependently typed functional languages promise to prevent broad classes of errors and vulnerabilities, and to enable program verification to proceed side-by-side with development. However, as recursion, effects, and rich libraries are added, using types to reason about programs, specifications, and proofs becomes challenging.

We present the design and implementation of a typechecker for verifying security properties of the source code of cryptographic protocols and access control mechanisms. The underlying type theory is a λ-calculus equipped with refinement types for expressing pre- and post-conditions within first-order logic. We derive formal cryptographic primitives and represent active adversaries within the type theory. Well-typed programs enjoy assertion-based security properties, with respect to a realistic threat model including key compromise. The implementation amounts to an enhanced typechecker for the general-purpose functional language F # ; typechecking generates verification conditions that are passed to an SMT solver. We describe a series of checked examples. This is the first tool to verify authentication properties of cryptographic protocols by typechecking their source code.

We propose a method for verifying the security of protocol implementations. Our method is based on declaring and enforcing invariants on the usage of cryptography. We develop cryptographic libraries that embed a logic model of their cryptographic structures and that specify preconditions and postconditions on their functions so as to maintain their invariants. We present a theory to justify the soundness of modular code verification via our method.

We present a declarative authorization language. Policies and credentials are expressed using predicates defined by logical clauses, in the style of constraint logic programming. Access requests are mapped to logical authorization queries, consisting of predicates and constraints combined by conjun ctions, disjunctions, and negations. Access is granted if the query succeeds against the current database of clauses. Predicates ascribe rights to particular principals, with flexible support for delegation and revocation. At the discretion of the delegator, delegated rights can be further delegated, either to a fixed depth, or arbitrarily deeply. Our language strikes a careful balance between syntactic and semantic simplicity, policy expressiveness, and execution efficiency. The syntax is close to natural language, and the semantics consists of just three deduction rules. The language can express many common policy idioms using constraints, controlled delegation, recursive predicates, and negated queries. We describe an execution strategy based on translation to Datalog with Constraints, and table-based resolution. We show that this execution strategy is sound, complete, and always terminates, despite recursion and negation, as long as simple syntactic conditions are met.

We enforce information flow policies in programs that run at multiple locations, with diverse levels of security.

We present the design and implementation of a compiler that, given high-level multiparty session descriptions, generates custom cryptographic protocols. Our sessions specify pre-arranged patterns of message exchanges and data accesses between distributed participants. They provide each participant with strong security guarantees for all their messages. Our compiler generates code for sending and receiving these messages, with cryptographic operations and checks, in order to enforce these guarantees against any adversary that may control both the network and some session participants. We verify that the generated code is secure by relying on a recent type system for cryptography. Most of the proof is performed by mechanized type checking and does not rely on the correctness of our compiler.We obtain the strongest session security guarantees to date in a model that captures the executable details of protocol code. We illustrate and evaluate our approach on a series of protocols inspired by web services.

We intend to narrow the gap between concrete implementations of cryptographic protocols and their verified models. We develop and verify a small functional implementation of the Transport Layer Security protocol (TLS 1.0). We make use of the same executable code for interoperability testing against mainstream implementations, for automated symbolic cryptographic verification, and for automated computational cryptographic verification. We rely on a combination of recent tools, and we also develop a new tool for extracting computational models from executable code. We obtain strong security guarantees for TLS as used in typical deployments.

We describe reference implementations for selected configurations of the user authentication protocol defined by the Information Card Profile V1.0. Our code can interoperate with existing implementations of the roles of the protocol (client, identity provider, and relying party). We derive formal proofs of security properties for our code using an automated theorem prover. Hence, we obtain the most substantial examples of verified implementations of cryptographic protocols to date, and the first for any federated identity-management protocols. Moreover, we present a tool that downloads security policies from services and identity providers and compiles them to a verifiably secure client proxy.

