Fast and Accurate Machine Learning-based Malware Detection via RC4 Ciphertext Analysis

Malware is dramatically increasing its viability while hiding its malicious intent and/or behavior by employing ciphers. So far, many efforts have been made to detect malware and prevent it from damaging users by monitoring network packets. However, conventional detection schemes analyzing network packets directly are hardly applicable to detect the advanced malware that encrypts the communication. Cryptoanalysis of each packet flowing over a network might be one feasible solution for the problem. However, the approach is computationally expensive and lacks accuracy, which is consequently not a practical solution. To tackle these problems, in this paper, we propose novel schemes that can accurately detect malware packets encrypted by RC4 without decryption in a timely manner. First, we discovered that a fixed encryption key generates unique statistical patterns on RC4 ciphertexts. Then, we detect malware packets of RC4 ciphertexts efficiently and accurately by utilizing the discovered statistical patterns of RC4 ciphertext given encryption key. Our proposed schemes directly analyze network packets without decrypting ciphertexts. Moreover, our analysis can be effectively executed with only a very small subset of the network packet. To the best of our knowledge, the unique signature has never been discussed in any previous research. Our intensive experimental results with both simulation data and actual malware show that our proposed schemes are extremely fast (23.06±1.52 milliseconds) and highly accurate (100%) on detecting a DarkComet malware with only a network packet of 36 bytes

MV3: A new word based stream cipher using rapid mixing and revolving buffers

MV3 is a new word based stream cipher for encrypting long streams of data. A direct adaptation of a byte based cipher such as RC4 into a 32- or 64-bit word version will obviously need vast amounts of memory. This scaling issue necessitates a look for new components and principles, as well as mathematical analysis to justify their use. Our approach, like RC4's, is based on rapidly mixing random walks on directed graphs (that is, walks which reach a random state quickly, from any starting point). We begin with some well understood walks, and then introduce nonlinearity in their steps in order to improve security and show long term statistical correlations are negligible. To minimize the short term correlations, as well as to deter attacks using equations involving successive outputs, we provide a method for sequencing the outputs derived from the walk using three revolving buffers. The cipher is fast -- it runs at a speed of less than 5 cycles per byte on a Pentium IV processor. A word based cipher needs to output more bits per step, which exposes more correlations for attacks. Moreover we seek simplicity of construction and transparent analysis. To meet these requirements, we use a larger state and claim security corresponding to only a fraction of it. Our design is for an adequately secure word-based cipher; our very preliminary estimate puts the security close to exhaustive search for keys of size < 256 bits.Comment: 27 pages, shortened version will appear in "Topics in Cryptology - CT-RSA 2007

Cryptanalysis of symmetric key primitives

Block ciphers and stream ciphers are essential building blocks that are used to construct computing systems which have to satisfy several security objectives. Since the security of these systems depends on the security of its parts, the analysis of these symmetric key primitives has been a goal of critical importance. In this thesis we provide cryptanalytic results for some recently proposed block and stream ciphers. First, we consider two light-weight block ciphers, TREYFER and PIFEA-M. While TREYFER was designed to be very compact in order to fit into constrained environments such as smart cards and RFIDs, PIFEA-M was designed to be very fast in order to be used for the encryption of multimedia data. We provide a related-key attack on TREYFER which recovers the secret key given around 2 11 encryptions and negligible computational effort. As for PIFEA-M, we provide evidence that it does not fulfill its design goal, which was to defend from certain implementation dependant differential attacks possible on previous versions of the cipher. Next. we consider the NGG stream cipher, whose design is based on RC4 and aims to increase throughput by operating with 32-bit or 64-bit values instead of with 8-bit values. We provide a distinguishing attack on NGG which requires just one keystream word. We also show that the first few kilobytes of the keystream may leak information about the secret key which allows the cryptanalyst to recover the secret key in an efficient way. Finally, we consider GGHN, another RC4-like cipher that operates with 32-bit words. We assess different variants of GGHN-Iike algorithms with respect to weak states, in which all internal state words and output elements are even. Once GGHN is absorbed in such a weak state, the least significant bit of the plaintext words will be revealed only by looking at the ciphertext. By modelling the algorithm by a Markov chain and calculating the chain absorption time, we show that the average number of steps required by these algorithms to enter this weak state can be lower than expected at first glance and hence caution should be exercised when estimating this numbe

