Editing Padding (cryptography) (section)

==Classical cryptography==
Official messages often start and end in predictable ways: ''My dear ambassador, Weather report, Sincerely yours'', etc. The primary use of padding with [[classical cipher]]s is to prevent the cryptanalyst from using that predictability to find [[Known-plaintext attack|known plaintext]]<ref>[[Gordon Welchman]], ''The Hut Six Story: Breaking the Enigma Codes'', p. 78.</ref> that aids in breaking the encryption. Random length padding also prevents an attacker from knowing the exact length of the plaintext message.

A famous example of classical padding which caused a great misunderstanding is "[[the world wonders]]" incident, which nearly caused an Allied loss at the World War II [[Battle off Samar]], part of the larger [[Battle of Leyte Gulf]]. In that example, [[Admiral Chester Nimitz]], the [[CINCPACFLT|Commander in Chief, U.S. Pacific Fleet]] in WWII, sent the following message to [[Admiral Bull Halsey]], commander of Task Force Thirty Four (the main Allied fleet) at the Battle of Leyte Gulf, on October 25, 1944:<ref name=Willmott>{{Cite book| publisher = Indiana University Press| isbn = 9780253003515| last = Willmott| first = H. P.| title = The Battle of Leyte Gulf: The Last Fleet Action| date = 19 August 2005 |section=The Great Day of Wrath: 25 October 1944}}</ref>

{{quote |Where is, repeat, where is Task Force Thirty Four?<ref name=Tuohy/>}}

With padding (bolded) and [[metadata]] added, the message became:

{{quote |<code>'''TURKEY TROTS TO WATER''' GG FROM CINCPAC ACTION COM THIRD FLEET INFO COMINCH CTF SEVENTY-SEVEN X WHERE IS RPT WHERE IS TASK FORCE THIRTY FOUR RR '''THE WORLD WONDERS'''</code><ref name=Tuohy>{{cite book|last=Tuohy|first=William|title=America's Fighting Admirals: Winning the War at Sea in World War II|publisher=MBI Publishing Company|year=2007|isbn=9780760329856|url-access=registration|url=https://archive.org/details/americasfighting00tuoh}}</ref>}}

Halsey's radio operator mistook some of the padding for the message and so Admiral Halsey ended up reading the following message:

{{quote |Where is, repeat, where is Task Force Thirty Four? The world wonders<ref name=Tuohy/>}}

Admiral Halsey interpreted the padding phrase "the world wonders" as a sarcastic reprimand, which caused him to have an emotional outburst and then lock himself in his bridge and sulk for an hour before he moved his forces to assist at the Battle off Samar.<ref name=Willmott /> Halsey's radio operator should have been tipped off by the letters ''RR'' that "the world wonders" was padding; all other radio operators who received Admiral Nimitz's message correctly removed both padding phrases.<ref name=Willmott />

Many classical ciphers arrange the plaintext into particular patterns (e.g., squares, rectangles, etc.) and if the plaintext does not exactly fit, it is often necessary to supply additional letters to fill out the pattern. Using nonsense letters for this purpose has a side benefit of making some kinds of cryptanalysis more difficult.
<!--Such padding is not used in modern cryptography because modern ciphers are designed to be secure even when the cryptanalyst chooses the message to encrypt.-->