End-to-End (E2E) encrypted messaging, which prevents even the service provider from learning communication contents, is gaining popularity. Since users care about maintaining access to their data even if their devices are lost or broken or just replaced, these systems are often paired with cloud backup solutions: Typically, the user will encrypt their messages with a fixed key, and upload the ciphertexts to the server. Unfortunately, this naive solution has many drawbacks. First, it often...

Fully Homomorphic Encryption (FHE) is a powerful tool that brings privacy and security to all sorts of applications by allowing us to perform additions and multiplications directly on ciphertexts without the need of the secret key. Some applications of FHE that were previously overlooked but have recently been gaining traction are data compression and image processing. Practically, FHE enables applications such as private satellite searching, private object recognition, or even encrypted...

Key Transparency (KT) systems enable service providers of end-to-end encrypted communication (E2EE) platforms to maintain a Verifiable Key Directory (VKD) that maps each user's identifier, such as a username or email address, to their identity public key(s). Users periodically monitor the directory to ensure their own identifier maps to the correct keys, thus detecting any attempt to register a fake key on their behalf to Meddler-in-the-Middle (MitM) their communications. We introduce and...

In May 2020, Zoom Video Communications, Inc. (Zoom) announced a multi-step plan to comprehensively support end-to-end encrypted (E2EE) group video calls and subsequently rolled out basic E2EE support to customers in October 2020. In this work we provide the first formal security analysis of Zoom's E2EE protocol, and also lay foundation to the general problem of E2EE group video communication. We observe that the vast security literature analyzing asynchronous messaging does not translate...

Hash-based signature (HBS) schemes are an efficient method of guaranteeing the authenticity of data in a post-quantum world. The stateful schemes LMS and XMSS and the stateless scheme SPHINCS are already standardised or will be in the near future. The Winternitz one-time signature (WOTS) scheme is one of the fundamental building blocks used in all these HBS standardisation proposals. We present a new fault injection attack targeting WOTS that allows an adversary to forge signatures for...

Video conferencing apps like Zoom have hundreds of millions of daily users, making them a high-value target for surveillance and subversion. While such apps claim to achieve some forms of end-to-end encryption, they usually assume an incorruptible server that is able to identify and authenticate all the parties in a meeting. Concretely this means that, e.g., even when using the “end-to-end encrypted” setting, malicious Zoom servers could eavesdrop or impersonate in arbitrary groups. In...

Jitsi Meet is an open-source video conferencing system, and a popular alternative to proprietary services such as Zoom and Google Meet. The Jitsi project makes strong privacy and security claims in its advertising, but there is no published research into the merits of these claims. Moreover, Jitsi announced end-to-end encryption (E2EE) support in April 2020, and prominently features this in its marketing. We present an in-depth analysis of the design of Jitsi and its use of cryptography....

In this paper, we present video-based cryptanalysis, a new method used to recover secret keys from a device by analyzing video footage of a device’s power LED. We show that cryptographic computations performed by the CPU change the power consumption of the device which affects the brightness of the device’s power LED. Based on this observation, we show how attackers can exploit commercial video cameras (e.g., an iPhone 13’s camera or Internet-connected security camera) to...

Key Transparency (KT) systems allow end-to-end encrypted service providers (messaging, calls, etc.) to maintain an auditable directory of their users’ public keys, producing proofs that all participants have a consistent view of those keys, and allowing each user to check updates to their own keys. KT has lately received a lot of attention, in particular its privacy preserving variants, which also ensure that users and auditors do not learn anything beyond what is necessary to use the...

Frequently, users on the web need to show that they are, for example, not a robot, old enough to access an age restricted video, or eligible to download an ebook from their local public library without being tracked. Anonymous credentials were developed to address these concerns. However, existing schemes do not handle the realities of deployment or the complexities of real-world identity. Instead, they implicitly make assumptions such as there being an issuing authority for anonymous...

We introduce the Spiral family of single-server private information retrieval (PIR) protocols. Spiral relies on a composition of two lattice-based homomorphic encryption schemes: the Regev encryption scheme and the Gentry-Sahai-Waters encryption scheme. We introduce new ciphertext translation techniques to convert between these two schemes and in doing so, enable new trade-offs in communication and computation. Across a broad range of database configurations, the basic version of Spiral...

