The objective of the 3rd ACM Workshop on Information Sharing and Collaborative Security is to advance the scientific foundations for sharing security-related data. Improving information sharing remains an important theme in the computer security community. A number of new sharing communities have been formed. Also, so called "threat intelligence" originating from open, commercial or governmental sources has by now become an important, commonly used tool for detecting and mitigating attacks in organizations. Security vendors are offering novel technologies for sharing, managing and consuming such data. The OASIS Technical Committee for Cyber Threat Intelligence (CTI) is creating a standard for structured sharing of information. This is the largest TC within OASIS attesting to the broad interest in the topic. As progress in real-life deployment of information sharing makes clear, the creation, analysis, sharing, and effective use of security data continues to raise intriguing technical problems. Addressing these problems will be critical for the ultimate success of sharing efforts and will benefit greatly from the diverse knowledge and techniques the scientific community brings. The 3rd ACM Workshop on Information Sharing and Collaborative Security (WISCS'16) brings together experts and practitioners from academia, industry, and government to present innovative research, case studies, and legal and policy issues. WISCS'16 is held in Vienna, Austria on October 24, 2016 in conjunction with the 23rd ACM Conference on Computer and Communications Security (ACM CCS 2016).

The mission of the 2nd ACM Workshop on Information Sharing and Collaborative Security is to advance the scientific foundations for sharing threat and security-related data among organizations. The call for better information sharing continues to be an important theme in the computer security community and with policy makers. The expectation is that sharing will significantly improve the ability of defenders to detect and mitigate attacks on their networks and systems. Several commercial offerings by security vendors that enable automated sharing have gone live and existing communities have begun to use them. Sharing of security and threat data at scale raises a number of interesting research questions, including on how to best collect, analyze and make use of these data to address important security concerns. In addition sharing raises privacy and other policy issues that need to be addressed.

Sharing of security related information is believed to greatly enhance the ability of organizations to defend themselves against sophisticated attacks. If one organization detects a breach the automated sharing of observed security indicators (such as IP addresses, domain names etc.) provide valuable, actionable information to others. Through analyzing shared data it seems possible to get much better insights into emerging attacks. Sharing higher level intelligence about campaigns, threat actors and mitigations is also of great interest. Both in the US and the EU there are major efforts underway to strengthen information sharing. Yet there are a number of technical and policy challenges to realizing this vision. The First ACM Workshop on Information Sharing and Collaborative Security (WISCS 2014) aims to bring together experts and practitioners from academia, industry and government to present innovative research, case studies, and legal and policy issues. WISCS 2014 is held in Scottsdale, Arizona, USA on Nov. 3, 2014 in conjunction with 21st ACM Conference on Computer and Communications Security (CCS 2014).

In this paper we give a new signature algorithm that allows for controlled changes to the signed data. The change operations we study are removal of subdocuments (redaction), pseudonymization, and gradual deidentification of hierarchically structured data. These operations are applicable in a number of practically relevant application scenarios, including the release of previously classified government documents, privacy-aware management of audit-log data, and the release of tables of health records. When applied directly to redaction, our algorithm improves on [18] by reducing significantly the overhead of cryptographic information that has to be stored with the original data.

The use of passwords is a major point of vulnerability in computer security, as passwords are often easy to guess by automated programs running dictionary attacks. Passwords remain the most widely used authentication method despite their well-known security weaknesses. User authentication is clearly a practical problem. From the perspective of a service provider this problem needs to be solved within real-world constraints such as the available hardware and software infrastructures. From a user's perspective user-friendliness is a key requirement.In this paper we suggest a novel authentication scheme that preserves the advantages of conventional password authentication, while simultaneously raising the costs of online dictionary attacks by orders of magnitude. The proposed scheme is easy to implement and overcomes some of the difficulties of previously suggested methods of improving the security of user authentication schemes.Our key idea is to efficiently combine traditional password authentication with a challenge that is very easy to answer by human users, but is (almost) infeasible for automated programs attempting to run dictionary attacks. This is done without affecting the usability of the system. The proposed scheme also provides better protection against denial of service attacks against user accounts.

