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Data Hiding in Slack Space

Written by Rick Leinecker

Data Hiding in Slack Space

One of the most important topics in Digital Forensics is data hiding. The black hats continually look for methods with which to plant data in ways that you, the investigator,

cannot find. It is almost like a perpetual catand-mouse game. Just when you think you know how to find their secrets, they find new ways to hide them. The data might be a list of passwords, credit cards numbers, or maybe the secret plans for a bomb. In this article we examine a technique for hiding data in file slack. First, you will learn the theoretical underpinnings of the technique. Then, you will understand an open-source program that was specially written for this article.

To get the discussion started, we need to talk about the topology of data on storage devices. The smallest and most granular unit is a bit. In RAM, single transistors represent bits. On magnetic storage devices, discreet units of magnetic matter represent bits. Eight bits are organized into a byte, which relates to data types such as ASCII characters. The text “Hello” can be represented by a series of five bytes with numeric values 71, 101, 108, 108, and 111.

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Scott C. Zimmerman is a CISSP qualified Information Security consultant and presenter


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