In 2015 cryptographer Michele Mosca posed the hypophoric question “How many physical qubits will we need to break RSA-2048? At the time he estimated more than a billion. Fast forward to today researchers Craig Gidney and Martin Ekera have published their findings: “How to factor 2048-bit RSA integers in 8 hours using 20 million noisy qubits".
They report that the number of qubits necessary has dropped two orders of magnitude! True that you'll still require about 20 million to factor a 2048-bit RSA modulus, but for all you skeptics out there, and I know there are a few😉the significance of the research is that now we have a precise and quantitative understanding of the performance of Shor’s algorithms on a quantum computer and the physical limitations that need to be overcome to effectively factor RSA.
When will RSA no longer be safe? That depends on advances in the design of quantum error correcting code, the engineering of physical qubits, and the construction of quantum circuits.
If your paranoid, and you should be, start using a modulus n = 3072 or higher.
