No abstract
Abstract-The primary goal of information security is to ensure the confidentiality, integrity, authenticity, and availability of information. Availability is often relegated to a discussion of denial of service attacks on network resources. Another form of denying availability is to prevent communication through the use of traditional jamming techniques. At the United States Air Force Academy Center for Information Security, we have been working on a new algorithm, BBC, which is based on a new type of coding theory known as concurrent codes, that is resistant to traditional jamming techniques. While the formal definition and proofs of concurrent codes can be daunting, the algorithm's effectiveness can be easily conveyed and appreciated through visual demonstration. This paper briefly introduces concurrent codes and describes an interactive applet that visually demonstrates the algorithm's effectiveness in a noisy environment.
Abstract-The advent of concurrent coding theory means that omnidirectional communication systems can possess a level of keyless jam-resistance comparable to that of traditional spread spectrum systems, all of which rely on shared secret keys. To achieve this, concurrent codecs possess the ability to efficiently separate multiple legitimate codewords that have been superimposed. This is achieved by leveraging a highly asymmetric sensitivity to bit errors and, consequently, a reliance on communication channels having correspondingly high degrees of asymmetry in their bit error probabilities. While suitable physical channels must possess inherently high degrees of asymmetry, this asymmetry can be artificially enhanced using post processing techniques with the effect that system designers can trade small amounts of jam-resistance for increases in noise immunity. Furthermore, to rob potential adversaries of the option of attacking the receiver's ability to synchronize with the transmitted signal, concurrent codecs do not perform real-time adaptive synchronization and instead use asynchronous protocols. To avoid bit misalignments over the length of the packet, such protocols normally require that transmitters and receivers have oscillators with frequency tolerances on the order of one part in ten times the packet length. However, a concurrent codec can use simple post-processing techniques to exploit the asymmetry in bit error sensitivity to give receivers high degrees of immunity to timing jitter as well as high tolerances to oscillator mismatch. This has implications not only for processing gain, but also for implementation cost since transceivers can utilize oscillators having greatly relaxed specifications compared to that required by traditional systems. This paper presents these techniques and analyzes their impact on jam-resistance and oscillator performance requirements.
A form of visual jam resistant coding is presented. Using Visual BBC, a modified form of BBC (Baird, Bahn, Collins) coding, it is shown that several images can be printed on clear plastic, such that when they are superimposed (i.e., a bitwise OR of the pixels is performed), the resulting image may look random, but the original images can still be recovered without any information about the original pictures and without any secret. BBC is a complex subject to understand, and so Visual BBC aids the teaching of how BBC coding works, by giving students a concrete, physical model. Examples are shown, illustrating that it is possible for legitimate BBC codewords to actually look like recognizable images, rather than just random binary strings. This allows us to superimpose arbitrary pictures and separate them again in linear time without using any keys or channels specific to each picture. This is not possible in any other coding systems, such as error correcting codes, superimposed codes, or steganography systems. In addition, a number of analysis problems are described that can be given to students, which are motivated by the issues arising in Visual BBC, and which further increase student understanding of the system.
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