We present the design and implementation of a typechecker for verifying security properties of the source code of cryptographic protocols and access control mechanisms. The underlying type theory is a λ-calculus equipped with refinement types for expressing pre- and post-conditions within first-order logic. We derive formal cryptographic primitives and represent active adversaries within the type theory. Well-typed programs enjoy assertion-based security properties, with respect to a realistic threat model including key compromise. The implementation amounts to an enhanced typechecker for the general purpose functional language F#; typechecking generates verification conditions that are passed to an SMT solver. We describe a series of checked examples. This is the first tool to verify authentication properties of cryptographic protocols by typechecking their source code.

In language-based security, confidentiality and integrity policies conveniently specify the permitted flows of information between different parts of a program with diverse levels of trust. These policies enable a simple treatment of security, and they can often be verified by typing. However, their enforcement in concrete systems involves delicate compilation issues.

Distributed applications can be structured as parties that exchange messages according to some pre-arranged communication patterns. These sessions (or contracts, or protocols) simplify distributed programming: when coding a role for a given session, each party just has to follow the intended messag e flow, under the assumption that the other parties are also compliant. In an adversarial setting, remote parties may not be trusted to play their role. Hence, defensive implementations also have to monitor one another, in order to detect any deviation from the assigned roles of a session. This task involves low-level coding below session abstractions, thus giving up most of their benefits. We explore language-based support for sessions. We extend the ML language with session types that express flows of messages between roles, such that well-typed programs always play their roles. We compile session type declarations to cryptographic communication protocols that can shield programs from any low-level attempt by coalitions of remote peers to deviate from their roles. Our main result is that, when reasoning about programs that use our session implementation, one can safely assume that all session peers comply with their roles – without trusting their remote implementations.

WS-SecurityPolicy is a declarative language for configuring web services security mechanisms. We describe a formal semantics for WS-SecurityPolicy and propose a more abstract language for specifying secure links between web services and their clients. We present the architecture and implementation of tools that (1) compile policy files from link specifications, and (2) verify by invoking a theorem prover whether a set of policy files run by any number of senders and receivers correctly implements the goals of a link specification, in spite of active attackers. Policy-driven web services implementations are prone to the usual subtle vulnerabilities associated with cryptographic protocols; our tools help prevent such vulnerabilities. We can verify policies when first compiled from link specifications, and also re-verify policies against their original goals after any modifications during deployment. Moreover, we present general security theorems for all configurations that rely on compiled policies.

We present an architecture and tools for verifying implementations of security protocols. Our implementations can run with both concrete and symbolic implementations of cryptographic algorithms. The concrete implementation is for production and interoperability testing. The symbolic implementation is for debugging and formal verification. We develop our approach for protocols written in F#, a dialect of ML, and verify them by compilation to ProVerif, a resolution-based theorem prover for cryptographic protocols. We establish the correctness of this compilation scheme, and we illustrate our approach with protocols for Web Services security.

We present a declarative authorization language that strikes a careful balance between syntactic and semantic simplicity, policy expressiveness, and execution efficiency. The syntax is close to natural language, and the semantics consists of just three deduction rules. The language can express many common policy idioms using constraints, controlled delegation, recursive predicates, and negated queries. We describe an execution strategy based on translation to datalog with constraints, and table-based resolution. We show that this execution strategy is sound, complete, and always terminates, despite recursion and negation, as long as simple syntactic conditions are met.

Distributed applications can be structured as parties that exchange messages according to some pre-arranged communication patterns. These sessions (or contracts, or protocols) simplify distributed programming: when coding a role for a given session, each party just has to follow the intended message flow, under the assumption that the other parties are also compliant. In an adversarial setting, remote parties may not be trusted to play their role. Hence, defensive implementations also have to monitor one another, in order to detect any deviation from the assigned roles of a session. This task involves low-level coding below session abstractions, thus giving up most of their benefits. We explore language-based support for sessions. We extend the ML language with session types that express flows of messages between roles, such that well-typed programs always play their roles. We compile session type declarations to cryptographic communication protocols that can shield programs from any low-level attempt by coalitions of remote peers to deviate from their roles. Our main result is that, when reasoning about programs that use our session implementation, one can safely assume that all session peers comply with their roles-without trusting their remote implementations.

