Author: Anthony Towns 2021-03-16 00:50:01
Published on: 2021-03-16T00:50:01+00:00
In a recent email thread on Bitcoin-dev, Karl-Johan Alm discussed the possibility of quantum computing being used to break an ECC key. According to the discussion, breaking a single key may take months initially. The constraint on using quantum techniques to break an ECC key is on the number of bits that can be entangled and how long they can be kept coherent. This means that having a break take longer time means maintaining the quantum state for longer, which is harder than having it happen quicker.It is suggested that the only way for it to take a substantial amount of time to break a key is if the quantum attack works quickly but very unreliably. For instance, if it takes a minute to reset and every attempt only has a probability of p of succeeding, then over t minutes you end up with probability 1-(1-p)^t of success. To achieve 50% odds after one month with one minute per attempt, you'd need a 0.0016% chance per attempt, whereas for 50% odds after one day, you'd need 0.048% chance per attempt.However, these odds assume only one QC making the attempts. If you have 30, you can make a month's worth of attempts in a day, and if you scale up to 720, you can make a month's worth of attempts in an hour. In other words, once you have one QC, it becomes a fairly straightforward engineering challenge at that point.Therefore, it seems unlikely that a "slow" attack would be possible. However, opinions may vary.
Updated on: 2023-05-21T01:58:43.308664+00:00