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See detailCase Study: Analysis and Mitigation of a Novel Sandbox-Evasion Technique
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Sgandurra, Daniele

in 3rd Central European Cybersecurity Conference (in press)

Malware is one of the most popular cyber-attack methods in the digital world. According to the independent test company AV-TEST, 350,000 new malware samples are created every day. To analyze all samples ... [more ▼]

Malware is one of the most popular cyber-attack methods in the digital world. According to the independent test company AV-TEST, 350,000 new malware samples are created every day. To analyze all samples by hand to discover whether they are malware does not scale, so antivirus companies automate the process e.g., using sand- boxes where samples can be run, observed, and classified. Malware authors are aware of this fact, and try to evade detection. In this paper we describe one of such evasion technique: unprecedented, we discovered it while analyzing a ransomware sample. Analyzed in a Cuckoo Sandbox, the sample was able to avoid triggering malware indicators, thus scoring significantly below the minimum severity level. Here, we discuss what strategy the sample follows to evade the analysis, proposing practical defense methods to nullify, in our turn, the sample’s furtive strategy. [less ▲]

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See detailNoCry: No More Secure Encryption Keys for Cryptographic Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL

in 2nd International Workshop on Emerging Technologies for Authorization and Authentication (2019, September 27)

Since the appearance of ransomware in the cyber crime scene, researchers and anti-malware companies have been offering solutions to mitigate the threat. Anti-malware solutions differ on the specific ... [more ▼]

Since the appearance of ransomware in the cyber crime scene, researchers and anti-malware companies have been offering solutions to mitigate the threat. Anti-malware solutions differ on the specific strategy they implement, and all have pros and cons. However, three requirements concern them all: their implementation must be secure, be effective, and be efficient. Recently, Genç et al. proposed to stop a specific class of ransomware, the cryptographically strong one, by blocking unauthorized calls to cryptographically secure pseudo-random number generators, which are required to build strong encryption keys. Here, in adherence to the requirements, we discuss an implementation of that solution that is more secure (with components that are not vulnerable to known attacks), more effective (with less false negatives in the class of ransomware addressed) and more efficient (with minimal false positive rate and negligible overhead) than the original, bringing its security and technological readiness to a higher level. [less ▲]

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See detailA Critical Security Analysis of the Password-Based Authentication Honeywords System Under Code-Corruption Attack
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL et al

in Information Systems Security and Privacy (2019, July)

Password-based authentication is a widespread method to access into systems, thus password files are a valuable resource often target of attacks. To detect when a password file has been stolen, Juels and ... [more ▼]

Password-based authentication is a widespread method to access into systems, thus password files are a valuable resource often target of attacks. To detect when a password file has been stolen, Juels and Rivest introduced the Honeywords System in 2013. The core idea is to store the password with a list of decoy words that are ``indistinguishable'' from the password, called honeywords. An adversary that obtains the password file and, by dictionary attack, retrieves the honeywords can only guess the password when attempting to log in: but any incorrect guess will set off an alarm, warning that file has been compromised. In a recent conference paper, we studied the security of the Honeywords System in a scenario where the intruder also manages to corrupt the server's code (with certain limiting assumptions); we proposed an authentication protocol and proved it secure despite the corruption. In this extended journal version, we detail the analysis and we extend it, under the same attacker model, to the other two protocols of the original Honeywords System, the setup and change of password. We formally verify the security of both of them; further, we discuss that our design suggests a completely new approach that diverges from the original idea of the Honeywords System but indicates an alternative way to authenticate users which is robust to server's code-corruption. [less ▲]

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See detailOn Deception-Based Protection Against Cryptographic Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Sgandurra, Daniele

in 16th Conference on Detection of Intrusions and Malware & Vulnerability Assessment (2019, June 19)

In order to detect malicious file system activity, some commercial and academic anti-ransomware solutions implement deception-based techniques, specifically by placing decoy files among user files. While ... [more ▼]

In order to detect malicious file system activity, some commercial and academic anti-ransomware solutions implement deception-based techniques, specifically by placing decoy files among user files. While this approach raises the bar against current ransomware, as any access to a decoy file is a sign of malicious activity, the robustness of decoy strategies has not been formally analyzed and fully tested. In this paper, we analyze existing decoy strategies and discuss how they are effective in countering current ransomware by defining a set of metrics to measure their robustness. To demonstrate how ransomware can identify existing deception-based detection strategies, we have implemented a proof-of-concept anti-decoy ransomware that successfully bypasses decoys by using a decision engine with few rules. Finally, we discuss existing issues in decoy-based strategies and propose practical solutions to mitigate them. [less ▲]

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See detailCrypren Decryptor
Genç, Ziya Alper UL

Software (2018)

Crypren Decryptor is software which recovers the files encrypted by Crypren ransomware. The decryptor targets the sample with SHA256 digest ... [more ▼]

Crypren Decryptor is software which recovers the files encrypted by Crypren ransomware. The decryptor targets the sample with SHA256 digest: ce53233a435923a68a9ca6987f0d6333bb97d5a435b942d20944356ac29df598. Further details about the design of this software can be found at the paper: http://orbilu.uni.lu/handle/10993/36627. [less ▲]