We consider the problem of statically verifying the conformance of the code of a system to an explicit authorization policy. In a distributed setting, some part of the system may be compromised, that is, some nodes of the system and their security credentials may be under the control of an attacker. To help predict and bound the impact of such partial compromise, we advocate logic-based policies that explicitly record dependencies between principals. We propose a conformance criterion, safety despite compromised principals, such that an invalid authorization decision at an uncompromised node can arise only when nodes on which the decision logically depends are compromised. We formalize this criterion in the setting of a process calculus, and present a verification technique based on a type system. Hence, we can verify policy conformance of code that uses a wide range of the security mechanisms found in distributed systems, ranging from secure channels down to cryptographic primitives, including encryption and public-key signatures.

JFK is a recent, attractive protocol for fast key establishment as part of securing IP communication. In this paper, we formally analyze this protocol in the applied pi calculus (partly in terms of observational equivalences and partly with the assistance of an automatic protocol verifier). We treat JFK's core security properties and also other properties that are rarely articulated and rigorously studied, such as plausible deniability and resistance to denial-of-service attacks. In the course of this analysis, we found some ambiguities and minor problems, such as limitations in identity protection, but we mostly obtain positive results about JFK. For this purpose, we develop ideas and techniques that should be more generally useful in the specification and verification of security protocols.

We address the problem of securing sequences of SOAP messages exchanged between web services and their clients. The WS-Security standard defines basic mechanisms to secure SOAP traffic, one message at a time. For typical web services, however, using WS-Security independently for each message is rather inefficient; moreover, it is often important to secure the integrity of a whole session, as well as each message. To these ends, recent specifications provide further SOAP-level mechanisms. WS-SecureConversation defines security contexts , which can be used to secure sessions between two parties. WS-Trust specifies how security contexts are issued and obtained. We develop a semantics for the main mechanisms of WS-Trust and WS-SecureConversation, expressed as a library for TulaFale, a formal scripting language for security protocols. We model typical protocols relying on these mechanisms and automatically prove their main security properties. We also informally discuss some pitfalls and limitations of these specifications.

Distributed systems and applications are often expected to enforce high-level authorization policies. To this end, the code for these systems relies on lower-level security mechanisms such as digital signatures, local ACLs, and encrypted communications. In principle, authorization specifications can be separated from code and carefully audited. Logic programs in particular can express policies in a simple, abstract manner. We consider the problem of checking whether a distributed implementation based on communication channels and cryptography complies with a logical authorization policy. We formalize authorization policies and their connection to code by embedding logical predicates and claims within a process calculus. We formulate policy compliance operationally by composing a process model of the distributed system with an arbitrary opponent process. Moreover, we propose a dependent type system for verifying policy compliance of implementation code. Using Datalog as an authorization logic, we show how to type several examples using policies and present a general schema for compiling policies.

We present an architecture and tools for verifying implementations of security protocols. Our implementations can run with both concrete and symbolic implementations of cryptographic algorithms. The concrete implementation is for production and interoperability testing. The symbolic implementation is for debugging and formal verification. We develop our approach for protocols written in F#, a dialect of ML, and verify them by compilation to ProVerif a resolution-based theorem prover for cryptographic protocols. We establish the correctness of this compilation scheme, and we illustrate our approach with protocols for Web services security

WS-SecurityPolicy is a declarative configuration language for driving web services security mechanisms. We describe a formal semantics for WS-SecurityPolicy, and propose a more abstract link language for specifying the security goals of web services and their clients. Hence, we present the architecture and implementation of fully automatic tools that (1) compile policy files from link specifications, and (2) verify by invoking a theorem prover whether a set of policy files run by any number of senders and receivers correctly implements the goals of a link specification, in spite of active attackers. Policy-driven web services implementations are prone to the usual subtle vulnerabilities associated with cryptographic protocols; our tools help prevent such vulnerabilities, as we can verify policies when first compiled from link specifications, and also re-verify policies against their original goals after any modifications during deployment.

This work addresses the problem of layer 2 topology discovery. Current techniques concentrate on using SNMP to query information from Ethernet switches. In contrast, we present a technique that infers the Ethernet (layer 2) topology without assistance from the network elements by injecting suitable probe packets from the end-systems and observing where they are delivered. We describe the algorithm, formally characterize its correctness and completeness, and present our implementation and experimental results. Performance results show that although originally aimed at the home and small office the techniques scale to much larger networks.

