Today’s
AI can crack second world war Enigma code ‘in short order’, experts say
Crowning
achievement of Alan Turing’s codebreakers is now ‘straightforward’, according
to computer scientists
Nicola Davis
Science correspondent
Wed 7 May
2025 05.00 BST
The Enigma
code was a fiendish cipher that took Alan Turing and his fellow codebreakers a
herculean effort to crack. Yet experts say it would have crumbled in the face
of modern computing.
While Polish
experts broke early versions of the Enigma code in the 1930s and built
anti-Enigma machines, subsequent security upgrades by the Germans meant Turing
had to develop new machines, or “Bombes”, to help his team of codebreakers
decipher enemy messages. By 1943, the machines could decipher two messages
every minute.
Yet while
the race to break the Enigma code has become famous, credited with shortening
the second world war by up to two years, and spawning various Hollywood films,
experts say cracking it would be a trivial matter today.
“Enigma
wouldn’t stand up to modern computing and statistics,” said Michael Wooldridge,
a professor of computer science and an expert in artificial intelligence (AI)
at the University of Oxford.
The Enigma
device used by the Axis powers was an electro-mechanical machine that resembled
a typewriter, with three rotors that each had 26 possible positions, a
reflector that sent the signal back through the rotors and a plugboard that
swapped pairs of letters.
Its set-up
meant that even if the same key was pressed twice, a different letter would be
produced each time. What’s more, the initial settings were changed every 24
hours.
“Essentially
the enigma devices got their power because the number of possible ways in which
a message could be encrypted was astronomically large. Far, far too large for a
human to exhaustively check,” Wooldridge said, adding that the “bombes” were
crude hardwired mechanical computers, searching through enormous numbers of
possible alternatives to decrypt Nazi messages.
Dr Mustafa A
Mustafa, a senior lecturer in software security at the University of
Manchester, added that the key to the success of Turing and his colleagues was
that Enigma had a number of weaknesses, including that no letter would be
represented as itself once enciphered.
“It was [a]
brute force attack, trying all different combinations out. But with these
weaknesses of the Enigma, they managed to do that. They managed to automate
this to do it fast enough to be able to crack the code,” he said.
Today,
however, the process would be far less arduous, not least because of a
technology Turing himself pioneered: AI.
“It would be
straightforward to recreate the logic of bombes in a conventional program,”
Wooldridge said, noting the AI model ChatGPT was able to do so. “Then with the
speed of modern computers, the laborious work of the bombes would be done in
very short order.”
Wooldridge
added that a range of modern statistical and computational techniques could
also be deployed. “And the power of modern datacentres is hard to imagine,” he
said, noting modern computing power would have astounded Turing. “Enigma would
not remotely be a match for these,” he said.
Using a
slightly different approach – that Wooldridge suggested might be slower –
researchers have previously used an AI system trained to recognise German using
Grimm’s fairytales, together with 2,000 virtual servers, to crack a coded
message in 13 minutes.
But while
modern computing would have rapidly defanged Enigma, techniques such as the
Rivest-Shamir-Adleman (RSA) cipher – a system initially developed in 1977 and
based on large prime numbers – remain robust.
“In the case
of RSA, it’s the problem of factoring very large numbers. Brute force
techniques – looking through all the alternatives – just won’t work on these
problems,” said Wooldridge, although he noted such techniques might not hold up
against future developments. “If quantum computers ever deliver their
theoretical promise, then we may need completely new techniques to keep our
data safe,” he said.
But while
the Enigma code would not stand up long to modern technology, Mustafa said
cracking it during the war was a huge achievement, not least as it was
considered unbreakable.
“To be able
to crack it – it took them months, more than a year – but to be able actually
to do this within the lifetime of the war, it was a huge thing,” he said. “God
knows what would have happened if we hadn’t cracked Enigma in time.”