I saw this thread about password hashing on the D language forums. The original post had a good question that didn’t get answered at the time: if you’re hashing a bunch of things, can it make any difference (for security) what order you do it?

The answer turns out to be yes, and it’s a neat example of the difference between theoretical ideals and real-world systems. Because I think this stuff is worth knowing if you’re using cryptographic hash functions for, you know, actual crypto, I thought I’d write up a blog post about why it can matter.