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See detailSecurity Analysis of Key Acquiring Strategies Used by Cryptographic Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL

in Advances in Cybersecurity 2018 (2018)

To achieve its goals, ransomware needs to employ strong encryption, which in turn requires access to high-grade encryption keys. Over the evolution of ransomware, various techniques have been observed to ... [more ▼]

To achieve its goals, ransomware needs to employ strong encryption, which in turn requires access to high-grade encryption keys. Over the evolution of ransomware, various techniques have been observed to accomplish the latter. Understanding the advantages and disadvantages of each method is essential to develop robust defense strategies. In this paper we explain the techniques used by ransomware to derive encryption keys and analyze the security of each approach. We argue that recovery of data might be possible if the ransomware cannot access high entropy randomness sources. As an evidence to support our theoretical results, we provide a decryptor program for a previously undefeated ransomware. [less ▲]

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See detailNo Random, No Ransom: A Key to Stop Cryptographic Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL

in Giuffrida, Cristiano; Bardin, Sébastien; Blanc, Gregory (Eds.) Proceedings of the 15th International Conference on Detection of Intrusions and Malware, and Vulnerability Assessment (DIMVA 2018) (2018)

To be effective, ransomware has to implement strong encryption, and strong encryption in turn requires a good source of random numbers. Without access to true randomness, ransomware relies on the pseudo ... [more ▼]

To be effective, ransomware has to implement strong encryption, and strong encryption in turn requires a good source of random numbers. Without access to true randomness, ransomware relies on the pseudo random number generators that modern Operating Systems make available to applications. With this insight, we propose a strategy to mitigate ransomware attacks that considers pseudo random number generator functions as critical resources, controls accesses on their APIs and stops unauthorized applications that call them. Our strategy, tested against 524 active real-world ransomware samples, stops 94% of them, including WannaCry, Locky, CryptoLocker and CryptoWall. Remarkably, it also nullifies NotPetya, the latest offspring of the family which so far has eluded all defenses. [less ▲]

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See detailA Security Analysis, and a Fix, of a Code-Corrupted Honeywords System
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL et al

in Proceedings of the 4th International Conference on Information Systems Security and Privacy (2018)

In 2013 Juels and Rivest introduced the Honeywords System, a password-based authentication system designed to detect when a password file has been stolen. A Honeywords System stores passwords together ... [more ▼]

In 2013 Juels and Rivest introduced the Honeywords System, a password-based authentication system designed to detect when a password file has been stolen. A Honeywords System stores passwords together with indistinguishable decoy words so when an intruder steals the file, retrieves the words, and tries to log-in, he does not know which one is the password. By guessing one from the decoy words, he may not be lucky and reveal the leak. Juels and Rivest left a problem open: how to make the system secure even when the intruder corrupted the login server’s code. In this paper we study and solve the problem. However, since “code corruption” is a powerful attack, we first define rigorously the threat and set a few assumptions under which the problem is still solvable, before showing meaningful attacks against the original Honeywords System. Then we elicit a fundamental security requirement, implementing which, we are able to restore the honeywords System’s security despite a corrupted login service. We verify the new protocol’s security formally, using ProVerif for this task. We also implement the protocol and test its performance. Finally, at the light of our findings, we discuss whether it is still worth using a fixed honeywords-based system against such a powerful threat, or whether it is better, in order to be resilient against code corruption attacks, to design afresh a completely different password-based authentication solution. [less ▲]

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See detailNext Generation Cryptographic Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL

in Secure IT Systems: 23rd Nordic Conference, NordSec 2018, Oslo, Norway, November 28-30, 2018, Proceedings (2018)

We are assisting at an evolution in the ecosystem of cryptoware - the malware that encrypts files and makes them unavailable unless the victim pays up. New variants are taking the place once dominated by ... [more ▼]

We are assisting at an evolution in the ecosystem of cryptoware - the malware that encrypts files and makes them unavailable unless the victim pays up. New variants are taking the place once dominated by older versions; incident reports suggest that forthcoming ransomware will be more sophisticated, disruptive, and targeted. Can we anticipate how such future generations of ransomware will work in order to start planning on how to stop them? We argue that among them there will be some which will try to defeat current anti-ransomware; thus, we can speculate over their working principle by studying the weak points in the strategies that seven of the most advanced anti-ransomware are currently implementing. We support our speculations with experiments, proving at the same time that those weak points are in fact vulnerabilities and that the future ransomware that we have imagined can be effective. [less ▲]

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See detailSecurity attacks and enhancements to chaotic map-based RFID authentication protocols
Kardaş, Süleyman; Genç, Ziya Alper UL

in Wireless Personal Communications (2017)

Radio frequency identification (RFID) technology has been increasingly integrated into numerous applications for authentication of objects or individuals. However, because of its limited computation power ... [more ▼]

