Although the size of groups can vary, deciphering is unambiguous because whenever the next element to be deciphered starts with a 2 or a 6, it is a pair otherwise, it is a singleton. The message can also be ciphered with a substitution cipher using the same straddling checkerboard to convert the digits back to letters again:ĭeciphering is simply the reverse of these processes. By passing digits through an additional transposition or substitution cipher stage can be used to secure message - to whatever extent transposition or substitution can be considered secure.įor example, securing the message above using as a secret key digits "0452" - digits of the secret key are repeated to get at least as many digits as there are digits in the message - and adding modulo 10 for transposition produces: The resulting message, 3113212731223655 has to be secured by other means if the straddling checkerboard table is not scrambled. The table below shows the conversion of string "ATTACK AT DAWN" into numbers using the straddling checkerboard setup above. This was the mechanism used in the VIC cipher.' Triple-Digit Scheme: As per the double-digit scheme above, but triple digits are used.This method cannot be used if the escape character is itself encoded by a double digit combination. In this way a stream of digits can be encoded with only one escape character. To 'escape' back to text the escape character is used. '26' in the example above), then multiple digits can be encoded by writing each out twice. Double-Digit Scheme: If the escape character is encoded by two different digits (e.g.In this scheme, each digit requires an escape character encoded before it. This means a digit is encrypted by 3 ciphertext characters 2 for the escape character, 1 for the digit itself. the slash '/') as per any letter, then write the required digit 'in-clear'. Single Digit Escape: Encode the numerical escape character (i.e.B=20)ĭigit-Encipherment: To encipher a digit, there are a few possible methods (which must be known/agreed beforehand): Characters in the third and fourth rows are replaced by a two-digit number representing their row and column numbers (with the row coordinate written first, i.e. Letter-Encipherment: To encipher a letter in the second row is simply replaced by the number labeling its column. Similar to the ordering of the digits in the header row, the alphabet characters can be presented in order (as it is here), or scrambled based on a secret keyword/phrase. The slash '/' is used as a numeric escape character (indicating that a numeral follows).The period '.' is used as a full stop or decimal separator,.The remaining two rows are labeled with one of the two digits that were not assigned a letter in the second row, and then filled out with the rest of the alphabet, plus the two symbols '.' and '/'. The second row is typically set up with eight high-frequency letters (mnemonics for the English language include 'ESTONIA-R', 'A SIN TO ER(R)', 'AT ONE SIR'), leaving two blank spots this row has no row coordinate in the first column. They can be presented in order, as in the above table, or scrambled (based on a secret key value) for additional security. The header row is populated with the ten digits, 0-9. It was later used as the basis for the message-to-digits step in the VIC cipher.Ī straddling checkerboard is set up something like this: In more modern times it was used by communist forces during the Spanish Civil War in order to protect their radio and written transmissions. Matteo is credited for designing what is now called the straddling checkerboard cipher. In the late 1580s, this position was held by members of the Argenti family, most notably Giovanni Batista and his nephew, Matteo. In 1555, Pope Paul IV created the office of Cipher Secretary to the Pontiff. It also is known as a monôme-binôme cipher. JSTOR ( January 2020) ( Learn how and when to remove this template message)Ī straddling checkerboard is a device for converting an alphanumeric plaintext into digits whilst simultaneously achieving fractionation (a simple form of information diffusion) and data compression relative to other schemes using digits.Unsourced material may be challenged and removed.įind sources: "Straddling checkerboard" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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