Final Fantasy Exploit Teaches 32-bit Integer Math

September 19, 2018 by Bryan Cockfield 18 Comments

One of the fun things about old video games, besides their obvious nostalgia, is that some of the more popular games have been pried apart and tinkered with for years, leading to a lot of new “development” within the games. This often uncovers some hidden gems that gamers might not have had any knowledge of during the game’s heyday, like this coding oddity found in Final Fantasy 7 that illustrates a lot about how 32-bit processors do math.

The original PlayStation used a 32-bit RISC processor, but the most significant bit could be used for integer signing. This means that if you have an integer that has a value of 2,147,483,647 (01111111111111111111111111111111 in binary) and you add one, the value is suddenly negative 2147483648 because the most significant digit is also an indicator of the integer’s sign. In this situation, the integer is said to “overflow”. In Final Fantasy 7, if you can somehow get a character to deal 262,144 damage in one hit (much less than two billion, due to the way the game does damage calculations), the game has a little bit of a meltdown.

[4-8Productions] had to do a lot of work to show how this glitch can be exploited in the game as well. Usually damage in this game is limited to 9,999 but under certain configurations (admittedly obtained by using other exploits and tools available for FF7 like a savegame editor) two of the characters can deal more damage than this critical value, exposing the 32-bit processor’s weak spot.

Even though integer signing is a pretty basic concept for most of us, the video is definitely worth a watch especially if you’re fans of the classic game. Of course, Final Fantasy 7 isn’t the only classic that has been exploited and reverse-engineered to the extreme. You can use a Super Mario World level to implement a calculator now, too.

Continue reading “Final Fantasy Exploit Teaches 32-bit Integer Math” →

Custom Alexa Skill In A Few Minutes Using Glitch

January 17, 2018 by Al Williams 18 Comments

As hackers, we like to think of ourselves as a logical bunch. But the truth is, we are as subject to fads as the general public. There was a time when the cool projects swapped green LEDs out for blue ones or added WiFi connectivity where nobody else had it. Now all the rage is to connect your project to a personal assistant. The problem is, this requires software. Software that lives on a publicly accessible network somewhere, and who wants to deal with that when you’re just playing with custom Alexa skills for the first time?

If you have a computer that faces the Internet, that’s fine. If you don’t, you can borrow one of Amazon’s, but then you need to understand their infrastructure which is a job all by itself. However, there is a very simple way to jump start an Alexa skill. I got one up and running in virtually no time using a website called Glitch. Glitch is a little bit of everything. It is a web hosting service, a programming IDE for Node.js, a code repository, and a few other things. The site is from the company that brought us Trello and helped to start Stack Overflow.

Glitch isn’t about making Alexa skills. It is about creating web applications and services easily. However, that’s about 90% of the work involved in making an Alexa skill. You’ll need an account on Glitch and an Amazon developer’s account. Both are free, at least for what we want to accomplish. Glitch has some templates for Google Home, as well. I have both but decided to focus on Alexa, for no particular reason.

Continue reading “Custom Alexa Skill In A Few Minutes Using Glitch” →

Glitching USB Firmware For Fun

October 4, 2016 by Elliot Williams 37 Comments

[Micah Elizabeth Scott], aka [scanlime], has been playing around with USB drawing tablets, and got to the point that she wanted with the firmware — to reverse engineer, see what’s going on, and who knows what else. Wacom didn’t design the devices to be user-updateable, so there aren’t copies of the ROMs floating around the web, and the tablet’s microcontroller seems to be locked down to boot.

With the easy avenues turning up dead ends, that means building some custom hardware to get it done and making a very detailed video documenting the project (embedded below). If you’re interested in chip power glitching attacks, and if you don’t suffer from short attention span, watch it, it’s a phenomenal introduction.

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Glitching Square Wave Clock Is Designed To Confuse

February 12, 2016 by Gerrit Coetzee 25 Comments

[Voja Antonic] has built a clock that tells the time in binary with square waves, and trolls the uninitiated in electronics.

The clock itself is very attractive. If you look closely you can see the circuitry backlit behind the dot LED matrix display. The whole thing is housed in a nicely folded steel case. RGB LEDs are used to good effect to highlight some additionally obfuscating circuit schematics. The workmanship is very top notch, and we would gladly host such an object on our desks.