We consider the problem of specifying and verifying cryptographic security protocols for XML web services. The security specification WS-Security describes a range of XML security tokens, such as username tokens, public-key certificates, and digital signature blocks, amounting to a flexible vocabulary for expressing protocols. To describe the syntax of these tokens, we extend the usual XML data model with symbolic representations of cryptographic values. We use predicates on this data model to describe the semantics of security tokens and of sample protocols distributed with the Microsoft WSE implementation of WS-Security. By embedding our data model within Abadi and Fournet's applied pi calculus, we formulate and prove security properties with respect to the standard Dolev-Yao threat model. Moreover, we informally discuss issues not addressed by the formal model. To the best of our knowledge, this is the first approach to the specification and verification of security protocols based on a faithful account of the XML wire format.

Polyphonic C ♯ is an extension of the C ♯ language with new asynchronous concurrency constructs, based on the join calculus. We describe the design and implementation of the language and give examples of its use in addressing a range of concurrent programming problems.

Stack inspection is a security mechanism implemented in runtimes such as the JVM and the CLR to accommodate components with diverse levels of trust. Although stack inspection enables the fine-grained expression of access control policies, it has rather a complex and subtle semantics. We present a formal semantics and an equational theory to explain how stack inspection affects program behavior and code optimisations. We discuss the security properties enforced by stack inspection, and also consider variants with stronger, simpler properties.

Stack inspection is a security mechanism implemented in runtimes such as the JVM and the CLR to accommodate components with diverse levels of trust. Although stack inspection enables the fine-grained expression of access control policies, it has rather a complex and subtle semantics. We present a formal semantics and an equational theory to explain how stack inspection affects program behaviour and code optimisations. We discuss the security properties enforced by stack inspection, and also consider variants with stronger, simpler properties.

We study the interaction of the "new" construct with a rich but common form of (first-order) communication. This interaction is crucial in security protocols, which are the main motivating examples for our work; it also appears in other programming-language contexts. Specifically, we introduce a simple, general extension of the pi calculus with value passing, primitive functions, and equations among terms. We develop semantics and proof techniques for this extended language and apply them in reasoning about some security protocols.

Adopting a programming-language perspective, we study the problem of implementing authentication in a distributed system. We define a process calculus with constructs for authentication and show how this calculus can be translated to a lower-level language using marshaling, multiplexing, and cryptographic protocols. Authentication serves for identitybased security in the source language and enables simplifications in the translation. We reason about correctness relying on the concepts of observational equivalence and full abstraction.

Communications processing is an important part of distributed language systems with facilities such as RPC (remote procedure call) and RMI (remote method invocation). For security, messages may require cryptographic operations in addition to ordinary marshaling. We investigate a method for wrapping communications processing around an entity with secure local communication, such as a single machine or a protected network. The wrapping extends security properties of local communication to distributed communication. We formulate and analyze the method within a process calculus.

Communication in distributed systems often relies on useful abstractions such as channels, remote procedure calls, and remote method invocations. The implementations of these abstractions sometimes provide security properties, in particular through encryption. In this paper we study those security properties, focusing on channel abstractions. We introduce a simple high-level language that includes constructs for creating and using secure channels. The language is a variant of the join-calculus and belongs to the same family as the pi-calculus. We show how to translate the high-level language into a lower-level language that includes cryptographic primitives. In this translation, we map communication on secure channels to encrypted communication on public channels. We obtain a correctness theorem for our translation; this theorem implies that one can reason about programs in the high-level language without mentioning the subtle cryptographic protocols used in their lower-level implementation.

By adding reflexion to the chemical machine of Berry and Boudol, we obtain a formal model of concurrency that is consistent with mobility and distribution. Our model provides the foundations of a programming language with functional and object-oriented features. It can also be seen as a process calculus, the join-calculus, which we prove equivalent to the π-calculus of Milner, Parrow and Walker.