Quantum computing threats to blockchain and cryptography

The first sign that quantum computing has broken modern cryptography probably won’t be a splashy theft of Satoshi Nakamoto’s dormant Bitcoin. It could just be a wave of unrelated crypto wallet breaches with no trace of how an attacker did it, according to the founder of blockchain startup Quantus.

“When someone cracks your key, you don’t get a memo saying how they did it,” Christopher Smith, CEO and co-founder of Quantus Network, told Cointelegraph. A sufficiently powerful quantum computer could derive a private key from public keys exposed onchain, allowing an attacker to move funds without compromising a wallet, device or exchange’s internal systems.

This makes the arrival of “Q-day” — a hypothetical future moment when quantum computers become powerful enough to break standard public-key cryptography — unusually difficult to detect. In a theft involving a highly secure organization, “the only forensic evidence would be that there was no breach,” Smith said.

Smith’s warning comes as advances in quantum algorithms have reduced estimates of computing resources needed to attack the elliptic-curve cryptography used by major blockchains.

First target may not be Satoshi’s Bitcoin

Much of the fear around Q-day in crypto is what will happen if a quantum computer cracks the keys securing Satoshi Nakamoto’s estimated Bitcoin holdings, worth $63 billion at the time of writing, which could be suddenly dumped on the market.

However, Smith said the first targets may be military systems and state secrets, while crypto attackers could go for even more valuable keys.

“If I’m focusing on blockchain, what’s the single most valuable key? It’s probably Tether’s minting key,” Smith said. A quantum attacker could mint tokens out of thin air from an administrative wallet and dump them on the market before the issuer could respond, he added.

USDT is a multi-chain stablecoin, and some of the networks on which it is deployed are already actively working on post-quantum migration.

Another theory is that attackers make a quieter opening move.

Sean Cheetham, a security researcher at Blockchain Capital, said an attacker would more likely target hot wallets at exchanges “that aren’t going to ring alarm bells rather than stealing Satoshi’s coins.”

Smith said an attacker may disguise a quantum theft as an ordinary compromise.

“There’s an alternative scenario where they… have these plausible, deniable [explanations]: ‘Oh, somebody just lost their keys somehow,’” he said.

Q-day timeline hard to pin down

In March, Google accelerated its post-quantum migration timeline to 2029 as an AI-assisted breakthrough showed elliptic curve cryptography can be cracked with far fewer physical qubits than previously forecasted.

NGRAVE CEO Roy Blackstone said earlier quantum forecasts failed to account for the parallel development of AI.

“Most threat models assumed we had well into the next decade before quantum technology could realistically crack the cryptography securing public keys, but it did not account for how fast AI would develop alongside it.”

Despite growing urgency, there is little agreement on when a quantum computer capable of breaking modern cryptography will be ready.

Smith, whose company is developing a blockchain network aiming to be quantum-resistant from launch, said there was a “50-50” chance it could happen by 2028, arguing that continued AI-assisted improvements in quantum algorithms and hardware research are making forecasts less reliable.

Cheetham said the early 2030s “definitely is almost a certainty” and that an earlier arrival was “more of a trailing probability.”

Michael Coates, the Solana Foundation’s chief information security officer, declined to give an estimate during an earlier interview, saying “there’s no way to know.”

“If you talk to people in the industry, it is always five years away, and it’s been that way for 10 years or more now. Perhaps today people say it’s four years away,” he said. But the uncertainty is not a reason to delay, he added.

“Thankfully, blockchains aren’t waiting and have started migrating to post-quantum signatures,” said Blackstone. “The damage would be catastrophic if they didn’t.”