Tap code: Difference between revisions

Revision as of 05:33, 16 July 2007

Revision as of 23:56, 14 August 2007

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The '''Tap Code''' is a [[code (cryptography)|code]], commonly used by prisoners in jail to communicate with one another. The method of communicating is usually by "tapping" either the metal bars or the walls inside the cell, hence its name. It is a very simple code, not meant to avoid interception, since the messages are sent in [[cleartext]].

It was reportedly invented in June [[1965]] by four [[POW]]s imprisoned in [[Hoa Lo]], [[Vietnam]]: [[Captain]] Carlyle ("Smitty") Harris, [[Lieutenant]] Phillip Butler, Lieutenant Robert Peel and [[Lieutenant Commander]] Robert Shumaker. Harris remembered an [[United States Air Force|Air Force]] instructor who had shown him a code based on a five-by-five alphabet [[matrix]] (a [[Polybius square]]), as shown on the graph below. Each letter was communicated by tapping two numbers: the first designated the row (horizontal) and the second designated the column (vertical). The letter "X" was used to break up sentences and the letter "C" replaced the letter "K".

The Tap Code is featured in [[Arthur Koestler]]'s classic work ''[[Darkness at Noon]]'', which was published in 1941. The prisoners refer to it as the knock code, but the technique is still the same.

The Tap Code is outlined in the table below:

::{| border="2" cellpadding="10" cellspacing="0" style="margin: 0 0 1em 0.5em; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 95%;"

|- bgcolor="lightgray"

! !! 1 !! 2 !! 3 !! 4 !! 5

|-

!bgcolor="lightgray"| 1

| A || B || C || D || E

|-

!bgcolor="lightgray"| 2 1

| A || B || C || D || E

|-

!bgcolor="lightgray"| 1 2

| F || G || H || I || J

|-

!bgcolor="lightgray"| 3

| L || M || N || O || P

|-

!bgcolor="lightgray"| 4

| Q || R || S || T || U

|-

!bgcolor="lightgray"| 5

| V || W || X || Y || Z

|}

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Or to communicate the word "WATER" the code would be the following (the time between each pair of numbers is smaller than the one between two different letters):

..... .. . . .... .... . ..... .... ..

(5,2) (1,1) (4,4) (1,5) (4,2)

W A T E R

Because of the difficulty and length of time required for specifying a single letter, most prisoners devised [[abbreviations]] and [[acronyms]] for common items or phrases, such as "GN" for ''Good Night'', or "GBU" for ''God Bless You''.

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==References==

* [http://www.airsoftgent.be/dbase/tapcode.htm The Tap Code]

* [http://www.braingle.com/brainteasers/codes/tapcode.php Online Tap Code Encoder/Decoder]

* Koestler, Arthur, ''Darkness at Noon'' (1941). Translated by Daphne Hardy. See page 19 of the Bantam Publishing paperback, 1981 printing for more info.

{{Crypto navbox | classical}}

[[Category:Encodings]]