The first public algorithm that solved many of the
problems
was introduced in 1975 by
IBM, the National Security Agency (NSA), and the National Bureau of
Standards (NBS) (now called NIST). This algorithm was simply known as
the Data Encryption Standard, or DES. DES is the U.S. Government's
Data Encryption Standard, a product cipher that operates on 64-bit
blocks of data, using a 56-bit key. Instead of defining just one
encryption algorithm, DES defines a whole family of them (several
quadrillion, in fact). With a few exceptions, a different algorithm is
defined for each number less than 
.
This means that everybody can be told about the algorithm and your
message will still be secure. This makes your secret key much
smaller. It is no longer necessary to send a copy of your algorithm to
each person you want to communicate with. You just need to tell them
your secret key, a number less than . The number is
also large enough to make it difficult to break the code using a brute
force attack (i.e., trying to break the cipher by using all possible
keys).
DES has withstood the test of time. Despite the fact that its algorithm is well known, it is impossible to break the cipher without using tremendous amounts of computing power. If you use DES three times on the same message with different secret keys, it is virtually impossible to break it using existing algorithms. Over the past few years several new, faster symmetric algorithms have been developed, but DES remains the most frequently used.