{"type":"rich","version":"1.0","title":"Anthony Towns [ARCHIVE] wrote","author_name":"Anthony Towns [ARCHIVE] (npub17r…x9l2h)","author_url":"https://yabu.me/npub17rld56k4365lfphyd8u8kwuejey5xcazdxptserx03wc4jc9g24stx9l2h","provider_name":"njump","provider_url":"https://yabu.me","html":"📅 Original date posted:2021-03-15\n📝 Original message:On Tue, Mar 16, 2021 at 08:01:47AM +0900, Karl-Johan Alm via bitcoin-dev wrote:\n\u003e It may initially take months to break a single key. \n\n\u003eFrom what I understand, the constraint on using quantum techniques to\nbreak an ECC key is on the number of bits you can entangle and how long\nyou can keep them coherent -- but those are both essentially thresholds:\nyou can't use two quantum computers that support a lower number of bits\nwhen you need a higher number, and you can't reuse the state you reached\nafter you collapsed halfway through to make the next run shorter.\n\nI think that means having a break take a longer time means maintaining\nthe quantum state for longer, which is *harder* than having it happen\nquicker...\n\nSo I think the only way you get it taking substantial amounts of time to\nbreak a key is if your quantum attack works quickly but very unreliably:\nmaybe it takes a minute to reset, and every attempt only has probability\np of succeeding (ie, random probability of managing to maintain the\nquantum state until completion of the dlog algorithm), so over t minutes\nyou end up with probability 1-(1-p)^t of success.\n\nFor 50% odds after 1 month with 1 minute per attempt, you'd need a 0.0016%\nchance per attempt, for 50% odds after 1 day, you'd need 0.048% chance per\nattempt. But those odds assume you've only got one QC making the attempts\n-- if you've got 30, you can make a month's worth of attempts in a day;\nif you scale up to 720, you can make a month's worth of attempts in an\nhour, ie once you've got one, it's a fairly straightforward engineering\nchallenge at that point.\n\nSo a \"slow\" attack simply doesn't seem likely to me. YMMV, obviously.\n\nCheers,\naj"}