Radio frequency identification (RFID) technology has been increasingly integrated into numerous applications for authentication of objects or individuals. However, because of its limited computation power, RFID technology may cause several security and privacy issues such as tracking the owner of the tag, cloning of the tags and etc. Recently, two chaotic map-based authentication protocols have been proposed for low-cost RFID tags in order to eliminate these issues. In this paper, we give the security analysis of these protocols and uncover their weaknesses. We prove that these protocols are vulnerable to tag tracing, tag impersonation and desynchronization attacks. The attack complexity of an adversary is polynomial and the success probability of these attacks are substantial. Moreover, we also propose an improved RFID authentication protocol that employs Chebyshev chaotic maps and complies with the EPC global Class 1 Generation 2 standard. Finally, we show that our protocol is resistant against those security issues. [less ▲]

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See detailExamination of a New Defense Mechanism: Honeywords
Genç, Ziya Alper UL; Kardaş, Süleyman; Kiraz,

in Proceedings of the 11th WISTP International Conference on Information Security Theory and Practice (2017)

Past experiences show us that password breach is still one of the main methods of attackers to obtain personal or sensitive user data. Basically, assuming they have access to list of hashed passwords ... [more ▼]

Past experiences show us that password breach is still one of the main methods of attackers to obtain personal or sensitive user data. Basically, assuming they have access to list of hashed passwords, they apply guessing attacks, i.e., attempt to guess a password by trying a large number of possibilities. We certainly need to change our way of thinking and use a novel and creative approach in order to protect our passwords. In fact, there are already novel attempts to provide password protection. The Honeywords system of Juels and Rivest is one of them which provides a detection mechanism for password breaches. Roughly speaking, they propose a method for password-based authentication systems where fake passwords, i.e., "honeywords" are added into a password file, in order to detect impersonation. Their solution includes an auxiliary secure server called "honeychecker" which can distinguish a user's real password among her honeywords and immediately sets off an alarm whenever a honeyword is used. However, they also pointed out that their system needs to be improved in various ways by highlighting some open problems. In this paper, after revisiting the security of their proposal, we specifically focus on and aim to solve a highlighted open problem, i.e., active attacks where the adversary modifies the code running on either the login server or the honeychecker. [less ▲]

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See detailThe Cipher, the Random and the Ransom: A Survey on Current and Future Ransomware
Genç, Ziya Alper UL; Lenzini, Gabriele UL; Ryan, Peter UL

in Advances in Cybersecurity 2017 (2017)

Although conceptually not new, ransomware recently regained attraction in the cybersecurity community: notorious attacks in fact have caused serious damage, proving their disruptive effect. This is likely ... [more ▼]

Although conceptually not new, ransomware recently regained attraction in the cybersecurity community: notorious attacks in fact have caused serious damage, proving their disruptive effect. This is likely just the beginning of a new era. According to a recent intelligence report by Cybersecurity Ventures, the total cost due to ransomware attacks is predicted to exceed $5 billion in 2017. How can this disruptive threat can be contained? Current anti-ransomware solutions are effective only against existing threats, and the worst is yet to come. Cyber criminals will design and deploy more sophisticated strategies, overcoming current defenses and, as it commonly happens in security, defenders and attackers will embrace a competition that will never end. In this arm race, anticipating how current ransomware will evolve may help at least being prepared for some future damage. In this paper, we describe existing techniques to mitigate ransomware and we discuss their limitations. Discussing how current ransomware could become even more disruptive and elusive is crucial to conceive more solid defense and systems that can mitigate zero-day ransomware, yielding higher security levels for information systems, including critical infrastructures such as intelligent transportation networks and health institutions. [less ▲]

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See detailSecurity and Efficiency Analysis of the Hamming Distance Computation Protocol Based on Oblivious Transfer
Kiraz, Mehmet Sabır; Genç, Ziya Alper UL; Kardaş, Süleyman

in Security and Communication Networks (2015), 8(18), 4123-4135

Bringer et al. proposed two cryptographic protocols for the computation of Hamming distance. Their first scheme uses Oblivious Transfer and provides security in the semi-honest model. The other scheme ... [more ▼]

Bringer et al. proposed two cryptographic protocols for the computation of Hamming distance. Their first scheme uses Oblivious Transfer and provides security in the semi-honest model. The other scheme uses Committed Oblivious Transfer and is claimed to provide full security in the malicious case. The proposed protocols have direct implications to biometric authentication schemes between a prover and a verifier where the verifier has biometric data of the users in plain form. In this paper, we show that their protocol is not actually fully secure against malicious adversaries. More precisely, our attack breaks the soundness property of their protocol where a malicious user can compute a Hamming distance which is different from the actual value. For biometric authentication systems, this attack allows a malicious adversary to pass the authentication without knowledge of the honest user’s input with at most O(n) complexity instead of O(2n), where n is the input length. We propose an enhanced version of their protocol where this attack is eliminated. The security of our modified protocol is proven using the simulation-based paradigm. Furthermore, as for efficiency concerns, the modified protocol utilizes Verifiable Oblivious Transfer which does not require the commitments to outputs which improves its efficiency significantly. [less ▲]

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