Regular Naked Security readers will know we’re huge fans of Alan Turing OBE FRS.

He was chosen in 2019 to be the scientist featured on the next issue of the Bank of England’s biggest publicly available banknote, the bullseye, more properly Fifty Pounds Sterling.

(It’s called a bullseye because that’s the tiny, innermost circle on a dartboard, also known as double-25, that’s worth 2×25 = 50 points if you hit it.)

Turing beat out an impressive list of competitors, including STEM visionaries and pioneers such as Mary Denning (first to unravel the paleontological mysteries of what is now known as Dorset’s Jurassic Coast), Rosalind Franklin (who unlocked the structure of DNA before dying young and largely unrecognised), and the nineteenth-century computer hacking duo of Ada Lovelace and Charles Babbage.

The Universal Computing Machine

Turing was the groundbreaking computer scientist who first codified the concept of a “universal computing machine”, way back in 1936.

At that time, and indeed for many years afterwards, all computing devices then in existence could typically solve only one specific variant of one specific problem.

They would need rebuilding, not merely “reinstructing” or “reprogramming”, to take on other problems.

Turing showed, if you will pardon our sweeping simplification, that if you could build a computing device (what we now call a Turing machine) that could perform a certain specific but simple set of fundamental operations, then you could, in theory, program that device to do any sort of computation you wanted.

The device would remain the same; only the input to the device, which Turing called the “tape”, which started off with what we’d now call a “program” encoded onto it, would need to be changed.

So you could program the same device to be an adding machine, a subtracting machine, or a multiplying machine.

You could compute numerical sequences such as mathematical tables to any desired precision or length.

You could even, given enough time, enough space, enough tape and a suitably agreed system of encoding, produce all possible alphabetic sequences of any length…

…and therefore ultimately, like the proverbially infinite number of monkeys working at an infinite number of typewriters, reproduce the complete works of William Shakespeare.

More on: You can extend the halting problem result in important ways for cybersecurity