Secure Audit Logs with Verifiable Excerpts

Log files are the primary source of information when the past peration of a computing system needs to be determined. Keeping correct and accurate log files is importantfor after-the-fact forensics, as well as for system administration, maintenance, and auditing. Therefore, a line of research has emerged on how to cryptographically protect the integrity of log files even against intruders who gain control of the logging machine. We contribute to this line of research by devising a scheme where one can verify integrity not only of the log file as a whole, but also of excerpts. This is helpful in various scenarios, including cloud provider auditing

Advanced Cryptographic Techniques for Protecting Log Data

This thesis examines cryptographic techniques providing security for computer log files. It focuses on ensuring authenticity and integrity, i.e. the properties of having been created by a specific entity and being unmodified. Confidentiality, the property of being unknown to unauthorized entities, will be considered, too, but with less emphasis. Computer log files are recordings of actions performed and events encountered in computer systems. While the complexity of computer systems is steadily growing, it is increasingly difficult to predict how a given system will behave under certain conditions, or to retrospectively reconstruct and explain which events and conditions led to a specific behavior. Computer log files help to mitigate the problem of retracing a system’s behavior retrospectively by providing a (usually chronological) view of events and actions encountered in a system. Authenticity and integrity of computer log files are widely recognized security requirements, see e.g. [Latham, ed., "Department of Defense Trusted Computer System Evaluation Criteria", 1985, p. 10], [Kent and Souppaya, "Guide to Computer Security Log Management", NIST Special Publication 800-92, 2006, Section 2.3.2], [Guttman and Roback, "An Introduction to Computer Security: The NIST Handbook", superseded NIST Special Publication 800-12, 1995, Section 18.3.1], [Nieles et al., "An Introduction to Information Security" , NIST Special Publication 800-12, 2017, Section 9.3], [Common Criteria Editorial Board, ed., "Common Criteria for Information Technology Security Evaluation", Part 2, Section 8.6]. Two commonly cited ways to ensure integrity of log files are to store log data on so-called write-once-read-many-times (WORM) drives and to immediately print log records on a continuous-feed printer. This guarantees that log data cannot be retroactively modified by an attacker without physical access to the storage medium. However, such special-purpose hardware may not always be a viable option for the application at hand, for example because it may be too costly. In such cases, the integrity and authenticity of log records must be ensured via other means, e.g. with cryptographic techniques. Although these techniques cannot prevent the modification of log data, they can offer strong guarantees that modifications will be detectable, while being implementable in software. Furthermore, cryptography can be used to achieve public verifiability of log files, which may be needed in applications that have strong transparency requirements. Cryptographic techniques can even be used in addition to hardware solutions, providing protection against attackers who do have physical access to the logging hardware, such as insiders. Cryptographic schemes for protecting stored log data need to be resilient against attackers who obtain control over the computer storing the log data. If this computer operates in a standalone fashion, it is an absolute requirement for the cryptographic schemes to offer security even in the event of a key compromise. As this is impossible with standard cryptographic tools, cryptographic solutions for protecting log data typically make use of forward-secure schemes, guaranteeing that changes to log data recorded in the past can be detected. Such schemes use a sequence of authentication keys instead of a single one, where previous keys cannot be computed efficiently from latter ones. This thesis considers the following requirements for, and desirable features of, cryptographic logging schemes: 1) security, i.e. the ability to reliably detect violations of integrity and authenticity, including detection of log truncations, 2) efficiency regarding both computational and storage overhead, 3) robustness, i.e. the ability to verify unmodified log entries even if others have been illicitly changed, and 4) verifiability of excerpts, including checking an excerpt for omissions. The goals of this thesis are to devise new techniques for the construction of cryptographic schemes that provide security for computer log files, to give concrete constructions of such schemes, to develop new models that can accurately capture the security guarantees offered by the new schemes, as well as to examine the security of previously published schemes. This thesis demands that cryptographic schemes for securely storing log data must be able to detect if log entries have been deleted from a log file. A special case of deletion is log truncation, where a continuous subsequence of log