JED - October 2012 - (Page 47)

EW 101 Spectrum Warfare – Part 18 Steganography By Dave Adamy S teganography is defi ned as “hidden writing,” and has been around for centuries. However, with the advent of digital communication, it has taken on a whole new life. If you look up steganography on your web browser, you will get many evenings of entertainment; including detailed history, theory, countermeasures, and available software products to implement and detect it. As usual with this kind of subject, we will focus on its utility in electronic and information warfare and particularly on its applicability to spectrum warfare. STEGANOGRAPHY VS. ENCRYPTION This comparison is analogous to the difference between transmission security and message security in transmitted signal paths. When we use spread spectrum techniques, particularly highlevel direct-sequence spread spectrum (DSSS), the signal received by an enemy who does not have access to the pseudorandom spreading code is “noise like.” That is, the signal appears to be only a slight increase in the noise level in the direction of the transmitter. Thus, without special equipment and techniques, an enemy will not even be able to detect that a transmission has taken place. On the other hand, encryption keeps an enemy from being able to recover the information sent. The spread spectrum modulation provides transmission security, which prevents an enemy from locating and attacking the transmitter. Encryption is also required because it keeps the enemy from learning our secrets after sophisticated means are used to detect the signal. (See Figure 1.) Steganography deals directly with the information we are sending – either by hard copy or electronic means. It covers our secret messages with seemingly unrelated data, as shown in Figure 2; so an enemy will not even know that we are conducting important (typically military) communication. This, in effect, provides transmission security. Encryption has the same function as above – protecting our information if the enemy discovers our hidden messages. However, an encrypted message displays random letters or bits – making it obvious that we are hiding something. This tells the enemy that we are communicating important information, and may trigger an effort to analyze and ultimately recover our information. Steganography, if successful, will deny the enemy this operational advantage. The Journal of Electronic Defense | October 2012 EARLY STEGANOGRAPHIC TECHNIQUES One early technique discussed in some articles was to shave the head of a messenger, tattoo a message on his bald head, and let his hair grow back. His head was then shaved to recover the message. Other techniques have included writing innocuous messages in which some pattern of letters scattered through the message contained the hidden information. There was also the use of micro-dots and invisible inks in seemingly innocent written communication. One particularly interesting approach (in a WWII spy movie) was to 47 ENCRYPTOR MESSAGE SECURITY TRANSMISSION SECURITY DECRYPTOR SPREADING MODULATOR XMTR SPREADING DEMODULATOR RCVR Figure 1: Spread spectrum communication provides transmission security, while encryption provides message security.

Table of Contents for the Digital Edition of JED - October 2012

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Pacing the Anti-Ship Missile Threat
Cognition: EW Gets Brainy
Inside IEWS
EW 101
AOC News
Index of Advertisers
JED Quick Look

JED - October 2012