The Cardano grille consists of a sheet of stiff material, such as cardboard, parchment, or metal, into which rectangular holes, the height of a line of writing and of varying lengths, are cut at irregular intervals. The encipherer lays this mask over a sheet of writing paper and writes the secret message through the perforations, some of which will take a whole word, others a single letter, others a syllable. He then removes the grille and fills in the remaining spaces with an innocuous-sounding cover message. Cardano prescribed copying the message three times to smooth out any irregularities in the writing that might give the secret away.
Kahn, David. The Codebreakers: The Comprehensive History of Secret Communications from Ancient Times to the Internet. New York: Scribner, 1996. 144.
Many ingenious methods of message concealment have been invented. Among these methods are hidden tattoos, covered writings, invisible inks, microdots, character arrangement (other than the cryptographic methods of permutation and substitution), null ciphers, code words, forms of digital signatures, covert channels, and spread-spectrum communications.
Steganography can be applied in many ways to digital media. One method of applying steganography is hiding information within images such as photographs or drawings. A common method for hiding information in an image is to store information bits within the least significant bits of the pixels comprising the image. Steganography can be used to hide information within plain text files or withing audio, video, and data transmissions.
Duric, Zoran, Sushil Jajodia and Neil F. Johnson. Information Hiding: Steganography and Watermarking – Attacks and Countermeasures. Norwell: Kluwer Academic Publishers, 2001. p. 2.
Steganography is the art of hiding and transmitting data through apparently innocuous carriers in an effort to conceal the existence of the data. The word steganography, as derived from Greek, literally means covered or hidden writing and includes a vast array of methods of secret communications that conceal the very existence of the message. Though steganography is an ancient craft, the onset of computer technology has given it new life. Computer-based steganographic techniques introduce changes to digital covers to embed information to the native covers. Such information may be communicated in the form of text, binary files, or provide additional information about the cover and its owner….
Steganography can be viewed as akin to cryptography. Both have been used throughout recorded history as means to add elements of secrecy to communication. Cryptographic techniques “scramble” a message so that if it is intercepted, it cannot be understood.
This process is known as encryption and the encrypted message is sometimes referred to as ciphertext. Steganography, in essence, “camouflages” a message to hide its existence and make it seem “invisible” thus concealing the fact that a message is being sent altogether. A ciphertext message may draw suspicion while an invisible message will not.
Duric, Zoran, Sushil Jajodia and Neil F. Johnson. Information Hiding: Steganography and Watermarking – Attacks and Countermeasures. Norwell: Kluwer Academic Publishers, 2001. p. 1-2.
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