(A)RC4 used to fit the bill, since it was so simple to write. But it's also less-than-secure these days. I'm wondering if there's a successor that's: Code is small enough to write & debug within an hour or so, using pseudo code as a template. Still considered secure, as of 2010. Optimized for software. Not encumbered by licensing issues. I can't use crypto libraries, otherwise all of this would be moot. Also, I'll consider block algorithms though I think most are pretty hefty. Thanks.