Null Cipher (Concealment)

Null cipher (or concealment cipher) is a text steganography method that involves hiding a secret message within seemingly innocuous text. Unlike conventional ciphers, it does not modify the characters in the text but rather exploits their position, structure, or arrangement to encode information. The goal is to transmit an encrypted message without arousing suspicion.

Encoding involves inserting a secret message into plain text according to a predefined rule. There are countless rules, but here are the most well-known:

— First letter of each word: the hidden message is read by taking the first letter of each word in the text.

— Fixed position: taking every nth letter, for example, the second letter of each word or the fifth letter of each sentence.

— Contextual rule: choosing words according to an implicit code (word length, use of capital letters, presence of punctuation, etc.)

Encoding relies on creating a natural text that masks the message, often handwritten to maintain a fluid style.

Decoding involves applying the reverse reading rule of the cipher to extract the hidden message.

dCode offers dedicated tools for each type of rule.

— The text is sometimes unusually long or unnaturally fluid.

— Sentences may be incoherent or have abnormal structures.

— Typographical irregularities (spaces, capital letters, punctuation) may be present.