he Frankfurt Book Fair, or in its native German, the Frankfurter Buchmesse, restarted in the aftermath of the Second World War as a symbol of post-war reconstruction, an engine of book industry capitalism, and a celebration of bookish cosmopolitanism. But by the late 1960s, it had become a contested site, encountering the revolutionary fervor of the period. In 1967, publishers had joined students in signing an anti-conglomerate declaration against the publisher Springer (which owned the tabloid newspaper Bild) on the grounds that too much power in one media group was dangerous. 1 In 1968, the organizers of the Buchmesse anticipated further trouble, particularly after the uprisings of the Prague Spring. "House rules" ("Hausordnung") were introduced, allowing the organizers to close the Fair to the public if the peace ("Messefrieden") was threatened, and requiring events (including receptions, press conferences, and musical performances) to have written approval. 2 Police were brought into the Fair and placed on standby with water cannons; the Fair was informally dubbed the "Polizeimesse" ("police Fair"). The route to an event celebrating the publication of a book by the German nance minister was blocked by protestors, with the latter making fun of the demand to let police through with the words "Macht aus Polizisten gute Sozialisten" ("turn policemen into good socialists"). 3 Some publishers reacted angrily to the Fair's authoritarianism, and threatened to stay away the following year if the "Herr im Haus" ("King of the Castle") approach from the Buchmesse continued. 4
A landmark security property of smart contracts is liquidity: in a non-liquid contract, it may happen that some funds remain frozen. The relevance of this issue is witnessed by a recent liquidity attack to the Ethereum Parity Wallet, which has frozen ∼160M USD within the contract, making this sum unredeemable by any user. We address the problem of verifying liquidity of Bitcoin contracts. Focussing on BitML, a contracts DSL with a computationally sound compiler to Bitcoin, we study various notions of liquidity. Our main result is that liquidity of BitML contracts is decidable, in all the proposed variants. To prove this, we first transform the infinite-state semantics of BitML into a finite-state one, which focusses on the behaviour of any given set of contracts, abstracting the context moves. With respect to the chosen contracts, this abstraction is sound and complete. Our decision procedure for liquidity is then based on model-checking the finite space of states of the abstraction.
We address the problem of how to "obfuscate" texts by removing stylistic clues which can identify authorship, whilst preserving (as much as possible) the content of the text. In this paper we combine ideas from "generalised differential privacy" and machine learning techniques for text processing to model privacy for text documents. We define a privacy mechanism that operates at the level of text documents represented as "bags-of-words" - these representations are typical in machine learning and contain sufficient information to carry out many kinds of classification tasks including topic identification and authorship attribution (of the original documents). We show that our mechanism satisfies privacy with respect to a metric for semantic similarity, thereby providing a balance between utility, defined by the semantic content of texts, with the obfuscation of stylistic clues. We demonstrate our implementation on a "fan fiction" dataset, confirming that it is indeed possible to disguise writing style effectively whilst preserving enough information and variation for accurate content classification tasks.
We present the foundations for a new dynamic information flow control (IFC) parallel runtime system, LIO _PAR . To our knowledge, LIO _PAR is the first dynamic language-level IFC system to (1) support deterministic parallel thread execution and (2) eliminate both internal- and external-timing covert channels that exploit the runtime system. Most existing IFC systems are vulnerable to external timing attacks because they are built atop vanilla runtime systems that do not account for security—these runtime systems allocate and reclaim shared resources (e.g., CPU-time and memory) fairly between threads at different security levels. While such attacks have largely been ignored—or, at best, mitigated—we demonstrate that extending IFC systems with parallelism leads to the internalization of these attacks. Our IFC runtime system design addresses these concerns by hierarchically managing resources—both CPU-time and memory—and making resource allocation and reclamation explicit at the language-level. We prove that LIO _PAR is secure, i.e., it satisfies progress- and timing-sensitive non-interference, even when exposing clock and heap-statistics APIs.
Checked C is a new effort working toward a memory-safe C. Its design is distinguished from that of prior efforts by truly being an extension of C: Every C program is also a Checked C program. Thus, one may make incremental safety improvements to existing codebases while retaining backward compatibility. This paper makes two contributions. First, to help developers convert existing C code to use so-called checked (i.e., safe) pointers, we have developed a preliminary, automated porting tool. Notably, this tool takes advantage of the flexibility of Checked C's design: The tool need not perfectly classify every pointer, as required of prior all-or-nothing efforts. Rather, it can make a best effort to convert more pointers accurately, without letting inaccuracies inhibit compilation. However, such partial conversion raises the question: If safety violations can still occur, what sort of advantage does using Checked C provide? We draw inspiration from research on migratory typing to make our second contribution: We prove a blame property that renders so-called checked regions blameless of any run-time failure. We formalize this property for a core calculus and mechanize the proof in Coq.
This paper investigates the effect of bucketing in security against timing channel attacks. Bucketing is a technique proposed to mitigate timing-channel attacks by restricting a system’s outputs to only occur at designated time intervals, and has the effect of reducing the possible timing-channel observations to a small number of possibilities. However, there is little formal analysis on when and to what degree bucketing is effective against timing-channel attacks. In this paper, we show that bucketing is in general insufficient to ensure security. Then, we present two conditions that can be used to ensure security of systems against adaptive timing channel attacks. The first is a general condition that ensures that the security of a system decreases only by a limited degree by allowing timing-channel observations, whereas the second condition ensures that the system would satisfy the first condition when bucketing is applied and hence becomes secure against timing-channel attacks. A main benefit of the conditions is that they allow separation of concerns whereby the security of the regular channel can be proven independently of concerns of side-channel information leakage, and certain conditions are placed on the side channel to guarantee the security of the whole system. Further, we show that the bucketing technique can be applied compositionally in conjunction with the constant-time-implementation technique to increase their applicability. While we instantiate our contributions to timing channel and bucketing, many of the results are actually quite general and are applicable to any side channels and techniques that reduce the number of possible observations on the channel.
With the proliferation of contactless applications, obtaining reliable information about distance is becoming an important security goal, and specific protocols have been designed for that purpose. These protocols typically measure the round trip time of messages and use this information to infer a distance. Formal methods have proved their usefulness when analysing standard security protocols such as confidentiality or authentication protocols. However, due to their abstract communication model, existing results and tools do not apply to distance bounding protocols. In this paper, we consider a symbolic model suitable to analyse distance bounding protocols, and we propose a new procedure for analysing (a bounded number of sessions of) protocols in this model. The procedure has been integrated in the Akiss tool and tested on various distance bounding and payment protocols (e.g. MasterCard, NXP).
