Algorithm on billpg industries™

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?

'First Past the Post' isn't.

Mon, 10 Jan 2011 22:03:00 +0000

I’m a bit of a nerd for vote counting systems. So I discovered with delight that in the UK, there will soon be a referendum on changing the way votes are counted. As I write this, most of the UK (and the USA) uses a method we call “First past the post”.

It’s called “First past the post”, but it isn’t. The name is about as ridiculous as calling North Korea; “The Democratic People’s Republic of Korea”. The country is on the Korean peninsula, so at least that name is a little bit honest.

Computers are fast!

Sun, 29 Nov 2009 18:15:00 +0000

Killer Sudoku is a popular variant on the perennial Sudoku game found in British newspapers. The same rules about the numbers 1 to 9 appearing only once in row, column and 3x3 box still apply, but unlike Sudoku, the puzzle doesn’t come with any numbers filled in. Instead, cells are groups with dotted lines and the total of all those cells are written in. Here’s part of a puzzle. The two cells grouped by a 10 could be 1+9, 2+8, 3+7 or 4+6. (It can’t be 5+5 because that would mean two 5s in same box.) Not a lot to work on, but also look at the three cells grouped by a 23 in the same 3x3 box; The only possible fit is 6+8+9. This means the only possible fit for the 10 group is 3+7, as all the possibilities would clash with the 6,8 or 9 required to make the 23. I could go on. If you want to complete the puzzle, its the Guardian’s puzzle number 166. The point of this article isn’t to solve the puzzle, but something I observed along the way. Am I sure there’s no other way to split 23 into three parts, 1 to 9, without duplicates? I confess, mental arithmetic is not my forte. Part of the puzzle solving process for me is going through each dotted group and building a crib sheet on all the possible ways to make the total, so I can cross them off later. This isn’t a part of the puzzle I particularly enjoy, so I decided to automate it. (Is that cheating? I don’t think so in my circumstances, but that’s another topic of conversation.) So I sat down and designed an algorithm…