It's a piece of history! Quite possibly the most heavily-scrutinised cipher so far.
My B. Tech. thesis (2018–9) was on side-channel attacks, and I thereby became acquainted with DES. At that time, my team put together a poorly-written copy-pasted implementation and messed around with it until we got it to work on an ATmega328P.
Several years later, with more programming experience and a better understanding of cryptographic specifications, I decided to revisit the horrible code and rewrite it properly. And here we are.
make
./des test
The test vectors are from sci.crypt.
./des [key] [data]
[key] is the secret key; [data] is the data to encrypt. They must contain only hexadecimal digits. Otherwise (or if
they are not provided), they will be set to zero.
./des [key] [data] decrypt
As above, except that [key] and [data] must be provided.