Covert channels are used for the secret transfer of information. Encryption only protects communication from being decoded by unauthorised parties, whereas covert channels aim to hide the very existence of the communication. Initially, covert channels were identified as a security threat on monolithic systems i.e. mainframes. More recently focus has shifted towards covert channels in computer network protocols. The huge amount of data and vast number of different protocols in the Internet seems ideal as a high-bandwidth vehicle for covert communication. This article is a survey of the existing techniques for creating covert channels in widely deployed network and application protocols. We also give an overview of common methods for their detection, elimination, and capacity limitation, required to improve security in future computer networks.

https://researchbank.swinburne.edu.au/file/5de97ea6-fcdf-43e5-98ae-0567cdd495f6/1/PDF (Published version).pdf

A survey of covert channels and countermeasures in computer network protocols

Recent research in sensor networks has raised security issues for small embedded devices. Security concerns are motivated by the deployment of a large number of sensory devices in the field. Limitations in processing power, battery life, communication bandwidth and memory constrain the applicability of existing cryptography standards for small embedded devices. A mismatch between wide arithmetic for security (32 bit word operations) and embedded data bus widths (often only 8 or 16 bits) combined with lack of certain operations (e.g., multiply) in the ISA present other challenges.This paper offers two contributions. First, a survey investigating the computational requirements for a number of popular cryptographic algorithms and embedded architectures is presented. The objective of this work is to cover a wide class of commonly used encryption algorithms and to determine the impact of embedded architectures on their performance. This will help designers predict a system's performance for cryptographic tasks. Second, methods to derive the computational overhead of embedded architectures in general for encryption algorithms are developed. This allows one to project computational limitations and determine the threshold of feasible encryption schemes under a set of the constraints for an embedded architecture.Experimental measurements indicate uniform cryptographic cost for each encryption class and each architecture class and negligible impact of caches. RC4 is shown to outperform RC5 for the Motes Atmega platform contrary to the choice of RC5 for the Motes project, a choice driven in large by memory constraints. The analytical model allows to assess the impact of arbitrary embedded architectures as a multi-variant function for each encryption scheme. Overall, our results are not only valuable to assess the feasibility of encryption schemes for existing embedded architectures, they also extend to assess the feasibility of encryption methods for new algorithms and architectures for sensor systems.

/pdf/analyzing-and-modeling-encryption-overhead-for-sensor-2x2qwkfo7f.pdf

Analyzing and modeling encryption overhead for sensor network nodes

XOM-based secure processor has recently been introduced as a mechanism to provide copy and tamper resistant execution. XOM provides support for encryption/decryption and integrity checking. However, neither XOM nor any other current approach adequately addresses the problem of information leakage via the address bus. This paper shows that without address bus protection, the XOM model is severely crippled. Two realistic attacks are shown and experiments show that 70% of the code might be cracked and sensitive data might be exposed leading to serious security breaches.Although the problem of address bus leakage has been widely acknowledged both in industry and academia, no practical solution has ever been proposed that can provide an adequate security guarantee. The main reason is that the problem is very difficult to solve in practice due to severe performance degradation which accompanies most of the solutions. This paper presents an infrastructure called HIDE (Hardware-support for leakage-Immune Dynamic Execution) which provides a solution consisting of chunk-level protection with hardware support and a flexible interface which can be orchestrated through the proposed compiler optimization and user specifications that allow utilizing underlying hardware solution more efficiently to provide better security guarantees.Our results show that protecting both data and code with a high level of security guarantee is possible with negligible performance penalty (1.3% slowdown).

/pdf/hide-an-infrastructure-for-efficiently-protecting-29igikubyx.pdf

HIDE: an infrastructure for efficiently protecting information leakage on the address bus

In an ideal world, interface design is the art and science of helping users accomplish tasks in a timely, efficient, and pleasurable manner. This paper studies the inverse situation, the vast emergence of deliberately constructed malicious interfaces that violate design best practices in order to accomplish goals counter to those of the user. This has become a commonplace occurrence both on and off the desktop, particularly on the web. A primary objective of this paper is to formally define this problem, including construction of a taxonomy of malicious interface techniques and a preliminary analysis of their impact on users. Findings are presented that gauge the self-reported tolerance and expectation levels of users with regard to malicious interfaces as well as the effectiveness and ease of use of existing countermeasures. A second objective of this paper is to increase awareness, dialogue, and research in a domain that we consider largely unexplored but critical to future usability of the WWW. Our results were accomplished through significant compilation of malicious interface techniques based on review of thousands of web sites and by conducting three surveys. Ultimately, this paper concludes that malicious interfaces are a ubiquitous problem that demands intervention by the security and human computer interaction communities in order to reduce the negative impact on the global user population.

