The laws of quantum mechanics make it impossible to copy quantum information, but that doesn’t mean quantum computers are unhackable. Two independent teams of researchers have now devised methods for disrupting calculations on quantum computers. They both rely a method used to hack traditional computers called a row-hammer attack.
Conventional row-hammer attacks target dynamic random-access memory (DRAM), a type of RAM that is essential for short-term information storage in conventional computers. They take advantage of unintended electrical interactions between parts of DRAM to change their contents, such as granting access privileges to hackers.
Quantum computers aren’t sophisticated enough for exactly the same method to apply, as they don’t have memories or complex software that would require privileges, but their information content can still be altered by changing the states of their quantum bits, or qubits, says at the University of Gdańsk in Poland.
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His team remotely accessed several , which offer cloud quantum computing services to distant users on separate groups of qubits in the same computer. The researchers ran many short programs that manipulated a group of the qubits they had access to. This induced unintended interactions – known as crosstalk – between the affected qubits and another neighbouring one. The researchers examined this adjacent qubit and found that the information it stored changed after the row-hammer-like attack.
Team member at the University of Gdańsk says they determined the most efficient way to implement this attack over the course of tens of thousands of experiments. “I was pretty sure we will get good results, but I was surprised by how strong crosstalk was in some of the cases,” says team leader , also at the University of Gdańsk.
A group led by at Northwestern University in Illinois was also inspired by row-hammer attacks and devised a method called QubitHammer that tweaked the microwave pulses that control and direct qubits. The researchers tested QubitHammer on an IBM quantum computer, finding that this also induced crosstalk and subsequently changed the information stored in some qubits. In this case, the targeted qubits didn’t have to be next-door neighbours – they could be much further away from the qubits being controlled.
If two different users could access different sets of qubits within the same quantum computer, then one of them could disrupt the other user’s calculations with a row-hammer attack, says team member , also at the University of Gdańsk.
IBM recently made it impossible for users to change the microwave pulses. But other firms that make quantum computers from superconducting circuits, such as and IQM, offer similar cloud access to their own superconducting quantum computers, including some control over microwaves.
at IBM says: “When using IBM’s quantum computers, there is no circumstance at present in which two users can run circuits on the same quantum hardware at the same time, making this and related techniques impossible to use in practice.” Yet, as quantum computers become larger and more commercially viable, some companies may want to allow for users to share time on one device, as is currently the case for many classical computers that are currently accessible through the cloud, says Szefer.
The new work reflects what is possible with the relatively small and noisy quantum computers that exist today, says at the University of California, Berkeley. Notions of what “quantum hacking” means are likely to change as quantum computers become better at catching and correcting their own errors and are better integrated into existing computing ecosystems, like being just one layer of computation alongside conventional supercomputers, he says.
Szefer says quantum computers are still at an early stage of development, so explorations of row-hammer-like attacks could lead to countermeasures being built into the next generation of devices. This didn’t happen with traditional computers, many of which are still susceptible to these kinds of techniques, simply because the hacking methods were discovered after computer memory architectures already became standard.
Both research teams say they now want to study how quantum row-hammer attacks can be adapted to quantum computers that are good at detecting and correcting their own errors.
This work is an early step towards understanding future hacking vulnerabilities in quantum computers, says Shenoy. “[In classical computers] error-mitigation techniques or countermeasures that were implemented to overcome certain kinds of row-hammer attacks, they themselves gave rise to newer kinds of row-hammer attacks.”
References:
arXiv ,
