Information hiding techniques have recently become important in a number of application areas. Digital audio, video, and pictures are increasingly furnished with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorised copying directly. Military communications systems make increasing use of traffic security techniques which, rather than merely concealing the content of a message using encryption, seek to conceal its sender, its receiver or its very existence. Similar techniques are used in some mobile phone systems and schemes proposed for digital elections. Criminals try to use whatever traffic security properties are provided intentionally or otherwise in the available communications systems, and police forces try to restrict their use. However, many of the techniques proposed in this young and rapidly evolving field can trace their history back to antiquity; and many of them are surprisingly easy to circumvent. In this article, we try to give an overview of the field; of what we know, what works, what does not, and what are the interesting topics for research.

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Abstract. In the last few years, a large number of schemes have been proposed for hiding copyright marks and other information in digital pictures, video, audio and other multimedia objects. We describe some contenders that have appeared in the research literature and in the field; we then present a number of attacks that enable the information hidden by them to be removed or otherwise rendered unusable. Information Hiding ApplicationsThe last few years have seen rapidly growing interest in ways to hide information in other information. A number of factors contributed to this. Fears that copyright would be eroded by the ease with which digital media could be copied led people to study ways of embedding hidden copyright marks and serial numbers in audio and video; concern that privacy would be eroded led to work on electronic cash, anonymous remailers, digital elections and techniques for making mobile computer users harder for third parties to trace; and there remain the traditional 'military' concerns about hiding one's own traffic while making it hard for the opponent to do likewise.The first international workshop on information hiding [3] brought these communities together and a number of hiding schemes were presented there; more have been presented elsewhere. We formed the view that useful progress in steganography and copyright marking might come from trying to attack all these first generation schemes. In the related field of cryptology, progress was iterative: cryptographic algorithms were proposed, attacks on them were found, more algorithms were proposed, and so on. Eventually, theory emerged: fast correlation attacks on stream ciphers and differential and linear attacks on block ciphers, now help us understand the strength of cryptographic algorithms in much more detail than before. Similarly, many cryptographic protocols were proposed and almost all the early candidates were broken, leading to concepts of protocol robustness and techniques for formal verification [7].

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This paper analyzes a network-based denial of service attack for IF (Inteme.t Protocol) The paper contributes a detailed analysis of the SYN flooding attack and a discussion of existing and proposed countermeasures. Furthermore, we introduce a new solution approach, explain its design, and evaluate its perfonnance. Our approach offers protection against SYN flooding for all hosts connected to the same local area network, independent of their operating system or networking stack implementation. It is highly portable, configurable, extensible, and neither requires special hardware, nor modifications in routers or protected end systems.attacks cun be launched with little effort. Presently, it is difficult to trace an attack uack to its originator.Several possible solutions to this attack have been proposed by others, und some implemented. We have developed an active monitoring tool that classifies IP source addresses with high probability as being falsified or genuine. Our approach finds connection establishment protocol messages that are coming from forged IP addresses, and takes actions to ensure that the resulting illegitimate half-open connections arc reset immediately. This paper is organized as follows. Section 2 describes backgroWld material, such as the IP and TCP protocols. Section 3 explains the SYN flooding attack. Section 4 discusses existing approaches to solve this problem, such as configuration improvements and firewall-based approaches. The technical details of our approach are described in Section 5, followed by a performance evaluation in Section 6. Sections 7 and B outline future work issues and present conclusions.