Michael Doornbos

Engineer, pilot, and accidental story teller. There's a good chance I'll be voiding a warranty today

Making and breaking Ciphers on the Commodore 64, er VIC-20 - Lagged Fibonacci Sequence and a little Monte Carlo while embracing contraints

Making and breaking Ciphers on the Commodore 64, er VIC-20 - Lagged Fibonacci Sequence and a little Monte Carlo while embracing contraints

We're on ANOTHER random number generation technique today. Let's work on the Lagged Fibonacci Sequence, a fun way to use the Fibonacci Sequence on itself to generate pseudo-random numbers. One of our long term goals is to add a bunch of tools to our toolbox. Making reusable components makes doing

Quick Post: XOR in Commodore BASIC 2

Quick Post: XOR in Commodore BASIC 2

Maybe on a weekday evening you find yourself in need of some exclusive OR (XOR) operations on a machine that curiously doesn't have one built in. Like... BASIC 2 on the Commodore VIC-20 and 64! Why it doesn't have XOR is probably just another example of trying to save precious

Running the 8 Bit Show and Tell VIC-20 Super Expander Programming Challenge on the Commodore 64

Running the 8 Bit Show and Tell VIC-20 Super Expander Programming Challenge on the Commodore 64

One of my favorite videos on the whole internet lately is this hidden gem by Robin. In it, he executes a programming challenge he found on Twitter to draw a pattern without using IF statements. His approach is one of my favorite math tricks of all time, and I was

The retro pinout project

The retro pinout project

One of my main goals in sharing retro computing is to help people DO things with these machines. They are useful for all sorts of reasons, not the least of which is education and demonstration. The constraints are wonderful for this. Using 30-50 year old hardware comes at a price.

Quick Post: Modulus in BASIC 2 without a cartridge

Quick Post: Modulus in BASIC 2 without a cartridge

I posted this on Twitter a few weeks ago, but a young lady has been exploring programming in Python and also with Commodore BASIC which is pretty neato. She's 11 and asked if there was a way to do modulo functions on Commodore BASIC because she's using her Dad's VIC-20

Making and breaking Ciphers on the Commodore 64 Part 12 - Pontifex - Solitaire from Cryptonomicon

Making and breaking Ciphers on the Commodore 64 Part 12 - Pontifex - Solitaire from Cryptonomicon

Cryptonomicon Pontifex/SolitaireWe're back to my favorite book for another round. We've done quite a bit with Cryptonomicon so far. One of my favorite moments is when Enoch Root introduces a cipher that two prisoners used to communicate using just a humble playing card deck. Drawing of the mine in

Making and breaking Ciphers on the Commodore 64 Part 11 - One time pads on a Commodore 64, probably a bad idea

Making and breaking Ciphers on the Commodore 64 Part 11 - One time pads on a Commodore 64, probably a bad idea

A while ago, I explained in detail how to generate one time pad sheets and use them to encrypt and decrypt messages. It turned out to be doable, only requiring a pencil and a way to create random numbers, but it's slow, error prone and tedious. WhyThe one time pad

Making and breaking Ciphers on the Commodore 64 Part 10 - Finding hash collisions with a type in game from 1984

Making and breaking Ciphers on the Commodore 64 Part 10 - Finding hash collisions with a type in game from 1984

HashesWe did an implementation of a once popular hashing function in Part 8 on RC4 without really going into why. A hash function is any function that is used to map data of an arbitrary size (input) to a fixed size output. An algorithm is applied to the input and

Making and Breaking Ciphers with Commodore 64 Part 9 - Finding Smallish Primes

Making and Breaking Ciphers with Commodore 64 Part 9 - Finding Smallish Primes

RecapSo far we've Reversed a stringShifted bits left and right (mostly right)Brute forced a known simple cipherChanneled our inner John Connor by cracking ATM machinesSearched through a large number looking for matchesLearned how to use XOR to recover dataCreated a Linear Feedback Shift Register to generate better random numbersImplemented

Quick Post: Slow text on the Commodore

Quick Post: Slow text on the Commodore

An "almost teenager", Josh, sent me an email yesterday asking how I do slow text on the Commodore. He is just starting assembly at 12 which is pretty impressive. He's been using KickAssembler, but wants to try it "on hardware". It's not difficult really. There are probably a lot of

The Commodore 64 N.O.O.C.U.L.A.R. futbal project

The Commodore 64 N.O.O.C.U.L.A.R. futbal project

ConceptI'm fortunate to have a number of vintage computers I've collected over the years. Some were fun finds, others donated. One I've had since 1983 (we think) and it's one of my most prized possessions. I travel a fair bit and not long ago I was looking for something for

Making and breaking Ciphers on the Commodore 64 Part 8 - RC4

Making and breaking Ciphers on the Commodore 64 Part 8 - RC4

RecapSo far in this 8 part series on doing weird things with Ciphers on old computers we've: Reversed a stringShifted bits left and right (mostly right)Brute forced a known simple cipherChanneled our inner John Connor by cracking ATM machinesSearched through a large number looking for matchesLearned how to use

