Neil F. Johnson. Steganography. Technical Report. November 1995.

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2. Steganography

2.1 Definition

The word steganography literally means covered writing as derived from Greek. It includes a vast array of methods of secret communications that conceal the very existence of the message. Among these methods are invisible inks, microdots, character arrangement (other than the cryptographic methods of permutation and substitution), digital signatures, covert channels and spread-spectrum communications.

Steganography is the art of concealing the existence of information within seemingly innocuous carriers. Steganography can be viewed as akin to cryptography. Both have been used throughout recorded history as means to protect information. At times these two technologies seem to converge while the objectives of the two differ. Cryptographic techniques "scramble" messages so if intercepted, the messages cannot be understood. Steganography, in an essence, "camouflages" a message to hide its existence and make it seem "invisible" thus concealing the fact that a message is being sent altogether. An encrypted message may draw suspicion while an invisible message will not [JDJ01].

David Kahn places steganography and cryptography in a table to differentiate against the types and counter methods used. Here security is defined as methods of "protecting" information where intelligence is defined as methods of "retrieving" information [Kahn67]:

Signal SecuritySignal Intelligence
Communication SecurityCommunication Intelligence
  • Steganography (invisible inks, open codes, messages in hollow heels) and Transmission Security (spurt radio and spread spectrum systems)
  • Interception and direction-finding
  • Cryptography(codes and ciphers)
  • Cryptanalysis
  • Traffic security(call-sign changes, dummy messages, radio silence)
  • Traffic analysis (direction-finding, message-flow studies, radio finger printing)
Electronic Security Electronic Intelligence
  • Emission Security (shifting of radar frequencies, spread spectrum)
  • Electronic Reconnaissance (eaves-dropping on radar emissions)
  • Counter-Countermeasures "looking through" (jammed radar)
  • Countermeasures (jamming radar and false radar echoes)
Table 1: Kahn's Security Table

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