<P> NSA did not tamper with the design of the algorithm in any way . IBM invented and designed the algorithm, made all pertinent decisions regarding it, and concurred that the agreed upon key size was more than adequate for all commercial applications for which the DES was intended . </P> <P> Another member of the DES team, Walter Tuchman, stated "We developed the DES algorithm entirely within IBM using IBMers . The NSA did not dictate a single wire!" In contrast, a declassified NSA book on cryptologic history states: </P> <P> In 1973 NBS solicited private industry for a data encryption standard (DES). The first offerings were disappointing, so NSA began working on its own algorithm . Then Howard Rosenblum, deputy director for research and engineering, discovered that Walter Tuchman of IBM was working on a modification to Lucifer for general use . NSA gave Tuchman a clearance and brought him in to work jointly with the Agency on his Lucifer modification ." </P> <P> NSA worked closely with IBM to strengthen the algorithm against all except brute - force attacks and to strengthen substitution tables, called S - boxes . Conversely, NSA tried to convince IBM to reduce the length of the key from 64 to 48 bits . Ultimately they compromised on a 56 - bit key . </P>

Which of the following is the most secure form of des implementations