# Layered Encryption

Layered Encryption is a way of encrypting a string or message so that it is more difficult to decrypt than normal. This is done by applying multiple codes or ciphers one after another, so that the ciphertext of the first becomes the plaintext of the next, and so on.

## Puzzle Application

Many commonly-used encryption methods in hunt puzzles are essentially just substitution ciphers. As a result, most can be decoded rather easily once discovered. Layering multiple encryptions is a way to remedy this problem. However, the resulting difficulty can vary from 'difficult to identify' to 'just taking longer', depending on what exactly is being used for each level of encoding.

Most commonly, puzzles using layered encryption will simply use a mix of Simple Substitution Ciphers, including Caesar Ciphers, Alphanumeric Substitution Ciphers (using 26-item sets), or Cryptograms. These ciphers in particular tend to avoid the symbols or numbers used in things like Binary, Braille, or Pigpen, meaning that a set of letters can usually become another set of letters relatively easily, even if an alphanumeric substitution cipher is used (assuming it uses written-out members of a size-26 set).

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## Examples

• Squad Car (MITMH 2007) (web) - The long string of text in this puzzle (once taken out of its police-car form) can be determined to be a cryptogram (as long as solvers spot that some sequences of letters repeat). Decrypting that gives them a series of NATO Phonetic Alphabet letters, which can be translated to get a NEW string of letters. This too can be treated as a cryptogram to get another set of things that become a new string of letters and so on. By the end, solvers will have gone through three cryptograms and three different word-to-letter substitutions.
• Infinite Cryptogram (MITMH 2013) (web) - Similar to Squad Car, this puzzle presents as a long string of text that can be decrypted (via Caesar Shift) to read a string of NATO Phonetic Alphabet letters, which can be decrypted again once translated to regular letters. The twist is that the string is given across multiple pages, 2000 letters per page, and there's approximately 1.79769e308 pages.
• Horse Code (MITMH 2017) (web) - A rare case of a puzzle using a symbol-based code in conjunction with a text-based cipher. In this puzzle, the plaintext gets encoded via a simple substitution cipher, only for the result to be translated into Morse Code (and all of the spaces removed).