http://www.rumint.org/gregconti/publications/201004_malchi.pdf

Malicious interface design: exploiting the user

Recent research in sensor networks has raised issues of security for small embedded devices. Security concerns are motivated by the deployment of a large number of sensory devices in the field. Limitations in processing power, battery life, communication bandwidth and memory constrain the applicability of existing cryptography standards for small embedded devices. A mismatch between wide arithmetic for security (32 bit word operations) and embedded data bus widths (often only 8 or 16 bits) combined with lack of certain operations (e.g., multiply) in the ISA present other challenges.This paper offers two contributions. First, a survey investigating the computational requirements for e a number of common cryptographic algorithms and embedded architectures is presented. The objective of this work is to cover a wide class of commonly used encryption algorithms and to determine the impact of embedded architectures on their performance. This will help designers predict a system's performance for cryptographic tasks. Second, methods to derive the computational overhead of embedded architectures in general for encryption algorithms are developed. This allows one to project computational limitations and determine the threshold of feasible encryption schemes under a set of the constraints for an embedded architecture.Experimental measurements indicate uniform cryptographic cost for each encryption class and each architecture class and negligible impact of caches. RC4 is shown to outperform RC5 for the Atmega platform. But when message authentication is required in addition to encryption, hash or block ciphers, such as RC5, have the advantage of providing support for both authentication and encryption. The analytical model allows to assess the impact of arbitrary embedded architectures as a multi-variant function for each encryption scheme. Overall, our results are not only valuable to assess the feasibility of encryption schemes for existing embedded architectures, they also extend to assess the feasibility of encryption methods for new algorithms and architectures for sensor systems.

/pdf/encryption-overhead-in-embedded-systems-and-sensor-network-2p3cvdayhr.pdf

Encryption overhead in embedded systems and sensor network nodes: modeling and analysis

Although smart cards are becoming used in an increasing number of applications, there is small literature of the implementation issues for smart cards. This paper describes the issues and considerations that need to be taken into account when implementing the key generation step of a cryptographic algorithm widely used nowadays, RSA.Smart cards are used in many applications that require a tamper resistant area. Therefore, smart cards that use cryptography have to provide encryption, decryption, as well as key generation inside its security perimeter. RSA key generation is a concern for on-card implementation of RSA cryptosystem, as it usually takes a long time. In this paper, two simple but efficient key generation algorithms are evaluated, in addition to a simple but not very efficient algorithm. The paper discusses in detail how to build fast implementations for the three algorithms presented, using smart cards with crypto-coprocessor.

Implementation of fast RSA key generation on smart cards

This paper presents a systematic solution to the problem of using ICMP tunneling for covert channel. ICMP is not multiplexed via port numbers and the data part of the ICMP packet provides considerable bandwidth for malicious covert channels. These factors make it an integral part of many malicious software like remote access and denial of service attack tools. These tools use ICMP to establish covert communication channels. In this paper a stateless model is proposed to prevent ICMP tunneling. A Linux kernel module was implemented to demonstrate the proposed stateless solution. The module enforces a fixed payload policy for ICMP packets and virtually eliminates ICMP tunneling which arises due to the data carrying capability of ICMP. The performance impact on end hosts and routers due to the stateless monitoring model is described.

Malicious ICMP tunneling: defense against the vulnerability

Users are often forced to trust potentially malicious terminals when trying to interact with a remote secure system. This paper presents an approach for ensuring the integrity and authenticity of messages sent through an untrusted terminal by a user to a remote trusted computing base and vice versa. The approach is both secure and easy to use. It leverages the difficulty computers have in addressing some artificial intelligence problems and therefore requires no complex computation on the part of the user. This paper describes the general form of the approach, analyzes its security and user-friendliness, and describes an example implementation based on rendering a 3-D scene.

/pdf/a-user-friendly-approach-to-human-authentication-of-messages-21a06xpssc.pdf

A user-friendly approach to human authentication of messages

As applications enabled by the Internet become information rich, ensuring access to quality information in the presence of potentially malicious entities will be a major challenge. Denial of information (DoI) attacks attempt to degrade the quality of information by deliberately introducing noise that appears to be useful information. The mere availability of information is insufficient if the user must find a needle in a haystack of noise that is created by an adversary to hide critical information. We focus on the characterization of information quality metrics that are relevant in the presence of DoI attacks. In particular, two complementary metrics are explored. Information regularity captures predictability in the patterns of information creation and access. The second metric, information quality trust, captures the known ability of an information source to meet the needs of its clients.

/pdf/guarding-the-next-internet-frontier-countering-denial-of-36hi6tmm4a.pdf

Guarding the next Internet frontier: countering denial of information attacks

Due to limited available memory (of the order of Kilobytes) on embedded devices (such as smart cards), we undertake an approach of partitioning a whole program. The program partitions are down-loaded from the server on demand into the embedded device just before execution. We devise a novel method of partitioning the code and data of the program such that no information regarding the control flow and behavior of the program is leaked out. In other words, by observing the program partitions that are down-loaded from the server, one is unable to guess which branches are taken in the program. The partitioning scheme generates minimal safe program regions which do not reveal the control flow information when transmitted on demand but any further partitioning of which will reveal such an information. Minimal safe regions allow minimal usage of memory on the embedded device and thus enable maximal number of multiple applications to simultaneously reside on the embedded device. The minimal safe regions can be merged on demand to create larger safe regions to improve runtime efficiency. The larger the number of regions to be downloaded on the device, the lower is the performance of the application and vice-versa. Our approach handles this tradeoff between the number of simultaneous applications that would reside on the embedded device and the performance of each application. This approach is scalable both to the number of simultaneous applications and to the amount of memory available. The worst case performance degradation is shown to be below 10% with the benefit of allowing arbitrarily large/multiple applications to be deployed.

Andre L. M. dos Santos

Papers

Implementation of fast RSA key generation on smart cards

Malicious ICMP tunneling: defense against the vulnerability

A user-friendly approach to human authentication of messages

Guarding the next Internet frontier: countering denial of information attacks

Leakage-proof program partitioning