Steganography Steganography is the art and science of hiding communication; a steganographic system thus embeds hidden content in unremarkable cover media so as not to arouse an eavesdropper's suspicion. In the past, people used hidden tattoos or invisible ink to convey steganographic content. Today, computer and network technologies provide easy-to-use communication channels for steganography.Essentially, the information-hiding process in a steganographic system starts by identifying a cover medium's redundant bits (those that can be modified without destroying that medium's integrity). 1 The embedding process creates a stego medium by replacing these redundant bits with data from the hidden message.Modern steganography's goal is to keep its mere presence undetectable, but steganographic systemsbecause of their invasive nature-leave behind detectable traces in the cover medium. Even if secret content is not revealed, the existence of it is: modifying the cover medium changes its statistical properties, so eavesdroppers can detect the distortions in the resulting stego medium's statistical properties. The process of finding these distortions is called statistical steganalysis.This article discusses existing steganographic systems and presents recent research in detecting them via statistical steganalysis. Other surveys focus on the general usage of information hiding and watermarking or else provide an overview of detection algorithms. 2,3 Here, we present recent research and discuss the practical application of detection algorithms and the mecha n i s m s for getting around them. The basics of embeddingThree different aspects in information-hiding systems contend with each other: capacity, security, and robustness. 4 Capacity refers to the amount of information that can be hidden in the cover medium, security to an eavesdropper's inability to detect hidden information, and robustness to the amount of modification the stego medium can withstand before an adversary can destroy hidden information.Information hiding generally relates to both watermarking and steganography. A watermarking system's primary goal is to achieve a high level of robustness-that is, it should be impossible to remove a watermark without degrading the data object's quality. Steganography, on the other hand, strives for high security and capacity, which often entails that the hidden information is fragile. Even trivial modifications to the stego medium can destroy it.A classical steganographic system's security relies on the encoding system's secrecy. An example of this type of system is a Roman general who shaved a slave's head and tattooed a message on it. After the hair grew back, the slave was sent to deliver the now-hidden message. 5 Although such a system might work for a time, once it is known, it is simple enough to shave the heads of all the people passing by to check for hidden messages-ultimately, such a steganographic system fails.Modern steganography attempts to be detectable only if secret information is known-namely, a secret

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This paper presents a new method for specifying and analyzing cryptographic protocols. Our method o ers several advantages over previous approaches. Our technique is the rst to allow reasoning about nonmonotonic protocols. These protocols are needed for systems that rely on the deletion of information. There is no idealization step in specifying protocols; we specify at a level that is close to the actual implementation. This avoids errors that might otherwise render a speci cation that passes the analysis, useless in practice. In our method, knowledge and belief sets for each principal are modi ed via actions and inference rules. Every message is considered to be broadcast, and we i n troduce the update function to maintain global knowledge. We show h o w our method uncovers the known aw in the Needham and Schroeder protocol 11 , and that the revision by the same authors 12 does not contain this aw. We also show that our method correctly handles protocols that are trivially insecure, such a s Nessett's noted example. 13 We then apply our method to our khat protocol 14. The analysis reveals a serious, previously undiscovered aw in our nonmonotonic protocol for long-running jobs; one that seems obvious in hindsight, but escaped the attention of the authors and over 300 USENIX conference attendees. In addition, our analysis reveals a previously unknown vulnerability in phase II of khat. These are stunning con rmations of the importance of tools for analyzing cryptographic protocols.

With the implantation of software-driven devices comes unique privacy and security threats to the human body. BY A.J. BURNS, M. ERIC JOHNSON, AND PETER HONEYMAN key insights ˽ The achievements of modern engineering and computer science are producing medical technologies that not only extend the lives of many patiences, but also enhance the quality of life for many more managing chronic illness. ˽ Though medical devices are unique, the cybersecurity threats to medical device security are not unlike those that threaten other software-controlled, network-enabled devices. ˽ All security-focused decisions involve trade-offs. To fully understand the security trade-offs involved in designing, deploying, and maintaining medical devices, we believe it is critical to pause and take stock of what is at stake.