In a broadcast encryption system, a sender can encrypt a message for any subset of users who are listening on a broadcast channel. The goal of broadcast encryption is to leverage the broadcasting structure to achieve better efficiency than individually encrypting to each user; in particular, reducing the bandwidth (i.e., ciphertext size) required to transmit securely, although other factors such as public and private key size and the time to execute setup, encryption and decryption are also...

Consider a server with a large set $S$ of strings $\{x_1,x_2, \dots,x_N\}$ that would like to publish a small hash $h$ of its set $S$ such that any client with a string $y$ can send the server a short message allowing it to learn $y$ if $y \in S$ and nothing otherwise. In this work, we study this problem of two-round private set intersection (PSI) with low (asymptotically optimal) communication cost, or what we call laconic private set intersection ($\ell$PSI) and its extensions. This...

In the wake of the global COVID-19 pandemic, video conference systems have become essential for not only business purposes, but also private, academic, and educational uses. Among the various systems, Zoom is the most widely deployed video conference system. In October 2020, Zoom Video Communications rolled out their end-to-end encryption (E2EE) to protect conversations in a meeting from even insiders, namely, the service provider Zoom. In this study, we conduct thorough security evaluations...

As people become more and more privacy conscious, the need for end-to-end encryption (E2EE) has become widely recognized. We study herein the security of SFrame, an E2EE mechanism recently proposed to the Internet Engineering Task Force for video/audio group communications over the Internet. Despite being a quite recent project, SFrame is going to be adopted by a number of real-world applications. We inspect the original specification of SFrame and find critical issues that will lead to...

Many video classification applications require access to personal data, thereby posing an invasive security risk to the users' privacy. We propose a privacy-preserving implementation of single-frame method based video classification with convolutional neural networks that allows a party to infer a label from a video without necessitating the video owner to disclose their video to other entities in an unencrypted manner. Similarly, our approach removes the requirement of the classifier owner...

Zoom Meeting is an enterprise online video conferencing solution with real-time messaging and content sharing. However, they are lack of privacy protection since centralized Zoom servers are capable of monitoring user’s messages. Thereby, to solve the privacy problem, in May 2020, Zoom acquired Keybase so that Keybase’s team can help it to build end-to-end encryption meeting while remain Zoom’s current scalability and high-performance. Nonetheless, according to the latest released Zoom’s...

As surveillance systems are popular, the privacy of the recorded video becomes more important. On the other hand, the authenticity of video images should be guaranteed when used as evidence in court. It is challenging to satisfy both (personal) privacy and authenticity of a video simultaneously, since the privacy requires modifications (e.g., partial deletions) of an original video image while the authenticity does not allow any modifications of the original image. This paper proposes a...

Oblivious RAM protocols (ORAMs) allow a client to access data from an untrusted storage device without revealing to that device any information about their access pattern. Typically this is accomplished through random shuffling of the data such that the storage device cannot determine where individual blocks are located, resulting in a highly randomized access pattern. Storage devices however, are typically optimized for \emph{sequential} access. A large number of random disk seeks during...

Physically Unclonable Functions (PUFs) promise to be a critical hardware primitive to provide unique identities to billions of connected devices in Internet of Things (IoTs). In traditional authentication protocols a user presents a set of credentials with an accompanying proof such as password or digital certificate. However, IoTs need more evolved methods as these classical techniques suffer from the pressing problems of password dependency and inability to bind access requests to the...

In order to keep privacy and to maintain security of a data; it was necessary to keep the data in hidden manner or in a crypt format. The proposed work describes the encryption and data hiding techniques for an H.264/ AVC video in a cloud environment. And it clearly specifies how the integrity of the data should be relevant enough in an unsecured and constrained communication medium. The proposed scheme is based on the stream cipher, RC4 encryption; while encrypting a data, it is necessary...

Random number generators have direct applications in information security, online gaming, gambling, and computer science in general. True random number generators need an entropy source which is a physical source with inherent uncertainty, to ensure unpredictability of the output. In this paper we propose a new indirect approach to collecting entropy using human errors in the game play of a user against a computer. We argue that these errors are due to a large set of factors and provide a...