Distribution of content, such as music, remains one of the main drivers of P2P development. Subscription-based services are currently receiving a lot of attention from the content industry as a viable business model for P2P content distribution. One of the main problems that such services face is that users may choose to redistribute content outside the community of subscribers, thereby facilitating large-scale piracy. Digital Rights Management (DRM) systems typically employ tamper resistance techniques to control this risk. We propose a system architecture that uses economic incentives instead of tamper resistance to motivate users to keep the content within the subscription community. The key technical contribution we make is to integrate a P2P file sharing service with an escrow service that reliably "pays" the party that is serving up the content. The payment itself can be realized in a number of ways, using "actual" money or bonus points such as frequent flyer miles.Moreover, our architecture facilitates trust between two unacquainted parties by offloading risk to a trusted third party, which can acquire a revenue stream by assuming this risk. To implement the escrow service securely we use cryptographic techniques, such as encryption, hashing, and error correcting codes. Our system motivates users to serve up content of high quality and verifies that users only share legitimate content and not spam, viruses or content that is not part of the subscription. We thereby address other important security concerns in P2P systems and problems like the free-rider phenomenon.

The area of "computing with encrypted data" has been studied by numerous authors in the past twenty years since it is fundamental to understanding properties of encryption and it has many practical applications. The related fundamental area of "secure function evaluation" has been studied since the mid 80's. In its basic two-party case, two parties (Alice and Bob) evaluate a known circuit over private inputs (or a private input and a private circuit). Much attention has been paid to the important issue of minimizing rounds of computation in this model. Namely, the number of communication rounds in which Alice and Bob need to engage in to evaluate a circuit on encrypted data securely. Advancements in these areas have been recognized as open problems and have remained open for a number of years. In this paper we give a one round, and thus round optimal, protocol for secure evaluation of circuits which is in polynomial time for NC/sup 1/ circuits. The protocol involves an input party sending encrypted input to a second party, a cryptocomputer, which evaluates the circuit (or a known circuit over its additional private input) non-interactively, securely and obliviously, and provides the output to the input party without learning it. This improves on previous (general) results that are specialized to the case of NC/sup 1/ circuits and require a constant number of communication rounds. We further suggest applications to network and mobile computing.

There are at least two major security challenges in mobile code distributed systems. First hosts have to be protected from potentially malicious actions of mobile code they are executing. Many techniques are known which address this problem. Second mobile agents themselves have to be protected against malicious hosts. Satisfactory ways to deal with the second problem are necessary features for many of the (security-sensitive) tasks mobile agent (MA) systems are envisioned for, e.g., in e-commerce applications where a shopping agent is sent out on the Internet, vendors have a high incentive in tampering with these agents. The key point is is that the originator of the agent needs to have sound guarantees that the results an agent brings back are correct. Why else should he send out the agent in the first place?.

Mobile code technology has become a driving force for recent advances in distributed systems. The concept of the mobility of executable code raises major security problems. In this paper, we deal with the protection of mobile code from possibly malicious hosts. We conceptualize the specific cryptographic problems posed by mobile code, and we are able to provide a solution for some of these problems. We present techniques to achieve "non-interactive evaluation with encrypted functions" in certain cases and give a complete solution for this problem in important instances. We further present a way in which an agent might securely perform a cryptographic primitive-digital signing-in an untrusted execution environment. Our results are based on the use of homomorphic encryption schemes and function composition techniques.

The polynomial time algorithm of Lenstra, Lenstra, and Lovasz (1982) for factoring integer polynomials and variants thereof have been widely used to show that various computational problems in number theory have polynomial time solutions. Among them is the problem of factoring polynomials over algebraic number fields, which is used itself as a major subroutine for several other algorithms. Although a theoretical breakthrough, algorithms based on factorization of polynomials are notoriously slow and hard to implement, with running times ranging between O(n/sup 12/) and O(n/sup 18/) depending on which variant of the lattice basis reduction is used. Here, n is an upper bound for the maximum of the degrees and the bit-lengths of the coefficients of the polynomials involved. On the other hand, in many situations one does not need the full power of factorization, so one may ask whether there exist faster algorithms in these cases. In this paper we develop more efficient Monte Carlo algorithms to decide certain properties of roots of integer polynomials, without factoring them. Such problems arise, e.g., when solving systems of algebraic equations. Our methods applied to this situation thus give information about the solutions of such systems of equations.