The Nostalgia Files: My all time favorite book

The Nostalgia Files: My all time favorite book

Those that know me well are very familiar with the book I talk about the most. Cryptonomicon by Neal Stephenson challenges me in new ways every time I read it. If you ask me what my favorite book is, I'll probably name Cryptonomicon with the Moon is a Harsh Mistress

Repairing a Commodore 128 and DIY Chris's RAM tester review

Repairing a Commodore 128 and DIY Chris's RAM tester review

I have several items from DIY Chris that we'll review over the next week including a GAL PLA and flash-able ROM drop in that can hold kernal, character or BASIC ROMs. First on the list is the RAM tester. The problem child 128I have a Commodore 128 which developed a

Making and breaking Ciphers on the Commodore 64 Part 7 - Pseudo Random with Linear Congruential Generators

Making and breaking Ciphers on the Commodore 64 Part 7 - Pseudo Random with Linear Congruential Generators

So far in this 7 part (shocked I've made it through 7!) series on doing weird things with Ciphers on old computers we've: Reversed a stringShifted bits left and right (mostly right)Brute forced a known simple cipherChanneled our inner John Connor by cracking ATM machinesSearched through a large number

Making and Breaking Ciphers with a Commodore 64 - Part 6: XOR is Magical - Data recovery

Making and Breaking Ciphers with a Commodore 64 - Part 6: XOR is Magical - Data recovery

ReviewSo far we've: Reversed a stringShifted bits left and right (mostly right)Brute forced a known simple cipherFaked it, but then looking for a 4 digit known pinSearched through a large number looking for matchesWe now have most of the basic skills in Assembly to start doing some real work.

Finding the Prodigal Easter Egg inside the Easter Egg on a Commodore 64

Finding the Prodigal Easter Egg inside the Easter Egg on a Commodore 64

If you REALLY want to get into the weeds on how I figured out the Easter Egg(s) inside the Easter Egg on a 35 Year old album on a 35 year old computer then you're in luck! This video is for you! I mention "the original author" in the

Quick post: Determining length in Commodore Assembly

Quick post: Determining length in Commodore Assembly

A common task in our code is to determine the length of something. In this example, let's check the length of a string like "are you keeping up?" In Python, this is crazy easy. #!/usr/bin/env python message = "are you keeping up?" len(message) Python 3In 6510 Assembly, this

Benchmarking Retro Computers (mostly Commodore) with marginal methods

Benchmarking Retro Computers (mostly Commodore) with marginal methods

Just the BASICs, pleaseOur friend in retro @NoelsRetroLab has a simple BASIC benchmarking tool that's fun to use to compare different basic systems execution speed. We're counting jiffies, which is roughly (sometimes very roughly) 1/60th of a second. We're using three variations of this code on the Commodore BASIC

Jiffies in Assembly

Jiffies in Assembly

Many of you know that you can use a "Jiffy" on a Commodore as a measure of time. Sorta. The short short version is that we have a 3 byte clock that increments once every interrupt, so 1/60th of a second. It's not considered reliable as a real time

Making and Breaking Ciphers with a Commodore 64 - Part 5: Wargames

Making and Breaking Ciphers with a Commodore 64 - Part 5: Wargames

Let's recap a littleSo far we've: Reversed a stringShifted bits left and right (mostly right)Brute forced a known simple cipherFaked it, but then looking for a 4 digit known pinWhat we need next in our toolbox is to be able to search through a large number of values to

Calculating Pi via the Gregory-Leibniz series in BASIC on the VIC-20

Calculating Pi via the Gregory-Leibniz series in BASIC on the VIC-20

It's Pi day tomorrow, and you know what that means! Cherry is favorite. Apple is second favorite. There is a well known and easy to understand method for calculating Pi with the Gregory Leibniz series. Leibniz built on the work on Gregory. It has the added benefit of being pretty

Quick Post: Commodore 64 Simple Addition Efficiency

Quick Post: Commodore 64 Simple Addition Efficiency

There are many hacks you can do in Assembly language on the Commodore. Here's a very easy one with impressive results according to my analog stopwatch. We want to count to $ffffff or 2563 (224) which is 16,777,216 We wont print to the screen to save a lot

c0pperdragon verdict

c0pperdragon verdict

Ahh, the quest for a better Vintage computer picture never ends. I'm having fun with it anyway. Side thought: At what point does a computer cross over from old: no one wants that 2007 Windows tower you built in your basement, to OMG, it's Vintage, let's drive up the eBay

Making and Breaking Ciphers with a Commodore 64 - Part 4: The PIN Program from Terminator 2

Making and Breaking Ciphers with a Commodore 64 - Part 4: The PIN Program from Terminator 2

A few minutes into Terminator 2, the young John Connor takes his Atari Portfolio out of his bag and inserts a foil covered card into an ATM machine and proceeds to crack a pin number and steal some cash from an unsuspecting account. This is a movie prop and doesn't