records from the end of the log file is deleted. Obtaining truncation resistance, i.e. the ability to detect truncations, is one of the major difficulties when designing cryptographic logging schemes. This thesis alleviates this problem by introducing a novel technique to detect log truncations without the help of third parties or designated logging hardware. Moreover, this work presents new formal security notions capturing truncation resistance. The technique mentioned above is applied to obtain cryptographic logging schemes which can be shown to satisfy these notions under mild assumptions, making them the first schemes with formally proven truncation security. Furthermore, this thesis develops a cryptographic scheme for the protection of log files which can support the creation of excerpts. For this thesis, an excerpt is a (not necessarily contiguous) subsequence of records from a log file. Excerpts created with the scheme presented in this thesis can be publicly checked for integrity and authenticity (as explained above) as well as for completeness, i.e. the property that no relevant log entry has been omitted from the excerpt. Excerpts provide a natural way to preserve the confidentiality of information that is contained in a log file, but not of interest for a specific public analysis of the log file, enabling the owner of the log file to meet confidentiality and transparency requirements at the same time. The scheme demonstrates and exemplifies the technique for obtaining truncation security mentioned above. Since cryptographic techniques to safeguard log files usually require authenticating log entries individually, some researchers [Ma and Tsudik, "A New Approach to Secure Logging", LNCS 5094, 2008; Ma and Tsudik, "A New Approach to Secure Logging", ACM TOS 2009; Yavuz and Peng, "BAF: An Efficient Publicly Verifiable Secure Audit Logging Scheme for Distributed Systems", ACSAC 2009] have proposed using aggregatable signatures [Boneh et al., "Aggregate and Verifiably Encrypted Signatures from Bilinear Maps", EUROCRYPT 2003] in order to reduce the overhead in storage space incurred by using such a cryptographic scheme. Aggregation of signatures refers to some “combination” of any number of signatures (for distinct or equal messages, by distinct or identical signers) into an “aggregate” signature. The size of the aggregate signature should be less than the total of the sizes of the orginal signatures, ideally the size of one of the original signatures. Using aggregation of signatures in applications that require storing or transmitting a large number of signatures (such as the storage of log records) can lead to significant reductions in the use of storage space and bandwidth. However, aggregating the signatures for all log records into a single signature will cause some fragility: The modification of a single log entry will render the aggregate signature invalid, preventing the cryptographic verification of any part of the log file. However, being able to distinguish manipulated log entries from non-manipulated ones may be of importance for after-the-fact investigations. This thesis addresses this issue by presenting a new technique providing a trade-off between storage overhead and robustness, i.e. the ability to tolerate some modifications to the log file while preserving the cryptographic verifiability of unmodified log entries. This robustness is achieved by the use of a special kind of aggregate signatures (called fault-tolerant aggregate signatures), which contain some redundancy. The construction makes use of combinatorial methods guaranteeing that if the number of errors is below a certain threshold, then there will be enough redundancy to identify and verify the non-modified log entries. Finally, this thesis presents a total of four attacks on three different schemes intended for securely storing log files presented in the literature [Yavuz et al., "Efficient, Compromise Resilient and Append-Only Cryptographic Schemes for Secure Audit Logging", Financial Cryptography 2012; Ma, "Practical Forward Secure Sequential Aggregate Signatures", ASIACCS 2008]. The attacks allow for virtually arbitrary log file forgeries or even recovery of the secret key used for authenticating the log file, which could then be used for mostly arbitrary log file forgeries, too. All of these attacks exploit weaknesses of the specific schemes. Three of the attacks presented here contradict the security properties of the schemes claimed and supposedly proven by the respective authors. This thesis briefly discusses these proofs and points out their flaws. The fourth attack presented here is outside of the security model considered by the scheme’s authors, but nonetheless presents a realistic threat. In summary, this thesis advances the scientific state-of-the-art with regard to providing security for computer log files in a number of ways: by introducing a new technique for obtaining security against log truncations, by providing the first scheme where excerpts from log files can be verified for completeness, by describing the first scheme that can achieve some notion of robustness while being able to aggregate log record signatures, and by analyzing the security of previously proposed schemes

