$ des  [-e|-d] -f <file> -k <key>

Key is 8 byte

In the encode mode, the file will be a stream of ASCII characters i.e, each visible character is read as a byte and the encrypted text is dumped as hex chars, therefore, in the decode mode, the file will be read as a stream of hex-chars, i,e each visible char as a nibble.

 ./des -e -k anitest1 -f adata.dat  > enc.dat
 ./des -d -k anitest1 -f enc.dat

Variable naming conventions are very awkward - that is to make it easier to understand when read with [2]

des.c - is the complete implementation of the encode as well as decode, easily read when [2] is referred.

flblkread.c - is the file reader to slurp the whole file at one go, if the file is too large to be handled error may be thrown.

getopts.c - option handler

Run a simple regression with regress.pl

Wikipedia Main entry and the supplementary material in: [1] http://en.wikipedia.org/wiki/DES_supplementary_material

Excellent Description With Example: [2] http://orlingrabbe.com/des.htm

[3] http://www.tropsoft.com/strongenc/des.htm