Securing Deployed Cryptographic Systems

In 2015 more than 150 million records and $400 billion were lost due to publicly-reported criminal and nation-state cyberattacks in the United States alone. The failure of our existing security infrastructure motivates the need for improved technologies, and cryptography provides a powerful tool for doing this. There is a misperception that the cryptography we use today is a "solved problem" and the real security weaknesses are in software or other areas of the system. This is, in fact, not true at all, and over the past several years we have seen a number of serious vulnerabilities in the cryptographic pieces of systems, some with large consequences. This thesis will discuss three aspects of securing deployed cryptographic systems. We will first explore the evaluation of systems in the wild, using the example of how to efficiently and effectively recover user passwords submitted over TLS encrypted with RC4, with applications to many methods of web authentication as well as the popular IMAP protocol for email. We will then address my work on developing tools to design and create cryptographic systems and bridge the often large gap between theory and practice by introducing AutoGroup+, a tool that automatically translates cryptographic schemes from the mathematical setting used in the literature to that typically used in practice, giving both a secure and optimal output. We will conclude with an exploration of how to actually build real world deployable systems by discussing my work on developing decentralized anonymous credentials in order to increase the security and deployability of existing anonymous credentials systems

Smashing WEP in A Passive Attack

In this paper, we report extremely fast and optimised active and passive attacks against the old IEEE 802.11 wireless communication protocol WEP. This was achieved through a huge amount of theoretical and experimental analysis (capturing WiFi packets), refinement and optimisation of all the former known attacks and methodologies against RC4 stream cipher in WEP mode. We support all our claims by providing an implementation of this attack as a publicly available patch on Aircrack-ng. Our new attacks improve its success probability drastically. We adapt our theoretical analysis in Eurocrypt 2011 to real-world scenarios and we perform a slight adjustment to match the empirical observations. Our active attack, based on ARP injection, requires 22 500 packets to gain success probability of 50% against a 104-bit WEP key, using Aircrack-ng in non-interactive mode. It runs in less than 5 seconds on an off-the-shelf PC. Using the same number of packets, Aicrack-ng yields around 3% success rate. Furthermore, we describe very fast passive only attacks by just eavesdropping TCP/IPv4 packets in a WiFi communication. Our passive attack requires 27 500 packets. This is much less than the number of packets Aircrack-ng requires in active mode (around 37 500), which is a huge improvement.We believe that our analysis brings on further insight to the security of RC4

Tornado Attack on RC4 with Applications to WEP & WPA

In this paper, we construct several tools for building and manipulating pools of biases in the analysis of RC4. We report extremely fast and optimized active and passive attacks against IEEE 802.11 wireless communication protocol WEP and a key recovery and a distinguishing attack against WPA. This was achieved through a huge amount of theoretical and experimental analysis (capturing WiFi packets), refinement and optimization of all the former known attacks and methodologies against RC4 stream cipher in WEP and WPA modes. We support all our claims on WEP by providing an implementation of this attack as a publicly available patch on Aircrack-ng. Our new attack improves its success probability drastically. Our active attack, based on ARP injection, requires 22500 packets to gain success probability of 50\% against a 104-bit WEP key, using Aircrack-ng in non-interactive mode. It runs in less than 5 seconds on an off-the-shelf PC. Using the same number of packets, Aicrack-ng yields around 3\% success rate. Furthermore, we describe very fast passive only attacks by just eavesdropping TCP/IPv4 packets in a WiFi communication. Our passive attack requires 27500 packets. This is much less than the number of packets Aircrack-ng requires in active mode (around 37500), which is a huge improvement. Deploying a similar theory, we also describe several attacks on WPA. Firstly, we describe a distinguisher for WPA with complexity 2^{42} and advantage 0.5 which uses 2^{42} packets. Then, based on several partial temporary key recovery attacks, we recover the full 128-bit temporary key of WPA by using 2^{42} packets. It works with complexity 2^{96}. So far, this is the best key recovery attack against WPA. We believe that our analysis brings on further insight to the security of RC4

Enhancing Message Privacy In Wired Equivalent Privacy.

