NOTE: The 1973 Fire at the National Personnel Records Center damaged or destroyed 16-18 million Army and Air Force records that documented the service history of former military personnel discharged from 1912-1964. Although the information in many of these primary source records was either badly damaged or completely destroyed, often alternate record sources can be used to reconstruct the service of the veterans impacted by the fire. Sometimes we are able to reconstruct the service promptly using alternate records that are in our holdings, but other times we must request information from other external agencies for use in records reconstruction. In some instances, therefore, requests that involve reconstruction efforts may take several weeks to a month to complete.
There have also been attacks proposed against reduced-round versions of the cipher, that is, versions of DES with fewer than 16 rounds. Such analysis gives an insight into how many rounds are needed for safety, and how much of a "security margin" the full version retains. Differential-linear cryptanalysis was proposed by Langford and Hellman in 1994, and combines differential and linear cryptanalysis into a single attack. An enhanced version of the attack can break 9-round DES with 2 chosen plaintexts and has a 2 time complexity (Biham and others, 2002).