The first sign that quantum computers can break the cryptography protecting cryptocurrency may look less like a historic quantum attack and more like a string of unexplained wallet thefts.
Bad actors with access to a cryptographically relevant quantum computer would have strong reasons to conceal that capability rather than announce it by targeting the dormant Bitcoin associated with Satoshi Nakamoto, according to cryptocurrency security executives interviewed by Cointelegraph.
That could make the arrival of so-called Q-day — the point when quantum computers become powerful enough to defeat widely used public-key cryptography — difficult to recognize in real time.
“When someone cracks your key, you don’t get a memo saying how they did it,” Christopher Smith, CEO and co-founder of blockchain startup Quantus Network, told Cointelegraph.
A sufficiently capable quantum computer could potentially calculate a cryptocurrency holder’s private key from a corresponding public key exposed on a blockchain. The private key is the secret information that allows an owner to authorize transactions. An attacker who obtains it can move the funds as though they were the legitimate owner.
Unlike a conventional cyberattack, such a theft might leave little evidence of how the key was obtained. There would be no need to compromise an exchange, steal a password or infect a device with malware.
In the case of a highly secure organization, the only forensic evidence would be that there was no breach, Smith told Cointelegraph.
A Quiet Start to Q-Day
The scenario challenges one of the more dramatic assumptions surrounding the quantum threat to cryptocurrency: that an attacker would demonstrate the technology by moving Satoshi Nakamoto’s long-dormant Bitcoin.
Satoshi’s estimated holdings were worth about $63 billion at the time of Cointelegraph’s report. Moving those coins would immediately attract attention across cryptocurrency markets and could alert governments, technology companies and blockchain developers that a cryptographically relevant quantum computer exists.
An attacker trying to preserve that advantage might instead choose targets that appear more ordinary.
Sean Cheetham, a security researcher at Blockchain Capital, told Cointelegraph that an attacker would more likely target hot wallets at exchanges that wouldn’t send out an immediate alarm.
Hot wallets are cryptocurrency wallets connected to online systems, making them more convenient for transactions but also creating more potential explanations for a theft. A quantum-enabled attacker could potentially hide among the steady stream of conventional cybercrime affecting cryptocurrency users and companies.
Smith also said cryptocurrency might not be the first target. A government or other sophisticated actor that secretly developed a cryptography-breaking quantum computer could place greater value on military communications, intelligence or state secrets.
Administrative Keys Could Be Bigger Targets
Within cryptocurrency, an attacker might also look beyond individual wallets for keys capable of providing greater financial leverage.
“If I’m focusing on blockchain, what’s the single most valuable key? It’s probably Tether’s minting key,” Smith told Cointelegraph.
A minting key is an administrative cryptographic key that can authorize the creation of new tokens. Smith said an attacker who obtained such a key could potentially create tokens and sell them before the issuer could respond.
USDT, Tether’s dollar-linked stablecoin, operates across multiple blockchain networks. Some of those networks are already working on migrations designed to protect against future quantum attacks, according to Cointelegraph.
The concern stems largely from Shor’s algorithm, a quantum algorithm that could allow a sufficiently powerful machine to solve mathematical problems underlying widely used forms of public-key cryptography. Major blockchains rely on elliptic-curve cryptography to prove that transactions have been authorized by the holder of a private key.
Today’s quantum computers are not considered capable of carrying out such an attack against major cryptocurrency networks. The dispute is over how quickly that could change.
Uncertain Timeline Raises Migration Pressure
Recent research has added to concerns by lowering estimates of the computing resources that might eventually be required to attack elliptic-curve cryptography.
Cointelegraph reported that Google accelerated its post-quantum migration timeline to 2029 in March following research suggesting that elliptic-curve cryptography could be attacked with fewer physical qubits than previously estimated. Qubits are the basic units of information in a quantum computer, although large numbers of physical qubits are generally needed to create the more reliable logical qubits required for complex calculations.
Roy Blackstone, CEO of hardware wallet company NGRAVE, told Cointelegraph that earlier estimates also failed to anticipate how rapidly artificial intelligence could develop alongside quantum computing.
While forecasts remain highly uncertain, Smith, whose company is developing a blockchain designed to resist quantum attacks from its launch, put the chance of a cryptographically relevant quantum computer arriving by 2028 at “50-50,” according to Cointelegraph. He pointed to AI-assisted improvements in algorithms and quantum hardware research as factors making long-term forecasts increasingly difficult.
Cheetham placed greater confidence in the early 2030s, telling Cointelegraph that period “definitely is almost a certainty,” while describing an earlier arrival as “more of a trailing probability.”
Michael Coates, chief information security officer at the Solana Foundation, told Cointelegraph that there’s no way to know when Q-Day will arrive
The uncertainty itself is increasingly shaping security planning. Post-quantum cryptography uses mathematical techniques designed to withstand attacks from both conventional and quantum computers, allowing networks to migrate before a cryptographically relevant machine exists.
“Thankfully, blockchains aren’t waiting and have started migrating to post-quantum signatures,” Blackstone said, as reported by Cointelegraph. “The damage would be catastrophic if they didn’t.”
