Cryptography on billpg industries™

"All files are numbers"

Fri, 27 Mar 2026 17:46:42 +0000

You hear this a lot. Someone wants to make a point about censorship, cryptography, or the futility of banning a particular blob of data. The argument goes like this: a file is just a sequence of 1s and 0s, and numbers are also sequences of 1s and 0s when written in binary. Therefore, banning a file is like banning a number. What next? Will the government outlaw 85?

It’s a neat rhetorical trick. But every time I see it, I wince just a little, because here’s the awkward truth…

Why do we repeatedly hash passwords in a loop?

Tue, 28 Mar 2023 16:49:34 +0000

If you’re building a website that allows the pubic to log-in, you need to store your passwords so you can check your users are who they say they are when logging-in. This is my introduction to the current state of the art for storing your users’ passwords in your database.

Make It Someone Else’s Problem

I’ll say this right up front, the best way is to get someone else to do it. Use an outsourced service or install a component that deals with the whole thing. You’ll have passed responsibility to someone who’s very speciality is already knowing everything I’ve written here, as well as all the nuances I’ve skipped over.

Vinegar - refined Vigenère - can you break my cipher?

Sat, 12 Feb 2011 16:32:00 +0000

I’m idly interested in cryptography, the art of scrambling a message so that it can be transmitted securely, and only someone with the magic key can understand the message.

When I was young, I designed a cryptographic algorithm. I thought I was so clever, but just because *I* couldn’t break it, that doesn’t make it secure.

In this article, I present my naive cryptographic algorithm. It’s very flawed, so please don’t use it for anything important. Can you find the flaw?