From: pauldf	Date: February 22nd, 2006 12:46 pm (UTC)		(Link)

yup, it's definitely doable.

I and a friend implemented DES for an undergrad class; I think it was in 1992, during my year as an exchange student in Norway. Our implementation wasn't getting the answer that some spec said we should, so I implemented it a second time in some spreadsheet program, probably Excel, partly so I could experiment with byte ordering (the description we were working from wasn't clear to me, at least at the time). Then we compared numbers in both implementations to find mismatches and fix them until we got the right answer both places.

Given CPU speeds at the time, it wasn't fast, but it worked.