Introduction

Howdy!

Do you remember that time away from home when you saw a sign promising the kind of food you’d been craving for days— only to find a bland, unpalatable imitation that was nothing like the real thing? Remember how your new friends and neighbors, whom you hoped to introduce to that wonderful, comforting taste of home just inwardly shrugged or awkwardly nodded?

This is the journey every one of us has made, whether or not we’ve left our home towns. For the world is full of shams and soulless imitations—and worse yet, the very people you care about are likely to have encountered the fake instead of the real thing and don’t even suspect it. They think they tried the real stuff, and either that it sucked or that maybe it was just not their thing anyhow.

The only chance then is to offer them some nifty morsel off-hand, hoping the erstwhile fake did not leave too painful an impression.

As surely as neighborliness is sharing, the phonies and quacks destroy more than taste. They destroy the opportunity to share. I will not ask you to share your stories of awkwardness; suffice it to say that mine involves differential equations.

From math to books, from music to food, this happens over and over. But it’s even worse when it happens on your home turf, in that tech that is—to steal a turn of phrase from Twain—both you vocation and your vacation. When that turns to bland clock-punching drudgery—and, alas, it happens all too often to good neighbors—then it’s you who needs to be reminded what the soul food of your home truly tasted like—and that is the hardest trick of all.

And this is where proofs of concept come in.

A good proof of concept is the soul food of tech. It is unassuming, as it doesn’t stand for anything grand and unapproachable. It leads to interesting places, but it doesn’t require you to drag along a dozen bags of jargon. It offers inspiration without demanding commitment right off the bat.

And it has the magic power to return that special something, to spark a light in even the tired mind, even in the mind that is sick of tech bros and yet another silly startup pitch for an intelligent bidet. A good PoC sneaks up on a clever reader’s mind under the radar, and brings back that forgotten taste of home in a flash, dispelling the fakes and bidding the swarming shams to GTFO.

Truly, neighbors, home is where your proofs of concept are. And in this third volume of PoC||GTFO, we bring you the really good stuff.

You’ll learn from an expert gambler how likely it is that a random block, such as from corrupted ciphertext, is valid ARM or Thumb2 code that won’t crash.⁰ You’ll learn how to dump a modern Sega Genesis game with its own memory controller by reprogramming the sound coprocessor to do the dirty work for you.¹ You’ll learn the gritty details of userland network card drivers in Masscan² and how to infect an ELF file to make it more secure, rather than to place a backdoor.³

You’ll learn how to confuse emulators in MIPS16,⁴ how to write exploits for RISC V,⁵ and how to reliably port symbols between reverse engineered Thumb2 code.⁶

Enjoy old computers? Why not learn how to crack one of the most protected games for the Apple ][,⁷ to design your own login screen for an IBM mainframe,⁸ or to remotely exploit a Tetrinet server on Windows NT.⁹

Enjoy modern computers? Learn how to make a network device with an emoji name in Linux,¹⁰ how to use stack canaries as a tell to recognize the pointers in a call stack,¹¹ and how to exploit heap memory corruption in the VLC media player.¹²

Hell, why not emulate the ECU of your car,¹³ dump the ROM of a GameBoy Advance by executing memory that doesn’t really exist,¹⁴ or sniff BTLE with a BBC Micro:Bit?¹⁵ Bit bang Ethernet frames,¹⁶ reverse engineer the scrambling of DDR3,¹⁷ or make two images, where one changes to another as it is scaled thanks to a quirk of gamma channel processing.¹⁸

Like I said, this is the really good stuff. Food for an engineer’s soul, with no sales pitch and no Ponzi scheme. Enjoy!

Feed your head,
–Manul Laphroaig, T.G. S.B.