RSA-2048, the high-end encryption protecting your bank accounts and data online, can be cracked with a quantum computer with 23,000 qubits. This was discovered by the French firm Alice & Bob after a detailed study. While this is an estimate, the quantum computing firm believes this could become a reality by the end of the decade. RSA-2048 is the gold standard of encryption. It secures our digital infrastructure, from websites and social media to online banking and data storage. It is considered incredibly difficult to break because it requires factoring a 617-digit modulus into two prime numbers. In practice, the encryption is easy to create but difficult to crack. This is because classical computers would spend astronomical amounts of money to solve the encryption, which would dwarf the gains made by breaking the encryption. With a quantum computer, though, the situation changes completely, and breaking the encryption can be relatively easy and cost-effective. What is Shor’s algorithm? In 1994, mathematician Peter Shor gave the world his famous algorithm that could crack the RSA-2048 encryption. The only hurdle is that this algorithm needs a quantum computer that is large enough and accurate enough to run it.Since physical qubits are error-prone, the quantum computer running Shor’s algorithm will also need an error-correction mechanism to ensure it gives the right answers. In 2019, Google Quantum AI researchers predicted that a quantum computer with 20 million physical qubits would be needed to break RSA-2048. Over the next six years, this number fell to below one million. This improvement is partly due to increased efficiency that mathematicians have brought to the algorithm itself over 30 years of its existence. The other is due to advances in quantum computing technologies that have led to better logical performance from qubits. Where cat qubits can helpA French quantum computing firm that uses cat qubits made a similar estimate for Shor’s algorithm in 2023 and found it would need only 350,000 qubits to crack it. A more updated estimate using improved cat qubits now puts this number at 23,000 and the time needed to crack the encryption at 3.14 days. While 23,000 qubits isn’t something that a quantum computer is capable of today, the number is relatively low to be reachable in the next few years. Along with the qubits, the run time is also important. So, a quantum computer with 610,530 cat qubits could do the same job in just 1.5 hours. The challenge of scaling to this many qubits is the additional infrastructure required to run such a quantum computer and still fit it all in a decently sized laboratory. Researchers at Alice & Bob reckon that building such a quantum computer will be possible in just a few years from now and RSA-2048 encryption would be rendered obsolete. Luckily, there are post-quantum encryption standards that already exist but have not been extensively tested. The paper encourages the cybersecurity community to test these more rigorously and transition systems to these new algorithms before quantum computers become more common. The research is not peer-reviewed and is published in the Cryptology ePrint Archive.