The diversity of computing platforms is increasing rapidly. In order to allow security applications to run on such diverse platforms, implementing and optimizing the same cryptographic primitives for multiple target platforms and heterogeneous systems can result in high costs. In this paper, we report our efforts in developing and benchmarking a platform-independent Crypto Tools Library (CTL). CTL is based on a dataflow programming framework called Reconfigurable Video Coding (RVC), which...

Over the last two decades FPGAs have become central components for many advanced digital systems, e.g., video signal processing, network routers, data acquisition and military systems. In order to protect the intellectual property and to prevent fraud, e.g., by cloning an FPGA or manipulating its content, many current FPGAs employ a bitstream encryption feature. We develop a successful attack on the bitstream encryption engine integrated in the widespread Virtex-II Pro FPGAs from Xilinx,...

We analyze how fast we can solve general systems of multivariate equations of various low degrees over \GF{2}; this is a well known hard problem which is important both in itself and as part of many types of algebraic cryptanalysis. Compared to the standard exhaustive-search technique, our improved approach is more efficient both asymptotically and practically. We implemented several optimized versions of our techniques on CPUs and GPUs. Modern graphic cards allows our technique to run more...

The number and diversity of electronic gadgets has been steadily increasing and they are becoming indispensable to more and more professionals and non-professionals alike. At the same time, there has been fairly little progress in secure pairing of such devices. The pairing challenge revolves around establishing on-the-fly secure communication without any trusted (on- or off-line) third parties between devices that have no prior association. The main security issue is the danger of so-called...

In modern cryptography, stream ciphers are most useful in applications where information needs to be encrypted/decrypted at high speed (e.g. high resolution streaming video data) or when low footprint (gates/memory) encryption is required. In the literature, there exist plenty of stream ciphers whose internal states are based on arrays and that they use modular additions to generate output streams. The abundance of array-based stream ciphers with modular additions can be attributed to the...

The informal goal of a watermarking scheme is to ``mark'' a digital object, such as a picture or video, in such a way that it is difficult for an adversary to remove the mark without destroying the content of the object. Although there has been considerable work proposing and breaking watermarking schemes, there has been little attention given to the formal security goals of such a scheme. In this work, we provide a new complexity-theoretic definition of security for watermarking schemes. ...

Recently several researchers and practitioners have begun to address the problem of secure device pairing or how to set up secure communication between two devices without the assistance of a trusted third party. McCune, et al. [12] proposed Seeing-is-Believing (SiB), a system which uses a visual channel. The SiB visual channel consists of one device displaying the hash of its public key in the form of a two-dimensional barcode, and the other device reading this information using a photo...

In recent years secret permutations have been widely used for protecting different types of multimedia data, including speech files, digital images and videos. Based on a general model of permutation-only multimedia ciphers, this paper performs a quantitative cryptanalysis on the performance of these kind of ciphers against plaintext attacks. When the plaintext is of size $M\times N$ and with $L$ different levels of values, the following quantitative cryptanalytic findings have been...

The Common Scrambling Algorithm (CSA) is used to encrypt streams of video data in the Digital Video Broadcasting (DVB) system. The algorithm uses a combination of a stream and a block cipher, apparently for a larger security margin. However these two algorithms share a common key. In this paper we present a fault attack on the block cipher which can be launched without regarding the stream cipher part. This attack allows us to reconstruct the common key and thus breaks the complete Algorithm.

One of the approaches to deliver real-time video encryption is to apply permutations to the bytes within a frame of a fully encoded MPEG stream as presented in [2]. We demonstrate that this particular algorithm is vulnerable to a known-plaintext attack, and hence its use should be carefully considered. We also discuss modifications that can make the algorithm resistant to our attack.

TaKE cryptography offers subliminal marking of a digital stream so that any tampering, induces an unacceptable distortion of the primary information. Encrypted audio and video streams are decrypted by one key to the original content (e.g. music), and through another key to the digital watermark (e.g. name of legitimate user). Unlike the prevailing methods which are based on distorting the protected contents, or locking it through a digital signature, TaKE -- Tailored Key Encryption --...