The 802.11 standard defines the Wired Equivalent Privacy (WEP) and encapsulation of data frames. It is intended to provide data privacy to the level of a wired network. WEP suffered threat of attacks from hackers owing to certain security shortcomings in the WEP protocol. Lately, many new protocols like WiFi Protected Access (WPA), WPA2, Robust Secure Network (RSN) and 802.11i have come into being, yet their implementation is fairly limited. Despite its shortcomings one cannot undermine the importance of WEP as it still remains the most widely used system and we chose to address certain security issues and propose some modifications to make it more secure. In this thesis we have proposed a modification to the existing WEP protocol to make it more secure. We achieve Message Privacy by ensuring that the encryption is not breached. The idea is to update the shared secret key frequently based on factors like network traffic and number of transmitted frames. We also develop an Initialization Vector (IV) avoidance algorithm that eliminates IV collision problem. The idea is to partition the IV bits among different wireless hosts in a predetermined manner unique to every node. We can use all possible 224 different IVs without making them predictable for an attacker. Our proposed algorithm eliminates the IV collision ensuring Message Privacy that further strengthens security of the existing WEP. We show that frequent rekeying thwarts all kinds of cryptanalytic attacks on the WEP

Cryptanalysis of Symmetric Cryptographic Primitives

Symmetric key cryptographic primitives are the essential building blocks in modern information security systems. The overall security of such systems is crucially dependent on these mathematical functions, which makes the analysis of symmetric key primitives a goal of critical importance. The security argument for the majority of such primitives in use is only a heuristic one and therefore their respective security evaluation continually remains an open question. In this thesis, we provide cryptanalytic results for several relevant cryptographic hash functions and stream ciphers. First, we provide results concerning two hash functions: HAS-160 and SM3. In particular, we develop a new heuristic for finding compatible differential paths and apply it to the the Korean hash function standard HAS-160. Our heuristic leads to a practical second order collision attack over all of the HAS-160 function steps, which is the first practical-complexity distinguisher on this function. An example of a colliding quartet is provided. In case of SM3, which is a design that builds upon the SHA-2 hash and is published by the Chinese Commercial Cryptography Administration Office for the use in the electronic authentication service system, we study second order collision attacks over reduced-round versions and point out a structural slide-rotational property that exists in the function. Next, we examine the security of the following three stream ciphers: Loiss, SNOW 3G and SNOW 2.0. Loiss stream cipher is designed by Dengguo Feng et al. aiming to be implemented in byte-oriented processors. By exploiting some differential properties of a particular component utilized in the cipher, we provide an attack of a practical complexity on Loiss in the related-key model. As confirmed by our experimental results, our attack recovers 92 bits of the 128-bit key in less than one hour on a PC with 3 GHz Intel Pentium 4 processor. SNOW 3G stream cipher is used in 3rd Generation Partnership Project (3GPP) and the SNOW 2.0 cipher is an ISO/IEC standard (IS 18033-4). For both of these two ciphers, we show that the initialization procedure admits a sliding property, resulting in several sets of related-key pairs. In addition to allowing related-key key recovery attacks against SNOW 2.0 with 256-bit keys, the presented properties reveal non-random behavior of the primitives, yield related-key distinguishers for the two ciphers and question the validity of the security proofs of protocols based on the assumption that these ciphers behave like perfect random functions of the key-IV. Finally, we provide differential fault analysis attacks against two stream ciphers, namely, HC-128 and Rabbit. In this type of attacks, the attacker is assumed to have physical influence over the device that performs the encryption and is able to introduce random faults into the computational process. In case of HC-128, the fault model in which we analyze the cipher is the one in which the attacker is able to fault a random word of the inner state of the cipher but cannot control its exact location nor its new faulted value. Our attack requires about 7968 faults and recovers the complete internal state of HC-128 by solving a set of 32 systems of linear equations over Z2 in 1024 variables. In case of Rabbit stream cipher, the fault model in which the cipher is analyzed is the one in which a random bit of the internal state of the cipher is faulted, however, without control over the location of the injected fault. Our attack requires around 128 − 256 faults, precomputed table of size 2^41.6 bytes and recovers the complete internal state of Rabbit in about 2^38 steps