BOOT CAMP 182 (05/07//01)




This weeks Boot Camp contains highly sensitive information and is issued to you strictly on an Eyes Only basis! We receive quite a lot of emails and letters asking about the security of emails and PCs, so we'd better start off by saying that your PC, the information contained on its hard drive and the emails you send and receive can be read by almost anyone who has a mind to. In short the average computer is about as secure as wet paper bag, and it's one of the last places where you would want to hide valuable data or use to communicate secret or sensitive information.


We all know that emails are as private as a seaside postcard; in addition to the well-publicised abilities of Western intelligence agencies to intercept electronic messaging, emails pass through many server computers, often in several countries, with widely varying degrees levels of security. Data on PC hard disc drives can be easily read if the computer in question has an Internet connection (see Boot Camp 144, September 28th 2000 on Trojans) Even if the PC is not connected to the Internet or a network there are still plenty of ways of getting at it, moreover deleting data and wiping or formatting the disc won't help. Data can still be retrieved even if it has been overwritten several times, in fact the only way to ensure that data cannot be read from a hard disc drive is to physically destroy it, which is precisely what the US military now does to its PCs when they are scrapped or replaced.


Of course data can be encrypted and this does indeed provide a degree of protection against all but the most determined and resourceful hackers and crackers. Powerful encryption systems like PGP (Pretty Good Privacy, are very secure and files can only be decoded and read by seriously well-equipped spooks and government agencies etc., but the very fact that you send or receive encrypted files or have them stored on your PC immediately suggests that you have got something to hide!


That brings us to this week's topic, Steganography sometimes referred to as electronic watermarking. Steganography, from the Greek meaning covered writing, is the science -- some say it's an art -- of hiding information or communications inside something innocuous, so that no one suspects it is there in the first place. It's certainly not a new idea and the Greek historian Herodotus (474 BC) tells of secret messages hidden beneath wax tablets, tattooed on the shaven head of a slave and secreted in the belly of an unskinned hare. Steganography also covers such stealthy practices as sending secret messages written in invisible ink, microdots and radio signals that resemble noise or static. Modern computer steganography works in a similar fashion, hiding data, be it text messages, images etc., inside other files -- and as a further precaution the data can be encrypted -- from the outside and even when closely examined by experts, everything looks perfectly innocent.


Steganography works on almost any type of host data but it works best with large files containing a lot of redundant information, typically image files (.jpg, .gif, .bmp, .tif, etc.) and sound and music files (mp3, .wav etc.,), all of which exist in abundance on most PCs and are commonly sent as email attachments so in the normal course of events their presence arouses little or no suspicion. Messages can also be hidden inside web pages, .pdf files, word processor documents and disguised as spam email messages. One very clever technique is to add a little bit of white space to the end of each line in an email, into which data can be invisibly embedded.


The real art of Stenography is to not arouse suspicion so that even though an image file contains thousands of words of text, the size of the file is not significantly larger than a normal, non-message bearing image file. However, steganography, like all cryptographic techniques is not infallible and equal, if not greater effort is applied to developing detection and counter measures. Sophisticated programs are available in the intelligence communities based on complex algorithms that carry out statistical tests on suspect files, capable of identifying stenographic 'fingerprints' though, given the massive volumes of emails now flying through cyberspace it is extremely unlikely that anything more than a tiny fraction of messages can be routinely analysed.


If you are wondering what all this cloak and dagger stuff has to do with you just consider the basic privacy issues. Whilst emails that you send may not contain any particularly secret or sensitive information, they are undoubtedly private, possibly very personal and almost certainly not for public consumption. The fact is that once an email has left your PC it can in theory be read by hundreds of people, and that's not counting all the people who have access to the recipients PC. Steganography is also extremely useful for business users and travellers visiting countries where email communications can be difficult or are known to be routinely intercepted. So how does it work in practice?


More than 50 powerful steganography and encryption programs are freely available for download from the Internet (see Links), most of them are quite small and they are generally easy to use. The usual procedure is to select the container file (image, document, music file etc.) then the secret data file, create a password and two files are combined resulting in a new data carrying file. This can then be treated in exactly the same way as a normal file of that type and stored on the PC or sent as an email attachment etc. Retrieval is a reversal of the encoding process, the same program is used to open the file, the user is asked for a password and the hidden file is extracted.


This issue of Dotcom will now self-destruct in ten seconds….





Next week – 10 things to do with a dead (or old) PC





Joint Photographic Experts Group, compressed image file 



Moving Picture Expert Group 3, CD quality sound file used for music on the Internet



Portable Document Format, interactive text file with web-like links



Tagged Image Format File, graphics file



Waveform, windows sound file



Hidden program on a PC, usually installed surreptitiously or by an email attachment that allows an external 'client' PC to access files stored on the hard disc drive when it is connected to the Internet or a network




Whilst we're on the subject of secrecy you might be interested in this little utility, called Scramdisk, which ferrets away information on your hard disc by creating a virtual encrypted drive. Files stored in this 'container' can only be accessed with a password, or passwords and to make doubly sure it stays safe the information in the file is encrypted using one of several powerful algorithms, or hidden from view using steganography. Scramdisc for Windows 95/98 is a very compact program and the download zip file is just 187kb. It's freeware and available from:

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