Logging integrity with blockchain structures

In developed countries, it is frequent for family members do not have the time, knowledge, or live in a close distance of their senior loved ones, so that many institutions offer their services to provide a good quality of life of older adults. To enable distributed local support, there is the need of digital platforms to allow the exchange of information. These platforms need to create trustful environments and to guarantee the integrity of the information exchanged. In this paper, it is presented a solution for a Logging Service that was developed for the SOCIAL platform, based on FHIR, which aims to solve the interoperability and data integrity of the platform user’s activity logs.publishe

sVote with control components voting protocol: computational proof of complete verifiability and privacy

This document details the cryptographic analysis of the sVote v2.2.1 system - an e-voting solution developed by Scytl for the Switzerland context. We prove the complete verifiability and privacy under the Swiss legislation's informally stated goals. First, we derive the trust model for complete verifiability and voting secrecy from the Swiss Chancellery's requirements, supporting our interpretation by quotes from and references to relevant excerpts of the ordinance and the corresponding technical annex. Then, based on the derived model, we prove that sVote with Control Components provides complete verifiability and guarantees voting secrecy and the non-disclosure of early provisional results. We demonstrate that sVote fulfills the requirements of the Swiss federal chancellery for completely verifiable E-voting systems. In other words, we show that an adversary cannot break the complete verifiability and voting secrecy properties of sVote without being detected by either the voter or auditors.sVote with Control components is a cryptographic voting protocol that provides complete verifiability and guarantees voting secrecy and the non-disclosure of early provisional results. This report demonstrates that sVote fulfills the requirements of the Swiss federal chancellery for completely verifiable E-voting systems. We extract precise requirements from the ordinance and the corresponding technical annex and model the sVote cryptographic voting protocol based on its design documents. Based on this model, we show in a detailed security analysis that an adversary cannot break the complete verifiability and voting secrecy properties of sVote without being detected by either the voter or by auditorsThis work has received funding from the European Commission under the auspices of PROMETHEUS Project, Horizon 2020 Innovation Action (Grant Agreement No. 780701).Preprin

Practical and Robust Secure Logging from Fault-Tolerant Sequential Aggregate Signatures

Keeping correct and informative log files is crucial for system maintenance, security and forensics. Cryptographic logging schemes offer integrity checks that protect a log file even in the case where an attacker has broken into the system. A relatively recent feature of these schemes is resistance against truncations, i.e. the deletion and/or replacement of the end of the log file. This is especially relevant as system intruders are typically interested in manipulating the later log entries that point towards their attack. However, there are not many schemes that are resistant against truncating the log file. Those that are have at least one of the following disadvantages: They are memory intensive (they store at least one signature per log entry), or fragile (i.e. a single error in the log renders the signature invalid and useless in determining where the error occurred). We obtain a publicly-verifiable secure logging scheme that is simultaneously robust, space-efficient and truncation secure with provable security under simple assumptions. Our generic construction uses forward-secure signatures, in a plain and a sequential aggregate variant, where the latter is additionally fault-tolerant, as recently formalized by Hartung et al. (PKC 2016). Fault-tolerant schemes can cope with a number of manipulated log entries (bounded a priori) and offer strong robustness guarantees while still retaining space efficiency. Our implementation and the accompanying performance measurements confirm the practicality of our scheme

Secure Logging in between Theory and Practice: Security Analysis of the Implementation of Forward Secure Log Sealing in Journald

This paper presents a security analysis of forward secure log sealing in the journald logging system, which is part of systemd and used in modern Linux distributions. Forward secure log sealing is a cryptographic technique used to ensure the integrity of past log entries even in the event of a full system compromise. We analyze the implementation of this technique in journald, identifying multiple security vulnerabilities resulting from a gap between the model of the cryptographic primitives and their usage in a larger context. In particular one vulnerability allows to forge arbitrary logs for past entries without the validation tool noticing any problem. We demonstrate the found attacks on the journald implementation by providing a concrete security definition for the larger system, an implementation close to the security experiment and a corresponding attacker defeating it when used with a vulnerable version of journald. For the more serious vulnerabilities, we provide patch recommendations, which prevent the implemented attack. Our findings break the security guarantee from log sealing completely, without the error resulting from an inconsistency in the theoretical model nor being a simple implementation mistake. This provides a practical example of the problems that can occur when applying cryptographic primitives to a complex system in reality and that fall in between theory and practice

