[crypto] Add implementation of the DES cipher

The DES block cipher dates back to the 1970s.  It is no longer
relevant for use in TLS cipher suites, but it is still used by the
MS-CHAPv2 authentication protocol which remains unfortunately common
for 802.1x port authentication.

Add an implementation of the DES block cipher, complete with the
extremely comprehensive test vectors published by NBS (the precursor
to NIST) in the form of an utterly adorable typewritten and hand-drawn
paper document.

Signed-off-by: Michael Brown <[email protected]>

Author: mcb30