The clock’s standard time telling mode is three sets of square waves showing the binary values for the hours, minutes, and seconds. Every now and then the clock will glitch out. The waves will distort. The colors will change. And every now and then, tantalizingly, the alpha-numeric time will show up for just a split second, before returning to those weird squiggles again.

We’ve seen a whole slew of binary clocks before. This one, for instance. But the waveform display makes us feel just that little bit more at home — it’s just like we’re sitting in front of our oscilloscope.

Reprogramming Super Mario World From Inside The Game

January 22, 2015 by Rick Osgood 72 Comments

[SethBling] recently set a world record speed run of the classic Super Nintendo game Super Mario World on the original SNES hardware. He managed to beat the game in five minutes and 59.6 seconds. How is this possible? He actually reprogrammed the game by moving specific objects to very specific places and then executing a glitch. This method of beating the game was originally discovered by Twitch user [Jeffw356] but it was performed on an emulator. [SethBling] was able to prove that this “credits warp” glitch works on the original hardware.

If you watch the video below, you’ll see [SethBling] visit one of the first available levels in the game. He then proceeds to move certain objects in the game to very specific places. What he’s doing here is manipulating the game’s X coordinate table for the sprites. By moving objects to specific places, he’s manipulating a section of the game’s memory to hold specific values and a specific order. It’s a meticulous process that likely took a lot of practice to get right.

Once the table was setup properly, [SethBling] needed a way to get the SNES to execute the X table as CPU instructions. In Super Mario World, there are special items that Mario can obtain that act as a power up. For example, the mushroom will make him grow in size. Each sprite in the game has a flag to tell the SNES that the item is able to act as a power up. Mario can either collect the power up by himself, or he can use his friendly dinosaur Yoshi to eat the power up, which will also apply the item’s effects to Mario.

The next part of the speed run involves something called the item swap glitch. In the game, Mario can collect coins himself, or Yoshi can also collect them by eating them. A glitch exists where Yoshi can start eating a coin, but Mario jumps off of Yoshi and collects the coin himself simultaneously. The result is that the game knows there is something inside of Yoshi’s mouth but it doesn’t know what. So he ends up holding an empty sprite with no properties. The game just knows that it’s whatever sprite is in sprite slot X.

Now comes the actual item swap. There is an enemy in the game called Chargin’ Chuck. This sprite happens to have the flag set as though it’s a power up. Normally this doesn’t matter because it also has a set flag to tell the game that it cannot be eaten by Yoshi. Also, Chuck is an enemy so it actually hurts Mario rather than act as a power up. So under normal circumstances, this sprite will never actually act as a power up. The developers never programmed the game to properly handle this scenario, because it was supposed to be impossible.

If the coin glitch is performed in a specific location within the level, a Chargin’ Chuck will spawn just after the coin is collected. When the Chuck spawns, it will take that empty sprite slot and suddenly the game believes that Yoshi is holding the Chuck in his mouth. This triggers the power up condition, which as we already know was never programmed into the game. The code ends up jumping to an area of memory that doesn’t contain normal game instructions.

The result of all of this manipulation and glitching is that all of the values in the sprite X coordinate table are executed as CPU instructions. [SethBling] setup this table to hold values that tell the game to jump to the end credits. The console executes them and does as commanded, and the game is over just a few minutes after it began. The video below shows the speed run but doesn’t get too far into the technical details, but you can read more about it here.

This isn’t the first time we’ve seen this type of hack. Speed runs have been performed on Pokemon with very similar techniques. Another hacker managed to program and execute a version of single player pong all from within Pokemon Blue. We can’t wait to see what these game hackers come up with next. Continue reading “Reprogramming Super Mario World From Inside The Game” →

Arduino VGA Glitching

April 3, 2009 by Caleb Kraft 9 Comments

glitch

For some people, mistakes or glitches has become an art form. We’ve seen it in circuit bending for a while, but the newest version is in video glitching. [Sebastian] has gone so far as to intentionally set up an Arduino to send a glitched signal to a monitor. His description sounds pretty easy. We’re just assuming this is in motion in some way, a video of it in action would be nice.