Vendors are Undermining the Structure of U.S. Elections

As we approach the 2008 general election, the structure of elections in the United States -- once reliant on local representatives accountable to the public -- has become almost wholly dependent on large corporations, which are not accountable to the public. Most local officials charged with running elections are now unable to administer elections without the equipment, services, and trade-secret software of a small number of corporations. If the vendors withdrew their support for elections now, our election structure would collapse. Case studies presented in this report give examples of the pervasive control voting system vendors now have over election administration in almost every state, and the consequences some jurisdictions are already experiencing.However, some states and localities are recognizing the threat that vendor-dependency poses to elections. They are using ingenuity and determination to begin reversing the direction. This report examines the situation, how we got here, and steps we can take to limit corporate control of our elections in 2008 and reduce it even further in the future

Distributed virtual environment scalability and security

Distributed virtual environments (DVEs) have been an active area of research and engineering for more than 20 years. The most widely deployed DVEs are network games such as Quake, Halo, and World of Warcraft (WoW), with millions of users and billions of dollars in annual revenue. Deployed DVEs remain expensive centralized implementations despite significant research outlining ways to distribute DVE workloads. This dissertation shows previous DVE research evaluations are inconsistent with deployed DVE needs. Assumptions about avatar movement and proximity - fundamental scale factors - do not match WoW’s workload, and likely the workload of other deployed DVEs. Alternate workload models are explored and preliminary conclusions presented. Using realistic workloads it is shown that a fully decentralized DVE cannot be deployed to today’s consumers, regardless of its overhead. Residential broadband speeds are improving, and this limitation will eventually disappear. When it does, appropriate security mechanisms will be a fundamental requirement for technology adoption. A trusted auditing system (“Carbon”) is presented which has good security, scalability, and resource characteristics for decentralized DVEs. When performing exhaustive auditing, Carbon adds 27% network overhead to a decentralized DVE with a WoW-like workload. This resource consumption can be reduced significantly, depending upon the DVE’s risk tolerance. Finally, the Pairwise Random Protocol (PRP) is described. PRP enables adversaries to fairly resolve probabilistic activities, an ability missing from most decentralized DVE security proposals. Thus, this dissertations contribution is to address two of the obstacles for deploying research on decentralized DVE architectures. First, lack of evidence that research results apply to existing DVEs. Second, the lack of security systems combining appropriate security guarantees with acceptable overhead

sVote with Control Components Voting Protocol. Computational Proof of Complete Verifiability and Privacy.

This document details the cryptographic analysis of the sVote v2.2.1 system - an e-voting solution developed by Scytl for the Switzerland context. We prove the complete verifiability and privacy under the Swiss legislation\u27s informally stated goals. First, we derive the trust model for complete verifiability and voting secrecy from the Swiss Chancellery\u27s requirements [1][2], supporting our interpretation by quotes from and references to relevant excerpts of the ordinance and the corresponding technical annex. Then, based on the derived model, we prove that sVote with Control Components provides complete verifiability and guarantees voting secrecy and the non-disclosure of early provisional results. We demonstrate that sVote fulfills the requirements of the Swiss federal chancellery for completely verifiable E-voting systems. In other words, we show that an adversary cannot break the complete verifiability and voting secrecy properties of sVote without being detected by either the voter or auditors. [1] Technical and administrative requirements for electronic vote casting v 2.0 https://www.bk.admin.ch/dam/bk/en/dokumente/pore/Annex_of_the_Federal_Chancellery_Ordinance_on_Electronic_Voting_V2.0_July_2018.pdf.download.pdf/Annex_of_the_Federal_Chancellery_Ordinance_on_Electronic_Voting_V2.0_July_2018.pdf [2] Federal Chancellery Ordinance on Electronic Voting https://www.fedlex.admin.ch/eli/cc/2013/859/e