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Newspaper code
A hidden communication technique where small holes are poked just above the letters in a newspaper article that will spell out a secret message. A variant of this technique is to use invisible ink in place of holes.
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A method of steganography that uses a special ink that is colorless and invisible until treated by a chemical, heat, or special light. It is sometimes referred to as sympathetic ink.
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A method of concealing a message by which a piece of paper has several holes cut in it (the grille); and when it is placed over an innocent looking message, the holes cover all but specific letters spelling out the message. It was named for its inventor Girolamo Cardano.
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An overlaid image that is invisible to the naked eye, but which can be detected algorithmically. There are two different types of invisible watermarks: fragile and robust.
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A cryptographic analysis or attack that looks for repetition of letters in an encrypted message and compares that with the statistics of letter usage for a specific language, such as the frequency of the letters E, T, A, O, N, R, I, S, and H in the English language.
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Cipher that uses an encryption algorithm to rearrange the letters of a plain-text message to form the cipher-text message.
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